Analytical Methods (v.5, #17)

Front cover (4275-4275).

Inside front cover (4276-4276).

Contents list (4277-4287).

The 2,2-diphenylpicrylhydrazyl (DPPH) assay is widely used in plant biochemistry to evaluate the properties of plant constituents for scavenging free radicals. The method is based on the spectrophotometric measurement of the DPPH concentration change resulting from the reaction with an antioxidant. Several protocols have been followed for this assay using different conditions such as different reaction times, solvents, pH and different compounds used as antioxidant standards. This review shows to what extent the mentioned parameters have the influence on the presented results.

This article reviews recent advances in electrochemical sensing and detection of explosive substances at nanomaterial-based electrode surfaces. The escalating threat of terrorist activities and growing environmental concerns have generated major demand for innovative, field-deployable tools for detecting explosives in a fast, sensitive, reliable and simple manner. Electrochemical sensors can address these demands as they possess attributes including high sensitivity and selectivity, speed, wide linear range, compatibility with microfabrication, minimal space and power requirements, and low-cost instrumentation. The redox properties of nitro-based explosives, namely the presence of easily reducible nitro groups, ideally lend themselves to electrochemical detection. Advances in the development of nanomaterials show strong potential to create electrochemical sensors for detecting explosives, with aspects such as very high surface area-to-volume ratio, convergent rather than linear diffusion, improved selectivity, catalytic activity, and unique electrical and optical properties which can be exploited for highly sensitive molecular adsorption detection. The goal of this article is to review recent advances in electrochemical detection of nitro-based explosives at working electrodes comprised of different nanomaterials. Specifically we will discuss the electroanalysis of nitro-based explosives on graphene, carbon nanotubes, nanoparticles and nanoporous material, and composites of these materials.

Developing a high-throughput microassay for large samples of fungal polysaccharides by Xiao-kui Ma; Qinqin Ruan; Hong Zhang; Weidong Qian (4310-4316).
The phenol–sulfuric acid method is routinely used for polysaccharide quantification. However, it represents a tedious procedure at a tube-scale and there is still no reliable procedure at the micro-scale for large sample analysis. By studying systematically the influence of the detecting conditions at the microplate scale, a colorimetric microassay has been developed with higher sensitivity, higher reproducibility, and higher absorbance response than the previous established protocol by Tatsuya Masuko and coworkers. As the key innovations, the influence of the vibration and the sequence of the chemical addition on the detection was elucidated for the first time at microplate scale. The microassay has been validated through the detection of large samples of polysaccharides generated from Phellinus sp under submerged cultures at the microplate scale. Moreover, its sensitivity, linear response, precision, reproducibility and feasibility were further validated through the detection of large samples containing various unknown amounts of polysaccharides from Phellinus sp. This study would contribute to the development of a reliable detection method for large samples of polysaccharides in a microplate format as an in-process analysis for the characterization of critical product/process attributes.

A rapid and simple colorimetric test for 2,2,2-cryptand (Kryptofix 2.2.2.) in solution by A. I. Anzellotti; A. R. McFarland; Ken F. Olson (4317-4320).
A new and versatile method for 2,2,2-cryptand determination in [18F]-labeled radiotracers is described. Proof of concept and applicability of the test method for the commercial radiotracer [18F]-FDG and model compounds FLT and FMISO were also proven.

The improvement of analytical accuracy and S/N (signal to noise ratio) based on conventional homogeneous fluorometry was always limited because of high background noise from complicated sample ingredients, buffer solution and lysates. Herein, a self-assembled Mn-doped ZnSe quantum dot–methyl viologen nanohybrid as an OFF–ON fluorescent probe is presented for the time-resolved fluorescence detection of tiopronin, showing high S/N and selectivity with a low detection limit of 0.1 μmol L−1 and a linear response ranging from 4 to 160 μM. We anticipate that this probe will have promising applications for sensitive biosensing and drug analysis.

An electrochemical sensor for the detection of antibiotic contaminants in water by Michael Jacobs; Vinay J. Nagaraj; Tim Mertz; Anjan Panneer Selvam; Thi Ngo; Shalini Prasad (4325-4329).
A nanochannel-based electrochemical sensor for the detection of trace amounts of erythromycin has been developed. The sensor is capable of specifically detecting erythromycin, at a sensitivity of 0.001 parts per trillion, in various water samples and has potential utility in the assessment of environmental water quality.

LC–ESI–MS/MS study of carvedilol and its stress degradation products by C. Purna Chander; B. Raju; Asmath Sulthana; R. Srinivas (4330-4335).
An isocratic liquid chromatography–electrospray ionization-mass spectrometry (LC–ESI–MS) method has been developed for the separation and identification of stress degradation products (DPs) of carvedilol (CAR), a non-selective β-blocker with vasodilatory properties. CAR was subjected to hydrolytic (acidic, alkaline and neutral), oxidative, photolytic and thermal stress conditions as per ICH guidelines Q1A (R2). The drug degraded under acidic, basic and photolytic stress conditions while it was stable under neutral, thermal and oxidative stress conditions. A total of five DPs were formed which were all well resolved from the parent drug as well as from each other on an Agilent XDB C-18 column (4.6 × 150 mm, 5 μm) using a mobile phase comprising of 20 mM ammonium acetate (pH adjusted to 6) (solvent A) and acetonitrile (solvent B) in an isocratic elution method. The structures of the degradation products were elucidated by using LC–ESI–MS/MS combined with accurate mass measurements.

Time domain nuclear magnetic resonance: a key complementary technique for the forensic differentiation of foam traces by Michele Mauri; Murali Krishna Dibbanti; Matteo Calzavara; Lucio Mauri; Roberto Simonutti; Valerio Causin (4336-4344).
Polymer foams have significant potential as contact traces for reconstructing the dynamics of felonies or for proving the presence of individuals at crime scenes. Discrimination of such items may be carried out using techniques, such as infrared spectroscopy or microscopy, which are commonly employed in the forensic examination of trace evidence. However, in the case of foams made of polyether urethane, the discriminating power attained by this approach is not satisfying. Time domain NMR (TD-NMR) allows the investigation of these materials in terms of total proton content (H%), rigid phase fraction and mobility of the soft phase (solid echo T2). Proton content and rigid fraction are partially correlated, in agreement with the chemistry of the material. The H% and T2 values are instead practically independent, and their simultaneous measurement allows discrimination of a specimen with high precision, comparable to TGA, without damaging the sample and using less than 50 mg of the material.

Mobile Raman spectroscopy analysis of ancient enamelled glass masterpieces by Maria Cristina Caggiani; Philippe Colomban; Claire Valotteau; Annarosa Mangone; Pierre Cambon (4345-4354).
Richly decorated enamelled glass objects and fragments of different provenance and epoch have been analysed using mobile and fixed Raman instruments: some fragments of the outstanding Begram treasure (Musée des arts asiatiques – Guimet, Paris) dated to the 1st century AD, mosque lamps and bottles of Syrian/Egyptian provenance dated to the 13th/14th century (collections of Musée du Louvre and of Musée des arts décoratifs, Paris). The techniques are compared using the data obtained from the study of a group of similar objects and fragments discovered in Melfi Castle in the South of Italy in an archaeological context dated to the last quarter of the 13th century. The glass body was difficult to analyse requiring the use of high-energy high-power laser beams and/or sampling that allowed determining the soda-lime type precisely. In contrast, a variety of colouring agents was identified: lapis lazuli and/or cobalt for blue, antimonate pyrochlore solid solution for yellow, with the addition of cobalt/lapis lazuli for green, hematite for red and calcium phosphate/cassiterite/calcium antimonate for white. Where present, gilding was found applied on a rough and matt red enamel base probably in order to guarantee the physical adherence of the gold leaves. The comparison between the above mentioned groups of objects and between them and data existing in the literature about Roman enamelled glass allowed us to follow the evolution of the technology of this class of precious artefacts and to discuss the potential of the mobile Raman analysis.

A rapid determination method for the preliminary thalassaemia screening indicators—haemoglobin (Hb), mean corpuscular Hb (MCH) and mean corpuscular volume (MCV)—based on near-infrared (NIR) spectroscopy was developed. Wavelength selections were accomplished using the improved moving window partial least squares (MWPLS) method for stability. Each model was established using an approach based on randomness, similarity and stability to obtain objective, stable and practical models. The optimal wavebands screened using MWPLS were 1538 nm to 1756 nm for Hb and 968 nm to 1028 nm for MCH and MCV, which were within the NIR overtone region. The validation root mean square error, validation correlation coefficients and relative validation root mean square error of prediction were 3.9 g L−1, 0.972 and 2.9% for Hb; 1.41 pg, 0.958 and 4.8% for MCH; and 4.09 fL, 0.929 and 4.9% for MCV, respectively. The three models achieved high validation accuracy, and the Hb, MCH and MCV prediction values were close to the clinical measured values. Based on the cut-off values (MCH = 27.0 pg, MCV = 80.0 fL) for the routine method, the sensitivity and specificity both reached 100% based on the spectral-predicted MCH and MCV values in the validation set. The spectral prediction was highly accurate for determining negative and positive samples in preliminary thalassaemia screening. The proposed method is rapid and simple compared with the conventional method. This technique is a promising tool for preliminary thalassaemia screening in population prevention and control programmes. This study provides valuable references for designing specialised spectrometers.

Rapid determination of trace sulfonamides in fish by graphene-based SPE coupled with UPLC/MS/MS by Linyao Chen; Tao Zhou; Yanping Zhang; Yanbin Lu (4363-4370).
An analytical protocol for simultaneous determination of thirteen sulfonamides in fish tissues has been developed. Target analytes were enriched by solid-phase extraction using graphene as a sorbent and quantified by ultra-high-performance liquid chromatography coupled with triple-quadrupole linear ion trap mass spectrometry. In the present work, graphene was systematically evaluated as a solid-phase extraction sorbent for analyte enrichment and clean-up. Under optimized conditions, average recoveries of individual sulfonamides were between 76.2 and 91.5% at three different spiked levels, the matrix-matched calibration curves were prepared at six concentration levels and a good linear relationship (R2 > 0.990) was observed. The mean values of relative standard deviation of intra- and inter-day precision ranging from 1.8 to 5.7% and from 2.9 to 7.6% were obtained, respectively. The proposed method has been successfully applied to the analysis of sulfonamides in grass carp fish samples, indicating the potential of graphene as a SPE sorbent for the enrichment of trace residues in food matrices.

Internal standardization using axially viewed inductively coupled plasma optical emission spectrometry (ICP OES) combined with pneumatic nebulization/aerosol desolvation was evaluated in the present study. The sample and internal standard (IS) solutions were mixed on-line. Spectral lines of In, Y, Ga and Ar were evaluated for internal standardization under robust plasma conditions to overcome matrix effects on Ba, Cd, Co, Cr, Zn, Pb, Sr, Mn, Cu, Ni and V quantification in digests of plant materials. In(ii)230.606 nm was only effective for Cd and Pb whereas Y(ii)371.029 nm or Ga(i)417.206 nm or Ga(i)294.364 nm were effective for the other investigated elements. Argon was not effective, suggesting that matrix effects were related to aerosol generation and its transport to the ICP. By using internal standardization accurate results were obtained for certified reference samples of plant materials and the relative standard deviation (RSD) was lower than 1% even for solutions with high acid concentration. The limits of quantification (LOQ) of Cr(i)357.869, Cr(ii)267.716, Cu(i)327.393, Cu(ii)224.700, Cd(i)228.802, Cd(ii)214.440, Pb(i)217.000, Pb(ii)220.353, Zn(i)213.857, Zn(ii)206.200, Sr(ii)407.771, Ba(ii)233.527, V(ii)292.464, Mn(ii)257.610, Ni(ii)232.003 and Co(ii)228.616 nm were 0.070, 0.041, 0.065, 0.094, 0.033, 0.056, 1.33, 0.45, 0.065, 0.10, 0.005, 0.20, 0.12, 0.015, 0.10 and 0.047 μg g−1, respectively. It was concluded that the method is feasible for routine applications.

Detection of drugs in latent fingermarks by mass spectrometric methods by Angelina Yimei Lim; Frederick Rowell; Cheryl Grace Elumbaring-Salazar; Jason Loke; Jan Ma (4378-4385).
The ability of two mass spectrometric methods, surface assisted laser desorption ionization mass spectrometry (SALDI-MS) and direct analysis in real time mass spectrometry (DART-MS), to detect the presence of 5 drugs in latent fingermarks has been examined. It was found that each drug could be detected with good sensitivity for marks resulting from direct finger contact with a glass probe by DART-MS or onto stainless steel target plates using SALDI-MS. In contrast, for latent marks lifted from 3 surfaces (ceramic tile, wood laminate and backing of adhesive tape), no drug could be detected in dusted marks on the surface of a commercial lifting tape by DART-MS due to high background interference from the tape material, whereas all the drugs could be detected by SALDI-MS on equivalent marks. Also, it was demonstrated that drug spiked latent fingermarks pre-dusted with regular fingerprint powder and lifted using conventional lifting tape could be redeveloped with carbon black doped silica particles to enable MS interrogation via SALDI-MS.

A novel test strip for toxicity assessment using luminescent bacteria in hydrogel by Xiaodong Nie; Jinling Zhang; Xiran Jiang; Sixiu Liu; Haisong Cui; Pengyuan Yang; Guodong Sui (4386-4390).
Herein we report a novel test strip capable of rapid water toxicity assessment, which is economical and easily applicable compared with conventional methods, and is especially useful for field application. The test trip is made from hydrogel containing Vibrio fischeri. The toxicity assessment is based on the measurement of the changing of bacterial bioluminescence when water pollutants exist. The test trip was validated with different metal ions and organic compounds representing various pollutants. Our tests showed a great linear relation between the gamma value (Γt) and the concentrations of pollutants. The strip also showed high reliability and reproducibility when tested with real water samples, which suggested its potential application in environmental applications.

A vapour dosing system was developed that gave constant concentrations of methamphetamine in the range 1 to 10 μg m−3. This was used to calibrate the response of solid phase microextraction (SPME) fibres in passive and dynamic sampling modes. Exposure of 100 μm polydimethylsiloxane SPME fibres to a constant concentration of 1–5 μg m−3 methamphetamine over 1–70 min followed by GC-MS analysis produced a curvilinear pre-steady state sorption curve sufficiently reproducible to enable calibration of the SPME absorption. There was no evidence for loss of methamphetamine from the polydimethylsiloxane fibre under static ambient conditions for 5 h or during exposure to 1 L min−1 airflow in a dynamic SPME sampler for 90 min at room temperature. Sequential exposure of SPME fibres to methamphetamine and d9-methamphetamine showed that both analytes were retained. These results demonstrate that solid phase microextraction can be used with pre-loaded isotopically substituted methamphetamine as an internal standard for accurate quantitation of airborne methamphetamine. The isotopic labeling experiments also showed that the dosing system had a small but significant reservoir of methamphetamine, even though it was constructed from mainly inert materials and much of it was at elevated temperature. We therefore recommend that separate vapour dosing units be used for labeled and unlabeled methamphetamine.

A reagentless enantioselective sensor for tryptophan enantiomers via nanohybrid matrices by Qing Zhang; Liju Guo; Yihan Huang; Yonghua Wang; Qian Han; Yingzi Fu (4397-4401).
A reagentless method for the selective electrochemical discrimination of tryptophan (Trp) enantiomers has been developed by means of adsorbing human serum albumin (HSA) onto a methylene blue–multi-wall carbon nanotubes nanohybrid (MB–MWNTs) modified glassy carbon electrode (HSA/MB–MWNT/GCE). Cyclic voltammetry (CV) was employed to monitor the immobilization processes and the electrochemical behavior of the Trp enantiomers on the HSA/MB–MWNT/GCE. It was found that the newly developed electrode exhibited different interactions toward the Trp enantiomers, with a stronger binding effect obtained between HSA and l-Trp. The linear range of the biosensor was investigated from 1.0 × 10−1 to 1.0 × 10−8 mol L−1 with a detection limit of 3.3 × 10−9 mol L−1. In addition, the values of the enantioselectivity coefficient (α) and the association constant (k) were calculated. This work appears to provide a reference for the development of a reagentless electrochemical chiral biosensor and improves understanding of the high selectivity between biological molecules and chiral amino acids.

Effect of hydrogen peroxide oxidation systems on human urinary steroid profiles by Unnikrishnan Kuzhiumparambil; Shanlin Fu (4402-4408).
In sports drug testing the steroid profile is the most versatile and informative screening tool for the detection of steroid abuse. Despite the introduction of observed urine collection procedures by the World Anti-Doping Agency (WADA), chemical manipulation of urine specimens by athletes to conceal drug use still occurs and poses an ongoing challenge for doping control laboratories worldwide. In vitro urine adulteration using highly oxidative chemicals have been reported several times in the past. In this study we report the effect of two oxidising agents, Fenton's reagent and peroxidase–peroxide system on the human urinary steroid profile. Varying concentrations of these oxidants were reacted with urine and the reactions monitored by gas chromatography-mass spectrometry. A significant decrease in the absolute concentrations of androsterone, etiocholanolone, 5α-androstane-3α,17β-diol, 5β-androstane-3α,17β-diol and epitestosterone was observed with consequent alteration of the steroid profile ratios. Adulteration of urine sample with these oxidants can thus mask the abnormality in a steroidal profile following steroid abuse. Drug testing authorities should take into account the effects of these oxidizing adulterants while interpreting the steroid profile data for doping control purposes.

Improvements are reported for a recently described instrument made up of an innovative headspace sampling and injection system built using a longitudinally modulating cryogenic system mounted around the sampling loop of a two-position loop injector, which had been hyphenated to a low thermal mass gas chromatograph. Replacing the bare capillary used previously for cryotrapping by a coated capillary opened additional potential fields of application for the instrument since more volatile analytes, with boiling points above 140 °C instead of 190 °C, could now also be quantitatively cryotrapped. Detection using a mass spectrometer instead of a flame ionization detector enabled the investigation of dynamic processes that release complex mixtures of volatile compounds in widely varying amounts. The performance of the improved system was illustrated by monitoring in real time, with 5 min resolution, of the stripping of volatile aroma compounds by fermentative carbon dioxide during beer fermentation. Compounds derived from hops, including monoterpenes, sesquiterpenes and some esters, which are present in the initial wort but are not formed subsequently, were observed to be stripped off early in the fermentation process. Fusel alcohols are the earliest volatile compounds derived from yeast metabolism, which are found to be released in significant amounts from the wort. More than ten fermentation-derived esters were observed to be stripped from the wort later into the fermentation. Although similar, their release kinetics exhibited clear differences which were the consequences of their different biosynthetic production rates and physical–chemical properties. The release curves of further compounds and how they can lead to the elucidation of their origin are also discussed.

A simple and rapid one-step displacement dispersive liquid–liquid microextraction method (D-DLLME) was developed for the selective preconcentration of silver followed by graphite furnace atomic absorption spectrometry determination. In the proposed method, Cu was reacted with diethyldithiocarbamate (DDTC) to form a Cu–DDTC complex, and it was used as a chelating agent instead of DDTC for dispersive liquid–liquid microextraction (DLLME) of silver. Because the stability of Ag–DDTC is higher than that of Cu–DDTC, Ag can displace Cu from the Cu–DDTC complex and be preconcentrated in a single DLLME procedure. Potential interference from co-existing metal ions with lower DDTC complex stability was largely eliminated as they cannot displace Cu from the Cu–DDTC complex, and the tolerance limits for these ions were improved by a long way compared with the conventional DLLME method. Under the optimal conditions, the limit of detection of this method was 16 ng L−1 (3σ) for silver, and an enhancement factor of 82 was achieved with a sample volume of 5.0 mL. The proposed method was successfully applied for the determination of trace silver in some environmental and biological samples with satisfactory results.

Online preconcentration of nickel(ii) in textile effluent and soil samples by SDS coated alumina modified with dithizone mini-column coupled with FAAS by Zaheer A. Chandio; Farah N. Talpur; H. I. Afridi; Humaira Khan; Ghulam Quadir Khaskheli; Mazhar Iqbal Khaskheli (4425-4429).
A simple, sensitive and low cost, flow injection time-based method was developed for on-line preconcentration and determination of nickel in textile effluent and soil samples. At the optimum pH, the nickel was retained on the sodium dodecyl sulphate coated alumina modified with dithizone, and subsequently eluted with HCl and determined by flame atomic absorption spectrometry. At a sample frequency of 30 h−1 and a 60 s preconcentration time, the enhancement factor was 100 and the detection limit was 0.54 μg L−1 (3σ). The accuracy of the developed method is sufficient and evaluated with spiked environmental samples.

Determination of streptomycin residues in animal-derived foods by a reliable and accurate enzyme-linked immunosorbent assay by Junping Wang; Huiying Zhang; Wei Sheng; Wei Liu; Lili Zheng; Xinzhe Zhang; Shuo Wang (4430-4435).
A highly reliable and accurate indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed for the detection of streptomycin (STR) in animal-derived foods. The half-maximum inhibition concentration (IC50) of the icELISA for STR was 2.00 ng mL−1 and the limit of detection (LOD, calculated as the IC15 value) was 0.24 ng mL−1. The cross-reactivities with other aminoglycoside antibiotics were very low except for dihydrostreptomycin (95.50%). The recoveries for all samples at five levels (15, 30, 120, 300, 600 ng g−1) ranged from 71.32% to 106.94%. The coefficients of variation of intra- and inter-assays were below 14%. There was a good correlation (R2 = 0.9854) between the data determined by this ELISA and the commercial kit. The analysis of variance of the recoveries showed the sufficiently high stability of the assay to STR in eight animal-derived foods (chicken, pork, chicken liver, pig liver, pig kidney, fish, shrimp, and cow milk). The ELISA allows for a rapid, low-cost, sensitive and accurate determination of STR residues in animal-derived foods.

New adsorbent M101 was obtained by loading multi-walled carbon nanotubes (MWCNTs) on 101 white support, and 3-aminopropyl silica gel–MWCNTs (APSG-MW) were prepared by chemical modification. Based on the early research, 15 kinds of adsorbents were tested to adsorb sulfide and amine compounds. Then 4 combinations of multi-sorbent tubes were prepared including Tenax TA/M101/Carbopack B (TMB), Tenax TA/M101/Carboxen 564 (TM564), Carbopack B/M101/Silica gel (BMS) and Carbopack B/APSG-MW/Silica gel (BAMS). The adsorption and desorption recoveries for alkanes, aromatic hydrocarbons, halogenated hydrocarbons, alcohols, esters, ketones, sulfides and amines were determined. The results showed that the recoveries of multi-layer adsorbents BMS and BAMS were above 90% for most of the target compounds, and 80% for amines. Then the influence of humidity on the sampling, storage stability and sampling precision of BMS and BAMS was tested. The results indicated that BMS and BAMS were more suitable for sampling both polar and non-polar compounds in the air.

A highly selective and sensitive quartz crystal microbalance (QCM) fabricated by mixing with polyvinyl chloride and molecularly imprinted polymer microspheres (MIPMs) immobilized in situ on a piezoelectric quartz crystal (PQC) chip as a recognition element for rapid endosulfan detection in drinking water and milk samples. Based on our previous studies, we investigated the performances of the MIPMs in situ modified QCM (MIPMs-QCM). The surface microstructure of the uniform mono-layer MIPMs on a PQC chip was characterized by scanning electron microscope (SEM). It remained relatively stable within 10–20 min. The specificity of the MIPMs-QCM was also investigated by using a series of concentrations of endosulfan and structurally related analogs, which showed good selectivity and specificity for the recognition of endosulfan. Analysis by MIPMs-QCM sensor responded in the presence of different concentrations of endosulfan and demonstrated a good linear correlation over 10 to 40 ng mL−1 (y (Hz) = 30.83lg x (ng mL−1) − 26.32, R = 0.9856), and 40 to 1280 ng mL−1 (y (Hz) = 93.79lg x (ng mL−1) − 120.40, R = 0.9980), respectively. The lowest detection limit (LDL) was 5.59 ng mL−1 (S/N = 3). It could be repeated six times and stored for 6 months. Detection of endosulfan in water and milk samples was observed with recoveries of 96.0–104.1% and 101.8–108.0% respectively. The developed MIPMs-QCM is a reliable method for analysis of endosulfan with simple operation, good selectivity, and is inexpensive and reusable.

Gold nanoparticle based capacitive immunosensor for detection of hepatitis B surface antigen by Elias Alipour; Hedayatollah Ghourchian; Seyed Mehdi Boutorabi (4448-4453).
A simple, rapid and label-free capacitive based immuno-biosensor was developed for the detection of the hepatitis B surface antigen (HBsAg). Two planar gold electrodes were used as capacitor plates. The surfaces of the electrodes were covered by a mixture of HS(CH2)11(OCH2CH2)3OH and HS(CH2)11(OCH2CH2)3COOH (20 : 1 weight ratio) as an insulating molecule layer. Then, the primary anti-HBsAg was immobilized on the insulating layer. After the addition of HBsAg, the distance between the plates and also the average surface area of the plates changed. The alteration of these factors led to a change in capacitance which could be used as an indicator of the antibody–antigen interaction. Also, in order to improve the sensitivity of the method, gold nanoparticles were attached to a secondary antibody. Due to the relatively large size of the particles, the thickness of the dielectric layer and thus the capacitance changed remarkably. Therefore, the detection limit was improved to about 10 ng ml−1.

Time-resolved optical waveguide absorption spectroscopy (OWAS) makes use of an evanescent field to detect the polarized absorption spectra of sub-monomolecular adlayers. This technique is suitable for the investigation of kinetics at the solid–liquid interface of dyes, pigments, fluorescent molecules, quantum dots, metallic nanoparticles, and proteins with chromophores. In this work, we demonstrate for the first time the application of non-negative matrix factorization (NMF) to the analysis of time-resolved OWAS data, because NMF prevents the negative factors from occurring, avoids contradicting physical reality, and makes factors more easily interpretable. Meanwhile, principal component analysis (PCA) is researched for the comparison of NMF. Two-factor loadings and scores derived by PCA and NMF are consistent with the results analyzed by the function of time/wavelength-absorbance. Moreover, NMF avoids contradicting physical reality, and makes factors more easily interpretable. We believe that NMF will provide a valuable analysis route to allow processing of increasingly large and complex data sets.

Corn silk (CS) modified by dilute nitric acid as a novel biosorbent has been used for the first time for solid phase extraction of trace copper in water samples. Characterizations of the modified CS have been investigated by means of FESEM images, FT-IR spectra and surface charge analysis. A new functional group, i.e., nitric ether (–O–NO2) is introduced onto the HNO3-modified CS, which is favorable for the adsorption of Cu2+. The abundant negative charges on the surface of the modified CS also provide great potential for the retention of Cu2+ on its surface. The maximum retention of Cu2+ ions is obtained under the pH range of 4.0–7.0, corresponding to a theoretical maximum adsorption capacity of 95.7 mg g−1. The adsorbed Cu2+ is then quantitatively eluted using a 1.5 mol L−1 nitric acid solution with detection by flame atomic absorption spectrometry (FAAS). With a sample volume of 30 mL, an enrichment factor of 39 and a precision of 1.6% RSD (40 μg L−1, n = 11) are achieved. The concentration of Cu2+ could be accurately quantified within a linear range of 1–120 μg L−1 and with a detection limit (3σ) of 0.35 μg L−1. The present procedure is validated by analyzing a certified reference material of Trace Elements in Water (GBW(E)080039). It is further applied to determine copper by spiking recovery tests in tap water, spring water, snow meltwater, lake water, river water and an electroplating water sample, giving rise to spiking recoveries in the range of 96.8–103.0%.

A data fusion method based on near infrared (NIR) spectra and ultraviolet (UV) spectra for simultaneous determination of six ginsenosides and four saccharides in Chinese herbal injection (CHI) was developed. Two data fusion strategies (low-level data fusion and mid-level data fusion) combined with partial least squares (PLS) regression and uninformative variable elimination by PLS (UVEPLS) regression were implemented, respectively. Compared with the models established by independent NIR or UV spectra, there was a significant improvement provided by two data fusion strategies, which benefited from the synergistic effect of complementary information obtained from near infrared spectroscopy (NIRS) and ultraviolet spectroscopy (UVS). The results in this work showed data fusion of NIR and UV spectra combined with a regression algorithm could be a promising strategy to determine the ginsenosides and saccharides in CHI rapidly and simultaneously.

Study on the electrochemical oxidation of glucose on different Cu–Cu2S integrated electrodes by Lingling Wang; Rong Ji; Liutao Yu; Guangfeng Wang; Xiaojun Zhang (4476-4479).
The electrocatalytic activities between glucose and three integrated electrodes made up of Cu2S nanoplates on Cu rods with different cross-sectional areas are studied. The results showed that the Cu2.5–Cu2S integrated electrode displayed the highest catalytic activity on glucose oxidation and the highest peak current density, which are due to the Cu2.5–Cu2S integrated electrode having the highest calculated active area.

Non-invasive characterization of polymeric materials in relation to art conservation using unilateral NMR combined with multivariate data analysis by Cindie Kehlet; Eleonora Del Federico; Hiba Schahbaz; Amelia Catalano; Jens Dittmer; Niels Chr. Nielsen (4480-4486).
This article shows how to interpret data obtained by unilateral NMR for the characterization of works of art using multivariate analysis. Transverse 1H relaxation decays acquired by a Carr–Purcell–Meiboom–Gill pulse sequence are directly treated by Principal Component Analysis (PCA) and projection to latent structure by partial least square (PLS). The advantage of this procedure is the avoidance of any ambiguity in the model. The NMR signal is formed by a number of different hydrogen spins rendering the resulting relaxation decays multi-exponential. Therefore conventional approaches of fitting call for the use of mono-, bi-, or multi-exponential models yielding results depending on the choice of the model function. We demonstrate the technique on three examples: characterization of a set of resins representative for modern materials in art and design artefacts, mapping the state of degradation of an art work made of latex, and the analysis of a depth profile of an aged urethane rubber sample. In situ measurements often result in low signal-to-noise ratio data and the suggested technique does not only allow an unambiguous model-free approach, but is also robust against such low sensitivity data.

Most analytical techniques used for the speciation analysis of butyltin compounds in biological tissues usually contain multiple procedures (e.g., extraction, derivatization, separation, preconcentration, determination) which may increase the risk of systematic errors. The use of reference materials (RM) makes it possible to correct most of these errors and improve the validity of quality control. In this study, a new candidate RM for butyltin compounds in mollusks was developed. It was prepared with a mollusk ‘Mya arenaria’ directly bought from the market. The preparation of this candidate RM, the homogeneity and stability studies, the value assignment and the evaluation of uncertainty were described. The certified values of 0.33 ± 0.08, 0.62 ± 0.09, 2.64 ± 0.20 μg Sn g−1 (based on dry mass) for monobutyltin (MBT, [Sn(C4H9)3+]), dibutyltin (DBT, [Sn(C4H9)22+]) and tributyltin (TBT, [Sn(C4H9)3+]) respectively have been assigned by inter-laboratory comparison. This work will be of great support to the monitoring of butyltin compounds in biota, as well as meeting the need for implementing international treaties in China.

Dumbbell-shaped stir bar coated with dendrimer-based MIPs for selective extraction and analysis of vardenafil and its analogue sildenafil in health foods by Yang Wang; Jinhua Wu; Cheng Xue; Ruoyu Wang; Tingting Wen; Junli Hong; Qin Hu; Fei Li; Xuemin Zhou (4494-4500).
A novel dendrimer-based molecularly imprinted polymers (MIPs) coated dumbbell-shaped stir bar (DSB) was developed to enrich and analyze two kinds of phosphodiesterase type 5 (PDE-5) inhibitors in health foods (Hfs). The MIPs, with vardenafil as the template molecule and methacrylic acid (MAA) as the functional monomer, were synthesized on the surface of the dendritic-grafting DSB which was filled with magnetic core as substrate. The MIPs-DSB possessed mechanical stability, high adsorption capacity and good selectivity for vardenafil and its analogue sildenafil. A method for the determination of vardenafil and sildenafil in Hfs was established by stir bar sorptive extraction (SBSE) coupled with HPLC-UV. The contents of vardenafil and sildenafil were found to be 3.65 and 2.66 μg g−1, respectively, and the average recoveries in spiked Hfs were 86.5–91.8% with a relative standard deviation (RSD) below 5%. All results revealed that the MIPs-DSB coupled with HPLC-UV could be applied to the highly selective extraction and sensitive determination of trace analytes in a complex matrix.

An on-line preconcentration system for the determination of selenium in seawater samples by Valfredo Azevedo Lemos; Mardson Vasconcelos Maciel (4501-4505).
A flow injection system was developed for the preconcentration and determination of selenium in water samples by hydride generation atomic absorption spectrometry (HG-AAS). The preconcentration is based on the sorption of species formed between Se(iv) and ammonium pyrrolidinedithiocarbamate (APDC) in a minicolumn packed with polytetrafluoroethylene (PTFE) and subsequent elution with an alkaline solution of sodium borohydride. After the formation and separation of volatile hydride, this species has been transported to a quartz cell for measuring absorbance. All steps involving separation and detection were performed in an online system. The factors influencing the sorption and desorption of Se(iv) were investigated. Under optimized conditions, the method showed linearity in the range from 0.1 to 1.0 μg L−1 of Se(iv). Analytical parameters of the method, such as the limit of detection (0.03 μg L−1 of Se(iv)), enrichment factor (20), concentration efficiency (20 min−1), consumption rate (0.54 mL) and analytical frequency (60 h−1), were also determined. The accuracy of the method was tested by the determination of selenium in certified reference materials (mussel tissue and wastewater). The proposed procedure was applied for the determination of selenium in seawater samples. The results obtained by analysis of seven different samples varied between 0.21 ± 0.01 and 0.35 ± 0.05 μg L−1 of Se(iv).

Effects of ultrahigh pressure extraction conditions on yields of berberine and palmatine from cortex Phellodendri amurensis by Shun Liu; Yan Chen; Lijuan Gu; Yongxia Li; Bingyi Wang; Jie Hao; Hui Zhu; Heran Li; Shilin Yang; Susumu Kitanaka (4506-4512).
A new method using ultrahigh pressure was used to extract palmatine and berberine from the barks of cortex Phellodendri amurensis. The optimal conditions for ultrahigh pressure extraction (UPE) of palmatine and berberine were quantified by HPLC-DAD with standard samples. Orthogonal design was applied to evaluate the effects of four independent factors (extraction pressure, extraction temperature, liquid/solid ratio and ethanol concentration) on the yield. The optimal conditions of ultrahigh pressure extraction were obtained at an extraction pressure of 400 MPa, extraction temperature of 40 °C, extraction time of 4 min, a liquid/solid ratio of 30 : 1 and an ethanol concentration of 50%. The results showed that the UPE method can produce palmatine and berberine with the highest yield. In addition, scanning electron microscope (SEM) images of the plant cells after ultrahigh pressure treatment were obtained to provide visual evidence of the disruption effect. Compared with other extraction techniques, such as reflux, ultrasonic, and soxhlet extraction, UPE shows several advantages, such as higher extraction yield, less extraction time, lower extraction temperature and energy consumption. Moreover, UPE may be also a better way to be applied in industry.

Plasticizers in PVC plastic films were extracted by homogeneous-ultrasonics using n-hexane, the extracted multiple phthalate plasticizers (PAEs) were simultaneously determined by GC-MS assisted with continuous wavelet transform (CWT), and then a novel method for simultaneous determination of multiple plasticizers in PVC packaging materials was established. While using the traditional GC-MS analysis to determine nine plasticizers in PVC packaging materials, the total ion current (TIC) chromatogram of diisononyl ortho-phthalate (DINP) and diisodecyl ortho-phthalate (DIDP) were seriously overlapped. For resolution of the overlapped and lower signal-to-noise ratio (SNR) TIC peaks of DINP and DIDP, twice CWT with symlet 2 (sym2) and scale parameter a = 30 was adopted. The results show that the overlapped noisy peaks of DINP and DIDP were successfully resolved with the SNR increasing more than 10 times, and the extraction efficiencies of PAEs increasing 18–29% compared to that of using ultrasonic extraction procedure. The proposed homogeneous-ultrasonic extraction GC-MS-CWT procedure provides an alternative novel way for simultaneous determination of multiple phthalate plasticizers in PVC packaging materials.

Collaborative trials are interlaboratory studies of the precision of data obtained from particular analytical methods. Increasingly many of these trials in the food sector are addressing analytes present at mass fractions between 10−11 and 10−7, that is, between 10 parts per trillion and 100 parts per billion. In 2000 the statistics from then-recently conducted collaborative trials of this type were examined. The trend of the inter-laboratory relative standard deviation took a value of 0.22. A similar trend can be seen in both older and more recent compilations of statistics. This paper demonstrates that the value emerges naturally in a fitness-for-purpose context and shows why a similar outcome would be likely in other application sectors.

Back cover (4521-4522).