Analytica Chimica Acta (v.703, #1)

Simultaneous electrochemical determination of arsenic, copper, lead and mercury in unpolluted fresh waters using a vibrating gold microwire electrode by Georgina M.S. Alves; Júlia M.C.S. Magalhães; Pascal Salaün; Constant M.G. van den Berg; Helena M.V.M. Soares (1-7).
Display Omitted► Simultaneous DPASV determination of four metals with a vibrating gold microwire. ► Multi-element detection in the presence of oxygen with short deposition time (30 s). ► Detection limits of As, Cu, Hg, Pb: 0.07, 0.4, 0.07, 0.2 μg L−1, respectively. ► Successful simultaneous determination of the four metals in real freshwaters.In this work, a simple, rapid, reliable and low cost method for simultaneous electrochemical determination of As, Cu, Hg and Pb ions, on a vibrating gold microwire electrode combined with stripping voltammetry, is described for the first time.The multi-element detection was performed in the presence of oxygen by differential pulse anodic stripping voltammetry (DPASV) in HCl 0.1 M with NaCl 0.5 M. This media was found optimum in terms of peak resolution, peak shape and sensitivities, and has a composition similar to seawater to which the method could potentially be applied. The gold microwire electrode presented well defined, undistorted, sharp and reproducible peaks for trace concentrations of Cu, Hg and Pb and As presented a reproducible peak with a small shoulder. Using a gold vibrating microwire electrode of 25 μm diameter and 30 s deposition time, the detection limits of As, Cu, Hg and Pb were 0.07, 0.4, 0.07 and 0.2 μg L−1, respectively. Possible effects of Al, Cd, Cr, Fe, Mn, Ni, Sb and Zn were investigated but did not cause any significant interferences.Finally, the method was applied for the simultaneous determination of these four metals in unpolluted river water samples and the results were validated by Atomic Absorption Spectroscopy with Electrothermal Atomization (AAS-EA) or by Inductively Coupled Plasma Mass Spectrometry (ICP-MS).
Keywords: Vibrating gold microwire electrode; Simultaneous determination; Trace metals; Anodic stripping voltammetry;

► Pressurized liquid extraction (PLE) improves the extraction yield, decreases time and solvent consumption, and protects sensitive compounds. ► PLE facilitates the use of solvent mixtures and other extraction additives that would enhance the extraction efficiency. ► The use of combined and hyphenated results in a substantial decrease in the amount of sample used with better efficiency and selectivity. ► Different studies discuss using PLE to enrich phenolic compounds, lignans, carotenoids, essential oils and other nutraceuticals from foods and herbal plants.Pressurized liquid extraction is a “green” technology for the extraction of nutraceuticals from foods and herbal plants. This review discusses the extraction principles and the optimization of the extraction parameters that improves the extraction efficiency. The use of different solvent mixtures and other extraction additives to enhance the efficiency of the extraction are discussed. Dynamic mode of extraction in Pressurized liquid extraction, and the use of combined and hyphenated sample preparation and analytical techniques are presented. This work discusses how different studies used Pressurized liquid extraction to enrich phenolic compounds, lignans, carotenoids, oils and lipids, essential oils and other nutraceuticals from foods and herbal plants.
Keywords: Pressurized liquid extraction; Pressurized hot water extraction; Food; Herbal plants; Nutraceuticals; Extraction parameters; Review article;

Tools for analyzing the phosphoproteome and other phosphorylated biomolecules: A review by Alexander Leitner; Martin Sturm; Wolfgang Lindner (19-30).
Display Omitted► The phosphate group possesses unique physicochemical properties. ► The relevance of protein phosphorylation drives development of analytical tools. ► Mass spectrometry is the central platform for phosphoproteomics. ► Enrichment methods target charge, polarity, structure or reactivity of phosphates. ► Methods for phosphoproteomics can be applied to other classes of analytes.Enrichment, separation and mass spectrometric analysis of biomolecules carrying a phosphate group plays an important role in current analytical chemistry. Application areas range from the preparative enrichment of phospholipids for biotechnological purposes and the separation and purification of plasmid DNA or mRNA to the specific preconcentration of phosphoproteins and -peptides to facilitate their later identification and characterization by mass spectrometry. Most of the recent improvements in this field were triggered by the need for phosphopeptide enrichment technology for the analysis of cellular protein phosphorylation events with the help of liquid chromatography–mass spectrometry. The high sensitivity of mass spectrometry and the possibility to combine this technique with different separation modes in liquid chromatography have made it the method of choice for proteome analysis. However, in the case of phosphoprotein analysis, the low abundance of the resulting phosphopeptides and their low quality fragment spectra interfere with the identification of phosphorylation events. Recent developments in phosphopeptide enrichment and fragmentation technologies successfully helped to overcome these limitations. In this review, we will focus on sample preparation techniques in the field of phosphoproteomics, but also highlight recent advancements for the analysis of other phosphorylated biomolecules.
Keywords: Mass spectrometry; Protein phosphorylation; Proteomics; Sample preparation; Enrichment;

.Display Omitted► Potentiometric stripping analysis (PSA) employed for the determination of antimony. ► Hexathia-18C6 and rice husk modified carbon paste electrode developed for the analysis. ► Lowest detection limit obtained for the determination of Sb(III) using PSA. ► Analysis of Sb in pharmaceutical formulations, human hair, blood serum, urine and sea water. ► Rice husk used as a modifier for the first time in electrochemistry.An electrochemical method based on potentiometric stripping analysis (PSA) employing a hexathia 18C6 (HT18C6) and rice husk (RH) modified carbon paste electrode (HT18C6–RH-CPE) has been proposed for the subnanomolar determination of antimony. The characterization of the electrode surface has been carried out by means of scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and chronocoulometry. By employing HT18C6–RH-CPE, a 12-fold enhancement in the PSA signal (dt/dE) was observed as compared to plain carbon paste electrode (PCPE). Under the optimized conditions, dt/dE (s V−1) was proportional to the Sb(III) concentration in the range of 1.42 × 10−8 to 6.89 × 10−11  M (r  = 0.9944) with the detection limit (S/N = 3) of 2.11 × 10−11  M. The practical analytical utilities of the modified electrode were demonstrated by the determination of antimony in pharmaceutical formulations, human hair, sea water, urine and blood serum samples. The prepared modified electrode showed several advantages, such as simple preparation method, high sensitivity, very low detection limit and excellent reproducibility. Moreover, the results obtained for antimony analysis in commercial and real samples using HT18C6–RH-CPE and those obtained by inductively coupled plasma-atomic emission spectrometry (ICP-AES) are in agreement at the 95% confidence level.
Keywords: Antimony; Hexathia 18 crown 6; Rice husk; Potentiometric stripping analysis;

Display Omitted► We developed a fully automated at-line MEPS-LVI in-port-derivatization-GC–MS method. ► The analytes were detected in the μg L−1–ng L−1 range with only 800 μL of sample. ► A high selectivity of the MIP material for estrogens’ recognition was demonstrated. ► Compared to a normal SPE, the time for a MEPS extraction is reduced to about 10 min due to the high automation and miniaturization grade. ► Less matrix co-extraction was of special value for analysis of wastewater samples.A fully automated protocol consisting of microextraction by packed sorbents (MEPS) coupled with large volume injection-in-port-derivatization-gas chromatography–mass spectrometry (LVI-derivatization-GC–MS) was developed to determine endocrine disrupting compounds (EDCs) such as alkylphenols, bisphenol A, and natural and synthetic hormons in river and waste water samples. During method optimization, the extraction parameters as ion strength of the water sample, the MEPS extraction regime, the volume of organic solvent used for the elution/injection step, the type of elution solvents and the selectivity of the sorbents were studied. For optimum in-port-derivatization, 10 μL of the derivatization reagent N,O-bis(trimethylsilyl)triufloroacetamide with 1% of trimethylchlorosilane (BSTFA + 1% TMCS) was used. 17β-Estradiol-molecularly imprinted polymer (MIP) and silica gel (modified with C-18) sorbents were examined for the enrichment of the target analytes from water samples and the obtained results revealed the high selectivity of the MIP material for extraction of substances with estrogen-like structures. Recovery values for most of the analytes ranged from 75 to 109% for the C18 sorbent and from 81 to 103% for the MIP material except for equilin (on C18 with only 57–66% recovery). Precision (n  = 4) of the entire analysis protocol ranged between 4% and 22% with both sorbents. Limits of detection (LODs) were at the low ng L−1 level (0.02–87, C18 and 1.3–22, MIP) for the target analytes.
Keywords: Estrogenic compounds; Environmental water samples; Microextraction by packed sorbent; Large volume injection in-port-derivatization; Molecularly imprinted polymer;

Convenient, inexpensive quantification of elemental sulfur by simultaneous in situ reduction and colorimetric detection by Misha T. Kwasniewski; Rachel B. Allison; Wayne F. Wilcox; Gavin L. Sacks (52-57).
Display Omitted► An inexpensive and convenient approach for quantifying elemental sulfur was developed. ► Sulfur is converted to hydrogen sulfide and quantified by a sulfide detection tube. ► Detection thresholds are comparable to the best existing methods. ► The method has good recovery and linearity across complex matrices. ► The method should be appropriate for both field and laboratory applications.Rapid, inexpensive, and convenient methods for quantifying elemental sulfur (S0) with low or sub-μg g−1 limits of detection would be useful for a range of applications where S0 can act as a precursor for noxious off-aromas, e.g., S0 in pesticide residues on winegrapes or as a contaminant in drywall. However, existing quantification methods rely on toxic reagents, expensive and cumbersome equipment, or demonstrate poor selectivity. We have developed and optimized an inexpensive, rapid method (∼15 min per sample) for quantifying S0 in complex matrices. Following dispersion of the sample in PEG-400 and buffering, S0 is quantitatively reduced to H2S in situ by dithiothreitol and simultaneously quantified by commercially available colorimetric H2S detection tubes. By employing multiple tubes, the method demonstrated linearity from 0.03 to 100 μg S0  g−1 for a 5 g sample (R 2  = 0.994, mean CV = 6.4%), and the methodological detection limit was 0.01 μg S0  g−1. Interferences from sulfite or sulfate were not observed. Mean recovery of an S0 containing sulfur fungicide in grape macerate was 84.7% with a mean CV of 10.4%. Mean recovery of S0 in a colloidal sulfur preparation from a drywall matrix was 106.6% with a mean CV of 6.9%. Comparable methodological detection limits, sensitivity, and recoveries were achieved in grape juice, grape macerate and with 1 g drywall samples, indicating that the methodology should be robust across a range of complex matrices.
Keywords: Wine; Grapes; S8; Pesticide residue;

Display Omitted► A robust and cost effective LC-MS/MS method was developed to calculate 5MedC/dG ratios. ► The LCMS method exhibited fast turn-around times without interference from ion suppression and from RNA nucleosides. ► Both orbitrap and tandem LCMS showed detection limit of 5MedC in femtomole range. ► The developed tandem LCMS method was vigorously validated to ensure robustness and precision.An affordable and fast liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the accurate and precise determination of global DNA methylation levels in peripheral blood. Global DNA methylation extent was expressed as the ratio of methylated 2′-deoxycytidine (5MedC) to 2′-deoxyguanosine (dG), which were obtained after DNA extraction and hydrolysis and determined by positive electrospray LC–ESI-MS/MS. The cost-effective internal standards 15N3-dC and 15N5-dG were incorporated for the accurate quantification of 5MedC and dG, respectively. The desired nucleoside analytes were separated and eluted by LC within 2.5 min on a reverse phase column with a limit of detection of 1.4 femtomole on column for 5MedC. Sample preparation in 96-well format has significantly increased the assay throughput and filtration was found to be a necessary step to assure precision. Precision was performed with repeated analysis of four DNA QC sample over 12 days, with mean intra- and inter-day CVs of 6% and 11%, respectively. Accuracy was evaluated by comparison with a previously reported method showing a mean CV of 4% for 5 subjects analyzed. Furthermore, application of the assay using a benchtop orbitrap LCMS in exact mass full scan mode showed comparable sensitivity to tandem LCMS using multiple reaction monitoring.
Keywords: Global DNA methylation assay; Liquid chromatography mass spectrometry; 5-Methyl-2′-deoxycytidine; Internal standard; Orbitrap MS;

A competitive immunoassay with a surrogate calibrator curve for aflatoxin M1 in milk by Di Guan; Peiwu Li; Yehan Cui; Qi Zhang; Wen Zhang (64-69).
Display Omitted► Polyclonal anti-idiotype antibodies were used as surrogate of AFM1. ► An excellent correlation was obtained between AFM1 and anti-idiotype antibodies. ► The anti-idiotype antibody was successfully used as surrogate calibrator curve for AFM1 in immunoassays. ► The recovery and accuracy results demonstrated that the method was feasible and reliable for the analysis of samples.A green enzyme-linked immunosorbent assay (ELISA) to measure aflatoxin M1 (AFM1) in milk was developed and validated with a surrogate calibrator curve. Polyclonal anti-idiotype (anti-Id) antibody, used as an AFM1 surrogate, was generated by immunizing rabbits with F(ab′)2 fragments from the anti-AFM1 monoclonal antibody (mAb). The rabbits exhibited high specificity to the anti-AFM1 mAb, and no cross-reactivity to either of the other anti-aflatoxin mAbs or the isotype matched mAb was observed. After optimizing the physicochemical factors (pH and ionic strength) that influence assay performance, a quantitative conversion formula was developed between AFM1 and the anti-Id antibody (y  = 31.91x  − 8.47, r  = 0.9997). The assay was applied to analyze AFM1 in spiked milk samples. The IC50 value of the surrogate calibrator curve was 2.4 μg mL−1, and the inter-assay and intra-assay variations were less than 10.8%; recovery ranged from 85.2 to 110.9%. A reference high-performance liquid chromatography method was used to validate the developed method, and a good correlation was obtained (y  = 0.81x  + 9.82, r  = 0.9922).
Keywords: Aflatoxin M1; Anti-idiotype antibody; Surrogate; Enzyme-linked immunosorbent assay;

The impact of water and hydrocarbon concentration on the sensitivity of a polymer-based quartz crystal microbalance sensor for organic compounds by Bobby Pejcic; Emma Crooke; Cara M. Doherty; Anita J. Hill; Matthew Myers; Xiubin Qi; Andrew Ross (70-79).
Display Omitted► The response of a polymer coated QCM sensor is affected by water soaking time. ► Polymer-water interfacial processes influence the QCM sensitivity for hydrocarbons. ► The QCM sensitivity of high Tg polymer films is affected by plasticization processes.Long-term environmental monitoring of organic compounds in natural waters requires sensors that respond reproducibly and linearly over a wide concentration range, and do not degrade with time. Although polymer coated piezoelectric based sensors have been widely used to detect hydrocarbons in aqueous solution, very little information exists regarding their stability and suitability over extended periods in water. In this investigation, the influence of water aging on the response of various polymer membranes [polybutadiene (PB), polyisobutylene (PIB), polystyrene (PS), polystyrene-co-butadiene (PSB)] was studied using the quartz crystal microbalance (QCM). QCM measurements revealed a modest increase in sensitivity towards toluene for PB and PIB membranes at concentrations above 90 ppm after aging in water for 4 days. In contrast, the sensitivity of PS and PSB coated QCM sensors depended significantly on the toluene concentration and increased considerably at concentrations above 90 ppm after aging in water for 4 days. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR–FTIR) showed that there is a change in the sorption mechanism at higher toluene levels for PS and PSB. Positron annihilation lifetime spectroscopy (PALS) studies were performed to investigate the free volume properties of all polymers and to monitor any changes in the free volume size and distribution due to water and toluene exposure. The PALS did not detect any considerable variation in the free volume properties of the polymer films as a function of solution composition and soaking time, implying that viscoelastic and/or interfacial processes (i.e. surface area changes) are probably responsible for variations in the QCM sensitivity at high hydrocarbon concentrations. The results suggest that polymer membrane conditioning in water is an issue that needs to be considered when performing QCM measurements in the aqueous phase. In addition, the study shows that the hydrocarbon response is concentration dependant for polymers with a high glass transition temperature, and this feature is often neglected when comparing sensor sensitivity in the literature.
Keywords: Quartz crystal microbalance; Attenuated total reflectance; Infrared spectroscopy; Positron annihilation lifetime spectroscopy; Polymer; Hydrocarbon sensor;

Surface plasmon resonance biosensor with high anti-fouling ability for the detection of cardiac marker troponin T by Jen Tsai Liu; Ching Jung Chen; Toshiyuki Ikoma; Tomohiko Yoshioka; Jeffrey S. Cross; Shwu-Jen Chang; Jang-Zern Tsai; Junzo Tanaka (80-86).
Display Omitted► A mixed self-assembled monolayer (SAM) detected cardiac troponin T by SPR. ► SPR limit of detection (LOD) of cardiac troponin T was 100 ng mL−1. ► OEG–MDHA mixed SAM showed 82% anti-fouling capability when tested with BSA. ► Label-free cardiac troponin T detection was detected in less than 2 min by SPR.Designing a surface recognition layer with high anti-fouling ability, high affinity, and high specificity is an important issue to produce high sensitivity biosensing transducers. In this study, a self-assembled monolayer (SAM) consisting of a homogeneous mixture of oligo(ethylene glycol) (OEG)-terminated alkanethiolate and mercaptohexadecanoic acid (MHDA) on Au was employed for immobilizing troponin T antibody and applied in detecting cardiac troponin T by using surface plasmon resonance (SPR). The mixed SAM showed no phase segregation and exhibited human serum albumin resistance, particularly with an antibody-immobilized surface. X-ray photoemission spectra revealed that the chemical composition ratio of OEG to the mixed SAM was 69% and the OEG packing density was 82%. The specific binding of troponin T on the designed surface indicated a good linear correlation (R  = 0.991, P  < 0.0009) at concentrations lower than 50 μg mL−1 with the limit of detection of 100 ng mL−1 using a SPR measuring instrument. It is concluded that the mixed SAM functions as designed since it has high detection capability, high accuracy and reproducibility, as well as shows strong potential to be applied in rapid clinical diagnosis for label-free detection within 2 min.
Keywords: Myocardial infarction; Troponin T; Anti-fouling ability; Surface plasmon resonance; Self-assembled monolayer; Oligoethylene glycol;

Display Omitted► The GOx–Fe3O4 composites provided a one-step assay for the fluorescence detection of glucose. ► GOx immobilized on the surface of the GOx–Fe3O4 composites is reusable for the detection of glucose. ► The GOx–Fe3O4 composites can be applied to detect glucose in a complex biological sample. ► Compared to peroxidase-like Fe3O4 NPs, a system of GOx–Fe3O4 composite and AU provided better sensitivity toward glucose.This study reports the development of a reusable, single-step system for the detection of specific substrates using oxidase-functionalized Fe3O4 nanoparticles (NPs) as a bienzyme system and using amplex ultrared (AU) as a fluorogenic substrate. In the presence of H2O2, the reaction pH between Fe3O4 NPs and AU was similar to the reaction of oxidase and the substrate. The catalytic activity of Fe3O4 NPs with AU was nearly unchanged following modification with poly(diallyldimethylammonium chloride) (PDDA). Based on these features, we prepared a composite of PDDA-modified Fe3O4 NPs and oxidase for the quantification of specific substrates through the H2O2-mediated oxidation of AU. By monitoring fluorescence intensity at 587 nm of oxidized AU, the minimum detectable concentrations of glucose, galactose, and choline were found to be 3, 2, and 20 μM using glucose oxidase–Fe3O4, galactose oxidase–Fe3O4, and choline oxidase–Fe3O4 composites, respectively. The identification of glucose in blood was selected as the model to validate the applicability of this proposed method.
Keywords: Amplex ultrared; Iron oxide nanoparticles; Fluorescence; Glucose Poly(diallyldimethylammonium chloride); Catalysis;

Enzyme-based NAND gate for rapid electrochemical screening of traumatic brain injury in serum by Nandi Zhou; Joshua R. Windmiller; Gabriela Valdés-Ramírez; Ming Zhou; Jan Halámek; Evgeny Katz; Joseph Wang (94-100).
Display Omitted► A ‘NAND’ enzyme logic gate is demonstrated for the rapid and decentralized assessment of TBI. ► The gate integrates glutamate and lactate dehydrogenase biomarkers to trigger an immediate alert. ► The gate mitigates physiological and electroactive interferences and is able to operate in serum.We report on the development of a rapid enzyme logic gate-based electrochemical assay for the assessment of traumatic brain injury (TBI). The concept harnesses a biocatalytic cascade that emulates the functionality of a Boolean NAND gate in order to process relevant physiological parameters in the biochemical domain. The enzymatic backbone ensures that a high-fidelity diagnosis of traumatic brain injury can be tendered in a rapid fashion when the concentrations of key serum-based biomarkers reach pathological levels. The excitatory neurotransmitter glutamate and the enzyme lactate dehydrogenase were used here as clinically-relevant input TBI biomarkers, in connection to the low-potential detection of the NADH product in the presence of methylene green at a glassy carbon electrode. A systematic optimization of the gate and the entire protocol has resulted in the effective discrimination between the physiological and pathological logic levels. Owing to its robust design, the enzyme-based logic gate mitigates potential interferences from both physiological and electroactive sources and is able to perform direct measurements in human serum samples. Granted further detailed clinical validation, this proof-of-concept study demonstrates the potential of the electrochemical assay to aid in the rapid and decentralized diagnosis of TBI.
Keywords: Glutamate; Lactate dehydrogenase; Traumatic brain injury; Assay; Electrochemical sensor; Amperometry;