Analytical Methods (v.7, #4)
Front cover (1223-1224).
Contents list (1225-1239).
Evaluation of Analytical Instrumentation. Part XXV: Differential Scanning Calorimetry by S. Gaisford (1240-1248).
The Analytical Methods Committee has received and approved the following report from the Instrumental Criteria Sub-Committee.
Evaluation of Analytical Instrumentation. Part XXVI: Instrumentation for Voltammetry by C. B. Braungardt (1249-1260).
The Analytical Methods Committee has received and approved the following report from the Instrumental Criteria Sub-Committee.
Spectrophotometric determination of ethyl carbamate through bi-enzymatic cascade reactions by Xiaoxia Lu; Nandi Zhou; Yaping Tian (1261-1264).
A highly sensitive spectrophotometric method for ethyl carbamate (EC) determination was established through glutamate dehydrogenase/urethanase cascade reactions and the corresponding change in NADH concentration. The absorbance at 340 nm is linearly related to the EC concentration within the range of 0.3–50 μM, with a low detection limit of 0.00928 μM. The assay was further applied to analyse EC in mimic Chinese rice wine samples.
Staining using the lipid dye LD540 in fluorous media: application to sebaceous latent fingermarks by Angelique Qi; Gordon M. Miskelly (1265-1268).
Enhancement of the sebaceous components of fingermarks is often performed using an aqueous staining solution. We propose an alternative approach using a bodipy-based lipid-selective dye (LD540) in a fluorous solvent. This fluorous approach can result in excellent retention of the spatial distribution of lipids and can be used on substrates unsuited to treatment with aqueous solutions. We demonstrate the new possibilities enabled by using fluorous solvents by staining fingermarks on an NaCl salt plate and on a block of ice.
Bacterial meningitis pathogens identified in clinical samples using a SERS DNA detection assay by Kirsten Gracie; Diane Lindsay; Duncan Graham; Karen Faulds (1269-1272).
This communication reports the first demonstration of the detection of Streptococcus pneumoniae and Neisseria meningitidis bacterial DNA extracted from anonymous patient CSF samples and assesses the applicability of a previously developed SERS based DNA detection assay as a platform for the detection of multiple meningitis pathogens from clinical samples.
Concurrent DNA preconcentration and separation in bipolar electrode-based microfluidic device by Hongjun Song; Yi Wang; Charles Garson; Kapil Pant (1273-1279).
This paper presents a bipolar electrode (BPE) device in a microfluidic dual-channel design for concurrent preconcentration and separation of composite DNA containing samples. The novelty of the present effort relies on the combination of BPE-induced ion concentration polarization (ICP) and end-labeled free-solution electrophoresis (ELFSE). The ion concentration polarization effect arising from the faradaic reaction on the BPE is utilized to exert opposing electrophoretic and electroosmotic forces on the DNA samples. Meanwhile, end-labeled free-solution electrophoresis alters the mass–charge ratio to enable simultaneous DNA separation in free solution. The microfluidic device was fabricated using standard and soft lithography techniques to form gold-on-glass electrode capped with a PDMS microfluidic channel. Experimental testing with various DNA samples was carried out over a range of applied electric field. Concentration ratios up to 285× within 5 minutes for a 102-mer DNA, and concurrent preconcentration and free-solution separation of binary mixture of free and bound 102-mer DNA within 6 minutes was demonstrated. The effect of applied electric field was also interrogated with respect to pertinent performance metrics of preconcentration and separation.
Determination of meloxicam in plasma samples using a highly selective and sensitive voltammetric sensor based on carbon paste electrodes modified by molecularly imprinted polymer nanoparticle–multiwall carbon nanotubes by Saman Azodi-Deilami; Ebadullah Asadi; Majid Abdouss; Fardin Ahmadi; Alireza Hassani Najafabadi; Sina Farzaneh (1280-1292).
In this study, a highly selective voltammetric sensor is introduced for the monitoring of meloxicam by using a new carbon paste electrode (CPE). A meloxicam molecularly imprinted polymer (MIP) and a non-imprinted polymer (NIP), polymerizing on the surface of functionalized multiwall carbon nanotubes (MWCNTs), were synthesized and then used for the preparation of carbon paste electrodes (CPEs) to improve the selectivity and conductivity of the prepared sensor. The sensor was applied for the determination of meloxicam using the cathodic stripping voltammetric method. The MIP@MWCNT–CP electrode showed higher recognition ability in comparison to the NIP@MWCNT–CP. Some parameters affecting the sensor response were optimized and then the calibration curve was plotted. Under optimized conditions, two linear dynamic ranges from 4.33 × 10−5 to 2.85 × 10−3 mg L−1 and 2.85 × 10−3 to 7.53 × 10−2 mg L−1 were obtained. The detection limit and quantitation limit of the sensor were calculated to be 3.22 × 10−5 and 1.1 × 10−4 mg L−1, respectively, which indicated the sensitivity of the proposed procedure. The proposed sensor is applied to determine meloxicam in plasma samples and the recovery results were found to be between 98.0 and 102.5% using the voltammetric method with acceptable precision of less than 3.1%.
A paperfluidic device for dental applications using a novel patterning technique by A. Jagirdar; P. Shetty; S. Satti; S. Garg; D. Paul (1293-1299).
Dental caries is an irreversible and potentially debilitating disease that can ultimately lead to the loss of the affected tooth structure. Due to a lack of awareness, caries is detected much later after its onset. Moreover, people do not have access to dental care or information in the rural areas of several developing countries. Hence, there is a need for a cheap and disposable point-of-care screening test to determine one's oral health. To cater to this unmet need, we have developed a paperfluidic chip that measures salivary pH to estimate its buffering capacity and also tests susceptibility to caries by checking for salivary reductase. The results of our paper-based reductase assay of 72 samples correlated well with the results obtained using the standard tube-based assay performed in dental clinics. Further, the results of the paper-based pH test matched with those of the caries test, i.e. those with lower saliva pH showed higher susceptibility to caries (since acidic environments promote caries). Here, we also report a new and green technique to chemically pattern paper by printing olive oil through an inkjet printer and turning paper (cellulose) hydrophobic in the oil-treated regions through heat-assisted esterification. In addition to patterning hydrophobic regions on paper, the same inkjet printer was used to print all the assay reagents, thus making our paperfluidic chip completely printable. Since our device is cheap, disposable and can be easily manufactured in large volumes by printing, it is suitable for regular monitoring of oral health as well as providing a basic screening test to those without routine access to dentists.
Preparation of magnetic core–shell nanoflower Fe3O4@MnO2 as reusable oxidase mimetics for colorimetric detection of phenol by Yuhao Xiong; Siheng Chen; Fanggui Ye; Linjing Su; Cong Zhang; Shufen Shen; Shulin Zhao (1300-1306).
In this paper, magnetic core–shell nanoflowers Fe3O4@MnO2 were fabricated via a solvothermal method. We demonstrated that the as-synthesized magnetic nanoflowers Fe3O4@MnO2 possess intrinsic oxidase-like activity in a wide pH range and can catalytically oxidize 4-aminoantipyrine (4-AAP) and phenol substrates to form pink color products without the requirement for additional oxidizing agents. On the basis of this phenomenon, a simple colorimetric method for the determination of phenol was developed. A wide linear detection range can be obtained from 1.0 μM to 120 μM (R2 = 0.9962) with a detection limit of 0.15 μM. And the method was applied to determine phenol in wastewater with good recoveries ranging from 96.0 to 101.5%. Furthermore, benefitting from chemical stability and easy recovery (by simple magnetic separation) of Fe3O4@MnO2, the oxidase mimetics have excellent reusability and reproducibility in cycle analysis.
SERS detection of expired tetracycline hydrochloride with an optical fiber nano-probe by Di Jin; Yuxue Bai; Haige Chen; Shupeng Liu; Na Chen; Jing Huang; Sujuan Huang; Zhenyi Chen (1307-1312).
In this paper, we have developed a Raman spectroscopy analytical method for the analysis of tetracycline hydrochloride. Surface enhanced Raman spectroscopy (SERS) was carried out with optical fiber nano-probe coated nanoparticles. Both normal and expired tetracycline hydrochloride were analyzed in direct detection mode and remote detection mode. The results showed that the surface-enhanced Raman spectra could provide chemical information for distinguishing normal drugs from the expired ones. It has been demonstrated that the drug could be analyzed rapidly by SERS with the optical fiber nano-probe.
A facile sensitive l-tyrosine electrochemical sensor based on a coupled CuO/Cu2O nanoparticles and multi-walled carbon nanotubes nanocomposite film by Wenxiu Gu; Miaomiao Wang; Xiaoqing Mao; Yuru Wang; Lei Li; Wenshui Xia (1313-1320).
l-tyrosine in human urine is an essential biomarker for the early detection of various cancers. A facile electrochemical method for preparing a coupled copper oxide/cuprous oxide nanoparticles and multi-walled carbon nanotubes nanocomposite film modified glass carbon electrode (CuO/Cu2O/MWCNTs/GCE) via in situ growth is proposed for electrochemical sensing of l-tyrosine. The electrocatalytic activity of CuO/Cu2O/MWCNTs/GCE was investigated for l-tyrosine by cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA), and the morphology and shape of the nanocomposite film were characterized by scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), transmission electron microscope (TEM) and X-ray powder diffraction (XRD). An irreversible oxidation peak for l-tyrosine at a potential of 0.645 V (vs. SCE) was observed in pH 8.0 of phosphate buffer solution at the CuO/Cu2O/MWCNTs/GCE electrode. The as-fabricated l-tyrosine sensor shows a fast response time (less than 2 s), a wide linear range 2 × 10−7–2 × 10−4 M, a high sensitivity of 1001 μA mM−1 cm−2 and a low detection limit of 9.6 × 10−9 M (at signal/noise = 3) in pH 8.0 phosphate buffer solution at 0.645 V. The nanocomposite film electrode has been successfully applied to determine l-tyrosine in human urine. It exhibits high electrocatalytic activity, satisfactory repeatability, stability, fast response and good selectivity against potentially interfering species, which suggests its potential for the development of a sensitive, selective, easy-operation and low-cost l-tyrosine sensor for practical routine analyses. The proposed new facile electrochemical growth method has the potential to expand the range of nanocomposite materials applied for the detection of various electroactive substances.
Preparative separation of isoflavones in plant extract of Pueraria lobata by high performance counter-current chromatography by Bo Li; Li Li; Anqi Zhao; Binhua Han; Yajun Fan; Chunming Liu; Jianjun Liu (1321-1327).
Five isoflavones, puerarin, daidzin, daidzein, 3′-hydroxy-puerarin and 3′-methoxy-puerarin were isolated and purified simultaneously from Pueraria lobata for the first time by high performance counter-current chromatography (HPCCC) using a system consisting of hexane–ethyl acetate–n-butanol–ethanol–water (0.5 : 2 : 1 : 0.5 : 3.5, v/v/v/v/v). In total, 155 mg of puerarin, 41 mg of daidzin, 12 mg of 3′-hydroxy-puerarin, 6 mg of 3′-methoxy-puerarin and 106 mg of daidzein were purified from 5.1 g of the ethyl acetate extract of P. lobata; the purities of the five isoflavones as determined by high performance liquid chromatography (HPLC) were 98.77%, 96.53%, 97.59%, 90.21% and 98.36%, respectively. The structures of the five compounds were identified by their retention time and the electrospray ionization multi-stage tandem mass spectrometry (ESI-MSn) in the positive ion mode, and confirmed by 1H-NMR experiments. The characteristic ESI-MS fragmentation patterns of the five compounds are discussed.
A novel photoelectrochemical sensor for the detection of α-fetoprotein based on a mesoporous TiO2–CdS QD composite film by Xiaoyan Yang; Jingyu Li; Junliang Fu (1328-1332).
In this article, a label-free photoelectrochemical immunosensor based on a CdS-modified mesoporous TiO2 film has been developed. The CdS quantum dots could be deposited onto the mesoporous TiO2 film by electrochemical deposition, which could enhance the photocurrent intensity in the visible region. Employing specific binding of antigen–antibody, α-fetoprotein (AFP) could be captured on the surface of the modified electrode. Based on the steric hindrances, the photocurrent intensity decreased with the increase in AFP concentration. A linear response from 0.05 ng mL−1 to 20 ng mL−1 was obtained for AFP detection and the detection limit was 0.02 ng mL−1. Moreover, the practical determination of AFP in human serum was also investigated.
Synthesis and characterization of diphenyl–phenyl polysiloxane as a high-temperature gas chromatography stationary phase by Pengchao Zhao; Shuang Teng; Miao Yu; Na Niu; Xinxin He; Bo Wu (1333-1338).
A new type of copolymer diphenyl–phenyl polysiloxane (DPPP) was synthesized and coated inside the fused-silica capillary columns, which were used as a novel stationary phase in gas chromatography (GC). The thermal stability, selectivity, polarity, column efficiency, and maximum allowable temperature for these capillary columns were characterized, and the results indicated that the prepared columns exhibited higher column efficiency (3560 plates per m compared to 3630 plates per m). The excellent film-forming capability on the inner surface of fused-silica capillary columns was proved by the analysis of Grob test compounds. The maximum allowable temperature was determined to be 360 °C, which indicated that the copolymer was highly suitable for high-temperature separation. In addition, superior peak shapes were observed when a DPPP column was used to separate a substituted mixture of benzene and polycyclic aromatic hydrocarbons, which suggests its great potential for application in GC analyses.
An electrochemical sensing method for the determination of levodopa using a poly(4-methyl-ortho-phenylenediamine)/MWNT modified GC electrode by Mohammad Ali Kamyabi; Najmeh Rahmanian (1339-1348).
A glassy carbon electrode (GCE) modified with poly 4-methyl-ortho-phenylenediamine (4-MoPD) and multi-wall carbon nanotubes (MWNTs) was used for selective and sensitive voltammetric determination of levodopa (l-Dopa) in phosphate buffer solution of pH 7.0. The mechanism of electrooxidation at this modified electrode was a purely diffusion-controlled reaction involving one-electron in the rate-determining step with a transfer coefficient (α) of about 0.60. The modified electrode exhibits good catalytic activity for oxidation of l-Dopa with high sensitivity (0.796 μA μmol−1), in a wide concentration range, (4.16 × 10−7–4.00 × 10−4 mol L−1), and a detection limit of 1.01 × 10−7 mol L−1. The anodic oxidation peak potential of l-Dopa (in PBS, pH 7.0) at the surface of the proposed modified electrode occurred at low overpotential (0.22 V vs. Ag/AgCl) and the oxidation current is about 16 times that of a bare GCE. Furthermore, the modified electrode can separate the signals of ascorbic acid (AA) and l-Dopa in a mixed solution with a peak separation of 183 mV. The present biosensor has been applied successfully for determination of low concentrations of l-Dopa in a pharmaceutical drug.
Gold-nanoparticle, functionalized-porous-polymer monolith enclosed in capillary for on-column SERS detection by Yingcheng Pan; Xuan Wang; Han Zhang; Yan Kang; Ting Wu; Yiping Du (1349-1357).
In this work, gold-nanoparticle, functionalized glycidyl methacrylate-ethylene dimethacrylate (GNPs@GMA-EDMA), porous-polymer monoliths were prepared via an on-site synthesis method and enclosed in silica capillary as sensitive, uniform, and stable surface-enhanced Raman scattering (SERS) substrates. The on-column detection technique was used for SERS detection. The 4-mercaptopyridine (4-Mpy) at 1 × 10−7 M concentration was successfully detected on the SERS substrate. Uniformity was examined by collecting 4-Mpy spectra at 10 random locations on the capillary column, and the relative standard deviations (RSDs) were 18.74% and 15.83% for corresponding Raman intensities. The GNPs@GMA-EDMA showed great SERS-active stability in the first month after synthesis and could provide stable SERS signals of 4-Mpy within 8 months. The detection ability of this SERS-active monolith for pesticides, dyes and biomolecules was demonstrated by phosmet, crystal violet and adenine. Phosmet in real samples was analyzed by this substrate, with recovery of 89.78–109.91% and RSDs of 4.14–8.78%. The SERS-active porous polymer monoliths could serve as a novel SERS substrate for rapid in situ analysis on a capillary column.
The development of a multiplex real-time PCR to quantify Fusarium DNA of trichothecene and fumonisin producing strains in maize by Viktoria Preiser; Daniela Goetsch; Michael Sulyok; Rudolf Krska; Robert L. Mach; Andreas Farnleitner; Kurt Brunner (1358-1365).
Contamination of cereals with Fusarium species is one of the major sources of mycotoxin contamination in food and feed. Despite great progress in plant breeding, a complete resistance to Fusarium species has not yet been achieved. Visual scoring of disease symptoms combined with the determination of mycotoxins are common approaches to identify new Fusarium tolerant lines, but these methods are only indirect and therefore of limited use to determine the level of resistance against Fusarium spp. Aiming at a rapid and sensitive quantification method for trichothecene and fumonisin producing Fusarium species in maize, a multiplex qPCR assay was developed. This method enables high-throughput screening of a large number of samples for Fusarium infection in a relatively short time due to simultaneous quantification of the mycotoxin-related genes tri5 and fum1. The multiplex method was applied to 24 maize field samples. All these were analyzed for the trichothecenes deoxynivalenol (DON), DON-3-glucoside (D3G), nivalenol (NIV), 3-acetyl-DON (3-ADON), T-2 toxin, HT-2 toxin, diacetoxyscirpenol (DAS) and neosolaniol (NEO) and the fumonisins fumonisin B1 (FB1), fumonisin B2 (FB2) and fumonisin B3 (FB3) by LC-MS/MS and for the mycotoxin producers by the new qPCR multiplex assay. The assay was found to be specific for fumonisin as well as for trichothecene producing Fusarium species. The limit of quantification was found to be 0.32 pg per μl for both Fusarium strains. To the best of our knowledge, this is the first report of the use of a multiplex qPCR for the quantification of trichothecene and fumonisin producing Fusarium species.
Evaluation of organochlorine pesticides in soil using ultrasound-assisted liquid phase microextraction by Wenting Zhao; Tong Wu; Jindong Li; Runhua Lu; Peng Wang; Yue Chen; Donghui Liu; Zhiqiang Zhou (1366-1371).
A simple and inexpensive sample pretreatment method, ultrasound-assisted liquid phase microextraction, combined with a novel solvent layering technique, was developed for extraction of organochlorine pesticides from soil. Samples were analyzed by gas chromatography with an electron capture detector. Of five possible extraction solvents tested, xylene, with a density of 0.86 g mL−1, was selected for further method development. Soil samples and solution were mixed in an ultrasonic water bath and separated using centrifugation. The extraction solvent was collected on the solution surface using a pipette. Parameters, such as extraction solvent type and volume, extraction time, and NaCl concentration were optimized. Under optimal conditions, recoveries ranged from 71.6% to 114.6% and correlation coefficients ranged from 0.9961 to 0.9996. Detection limits, calculated as 3× the signal-to-noise ratio, were from 0.04 to 0.18 μg L−1. The standard deviations ranged from 6.7% to 19.6%.
Determination of unconjugated non-steroidal anti-inflammatory drugs in biological fluids using air-assisted liquid–liquid microextraction combined with back extraction followed by high performance liquid chromatography by Mir Ali Farajzadeh; Mohammad Reza; Afshar Mogaddam; Mahdi Bamorowat (1372-1379).
An analytical method based on air-assisted liquid–liquid microextraction and high performance liquid chromatography-variable wavelength detector is presented for the extraction and determination of naproxen, diclofenac, and ibuprofen in biological fluids. In this technique, the target drugs are extracted into several microliters of chloroform from an aqueous sample (human plasma or urine) by using a syringe to repeatedly aspirate and disperse the aqueous solution and chloroform mixture. The enriched analytes are then back-extracted into an alkaline aqueous phase prior to their injection into the separation system. Various parameters affecting the extraction efficiency such as type and volume of extraction solvent, extraction times, salt addition, and pH were evaluated. Under optimum extraction conditions, this method showed low limits of detection and quantification between 0.20–0.52 and 0.58–1.60 ng mL−1, respectively. Enrichment factors and extraction recoveries were in the ranges of 390–470 and 78–94%, respectively. The method was successfully applied to determine the unconjugated selected drugs in biological samples.
Hollow fiber supported liquid membrane coupled with high performance liquid chromatography for highly sensitive determination of bisphenols in environmental water samples by Li-Jie Dong; Zhi-Qiang Tan; Ming Chen; Jing-Fu Liu (1380-1386).
Hollow fiber supported liquid membrane (HFSLM) was applied for the extraction of bisphenols (BPs), including bisphenol S, bisphenol AF, tetramethylbisphenol A, tetrachlorobisphenol A and tetrabromobisphenol A from water samples. The undecane solution of 1.0% (m/v) tri-n-octylphosphine oxide was supported on the pores of the polypropylene hollow fiber membranes (280 μm i.d., 50 μm wall thickness, 0.1 μm pore size, 60 cm length) to form a liquid membrane. The lumen of the hollow fiber membranes was then filled with 0.3 M NaOH as an acceptor to prepare the extraction device, which was placed into a 500 mL water sample (donor) adjusted to pH 4.0 with HCl. After shaking at 200 rpm for 180 min, the acceptor (∼30 μL) was collected and injected into the high performance liquid chromatography system for the determination of the BPs. The proposed HFSLM method provided good enrichment factors (1370–2138), low detection limits (0.1–0.2 μg L−1) and good repeatability (RSD = 2.6–8.8%, n = 5). The proposed method was applied to determine the five target BPs in waste water, tap water, river water and lake water samples with satisfactory spiked recoveries (68.6% to 134%) at 0.5 and 1 μg L−1 spiking levels, demonstrating the practicality of the proposed method for the determination of BPs in environmental water samples.
An l-dopa electrochemical sensor based on a graphene doped molecularly imprinted chitosan film by Lu Lin; Hui-Ting Lian; Xiang-Ying Sun; Ya-Ming Yu; Bin Liu (1387-1394).
A molecularly imprinted polymer (MIP) based sensor for detecting l-dopa was fabricated based on the composite of graphene (GR) and chitosan (CS). The microstructure and composition of the imprinted films characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Raman spectroscopy and electrochemical impedance spectroscopy (EIS) indicated that the modified film of GR-MIPs had been formed successfully. Electrochemical evaluation results showed that the sensor exhibited a satisfactory selectivity for molecular binding with an imprinting factor (IF) of 6.2 and a wide linear range from 0.4 μM to 100 μM with a low detection limit of 0.012 μM. This electrochemical sensor exhibited great promise for accurate determination of l-dopa in pharmaceutical preparations and human blood serum for recoveries ranging from 95.0 to 108.0%. Furthermore, compared to imprinted films without graphene doping, GR-MIPs showed a superior chiral sensing for l-dopa in the presence of d-dopa. The results reveal that the insertion of graphene brought about an enhanced sensitivity for chiral sensing and has the potential for application in chiral recognition.
Cathodic electrochemiluminescence of a CdSe/ZnS QDs-modified glassy carbon electrode and its application in sensing of Pb2+ by Li Wang; Di Luo; Dongdong Qin; Duoliang Shan; Xiaoquan Lu (1395-1400).
This paper reports the electrochemiluminescence (ECL) behavior of CdSe/ZnS with K2S2O8 as the coreactant. The effects of pH, K2S2O8 concentration, the duration of the reaction of 4-ATP with GCE and the duration of the reaction of 4-ATP/GCE with QDs on ECL intensity were studied in detail. A possible ECL reaction mechanism was then proposed. In addition, it was observed that the ECL intensity was efficiently quenched by trace amounts of heavy metal ion. Based on the quenching effect of Pb2+ upon the ECL of CdSe/ZnS QDs, a QDs-ECL sensor was constructed to detect Pb2+ in preserved duck egg. The sensor showed good reproducibility and stability.
Humidity effects on resolution and sensitivity of UV-FAIMS in VOCs detection by Hong-Wei Wang; Chi-Lai Chen; You-Jiang Liu; Xiao-Tian Zhang; De-Yi Kong; Xiao-Zhi Wang; Ji-Kui Luo (1401-1406).
Humidity is a key environmental parameter for VOCs detection technology. A study of the effects of humidity on both resolution and sensitivity of UV-FAIMS was performed at ambient temperature and pressure. This study was based on the detection and analysis of the differences in spectra (height, position and shape) and the α function of VOCs under different degrees of humidity. A total of three types of VOCs (ketones, alcohols and aromatics) were chosen as detection samples and a self-developed UV-FAIMS as a measurement instrument. The results show that sensitivity is inversely proportional to humidity for all VOCs. In addition, the resolution–humidity relationship exhibits strong dependence on the polarity of the sample ions. As relative humidity increased from 0% to 100%, the sensitivity of ketones, alcohols and aromatics was reduced by 30.9–73.0%, 40.3–64.3% and 75.1–91.6%, respectively. However, increasing humidity significantly enhanced the resolution of ketones and alcohols in the ranges of 1.82–11.82 times and 1.23–6.69 times, respectively, and hardly affected that of aromatics. Consequently, the appropriate humidity of carrier gas is of great importance in the use of UV-FAIMS.
A metal-enhanced fluorescence study of primary amines: determination of aminoglycosides with europium and gold nanoparticles by Mehmet Gokhan Caglayan; Feyyaz Onur (1407-1414).
This paper describes a lipoic acid capped europium nanoparticle-based assay for the fluorimetric detection of primary amines. The assay is based on fluorescence quenching resulting from complex formation between amines and lipoic acid on the surface of europium nanoparticles. For the application of the assay, the aminoglycosides were determined in pharmaceuticals and milk. The determination of the aminoglycosides were conducted via fluorescence quenching at 315 nm (λex = 280 nm) at a pH of 5. The metal enhanced fluorescence method with gold nanoparticles was used, in order to enhance the fluorescence of europium nanoparticles. In this manner, the detection limits of aminoglycosides were lowered. The Stern–Volmer constants and the ground-state UV spectra of interaction proved the static quenching that stemmed from the reaction between amines and lipoic acid. Three members of aminoglycosides; amikacin, gentamicin and tobramycin were quantified in the range of 0.75–27.5 μg mL−1, 0.40–26 μg mL−1 and 0.20–25 μg mL−1, respectively.
Chemical identification of cannabinoids in street marijuana samples using electrospray ionization FT-ICR mass spectrometry by Iendel R. Nascimento; Helber B. Costa; Lindamara M. Souza; Letícia C. Soprani; Bianca B. Merlo; Wanderson Romão (1415-1424).
The Cannabis sativa L. plant is a species rich in a variety of cannabinoid compounds and Δ9-tetrahydrocannabinol (Δ9-THC) has been reported as a main psychotropic substance. In this study, electrospray ionization (ESI), coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), was used in order to perform a direct and fast analysis of street marijuana samples. ESI(−)-FT-ICR MS detected 21 cannabinoid species in the deprotonated form, [M − H]−. Other species were detected in regions of m/z 600–800 and 800–1000, corresponding to dimers and trimers of cannabinoids. In addition, ESI(−) was better able to analyze the chemical profile of terpenophenolic species (CcHhOo) than ESI(+). ESI(+)-FT-ICR MS detected the presence of adulterants such as cocaine, lidocaine, and nicotine. Finally, the sensitivity of fast blue B colorimetric testing was also evaluated and the results were compared to the ESI(−)FT-ICR MS data.
Simultaneous determination of twenty-six components of Flos Lonicerae japonicae–Fructus Forsythiae herb couple using UPLC-ESI-MS/MS: application to its preparations by Wei Zhou; Jinjun Shan; Wenzheng Ju; Shouchuan Wang; Minxin Meng; Baochang Cai; Liuqing Di (1425-1437).
In this study, we developed a method using UPLC-ESI-MS/MS to simultaneously determine the contents of forsythoside B, loganin, macranthoidin B, dipsacoside B, rutin, arctiin, phillyrin, pinoresinol-β-d-glucoside, 3,5-dicaffeoylquinic acid, 3,4-dicaffeoylquinic acid, isoquercitrin, hyperoside, astragalin, luteoloside, genistin, arctigenin, neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, quercetin, luteolin, genistein, quinic acid, caffeic acid, isoforsythoside and forsythoside A in Flos Lonicerae japonicae–Fructus Forsythiae herb couple with a run time of only 8 min. The separation was performed on an Acquity UPLC HSS T3 C18 column (100 mm × 2.1 mm, 1.8 μm) at a flow rate of 0.4 mL min−1, and acetonitrile/methanol (4 : 1, v/v) – 0.4% formic acid was used as the mobile phase. Variations in the intra- and inter-day precision of all analytes were below 5.00%; the matrix effect of all the analytes was found to be within the acceptable range; and the accuracy was evaluated by a recovery test within the range of 95.63–103.10%. The method successfully quantified the twenty-six compounds in the Flos Lonicerae japonicae–Fructus Forsythiae herb couple. Moreover, it transpired through hierarchical cluster analysis and principal component analysis that the consistency of the Flos Lonicerae japonicae–Fructus Forsythiae herb couple as the two important herbs in Flos Lonicerae japonicae–Fructus Forsythiae herb couple preparations (Shuang-Huang-Lian oral liquid, Yin-Qiao-Jie-Du tablet and Fufang Qin-Lan oral liquid), except that in Qin-Re-Jie-Du oral liquid was relatively good. The results showed that the method was accurate, sensitive and reliable.
In situ electrochemical synthesis of Ni-capped electrochemiluminescence nanoprobe for ultrasensitive detection of cancer cells by Qingqing Wen; Pei-Hui Yang (1438-1445).
A facile, novel and in situ electrochemical synthesis of a Ni-capped (NiS@CdS/PANINF) composite electrochemiluminescence (ECL) nanoprobe was developed to fabricate an ECL cytosensor for the ultrasensitive detection of cancer cells. Polyaniline nanofibers (PANINF) films were electropolymerized onto the surface of a bare GCE electrode, and then Ni-capped (NiS@CdS/PANINF) composite nanoprobes were successfully prepared by the in situ electrochemical approach using PANINF as a template. The ECL performance of the proposed nanoprobe showed a ∼5-fold enhancement compared to pure CdS NCs, which were synthesized in an aqueous solution system. Further, aptamer was modified to the electrode surface to fabricate an ECL cytosensor, which was identified as a recognition element of MCF-7 cancer cells. The fabricated ECL cytosensor achieved a wide dynamic range from 12 to 1.2 × 106 cells per mL for the detection of MCF-7 cancer cells, with a low detection limit of 8 cells per mL (S/N = 3). This ECL cytosensor exhibited not only high sensitivity, selectivity and stability but also showed a novel strategy for developing ECL biosensor systems. In addition, it could be extended to the highly sensitive detection of other biological samples.
The development of a sensitive and rapid liquid-phase microextraction method followed by liquid chromatography mass spectrometry for the determination of zearalenone residues in beer samples by Ioanna E. Rempelaki; Vasilios A. Sakkas; Triantafyllos A. Albanis (1446-1452).
In this work, a new, rapid and sensitive, dispersive suspended microextraction procedure, followed by liquid chromatography mass spectrometry, was employed for the determination of zearalenone in beer samples. The liquid-phase microextraction method is based on solvent dispersion and magnetic stirring. Validation was carried out according to the Commission Decision 2006/406/EC guidelines. Under the optimum conditions, the limit of detection (LOD) was determined to be 0.44 μg kg−1 and the limit of quantification was calculated to be 1.45 μg kg−1. The relative standard deviation (RSD, n = 5) for inter-day precision was found to be 5.4% and for intra-day precision it was found to be 3.6%. The linearity was obtained using five points in the concentration range of 1.5–45 μg kg−1 and the recovery was >91%. The occurrence of the selected mycotoxin was studied in several beer samples collected from the local market from the region of Epirus.
Colorimetric detection of melamine based on the size effect of AuNPs by Ida Evangeline Paul; A. Rajeshwari; T. C. Prathna; Ashok M. Raichur; N. Chandrasekaran; Amitava Mukherjee (1453-1462).
A simple colorimetric detection of melamine was studied using 15 nm (AuNPs-I), 30 nm (AuNPs-II), and 40 nm (AuNPs-III) citrate-capped gold nanoparticles (AuNPs). The AuNPs aggregated in aqueous solution in the presence of melamine, showing a visual color change from red to blue. This color change led to a shift in the absorption peak from 527 nm, 526 nm, and 525 nm to 638 nm, 626 nm, and 680 nm for AuNPs-I, AuNPs-II, and AuNPs-III, respectively. For all the three AuNPs, linearity was observed between the melamine concentration in aqueous solution and the absorbance ratios, A638/527, A626/525, and A680/526, respectively. The limit of detection (LOD) for melamine for the AuNPs-II was found to be 2.37 × 10−8 M (correlation coefficient R2 = 0.9745), which showed better sensitivity as compared to the LOD of the AuNPs-I and AuNPs-III, which were 3.3 × 10−8 M and 8.9 × 10−8 M, respectively. The synthesis of AuNPs-II also involved a lower HAuCl4 concentration compared with the other two types of AuNPs, which may reduce the process cost. The AuNPs-II was selected to analyze melamine in pre-treated milk samples, and the recovery percentage was in the range of 91–106%. Thus, the efficient detection of melamine was possible using AuNPs-II for the on-site detection without the aid of expensive instruments.
Investigation of the adsorption behaviour of different types of dyes on MIL-100(Fe) and their removal from natural water by Yaoyao Jia; Qing Jin; Yan Li; Yuxiu Sun; Jianzhong Huo; Xiaojun Zhao (1463-1470).
Metal–organic framework MIL-100(Fe) has high surface area, mesoporous cages, metal active sites and excellent water stability. These fascinating properties endow MIL-100(Fe) with the potential to extract organic dyes from environmental water samples. In the present work, MIL-100(Fe) is synthesized and applied as an adsorbent to remove three different types of dyes from aqueous solution in view of assessing the adsorption isotherms, kinetics and thermodynamics, desorption, and adsorbent regeneration. The adsorption for methylene blue and methyl blue follows a pseudo-second-order kinetics and fits the Freundlich model. The adsorption is a spontaneous process, but is controlled by different thermodynamic parameter changes. Moreover, MIL-100(Fe) could hardly adsorb isatin. Variables influencing the adsorption efficiency, such as adsorption time, temperature, solution pH, adsorbent dosage and salt concentration, are investigated. No remarkable effects of pH and ionic strength are observed for the adsorption of methylene blue and methyl blue on MIL-100(Fe). The used MIL-100(Fe) could be regenerated effectively and recycled without a significant loss of adsorption ability. The adsorption efficiency is about 100% for methylene blue and 52.1% for methyl blue, and the developed method is applied to remove two types of dyes in local water samples.
Simultaneous determination of dopamine, ascorbic acid and uric acid using a multi-walled carbon nanotube and reduced graphene oxide hybrid functionalized by PAMAM and Au nanoparticles by Siyuan Wang; Wen Zhang; Xia Zhong; Yaqin Chai; Ruo Yuan (1471-1477).
A nanohybrid based on reduced graphene oxide functionalized by poly(amido-amine), multi-walled carbon nanotubes and Au nanoparticles (RGO–PAMAM–MWCNT–AuNPs) for simultaneous electrochemical determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) was reported in this paper. The RGO–PAMAM–MWCNT–AuNP-modified electrode showed a high selectivity towards the oxidation of AA, DA, and UA, and resolved their overlapped oxidation peaks into three well-defined peaks. The RGO–PAMAM–MWCNT–AuNP nanohybrids were characterized by scanning electron microscopy (SEM). Several important parameters that control the performance of the electrochemical sensor were investigated and optimized. Under optimal conditions by a differential pulse voltammetry (DPV) method, the linear response ranges for the determination of AA, DA, and UA are 20 μM to 1.8 mM, 10 μM to 0.32 mM, and 1 μM to 0.114 mM in the co-existence systems, respectively. The corresponding detection limits are 6.7 μM, 3.3 μM and 0.33 μM (S/N = 3), respectively.
Gold nanoparticles as a colorimetric probe for the determination of N-acetyl-l-cysteine in biological samples and pharmaceutical formulations by Saadat Rastegarzadeh; Fatemeh Hashemi (1478-1483).
In this study, gold nanoparticles (AuNPs) have been synthesised using ascorbic acid as a reducing agent and employed in the design of an in situ colorimetric probe for the spectrophotometric detection of N-acetyl-l-cysteine (NAC). The analyte induced an intensity decrease in the plasmon resonance absorbance of the AuNPs, and this represents a simple and reliable colorimetric assay for the quantification of NAC. The proposed approach allows the determination of NAC ranging from 3.0 to 100.0 μmol L−1 with a limit of detection of 2.7 μmol L−1. The relative standard deviations for eight replicate measurements of NAC at concentration levels of 5.0 and 30.0 μmol L−1 were calculated to be 3.8 and 0.6%, respectively. This probe was successfully applied for the rapid determination of NAC in human urine samples and tablet formulations.
Local linear embedded regression in the quantitative analysis of glucose in near infrared spectra by Krishna Chaitanya Patchava; Mohammed Benaissa; Bilal Malik; Hatim Behairy (1484-1492).
This paper investigates the use of Local Linear Embedded Regression (LLER) for the quantitative analysis of glucose from near infrared spectra. The performance of the LLER model is evaluated and compared with the regression techniques Principal Component Regression (PCR), Partial Least Squares Regression (PLSR) and Support Vector Regression (SVR) both with and without pre-processing. The prediction capability of the proposed model has been validated to predict the glucose concentration in an aqueous solution composed of three components (urea, triacetin and glucose). The results show that the LLER method offers improvements in comparison to PCR, PLSR and SVR.
Highly sensitive electrochemical sensor based on pyrrolidinium ionic liquid modified ordered mesoporous carbon paste electrode for determination of carbendazim by Yu Ya; Tianshun Wang; Liping Xie; Junjie Zhu; Li Tang; Dejiao Ning; Feiyan Yan (1493-1498).
A simple, highly sensitive electrochemical sensor based on a pyrrolidinium ionic liquid (PIL) modified ordered mesoporous carbon (OMC) paste electrode (PIL/OMCPE) was developed for the determination of carbendazim by differential pulse voltammetry. The structure of the synthesized OMC was characterized by transmission electron microscopy. The electrochemical characteristics of the modified electrodes were investigated using [Fe(CN)6]3−/4− as the electrochemical probe. Compared with other electrodes, the PIL/OMCPE exhibited a larger electrode surface and a faster electron-transfer rate. The electrochemical behavior of carbendazim at the modified electrode was investigated by cyclic voltammetry. The PIL/OMCPE exhibited good performance for the electrochemical oxidation of carbendazim. The peak current of carbendazim at the PIL/OMCPE significantly increased in comparison with those at the bare carbon paste electrode (CPE), OMCPE, and PIL modified CPE. Under optimal conditions, the relationship between the carbendazim concentration and peak current was studied, and the developed PIL/OMCPE sensor exhibited good linearity in a wide range from 1.25 to 800 μg L−1. The limit of detection was estimated to be 0.500 μg L−1 (signal-to-noise ratio = 3). The proposed sensor was successfully applied for the determination of carbendazim in sugarcane samples with satisfactory results.
Study of modern artistic materials using combined spectroscopic and chromatographic techniques. Case study: painting with the signature “Picasso” by Maria Rosa López-Ramírez; Natalia Navas; Luis R. Rodríguez-Simón; Juan C. Otero; Eloisa Manzano (1499-1508).
A painting bearing the signature “Picasso” was investigated and its components – pigments and binders – were characterised using micro-Raman spectroscopy (mRS) combined with other analytical techniques such as Scanning Electron Microscopy with Energy Dispersive X-ray analysis (SEM/EDX), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Gas Chromatography-Mass Spectrometry (GC-MS). We identified the pigments in order to assess chronological inconsistency (anachronistic pigments) with the work of the Spanish artist Pablo Picasso (1881–1973) by means of in situ and cross-section analyses by mRS. Using mRS we identified the pigments ‘phthalocyanine blue’, ‘phthalocyanine green’, ‘pyrazolone orange’, ‘anatase’ and ‘rutile’ (titanium dioxide). These results were corroborated by SEM/EDX elemental analysis, which detected Ba, S and Zn among others, so prompting discussion about the use of ready-mixed house paints (Ripolin®). The ground layer was also investigated by mRS, which confirmed the use of rutile (titanium dioxide), calcite and phyllosilicates (Al, Fe). mRS on the white area identified the binding media as beeswax, the most important wax used in art. ATR-FTIR and GC-MS analysis support the presence of a wax and an oil–resin mixture as the binder, described in previous research as being used by Picasso. All the artist materials identified were widely used in art at the beginning of the twentieth century according to the available bibliography and are therefore consistent with the Picasso era. To the best of our knowledge this is the first attempt to investigate a painting related to Picasso using the combination of analytical techniques proposed here.
A novel micro pressurized liquid extraction method for very rapid solid sample preparation by Fadi L. Alkhateeb; Kevin B. Thurbide (1509-1516).
A novel micro pressurized liquid extraction (μPLE) method is introduced, which employs rapid heating in a static mode to remove analytes from 5–10 mg samples in as little as 10 seconds using only 125 μL of solvent. For example, using pharmaceutical tablets and green tea leaves as test samples, 99 ± 5% of acetylsalicylic acid and 97 ± 4% of acetaminophen (both n = 4) were each extracted into methanol from tablets in 10 seconds at 150 °C. For green tea, 100 ± 20% (n = 4) of the caffeine present could be extracted into methanol after only 20 seconds at 275 °C. These extraction results compared very well with those of conventional PLE trials on the same samples, although μPLE was much faster and less solvent intensive. As an application, μPLE was found to extract 101 ± 7% (n = 6) of Fluoxetine Hydrochloride from dried blood spot analysis cards after only 20 seconds at 250 °C. The instrumentation and procedure required for this technique are relatively simple, inexpensive, and can easily be adapted in most laboratories. Overall, the results indicate that μPLE may provide a useful method for rapidly preparing solid samples for analysis using little solvent. The potential advantages and limitations of the method are presented and discussed.
Multi-commutation flow system with on-line solid phase extraction exploiting the ion-imprinted polymer and FAAS detection for chromium speciation analysis in sewage samples by Barbara Leśniewska; Laura Trzonkowska; Elżbieta Zambrzycka; Beata Godlewska-Żyłkiewicz (1517-1526).
A multi-commutation flow analysis system using on-line solid phase extraction and flame atomic absorption spectrometric detection (MCFA-FAAS) was developed for the study of chromium speciation in sewage samples. A new chromium imprinted polymer was prepared and applied as a selective sorbent for the separation and preconcentration of Cr(iii) ions. The polymer was prepared using a Cr(iii)-8-hydroxyquinoline complex as a template, styrene as a functional monomer, and divinylbenzene as a crosslinking monomer using 2,2′- azobisisobutyronitrile as an radical initiator for bulk polymerization. The chromium imprinted polymer exhibits good chemical and mechanical stability, sorption capacity and selectivity towards Cr(iii) ions. The analyte, Cr(iii) ions, was quantitatively retained on the sorbent at pH 9, eluted with 0.3 mL of 0.1 mol L−1 nitric acid and determined by FAAS with a detection limit of 2.1 ng mL−1 and a 33-fold preconcentration factor obtained with a 10 min loading time. The MCFA-FAAS system is fully automated and enables analysis of 1 mL of sample in 4.5 min, which gives a throughput of 12 samples per hour. The accuracy of the proposed method was proved by analysis of a reference material of wastewater RES 10.2 (ielab). The method was successfully applied to the determination of trace amounts of Cr(iii) in municipal sewage samples.
Differentiation of vehicle top coating paints using pyrolysis-gas chromatography/mass spectrometry and multivariate chemometrics with statistical comparisons by Sheng-Hsiung Yang; Jermiah Y. Shen; Matt S. Chang; Gaston J. Wu (1527-1534).
The aim of this work was to evaluate the capabilities and feasibility of using the averaged mass spectra obtained from pyrograms for assessing the group distributions and similarities of vehicle paint samples. To achieve this, all the profiles of averaged mass spectra were examined using hierarchical cluster analysis and principal component analysis after data processing. The pyrograms of 54 vehicle top coating samples were characterized by mass fragments chosen from 15 major paint constituents commonly used in the paint industry and multivariate chemometric analysis based on 76 variables, used as indicators for the classification of paint samples. Not only the characteristics of the variables were discussed, but the discriminating power among the samples was also evaluated by adding six blind test samples. In addition, validation of this method was accomplished by mixing three sets of international proficiency test samples and 23 randomly selected paired samples for comparison purposes, and the results of these gave the expected discriminating capability of the technique developed. The results indicated that this method was a promising, efficient and time saving tool for examining top-coating paint traces, with the application of combined pyrolysis-gas chromatography/mass spectroscopy with multivariate chemometrics for forensic purposes.
Rapid assay for testing superoxide anion radical scavenging activities to natural pigments by ultra-high performance liquid chromatography-diode-array detection method by Lu Wang; Shu Liu; Zhong Zheng; Zifeng Pi; Fengrui Song; Zhiqiang Liu (1535-1542).
As a result of the donation of one electron, superoxide anion radicals (O2˙−) are produced in vivo, which are closely linked with several diseases in humans. In the past decades, some analytical methods for the determination of O2˙− scavenging capacity have been established. The most common methods in vitro are spectrum-based microplate screening assay using nitroblue tetrazolium (NBT) or cytochrome c as the target/probe for evaluating O2˙− scavenging activity. The target/probe is spectrophotometrically monitored at the ultraviolet-vis (UV-vis) region in the analysis of the samples with restraining UV-vis absorption. Nevertheless, the results of these methods were severely compromised when they were applied to analyze the samples with strong absorption in the visible region, such as natural pigments. To solve these problems, a simple and rapid assay combined with a new probe, a highly water-soluble tetrazolium salt, 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium sodium salt (WST-1) and ultra-high performance liquid chromatography-diode-array detection (UPLC-DAD) method was developed. Above all, this method could be adapted to samples of strong absorption in the visible region. In this study, the superoxide anion radical scavenging activities of various natural pigments were evaluated.
A simple and sensitive assay for the determination of nitrite using folic acid as the fluorescent probe by Lixia Lu; Chuanxia Chen; Dan Zhao; Fan Yang; Xiurong Yang (1543-1548).
Nitrite, which poses a serious threat to human health despite finding wide application in industry and architecture, has aroused more and more attention. In this study, a simple yet sensitive and selective fluorimetric assay for the determination of trace nitrite using folic acid as the probe has been established. Folic acid exhibited weak fluorescence in strong acidic conditions. However, a dramatic enhancement in the fluorescence intensity occurred when folic acid was exposed to ultraviolet (UV) radiation with the addition of nitrite. In particular, the UV radiation time played a vital role. Furthermore, the fluorescence intensity could reach the maximum by adjusting the pH value of the solution within a certain range. The excellent selectivity was attributed to the specificity of diazo reaction. The “turn-on” fluorescence strategy endows this assay with high sensitivity down to the 18 nM detection limit and a wide detection range from 50 nM to 32 μM. Finally, this assay was applied to detect nitrite in real samples with satisfactory results.
A multi-residue analysis of sulphonamides in edible animal tissues using QuEChERS extraction and HPLC-MS/MS by Hiba Abdallah; Carine Arnaudguilhem; Ryszard Lobinski; Farouk Jaber (1549-1557).
A HPLC double reaction monitoring MS/MS method was developed for the determination of a wide range (>20) of sulphonamide residues in several edible animal (sheep, pork, beef, chicken and dromedary) tissues. Sample preparation was based on the simultaneous extraction into acetonitrile solution followed by a clean-up using primary secondary amine beads. Quantification was carried out using matrix-matched calibration curves. The limit of detection (LOD) and limit of quantification (LOQ) ranged from 0.5 to 14.5 μg kg−1 and from 1.8 to 48.4 μg kg−1, respectively. The decision limit (CCα) and decision capability (CCβ) obtained were below 100 μg kg−1 for sulphonamides and below 5 μg kg−1 for dapsone. The method was validated in terms of recoveries and inter- and intra-day precision by reference analyses of meat samples using LC-Orbitrap MS and by the analysis of a reference material. The method was applied to the analysis of several animal tissue samples collected in Lebanon. The highest values were observed for sulfamethazine and sulfadimethoxine at 70.2 and 62.5 μg kg−1 in sheep tissues.
Glutathione-protected silver nanoclusters for sensing trace-level Hg2+ in a wide pH range by Yaping Zhong; Chun Deng; Yu He; Yili Ge; Gongwu Song (1558-1562).
An effective fluorescence method for the selective and rapid determination of trace-level Hg2+ in a wide pH range had been proposed based on the glutathione-protected Ag nanoclusters (NCs). Factors affecting the fluorescence intensity of GSH–Ag NCs were investigated. We found that the fluorescence intensity of Ag NCs remained high and stable under pH from 4 to 10, which benefits the monitoring of Hg2+ under different pH conditions in real samples. The fluorescence quenching mechanism is also discussed. The fluorescence of Ag NCs could be quenched in the presence of Hg2+ with a detection limit as low as 1 nM. Good linear correlations were obtained over the concentration range from 0 to 2.5 μM under different pH values (pH = 7, pH = 4 and pH = 9). In addition, this method was successfully applied to the determination of Hg2+ in real samples.
Preparation of a restricted access material–macroporous hybrid monolithic column – for on-line solid-phase extraction of the sulfonamides residues from honey by Yun-Kai Lv; Zhi-Yong Guo; Jin-Zhi Wang; Meng-Meng Guo; Lin-Kang Yu; Hui Fang (1563-1571).
A novel restricted access material–hybrid monolithic column (RAM–HMC) was prepared by the sol–gel method in a stainless-steel column and an in situ modification method in the through-hole of the HMC. The hydrophobic HMC was prepared by the acid-catalytic reaction of methyltrimethoxysilane and tetraethoxysilane. The hydrophilic structures were formed on the through-hole surface of the HMC by grafting 3-(2,3-epoxypropoxy) propyltrimethoxysilane. The synthetic conditions were optimized for obtaining the uniform microchannel and the stable skeleton structure. The chemical group, morphology, dynamic adsorption capacity, swelling, and hydrophilic and hydrophobic characteristics of the monolithic column were characterized by the IR, SEM, dynamic binding, solvent adsorption, chromatographic analysis of serum proteins and benzene series, respectively. When the RAM–HMC was used as a precolumn for the on-line extraction of sulfonamide residues from the honey samples, an enrichment factor of 16.9 and a better sample clean-up effect were obtained under the optimized conditions. The average recoveries of three sulfonamide antibiotics from honey spiked at 0.05, 0.1 and 0.2 mg kg−1 were in the range of 73.50–105.80% with a precision of 2.25–5.32%. The limits of detection and quantitation of the proposed method ranged from 6.9–14.6 μg kg−1 and 23.0–48.2 μg kg−1, respectively. The proposed method was successfully applied to the on-line extraction and determination of sulfonamide antibiotics in the honey sample.
Towards the development of a sensitive electrochemical sensor for the determination of chloramphenicol residues in milk by Guoyan Liu; Chunyan Chai (1572-1577).
A simple and sensitive bioelectrochemical immunoassay method has been developed to detect chloramphenicol (CAP) residues in milk. Monoclonal anti-CAP antibodies and conjugates of ovalbumin–CAP (OVA–CAP) were used to establish the indirect competitive enzyme-linked immunosorbent reaction, in which the CAP in standard solutions or samples competed with the OVA–CAP immobilized on 96-well polystyrene reaction plates for the limited binding sites on the CAP monoclonal antibodies. After the competitive immunoreaction, the plate was rinsed and HRP-labeled goat anti-mouse IgG was added into the testing wells. o-Phenylenediamine (o-PD)-hydrogen peroxide was applied as the hydrogen donor. The reaction solutions were transferred into the testing cells of a voltammetric analyzer and the electrochemical signals (oxidation peak currents of o-PD) were recorded by Differential Pulse Voltammetry (DPV) after the HRP-catalyzed reaction on the plate was stopped by 1 M H2SO4. The results showed that the sensitivity of the electrochemical immunoassay was higher than that of c-ELISA (competitive ELISA) in detecting chloramphenicol residue in milk. This method also demonstrated a linear response of oxidation peak current to chloramphenicol concentration over the 0.1–300 ng mL−1 range with a detection limit of 0.03 ng mL−1 CAP. The average recovery rate reached 87.7% based on the milk samples. Furthermore, the immuno-voltammetric apparatus is portable and can be used on site for detecting chloramphenicol residue in milk.
Role of electrostatic contributions in the separation of peptides with silica hydride stationary phases by Chadin Kulsing; Yuanzhong Yang; Reinhard I. Boysen; Maria T. Matyska; Joseph J. Pesek; Milton T. W. Hearn (1578-1585).
In this study a general analytical approach has been investigated with a focus on elucidating the impact of the free energy of electrostatic interactions associated with peptide retention with silica hydride stationary phases. In particular, the contributions from electrostatic interactions between peptides and the stationary phase in the presence of water-organic mobile phases of varying organic modifier content, and containing different percentages of formic or acetic acid, were assessed using a 4 μm silica hydride adsorbent (the Diamond Hydride™ phase) in capillary chromatographic format. The magnitudes of the electrostatic contributions were calculated from the effective peptide charge and the measured zeta potential values of the stationary phase as a function of mobile phase compositions. These studies revealed that in acidic mobile phases, and depending on the peptide structure, a significant proportion of the change in the overall free energy associated with peptide retention with the Diamond Hydride™ phase can be attributed to attractive electrostatic interactions. Multi-parametric relationships have been elaborated to include the electrostatic contribution in these retention-free energy dependencies. The general application of the presented analytical methods is expected to significantly broaden the application potential and the interpretation of the retention behaviour of peptides and other compound classes separated with silica hydride and related types of silica-based stationary phases.
Extraction and determination of sulfadiazine and sulfathiazole in milk using magnetic solid phase extraction-HPLC-UV by Rouhollah Karami-Osboo; Ramin Miri; Katayoun Javidnia; Mohammad Hossein Shojaee; Farzad Kobarfard (1586-1589).
Sulfonamides are heat-stable antibacterial drugs and their residues in milk increase the risk of human exposure and may cause food-borne illness. In this study, Fe3O4 magnetic nanoparticles (Fe3O4 MNPs) have been successfully used for the extraction of sulfadiazine (SDZ) and sulfathiazole (STZ) from milk samples. The effect of the amount of magnetic adsorbents, volume of extracted milk and sample pH were investigated and optimized. The experimental results showed that the suggested method possessed suitable analytical performance. Linearity was obtained over a concentration range of 0.25, 0.5, 1.0, 2.0 and 4 MRL with regression coefficients ranging from 0.9985 to 0.9978 for SDZ and STZ. The limits of detection (LOD) and quantification (LOQ), for the two analytes, were 10 and 30 ng mL−1, respectively. The proposed method was used for the analysis of different milk samples, and excellent recoveries in the range of 92.9–102.4% were obtained. These results indicated that the proposed method can be broadly used in the monitoring of low concentrations of drugs in milk samples and open fascinating perspectives in future studies.
A validated method to measure benzo[a]pyrene concentrations in tobacco by high-performance liquid chromatography-fluorescence detection by M. Carradus; K. G. McAdam; J. D. H. van Heemst; C. H. A. Goss; C. Wright (1590-1599).
This publication describes a validated method suitable for the quantification of Benzo[a]Pyrene (B[a]P) in tobacco blend and smokeless tobacco products by High-Performance Liquid Chromatography-Fluorescence Detection (HPLC-FLD). Samples were hydrated and extracted with a mixture of hexane and acetone. For the quantification of levels of B[a]P the sample extracts were subjected to adsorption chromatography using base-modified silica to remove co-extracted substances. The concentrated final extract was re-dissolved in acetonitrile and analysed by HPLC with fluorescence detection (FLD). B[a]P and the internal standard, deuterated B[a]P (D12-B[a]P) were resolved chromatographically. The method was validated and determined to be fit for purpose for the quantification of B[a]P in tobacco from 3R4F Kentucky reference cigarettes, a flue-cured Virginia cigarette tobacco blend containing 10% air-cured Burley tobacco, and a Tanzanian dark fire-cured cigarette blend. The method was also validated for smokeless tobacco products including commercially available dry snuff, soft pellet tobacco and pouched snus products over the concentration range of 0.38 ng g−1 to 150 ng g−1, based on extraction of a 0.5–2 g aliquot of sample. The measurement uncertainty at a confidence interval of approximately 95% was estimated from data generated by three analysts using two instruments on three separate occasions using matrix (pouched snus) fortification experiments. The expanded uncertainty of the method was ±21.3% of the mean B[a]P concentration.
A novel approach to determine the tyrosine concentration in human plasma by DART-MS/MS by Yu-qiao Song; Jie Liao; Cheng Zha; Bin Wang; Charles C. Liu (1600-1605).
A novel method for determining the tyrosine (Tyr) concentration in human plasma using direct analysis in real time mass spectrometry (DART-MS/MS) was developed. DART-MS/MS was performed in the positive ionization mode with multiple reaction monitoring (MRM) while using the ion transitions at m/z of 182.2/136.2 (Tyr). The experimental conditions and the sample preparation method were optimized to maximize the signal intensity. The linear range was determined to be 2–50 μg mL−1 from the calibration curve. The limit of quantification (LOQ) was 2 μg mL−1. The intra- and inter-day precisions did not exceed 15%, and the accuracies were less than ±15% for the 4, 18 and 38 μg mL−1 quality control (QC) samples. In addition, the extents of the matrix effects for the QC samples were also evaluated. Using the proposed method, samples could be analyzed simultaneously. The proposed DART-MS/MS-based method is not only rapid and simple with a high throughput but is also economical, as a mobile phase is not used. Furthermore, the method was used successfully to determine the Tyr levels in the plasmas of healthy volunteers and liver cancer patients. The proposed method should also be theoretically suitable for screening newborn babies for the hereditary tyrosinemia.
Magnetic solid-phase extraction based on Fe3O4@polyaniline particles followed by ultrafast liquid chromatography for determination of Sudan dyes in environmental water samples by Bo Xu; Yuanpeng Wang; Rui Jin; Xinpei Li; Daqian Song; Hanqi Zhang; Ying Sun (1606-1614).
Magnetic Fe3O4@polyaniline (Fe3O4@PANI) particles were successfully prepared and used as an adsorbent in the magnetic solid-phase extraction of Sudan dyes in environmental water samples. The Fe3O4@PANI particles adsorbed analytes were isolated from the sample matrix using an external magnetic field. The analytes were separated and determined by ultrafast liquid chromatography. Significant influential factors, including amount of Fe3O4@PANI particles, pH value, ion strength, extraction time, type of desorption solvent, volume of desorption solvent, desorption time and sample volume, were optimized. Satisfactory extraction recoveries were obtained with only 8 mg of Fe3O4@PANI particles. In addition, the Fe3O4@PANI particles can be reused after a facile washing process. The limits of detection for Sudan I, II, III and IV were 0.041, 0.080, 0.147 and 0.151 ng mL−1, respectively. The intra-day and inter-day precisions with relative standard deviations were 1.3–5.4% and 2.6–7.3%, respectively. Recoveries obtained by analyzing spiked environmental water samples were between 92.4% and 106.9%.
Non-destructive evaluation of total volatile basic nitrogen (TVB-N) and K-values in fish using colorimetric sensor array by Xingyi Huang; Riqin Lv; Liya Yao; Chao Guan; Fangkai Han; Ernest Teye (1615-1621).
For rapid evaluation of fish freshness, a colorimetric sensor array has been developed for the sensitive detection to measure simultaneously TVB-N and K value of fish during its storage period. Silver carps were taken as fish samples which were stored at constant temperature of 4 °C during experiment period. 10 kinds of porphyrin compounds and 6 pH indicators were selected as chromogenic materials in this experiment according to the previous study and the theoretical research. For comparison, total volatile basic nitrogen (TVB-N) values of fishes were tested by conventional chemical method, and the K-values were measured using High Performance Liquid Chromatography (HPLC). As sensing materials used in the sensor array were chromogenic, the color of the sensor array changed when reacting with odor emitted by fish sample. The color change profiles of the sensor array before and after exposure to the odor of each sample were got using image processing method. And color features were extracted to be analyzed using principal component analysis (PCA), linear discriminant analysis (LDA). The relationship between these analysis results and the TVB-N values and K-values obtained by conventional methods were established using support vector regression (SVR). And therefore models were set up for rapid prediction of TVB-N values and K-values, respectively. For the SVR model of TVB-N content and K-values, calibration correlation coefficient (Rtr) was 0.8564 and 0.8712, and the root mean square error of calibration (RMSEC) was 4.2177 and 0.06127, respectively. It is feasible to predict TVB-N values and K-values according to experiment results of colorimetric sensor array. The results indicated that the novel method based on colorimetric sensor array developed provide a feasible way for rapid and nondestructive evaluation of fish freshness.
Integration of a bio-chip technique with technetium-99m labeling provides zeptomolar sensitivity in liver cancer biomarker detection by L. Ma; B. C. Tang; W. J. Yang; Y. Liu; Y. L. Zhao; M. Li (1622-1626).
In the present work, we integrated a prepared bio-chip with 99mTc labeling to improve the immunoassay for cancer biomarker protein detection. Efficient binding of a 99mTc isotope-labeled secondary antibody to the biomarker protein pre-anchored to the bio-chip was followed by detection of γ rays from 99mTc decay via a Gamma Well Counter. We show that alpha-fetoprotein (AFP), a biomarker of liver cancer, can be detected down to 10−18 M concentration in a buffer solution with good reproducibility. This ultra-high sensitivity is attributed to the aggregation of the 99mTc isotope-labeled secondary antibody which greatly amplifies the γ rays emitted per AFP binding event. The tendency of the isotope-labeled secondary antibody to aggregate was indicated by dynamic light scattering studies on a rhenium/secondary antibody conjugate, a stable structural analogue of the 99mTc conjugate. The successful zeptomolar-range detection of cancer biomarkers opens new avenues for early disease diagnoses via integrating bio-chips with isotope-labeling techniques.
Is your ‘homogeneity test’ really useful? by Michael Thompson (1627-1629).
‘Homogeneity testing’ is a formal requirement in the preparation of reference materials for certification and for proficiency testing. Few scientists, however, seem to be aware of the rather severe limitations that apply to the outcome of any such test of a size that is economically feasible. Typically the tests have low statistical power to detect significance, and the resulting estimates of between-bottle standard deviation have wide confidence limits. Scientists should bear these limitations in mind and avoid being over-prescriptive when drafting standards and guides.
Determination of formaldehyde residue in cosmetics by short-column high performance liquid chromatography with mass spectrometric confirmation by Chunhua Lv; Jiannan Sun; Heyong Cheng (1630-1634).
In this work, we report a rapid analytical method for the determination of trace formaldehyde in cosmetics on a 12.5 mm C18 guard column. The shortest time (0.5 min) was obtained for one separation with 1.5 mL min−1 of methanol–water 50 : 50 (v/v) as the mobile phase at a column temperature of 30 °C. A linear response between peak area and the concentration of formaldehyde was obtained over the range 0.1 to 20 mg L−1 with a relative standard deviation of 1.4% (n = 10) at the concentration of 1.0 mg L−1 and a detection limit of 5.1 μg L−1. The confirmation assay by liquid chromatography tandem mass spectrometry indicated that there was no interfering effect from other carbonyl compounds. The proposed method was applied for the determination of formaldehyde residue in cosmetics at the mg L−1 level. Free formaldehyde up to 27 mg kg−1 was found in cosmetics and the spike recovery at the spiked levels of 1.0 and 10.0 mg L−1 varying from 92% to 105% was also obtained. The difference between the values determined by the proposed method and the standard spectrophotometric method was below 3.7%. The results proved the accuracy and precision of the method, showing potential for the routine analysis of formaldehyde residue.
Back cover (1635-1636).