Analytical Methods (v.9, #3)
Front cover (361-362).
Contents list (363-369).
Analysis of phthalate esters in dairy products—a brief review by Yingying Fan; He Chen; Hejiang Liu; Fulan Wang; Sha Ma; Aierken Latipa; Shuai Wang; Cheng Wang (370-380).
This review provides a brief survey of the physicochemical properties of phthalate esters (PAEs) and their harm to human health. The present analytical methods available for the determination of these compounds in dairy products are critically evaluated. The attention is primarily devoted to the methods for sample pretreatment, which are the main source of errors and are usually the most time-consuming step of the whole analysis. The characteristics of instrumental analysis methods, including gas chromatography, liquid chromatography, tandem mass spectrometry, capillary electrophoresis and immunoassay are discussed. Furthermore, the future development of analysis of PAEs is discussed.
A “molecule pump” prototype for exceptionally high efficiency adsorption and decomposition of rhodamine B based on the TiO2@MIL-100 composite by Na Chang; Yi-Xin Li; Dong-Ying He; Zhi-Wei Tang; Yan-Feng Huang; Jing-Jian Yu (381-384).
The fabricated TiO2@MIL-100 composite not only demonstrates high capacity in adsorption of Rhodamine B (RhB) but also plays an important role as a “molecule pump” which offers excellent feature and facilitates the following degradation of RhB with exceptionally high efficiency.
Analysis of raw biofluids by mass spectrometry using microfluidic diffusion-based separation by Joshua Heinemann; Brigit Noon; Daniel Willems; Katherine Budeski; Brian Bothner (385-392).
Elucidation and monitoring of biomarkers continues to expand because of their medical value and potential to reduce healthcare costs. For example, biomarkers are used extensively to track physiology associated with drug addiction, disease progression, aging, and industrial processes. While longitudinal analyses are of great value from a biological or healthcare perspective, the cost associated with replicate analyses is preventing the expansion of frequent routine testing. Frequent testing could deepen our understanding of disease emergence and aid adoption of personalized healthcare. To address this need, we have developed a system for measuring metabolite abundance from raw biofluids. Using a metabolite extraction chip (MEC), based upon diffusive extraction of small molecules and metabolites from biofluids using microfluidics, we show that biologically relevant markers can be measured in blood and urine. Previously it was shown that the MEC could be used to track metabolic changes in real-time. We now demonstrate that the device can be adapted to high-throughput screening using standard liquid chromatography mass spectrometry instrumentation (LCMS). The results provide insight into the sensitivity of the system and its application for the analysis of human biofluids. Quantitative analysis of clinical predictors including nicotine, caffeine, and glutathione are described.
GC columns as micro-air samplers for the quantitative analysis of naphthalene vapours by Sigalit Gura; Moran Madmon; Nitzan Tzanani; Ruth Barak; Israel Shacht; Shai Dagan (393-401).
Although linked to a number of adverse health effects, studies of naphthalene are lacking in the exposure-relevant literature. This compound, a major by-product of the incomplete combustion of most organic materials (traffic vehicle exhaust, power generation, tobacco smoke, etc.), has characteristics that are in between those of volatile and semivolatile organic compounds (VOCs and SVOCs) and has consequently often been excluded from studies of both compound classes. A new, highly quantitative, rapid and spatially well-resolved micro-sampling method was developed for the sampling of naphthalene vapours in indoor, outdoor and personal air. The method is based on GC capillary columns as air samplers, solvent extraction and GC-MS analysis. For the first time, naphthalene concentrations were quantitatively determined at the surface level (around the boundary layer) and at 1 mm height intervals above an emitting surface. Minimal sampling flow rates of 5 mL min−1 were applied to reduce any geometrical or dynamical disturbance to the environmental air flow regime to a minimum. Toluene was highly efficient, precise and easy to apply in the extraction of the target compound from the GC column sampler. Method quantification was confirmed using a unique calibrated vapour generator based on an inert GC inlet. Using this source, a 13 ng L−1 limit of quantitation (LOQ) with 90% mass recovery over a linear dynamic range of five orders of magnitude in high precision and accuracy of ±13% and 35%, respectively, were determined and validated. The applicability and flexibility of the method was demonstrated by investigating the vapour concentration profiles generated “0”–20 mm above a naphthalene-emitting surface in outdoor air. The concept introduced in this research could be easily adopted for the reliable, sensitive and quantitative monitoring of other VOCs and SVOCs in different micro-spaces for various applications.
Monitoring carnosine uptake by RAW 264.7 macrophage cells using microchip electrophoresis with fluorescence detection by Claudia G. Fresta; Michael L. Hogard; Giuseppe Caruso; Elton E. Melo Costa; Giuseppe Lazzarino; Susan M. Lunte (402-408).
Carnosine, a dipeptide found in a variety of tissues, is believed to possess antioxidant properties. It serves as a scavenger of reactive nitrogen and oxygen species (RNOS), which are important stress mediators of pro-inflammatory conditions and can lead to macrophage activation. In this study, intracellular concentrations of carnosine in murine RAW 264.7 macrophage cells were determined using microchip electrophoresis with laser-induced fluorescence detection following derivatization with naphthalene-2,3-dicarboxaldehyde and cyanide. The method was linear from 25 nM to 5 μM with a limit of detection in cell lysate samples of 65 nM. Using the method of standard additions, the basal intracellular content of carnosine in macrophage cells was determined to be 0.079 ± 0.02 nmol per 106 cells. The uptake of carnosine by these cells was then investigated under both physiological and pro-inflammatory conditions. There was a 2.8-fold increase in carnosine uptake for macrophages exposed to lipopolysaccharides and interferon-γ prior to incubation, compared to the controls. This suggests that macrophages may use carnosine uptake as a defense mechanism under pro-inflammatory conditions. Future studies will investigate the role of the carnosine transporter in carnosine uptake and its possible correlation with cell morphological changes observed after stimulation.
Quantification of prospective type 2 diabetes mellitus biomarkers by stable isotope dilution with bi-labeled standard glycated peptides by Alena Soboleva; Maciej Modzel; Anna Didio; Halina Płóciennik; Monika Kijewska; Tatiana Grischina; Tatiana Karonova; Tatiana Bilova; Vasily Stefanov; Piotr Stefanowicz; Andrej Frolov (409-418).
Type 2 diabetes mellitus (T2DM) is a complex group of disorders, characterized by hyperglycemia, insulin resistance and insulin deficiency. In human blood, hyperglycemia ultimately results in the enhancement of glycation – a posttranslational modification formed by the interaction of protein amino groups with glucose. The resulting fructosamines (Amadori compounds) readily undergo further degradation resulting in advanced glycation end products (AGEs), known to be pro-inflammatory in humans. These compounds are highly heterogeneous and characteristic of advanced stages of the disease, whereas fructosamines are recognized markers of early diabetes stages (HbA1C, glycated albumin). Recently, individual plasma protein glycation sites were proposed as promising T2DM biomarkers sensitive to short-term fluctuations of plasma glucose. However, corresponding absolute quantification strategies, applicable in regular clinical practice, are still not established. Therefore, here we propose a new analytical approach aiming at reproducible and precise quantification of multiple glycated peptides in human plasma tryptic digests. Thereby, the standard peptides comprised a 13C,15N-labeled lysyl residue, a dabsyl moiety for determination of standard amounts, and a cleavable linker. Known amounts of these peptides were spiked to plasma samples prior to tryptic digestion, quantification relying on stable isotope dilution. The method was demonstrated to be applicable for quantification of individual glycated sites in T2DM patients and non-diabetic controls.
Evaluation of methylations and external/internal standard quantification of lipids using gas chromatography-mass spectrometry by Yang Qin; Wang Shunhe; Chen Haiqin; Gu Zhennan; Zhang Hao; Chen Wei; Chen Yong Q. (419-426).
In the present work, we evaluated different widely accepted methyl derivatization procedures which are almost obligatory in gas chromatography analysis of fatty acids (FAs), both acid- and base-catalyzed ones. We determined their derivatization efficiency and rapidity and found that combined base–acid methylation, the NaOH–BF3–MeOH method, out-performed all other methods. The analyses of FAME standards and samples were performed on a conventional 30 m × 0.25 mm Wax column, with a single run of 51 min. To accelerate the analysis while maintaining resolution, a more polar 0.1 mm ID column was used to analyze 52 FAMEs. This way, we were able to obtain results within one-third of the analysis time with almost equal separation, if not better. To further evaluate the quantification methods that are performed with or without internal standards, we constructed new calibration curves by removing a known quantity from the original calibration curves, and used them to recalculate the concentration of the known removed quantity. Comparison of the calculated and actual concentration values revealed that, when performed carefully, the external standard method could achieve results that were comparable to results obtained with the internal standard method, and thus is recommended for daily analysis.
Assessing the feasibility of electrophoretic separation of CaCO3 polymorphs for archaeological applications by Chuan Xu; Cole Walsh; Elisabetta Boaretto; Kristin M. Poduska (427-433).
We demonstrate a proof-of-principle method to separate particles of two CaCO3 polymorphs, calcite and aragonite, based on surface charge density differences that affect electrophoretic mobility values. Calcite and aragonite standards show significant differences in their electrophoretic mobility distributions in polyphosphate-containing suspensions. Phosphate additives, which are commonly used to reduce particle aggregation, have a serendipitous added benefit of stabilizing CaCO3 against dissolution. However, the mobility differences among archaeologically relevant samples, such as lime plasters and chalk, are not consistently different enough to make this a reliable separation strategy. Nevertheless, this study is important because it takes a new and fundamentally different approach to non-destructive separation of archaeological materials.
Fabrication of fluorescence enhancement of quantum dots on a gold colloid formed film for oligonucleotide DNA detection by Jie Yang; Ji-Tao Song; Wei Hu; Yan Huang; Li-Juan Deng; Han-Na Hou; Bo Liu (434-442).
A new method based on metal-enhanced quantum dot (QD) fluorescence on a gold colloid formed film has been developed for DNA detection. Gold nanoparticles (Au NPs) with negative charge were uniformly spread on a polylysine-modified glass substrate through electrostatic adsorption to form an Au NP film. The surface plasma resonance of the Au NP film was tuned by heating in an oven for 5 min at 70 °C to match with the fluorescence emission of QDs. DNA was chosen as a spacer to study the distance effect on the metal-enhanced fluorescence of QDs. The maximum enhancement was achieved when the base number of the DNA spacer was 37 (about 12.6 nm). A three segment system based on the optimal length of the DNA spacer has been developed for DNA detection. The lowest detectable limit with this system was 50 nM.
Ti4+-immobilized chitosan-coated magnetic graphene oxide for the highly selective enrichment of phosphopeptides by Yiman Zhao; Lingyi Zhang; Zhanying Chu; Zhichao Xiong; Weibing Zhang (443-449).
For in-depth analysis of phosphorylated proteomics, the highly sensitive and selective capture of phosphopeptides from intricate biological samples is extremely significant. In this work, a late-model immobilized metal ion affinity chromatography (IMAC) material was fabricated and applied to enriching phosphopeptides from biological samples by abundant Ti4+ ions, which were chelated to crosslinked chitosan (CS) loaded on the surface of magnetic graphene oxide (GO) (denoted as mag GO–CS–Ti4+). The high amount of crosslinked CS endowed the IMAC material with highly hydrophilic properties and abundant active sites for Ti4+ ions on the surface. These characteristics ensure the great performance of mag GO–CS–Ti4+ in the selective enrichment of phosphopeptides from the tryptic digest of β-casein with high selectivity (phosphopeptides to non-phosphopeptides at a molar ratio of 1 : 400), high sensitivity (0.5 fmol), large enrichment capacity (66.6 mg g−1), prominent phosphopeptide recovery (93.11%), and excellent reusability. What's more, mag GO–CS–Ti4+ was applied to capturing phosphopeptides from real biological samples, human serum from both healthy people and patients and nonfat milk. The results successfully manifested that the mag GO–CS–Ti4+ could be a great affinity material for the enrichment of low-abundant phosphopeptides from biological samples.
A method employing SPE, MRM LC-MS/MS and a THF–water solvent system for the simultaneous determination of five antiretroviral drugs in human blood plasma by Elliott Mwando; Amos Massele; Enoch Sepako; Kwenga Sichilongo (450-458).
A multiple reaction monitoring liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method for the simultaneous determination of five antiretroviral drugs i.e. emtricitabine, tenofovir, efavirenz, lopinavir and ritonavir using commercially sterilized human blood plasma as the matrix and a THF/water solvent system was developed for therapeutic drug monitoring purposes and partially validated using the United States Food and Drug Administration (US FDA) guidelines. The analytical performance characteristics that were examined were limits of detection (LODs), lower limits of quantification (LLOQs), upper limits of quantification (ULOQs), selectivity, percent mean recoveries, precision measured as percent relative standard deviations and accuracy. Optimized LC-MS/MS parameters were employed for this purpose. The percent mean recoveries were between 77.3 and 90.1% using solid phase extraction (SPE) for sample preparation. These recoveries were obtained at three spike levels i.e. the LOD, the LLOQ and the ULOQ. The precision of the SPE technique was within an acceptable range of <15% i.e. between 2.7 and 9.2% at the LLOQ. Accuracy was calculated as the percent deviation of the mean value from the true value and the values ranged between 9.9 and 22.7%. The SPE technique satisfied all the requirements of the US FDA guidelines except for efavirenz whose accuracy was slightly higher than recommended at the LLOQ i.e. 22.7% as opposed to 20%. The limits of detection using SPE also fell below the clinically relevant therapeutic range (3–8 mg L−1) for most of the drugs and therefore the method could be useful for therapeutic drug monitoring in HIV patients.
Electrostatic-driven solid phase microextraction coupled with surface enhanced Raman spectroscopy for rapid analysis of pentachlorophenol by Weiwei Bian; Sha Zhu; Mingying Qi; Lanlan Xiao; Zhen Liu; Jinhua Zhan (459-464).
Pentachlorophenol (PCP) is a very high toxicity and slowly biodegraded organic pollutant. People may be exposed to PCP in environmental media through the inhalation of contaminated air, and ingestion of water and hazardous waste. Even low PCP intake will have serious effects on renal, metabolic and neurological functions, particularly in terms of carcinogenicity. Here, an electrostatic interaction driven solid phase microextraction (SPME) combined with surface enhanced Raman spectroscopy (SERS) was proposed for rapid detection of PCP in environmental water. The nanoporous Ag coating was in-situ electrochemically synthesized and modified by cysteamine to form a positive stationary phase on a fiber surface. The PCP was extracted using the DI-SPME mode and its SERS spectra were investigated; the characteristic bands at 338 cm−1, 378 cm−1 and 480 cm−1 were identified as the fingerprint peaks. The extraction procedure was optimized, and the adsorption mechanism was also discussed by the electric double layer model. The good stability and uniformity of the substrate provide a high enhancement factor of 3.7 × 105 and low LOD of 6.4 × 10−9 M for quantitative determination. This work provides a versatile strategy for rapid on-site detection of ionic or polar organic pollutants in environmental media.
On-site determination of the migration amount of fluorescent whitening agents from paper to finger by fluorescence spectrophotometry by Yang Yu; Xinghua Wang; Qiang Fei; Yong Yu; Sizhu Tian; Kun Wang; Jia Jiang; Daqian Song; Aimin Yu; Ziwei Zhang (465-472).
A fluorescence collecting unit was self-assembled in our lab. This unit in combination with a fluorescence spectrophotometer was applied to quantify fluorescent whitening agents (FWAs) in paper samples. The unit is small and portable, containing three light emitting diodes and a lens. The light emitting diodes were used as excitation light sources, and the emitted fluorescence entered the fluorescence spectrophotometer for signal detection after passing through the lens and a fiber. With high sensitivity, not only the total amount of FWAs in the paper samples could be determined but also the trace amount of FWAs migrated from paper to finger could also be obtained. The limit of detection was 0.12 mg m−2. Thirty practical paper notebook samples were analyzed for their FWA content before and after finger touch. For the purpose of comparison, the European standard method was also applied to determine the migration of FWA in these paper notebook samples. The correlation of the analytical results obtained by the present method with those obtained by the well-established European standard method was satisfactory.
Analysis of perfluoroalkyl and polyfluoroalkyl substances in serum and plasma by solvent precipitation-isotope dilution-direct injection-LC/MS/MS by Laura M. Harrington (473-481).
A validated liquid chromatography tandem mass spectrometry (LC/MS/MS) method is presented for the analysis of per- and polyfluoroalkyl substances (PFAS) in serum and plasma. The method employs stable-isotope labeled internal standard (IS) and surrogate recover standard (SRS) spiked serum or plasma samples that are mixed and precipitated with acetonitrile. Quantitation is performed with stable-isotope IS solvent (50 : 50 acetonitrile : water) calibration using one direct injection (DI) chromatographic analysis of precipitated sample supernate. The analytical method includes fifteen stable isotope labeled ISs, four SRSs ([1,2,3,4-13C4]PFOA, [1,2-13C2]PFUnA, [1,2,3,4-13C4]PFOS, [2,3,4-13C3]PFBA), and sixteen target analytes perfluoroalkyl carboxylic acids (PFCAs) (C4–C12), perfluoroalkyl sulfonic acids (PFSAs) (C4, C6, C8), N-ethyl perfluorooctane sulfonamido acetate (EtFOSAA), N-methyl perfluorooctane sulfonamido acetate (MeFOSAA), perfluorooctane sulfonamide (FOSA), and perfluorobutane sulfonamide (FBSA). Mean recoveries of control human plasma fortified with method target analytes over the range 2.5–175 ng mL−1 (10–700 ng mL−1 PFOS) are 83.7–103% with relative standard deviations (RSDs) of ≤14% (PFBA = 19%). Mean recoveries and RSDs of control human plasma fortified with mixed branched and linear isomer PFOA and PFHS (2.5 & 10.0 ng mL−1), and PFOS (10 & 40 ng mL−1) were 83.2% (RSD ± 7.7%), 101% (RSD ± 4.9%), and 101% (RSD ± 6.5%) respectively. Mean recoveries of control bovine serum fortified with the method target analytes over the lower concentration range 0.250–175 ng mL−1 (1–700 ng mL−1 PFOS) are 82.8–103% with RSDs ≤15% (MeFOSAA = 16%, EtFOSAA = 17%). Mean recoveries and RSDs for 736 American Red Cross (ARC) study plasma samples fortified with SRSs at 1 ng mL−1 were 89.0% (±7.3% RSD) for [1,2,3,4-13C4]PFOA, 91.8% (±10% RSD) for [1,2-13C2]PFUnA, and 89.4% (±7.9% RSD) for [1,2,3,4-13C4]PFOS.
One-step extraction prior to two-step detection by ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) to determine different groups of antibacterial agents in infant disposable hygiene products by Hua Dang; Donghong Liu; Xiangchang Hou; Yuluan Wu; Bin Wang; Hao Dong; Yanping Xian (482-489).
One-step extraction prior to a two-step detection method based on UHPLC-MS/MS was developed to determine seven quaternary ammonium salts (QACs), three isothiazolinone antibacterial agents and seven phenolic antibacterial agents in infant disposable hygiene products. Samples were ultrasonically extracted by acetonitrile; the extraction solution was directly used to separate seven QACs on a hydrophilic chromatographic column (HILIC column) by isocratic elution (0.1% formic acid acetonitrile and 10 mmol L−1 ammonium acetate solution as the mobile phases). QACs were then detected in multiple reaction monitoring (MRM) of MS/MS under an electro-spray ionization source in positive mode (ESI+). For the remaining ten analytes, the extraction solution was dried by nitrogen gas blowing and re-dissolved with acidulated methanol water solution. Then they were separated on a C18 chromatographic column with gradient elution program using methanol and water as mobile phases. Finally, ten analytes were simultaneously ionized by using a electro-spray source in positive and negative modes and acquisition was achieved in MRM. The developed methods were validated in terms of the method limit of detection and quantitation (MLOD and MLOQ), matrix effects, recovery and precision. Results indicated that favorable linear relations (r > 0.997) were obtained over the selected concentration ranges of 0.1–50 μg L−1, 1.0–500 μg L−1 and 50–2000 μg L−1 for QACs, isothiazolinone antibacterial agents and phenolic antibacterial agents, respectively. The MLODs of the three groups of antibacterial agents were 0.8 μg kg−1, 1.5–6.5 μg kg−1 and 200–500 μg kg−1, respectively. Recoveries were calculated at three concentration levels spiked in negative paper diaper samples and the values were found between 83.7% and 112% with relative standard deviation (RSD) values less than 13% for intra-day precision (n = 6) and less than 16% for inter-day precision (n = 5). The developed and validated methods were successfully applied to determine the concentrations of antibacterial agents in real samples and QACs and isothiazolinone antibacterial agents were detected in several samples. These methods are rapid, sensitive and suitable for the determination of antibacterial agents in infant disposable hygiene products and some other similar products.
Fast and feasible sample preparation methods for extraction of trace elements from deposited particulate matter samples by A. M. S. Mimura; C. C. M. Ferreira; J. C. J. Silva (490-499).
In this study, two alternative sample preparation procedures are proposed, using ultrasound and microwave, for rapid, reliable and easy extraction of trace elements from particulate matter samples. The methods (ultrasound-assisted extraction and microwave-assisted extraction) were compared to conventional acid extraction (literature method). The determination of trace elements by flame atomic absorption spectrometry (F AAS) and graphite furnace atomic absorption spectrometry (GF AAS) was investigated. The results of the three methods did not show any significant difference at a confidence level of 95% for all analytes. The two new methods showed good precision (RSD < 10%), accuracy (the recoveries from suspended particulate samples ranged from 83 to 114%) and reduced time required for sample preparation (approximately 10 min) with small volumes of acid. Using diluted aqua regia, the microwave extraction method was then employed to determine Al, As, Cd, Cr, Cu, Fe, Mn, Pb and Zn from deposited particulate matter (DPM) samples from the city of Juiz de Fora, MG, Brazil, from samples collected passively on cellulose acetate filters. Fe, Al, Zn and Mn were the most abundant elements present in the samples, followed by Cu, Pb, Cr, As and Cd.
Screening of neuraminidase inhibitors from the leaves of Syringa velutina Kom. via compound fractionation and in vitro activity evaluation by Yuchi Zhang; Jingying Xu; Chunming Liu; Sainan Li (500-510).
A novel hyphenated technique comprised of circulating ultrasound-assisted extraction (CUAE) coupled with an online solvent concentration tank (SCT), centrifugal partition chromatography (CPC), ultra-high performance liquid chromatography (UPLC), and mass spectrometry (MS) was established. Chemical compounds from the leaves of Syringa velutina Kom. were extracted, isolated, and fractionated by CPC and then analyzed using the hyphenated technique. In this study, 60% aqueous ethanol was used as the CUAE solvent. After extraction, the extraction solution was pumped into the SCT and concentrated. The concentrated solution was then pumped into the CPC column and eluted using a biphasic solvent system of ethyl acetate/n-butanol/acetonitrile/water (0.8 : 0.2 : 0.15 : 1.0, v/v/v/v). The CPC fractions were monitored using a UV detector at 250 nm and an online UPLC/PDA system at 5 min intervals. The CPC fractions were collected by a sample loop via a six-port valve, and the neuraminidase inhibitory activities of the CPC fractions were analyzed using a fluorescence method. The pure compounds were analyzed directly, and the activities of the mixed compounds were calculated using mathematical equations. The results indicated that the inhibition rates of syringin, oleuropein aglycone, luteoloside, and syringopicroside were above 50.00% at a concentration of 40 μM, and they have the potential for further development. These results were proven using authentic standards.
Analysis of single malt Scotch whisky using Raman spectroscopy by Johannes Kiefer; Agnita Lynda Cromwell (511-518).
Counterfeit and adulterate alcoholic beverages represent an economic problem for the producer but also a potential health issue for the consumer. This is particularly true for single malt Scotch whisky after decades of maturation resulting in high monetary as well as non-material value. A nonintrusive approach for analyzing the content of a whisky bottle without opening the lid is used in the present work. Raman spectra are acquired through the glass wall of the bottle using a 785 nm laser as excitation source. This wavelength is beneficial as moderate fluorescence signals contribute to the spectra and carry additional information. The systematic analysis of the data yields information about the production and maturation procedure. Principal component analysis (PCA) mainly allows determining the cask type, in which the whisky was aged. Partial least-squares regression facilitated the determination of the age, the alcohol content, the filtering process, and whether or not a whisky contains artificial colorants. Hence, it can be concluded that Raman spectroscopy is ideally suited for analyzing whisky and for its authentication.
Paper-based thioglycolic acid (TGA)-capped CdTe QD device for rapid screening of organophosphorus and carbamate insecticides by A. Apilux; W. Siangproh; N. Insin; O. Chailapakul; V. Prachayasittikul (519-527).
A paper-based device, based on the fluorescence switching of water-soluble thioglycolic acid (TGA)-capped CdTe QDs, was developed for the simple, rapid and sensitive detection of organophosphorus (OP) and carbamate (CM) insecticides. A new design platform for the developed device was created, comprising a foldable sheet with a detection zone and a buffer solution loading channel, to simplify the multi-step reaction of a bi-enzyme assay with a signal enhancement system. This device was very useful for fast screening and on-site detection, without requiring many reagents. The bi-enzyme includes acetylcholinesterase (AChE), choline oxidase (ChOx) and TGA-capped CdTe QDs, which were coated on the paper-based device at the detection zone in a separated sheet, starting with an acetylcholine (ACh) substrate coating. After incubation of the sample at the detection zone, the device was closed to initiate enzyme catalyzed hydrolysis of the pre-spotted ACh. Subsequently, the buffer solution was applied to the device, allowing for the pre-spotted chemicals to mix well and importantly, result in signal enhancement. The hydrolysis of ACh was catalyzed by AChE followed by ChOx to yield H2O2, which can quench the fluorescence of the TGA-capped CdTe QDs. In the presence of OP and CM insecticides, the AChE activity was inhibited, resulting in decreased quenching of the TGA-capped CdTe QDs. The change in the fluorescence intensity of the TGA-capped CdTe QDs can be observed using the naked eye under UV-black light. Under optimized conditions, the limit of detection for pirimicarb, dichlorvos and carbaryl were found to be 0.05, 0.01 and 0.01 ppm, respectively, using visual measurements. This developed device was successfully applied to the detection of OP and CM insecticide residues in agricultural products. The data correlated well with the data obtained using gas chromatography-tandem mass spectrometry (GC-MS/MS). This developed device shows good selectivity and sensitivity for the rapid screening of insecticides and could be useful for on-site applications.
A novel soil nutrient detection method based on combined ATR and DRIFT mid-infrared spectra by Chen Chen; Daming Dong; Zhiwei Li; Xiaoke Wang (528-533).
Conventional soil nutrient detection methods are time-consuming and laborious and cannot realize rapid measurement. Mid-infrared spectroscopy with the advantages of high detection speed, non-destructive testing, and a pretreatment-free process has been widely applied in soil nutrient analysis. In previous studies on the detection of soil compositions, diffuse reflection and attenuated total reflection are two commonly adopted ways in mid-infrared spectroscopy. In this paper, we developed a method which could simultaneously measure the infrared attenuated total reflection (ATR) and diffuse reflection infrared Fourier transform (DRIFT) spectra of soils, in order to obtain more abundant spectral information. We analyzed and predicted the contents of organic matters, organic carbon and total nitrogen quantitatively in soils by using chemometrics. The results showed that after combining ATR spectra and DRIFT spectra, the MSC-processed PLS models allowed a higher prediction accuracy than that of using ATR or DRIFT spectra alone. The coefficients of determination of organic matters, organic carbon and total nitrogen models were 0.93, 0.952 and 0.971, respectively. By combining ATR and DRIFT spectral information, the analytical ability of infrared spectroscopy was enhanced. This study provided a new method for the rapid measurement of soil nutrients.
Paper-based microfluidics for experimental design: screening masking agents for simultaneous determination of Mn(ii) and Co(ii) by Nathan A. Meredith; John Volckens; Charles S. Henry (534-540).
This work describes an efficient, generalizable approach towards the identification (and mitigation) of interferences for colorimetric detection using microfluidic paper-based analytical devices. Colorimetric detection is commonly used in conjunction with microfluidic paper-based analytical devices; however, many colorimetric reagents lack selectivity. The selectivity problem is particularly true for metal detection where colorimetric ligands can complex with multiple metals. Many solution-based studies have investigated methods to mask interfering metals, but solution-based procedures do not always apply to paper sensors where the reagents are dried and the cellulosic functional groups may also interact with metals. Here, a simple eight-armed microfluidic paper-based analytical device has been designed to rapidly screen masking agents for the detection of transition metals using the non-specific colorimetric ligand 4-(2-pyridylazo)resorcinol as a model system to optimize conditions. The combination of dimercaptosuccinic acid and triethylenetetramine in pH 10 borate buffer was identified for selective determination of Mn(ii) with greater than 87% masking of interfering metals. A combination of ethylenediaminetetracetic acid and triethylenetetramine in pH 10 phosphate buffer was identified for selective determination of Co(ii) with greater than 96% masking for most of the interfering metals although Fe(ii), Fe(iii), and Ni(ii) still interfere. While used for this specific system, the approach described here is generalizable for ligand and interference screening with potential applications to a number of different assays performed on μPADs.
Back cover (541-542).