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Analytical Methods (v.3, #8)

Front cover (pp. 1695-1696).

By screening uronic acid-based surfactant interfacial properties, the effect of the hydroxyl group stereochemistry (OH-4) on the conformation of bicatenary (disubstituted) derivatives at the air–water interface has been evidenced by experimental and computational approaches. Physical and optical properties of a monolayer characterized by Langmuir film balance, Brewster angle microscopy, and ellipsometry at 20 °C reveal that the derivative of glucuronate (C14/14–GlcA) forms a more expanded monolayer, and shows a transition state under compression, in the opposite to that of galacturonate (C14/14–GalA). Both films are very mechanically resistant (compression modulus > 300 mN m⁻¹) and stable (collapse pressure exceeding 60 mN m⁻¹), while that of C14/14–GalA exhibits a very high compression modulus up to 600 mN m⁻¹ like films in the solid state. Computational approaches provide single and assembly molecular models that corroborate the molecule expansion degree and interactions data from experimental results. Differences in the molecular conformation and film behaviours of uronic acid bicatenary derivatives at the air–water interface are attributed to the intra-H-bonding formation, which is more favourable with an OH-4 in the axial (C14/14–GalA) than in the equatorial position (C14/14–GlcA).

Contents (pp. 1697-1708).

In order to assess and avoid risks for both human and environmental health, there is a high need for cost-effective and sensitive detection systems suitable for the monitoring of chemical contaminants in food and the environment. Due to their high sensitivity and selectivity, affinity-based detection systems are interesting for monitoring tools. Antibodies have long been the most popular affinity-based recognition elements, however, recently different novel affinity-based recognition elements with improved characteristics, like specificity, stability and cost-efficiency, have gained attention. In the present study, one type of such novel affinity-based recognition elements, namely landscape phages were evaluated as substitute antibodies for detection of PCB. These phages with affinity for PCBs were selected from a landscape phage library, in which each phage displays an 8-mer peptide at all 4000 major coat proteins pVIII. Landscape phages have potential as biorecognition elements, because of their excellent characteristics, such as high affinity and specificity, fast, cheap and animal-friendly manufacturing process with low batch-to-batch variations and superior stability, which allow them to operate as elements of detector systems in complex environmental and food matrices. Phages with a high specificity for PCB106 were isolated from the landscape phage library. Using surface plasmon resonance (SPR) it was shown that the selected phages bind specifically PCB106 and do not bind PCB72 and PCB118. The dissociation constants (Kd) of the phage binding with PCB106 were in μM range. After further improvement of their binding activity, the specific PCB-binding phages can be used as biorecognition elements for food and environmental monitoring.

Analytical methods used in conjunction with dried blood spots by Sangeeta Tanna; Graham Lawson (pp. 1709-1718).

This review covers the wide range of different methods that have been used for the microanalysis of dried blood spots (DBS) from the ones reported in 1914 to the sophisticated processes used, for example, in newborn screening, new drug discovery research and application of PCR based DNA studies of HIV in countries with limited infrastructure. The value of the dried blood spot as a sampling tool and the many advantages it offers in combination with suitable analytical methods is discussed. Current developments in both automating the DBS extraction process and the potential for direct analysis of the sample without prior extraction are reviewed. Possible future directions in the analytical methods used for DBS samples are also highlighted.

Sample treatments based on dispersive (micro)extraction by M. Cruz-Vera; R. Lucena; S. Cárdenas; M. Valcárcel (pp. 1719-1728).

Sample treatment has evolved in the last few years following basic trends, simplification, automation and miniaturization being the most remarkable ones. Microextraction techniques, including solid phase microextraction (SPME) and liquid phase microextraction (LPME), have emerged in this context showing very competitive features if they are compared with their classic counterparts. Essentially, extraction techniques are surface dependent processes since their kinetics depend directly on the contact surface between the sample and the extractant phase. This aspect, which is important in any extraction procedure, becomes critical when the amount of extractant is reduced to the microscale. In this context, dispersive-based procedures have gained importance as rapid and efficient sample treatment methodologies. This review article deals with the use of dispersion in micro-solid phase extraction (μ-SPE) and LPME. The main techniques as well as their powerful combinations will be described in depth with references to the most relevant applications.

Highlighting anatomical sub-structures in rat brain tissue using lipid imaging by Alice M. Delvolve; Benoit Colsch; Amina S. Woods (pp. 1729-1736).

Cell membranes are made up of a mixture of glycerolipids, sphingolipids, gangliosides and cholesterol. Lipids play important roles in a cell's life. However many of their functions have still to be discovered. In the present work, we describe an efficient, easy and rapid methodology to accurately localize phosphatidylcholines and sphingomyelins from a single coronal rat brain section in the cerebrum area. Matrix assisted laser desorption/ionization (MALDI) mass spectrometry was used to profile and image lipids. The best resolved structure was 25–50 μm in the hippocampus.

Preparation and evaluation of superparamagnetic surface molecularly imprinted polymer nanoparticles for selective extraction of bisphenol A in packed food by Zhou Xu; Li Ding; Yanjiao Long; LiGuang Xu; Libing Wang; Chuailai Xu (pp. 1737-1744).

Molecularly imprinted polymer (MIP) coated Fe3O4 nanoparticles (Fe3O4@MIP) were synthesized by atom transfer radical polymerization (ATRP) and used as highly selective magnetic solid-phase extraction (MSPE) sorbents for trace bisphenol A (BPA) from packed food. The morphological and polymeric characteristics of the Fe3O4@MIP were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. In this work, competitive recognition compounds (4-n-octylphenol and bisphenol A diglycidyl ether) exhibited lower binding capability to the Fe3O4@MIP than BPA. A high performance liquid chromatography with fluorescence detection (HPLC-FLD) method was developed for the determination of BPA in canned orange and milk samples. The main factors influencing the extraction efficiency, including high specificity, the amount of surfactant, the shaking time and the desorption ability of complex food matrices were investigated and optimized. Various parameters such as the pH of thesample, the amount of Fe3O4@MIP sorbent, the extraction time, and the desorption conditions were optimized. Notably, the extraction can be carried out quickly, and the extraction time for BPA onto Fe3O4@MIP sorbents can be clearly shortened to 5 min. Good linearities (r² > 0.9965) for all calibration curves were obtained, and the limit of detection (LOD) for BPA was 0.1 and 0.3 ng mL⁻¹ in canned orange and milk samples, respectively. To the best of our knowledge, this is the first time that surface molecularly imprinted polymer nanoparticles have been used for the pretreatment of packed food.

Synthesis and cell-surface binding of lectin-gold nanoparticle conjugates by Jine Wang; Dianjun Liu; Zhenxin Wang (pp. 1745-1751).

In this paper, we report a generalized functionalisation strategy, which enables conjugation of lectin to a gold nanoparticle (GNP) surface without affecting the lectin properties. The lectin-GNP conjugates are prepared by coupling lectins to the GNP surfaces through a bifunctional linker PEG NHS ester disulfide (NHS-PEG-S-S-PEG-NHS). Subsequently, additional PEG-thiol (mPEG-SH) ligand is applied to the GNP suspension in order to block nonspecific adsorption sites on the GNP surface and improve the stability of the lectin-GNP conjugate. The interactions of six lectin-GNP conjugates with six cell lines have been visualized by conventional microscopy and semi-quantitatively analyzed by the UV-visible spectroscopic technique, respectively. The experimental results demonstrate that the lectin-GNP conjugates can bind to living cells with high efficiency and have a great promise to be used as optical probes for monitoring specific affinities of cells with lectins, and evaluating glycosyl complexes on living cell surfaces.

Testing a new method for quantifying Si in silica-rich biomass using HF in a closed vessel microwave digestion system by Jennifer S. Le Blond; Stanislav Strekopytov; Catherine Unsworth; Ben J. Williamson (pp. 1752-1758).

Biomass is increasingly being used as an alternative energy source to fossil fuels. Of particular concern is that during combustion of biomass rich in silica (SiO2), such as sugarcane and many other grasses, the silica can convert into a crystalline form. Exposure to crystalline silica can potentially cause respiratory disease, such as silicosis. To improve understanding of the potential health risk, a robust and rapid method for quantifying the amount of silicon (Si) in plant material is required. Traditional methods do not usually account for Si in organic materials. This paper, therefore, proposes a new methodology based on a closed vessel microwave digestion using hydrofluoric acid (HF). To test the method, sugarcane leaves were digested and the solutions analysed by inductively coupled plasma atomic emission spectroscopy (ICP-AES), with an HF-resistant setup, and two external calibration standard sets in an HF-H3BO3-matrix and HNO3-matrix. The concentration of Si found in the reference materials was consistent with previously published values and Si loss during the sample preparation was minimal. The elemental recoveries from the reference materials were generally good (85–115% for Al, Ca, Cu, Fe, K, Mg, P, Si, Sr, Ti and 78–125% for K and S). The new methodology can be constructive in building a new database on Si and some other elements in biofuel plant varieties.

Development of high-throughput HILIC-MS/MS methodology for plasma citrulline determination in multiple species by Prem K. Gupta; Joshua Brown; Prabath G. Biju; John Thaden; Nicolaas E. Deutz; Sree Kumar; Martin Hauer-Jensen; Howard P. Hendrickson (pp. 1759-1768).

Circulating citrulline originates almost exclusively from the small intestinal enterocytes in mammals and therefore is a potential biomarker of disease states affecting enterocyte mass including exposure to ionizing radiation. There is a need for a simple and rapid method for citrulline quantification in plasma. To achieve this goal, a high-throughput separation and tandem mass spectrometric detection strategy has been developed and validated in six different species. HILIC separation was achieved on a 1.7 μm fused-core Diol column using an acidic acetonitrile/water gradient. A surrogate analyte (citrulline stable isotope) was used to determine the lower-limit-of-quantitation, extraction recovery, and matrix ion effects. Mass spectrometric detection was achieved in the multiple reaction-monitoring mode using m/z 176 → 159, 177 → 160, and 181 → 164, for citrulline, citrulline+1, and citrulline+5, respectively. The retention time of citrulline and total chromatographic run time were 1.1 min and 2.5 min, respectively, while effectively eliminating matrix-ion effects and achieving baseline separation from the confounding amino acid arginine. Quantitation was precise (CV <4.3%), accurate (90–110%), and sensitive (lower-limit-of-quantitation; 0.125 μM) without interference from the confounding amino acid, arginine. The throughput of the method was enhanced by incorporation of a 96-well filter plate for final sample cleanup. The method was used to determine plasma citrulline in six different species and in mice treated with escalating doses of radiation. This simple, accurate and high-throughput (up to 200 samples/day) methodology provides the first quantitative assay to meet the growing demand for a rapid and simple citrulline assay with high sensitivity.

Chitosan/carbon nanotube composites for the isolation of hemoglobin in the presence of abundant proteins by Xuwei Chen; Wenjing Wang; Zhining Song; Jianhua Wang (pp. 1769-1773).

A cross-linked chitosan/multi-wall carbon nanotube (MWCNTs) nanocomposite is prepared via surface deposition-cross linking. The nanocomposite is characterized by means of FT-IR, SEM and TGA analysis, indicating that a chitosan layer is well coated on the surfaces of the MWCNTs, weighing about 35% of the total mass. Investigations on the performance of the chitosan/MWCNTs nanocomposite to the adsorption or loading of hemoglobin indicated that the adsorption equilibrium time is reduced from a few hours in the conventional protocols to 25 min in the present case. A theoretical adsorption capacity of 15.41 μg mg⁻¹ is achieved, corresponding to a 6-fold improvement when compared to that obtained by using conventional chitosan particles in the micrometre range at a same mass condition. The nanocomposite is used as an adsorbent for the isolation of hemoglobin from human whole blood, the SDS-PAGE results indicated that successful separation of hemoglobin is obtained in the presence of large amount of abundant protein, e.g., human serum albumin.

Rapid high performance screening method using UHPLC-MS to quantify 12 polyphenol compounds in fresh apples by Maria Ceymann; Eva Arrigoni; Hans Schärer; Daniel Baumgartner; Anna Bozzi Nising; Richard F. Hurrell (pp. 1774-1778).

A rapid screening method for quantifying different polyphenol compounds in fresh apples using UHPLC-MS was developed. Apples were frozen and ground to a fine powder, which was extracted with methanol containing 1% formic acid. The resulting supernatant was used directly for total polyphenol determination with the Folin–Ciocalteu reagent and after dilution and filtration for UHPLC-MS analysis. Quantification of individual polyphenols was achieved with an external standard calibration. Four different apple cultivars were analysed with both methods. Braeburn contained the lowest amount of polyphenols (calculated as sum of polyphenols by UHPLC-MS) followed by Gala Galaxy and Golden Reinders with average amounts while Fuji contained the highest concentrations ranging from 24.2 to 50.0 mg per 100 g of edible fresh matter. Total polyphenol content by the Folin-Ciocalteu method showed the same trend, but was 3–4 times higher. Using the rapid high performance screening method the 12 most important polyphenols of apples (catechin, epicatechin, procyanidin B1 and B2, chlorogenic acid, coumaroylquinic acid, phloridzin, phloretin-xyloglucoside, quercetin-galactoside/-glucoside, rutin, quercetin rhamnoside) were quantified.

Investigation of organophosphate esters in fresh water, salt and brine samples by GC-TOF MS by Jaime Nácher-Mestre; Roque Serrano; Tania Portolés; Félix Hernández (pp. 1779-1785).

Advanced analytical methodology based on gas chromatography coupled to a high resolution time-of-flight mass analyzer (GC-TOF MS) is proposed for investigation of organophosphate esters (OPEs) in environmental water, marine salts and brine samples. The target screening was carried out for 12 OPEs by evaluating the presence of up to four m/z ions for every compound. The identification criteria were the presence of, at least, two m/z ions at the expected retention time, measured at their accurate mass, and the agreement of the Q/qi ratio when compared to reference standards. This procedure allows the detection and reliable identification of the compounds in the samples at very low concentration levels (ng g⁻¹). The developed methodology was applied to commercial marine salt, brines and different environmental water samples obtaining positive findings for several OPEs such as tri(chloro-propyl)phosphate, tributyl phosphate, triphenyl phosphate among other organophosphate compounds. Thanks to the full-spectrum acquisition performed in GC-TOF MS, it is possible to make a retrospective data evaluation without the need for performing additional analysis. This allowed in this work re-evaluation of data acquired in a previous GC-TOF MS non-target analysis of some marine salt and water samples with the result of discovering several of the OPEs investigated in those samples.

Electrochemiluminescence of tris(2,2′-bipyridyl)ruthenium(ii) in the presence of hydrazine and its derivatives by Lianzhe Hu; Jie Gao; Yi Wang; Guobao Xu (pp. 1786-1789).

In this study, we report the electrochemiluminescence (ECL) of tris(2,2′-bipyridyl)ruthenium(ii) (Ru(bpy)3²⁺) in the presence of hydrazine and its derivatives in solution phase for the first time. Hydrazine and isoniazid were found to be able to enhance the ECL of Ru(bpy)3²⁺, while phenylhydrazine and hydroxylamine were observed to decrease the ECL. The possible ECL mechanisms are discussed, and the method was used to detect hydrazine and isoniazid in aqueous solutions. Under the optimum experimental conditions, the dynamic ranges were 10⁻⁷–10⁻³ M and 10⁻⁶–10⁻³ M for hydrazine and isoniazid, respectively. The detection limits were 3.8 × 10⁻⁸ M for hydrazine and 4.8 × 10⁻⁷ M for isoniazid. The proposed method has been applied to detect the content of isoniazid in pharmaceutical samples with satisfactory results.

Uninformative variable elimination for improvement of successive projections algorithm on spectral multivariable selection with different calibration algorithms for the rapid and non-destructive determination of protein content in dried laver by Di Wu; Xiaojing Chen; Xiangou Zhu; Xiaochun Guan; Guichu Wu (pp. 1790-1796).

The potential of using partial least square based uninformative variable elimination algorithm (UVEPLS) on successive projections algorithm (SPA) for spectral multivariable selection was evaluated. A case study was done on the visible and shortwave-near infrared (Vis-SNIR) spectroscopy for the rapid and non-destructive determination of protein content in dried laver. Three calibration algorithms, namely multiple linear regression (MLR), partial least square regression (PLS) and least-square support vector machine (LS-SVM), were used for the model establishment based on the selected variables of SPA, UVEPLS and UVEPLS-SPA, respectively. A total of 175 samples were prepared for the calibration (n = 117) and prediction (n = 58) sets. The performances of different pretreatments were compared. Both linear calibration algorithms of MLR and PLS and non-linear calibration algorithms of LS-SVM with linear kernel and RBF kernel obtained similar results based on certain variable selection strategies of SPA, UVEPLS and UVEPLS-SPA. The average improvement percentage of RPD values of four calibration algorithms was 38.66% by calculating SPA on UVEPLS processed variables. Therefore there was much improvement of using UVEPLS on SPA spectral multivariable selection with both linear and nonlinear calibration algorithms in this case. Moreover, the RPD values of both linear and non-linear models based on the thirteen selected variables of UVEPLS-SPA show that coarse quantitative predictions of the protein determination in dried laver is possible based on Vis-SNIR spectra. We hope that the results obtained in this study will help both further chemometric (multivariate selection and calibration analysis) investigations and investigations in the sphere of applied vibrational (Near infrared, Mid-infrared and Raman) spectroscopy of sophisticated multicomponent systems.

A sensitive and selective quantum dots-based FRET biosensor for the detection of cancer marker type IV collagenase by Hongying Liu; Guoxi Liang; E. S. Abdel-Halim; Jun-Jie Zhu (pp. 1797-1801).

A sensitive and selective quantum dots (QDs)-based fluorescence resonance energy transfer (FRET) biosensor was successfully fabricated for the detection of the cancer marker type IV collagenase. The cancer marker type IV collagenase could be determined by linking peptide between the donor-luminescent QDs and the acceptor-gold nanoparticles with small size (SAuNPs) based on FRET. Firstly, peptide terminated with cysteine could be bound to the surface of SAuNPs via the formation of Au–S bonds. Then QDs combined with the SAuNPs through the peptide. At this moment, the photoluminescence (PL) of the QDs was quenched. After type IV collagenase was added into the system, the SAuNPs could detach from QDs because the enzyme cleaves the peptide to lead to the disappearance of FRET, which allowed the fluorescence of the QDs to return. The enzymatic activity of type IV collagenase was related to the PL change of QDs-based FRET probes. The concentration of type IV collagenase was determined in the linear range of 0.05–10 μg mL⁻¹ with a detection limit of 18 ng mL⁻¹. This sensor opens a new route for monitoring the low activities of type IV collagenase in normal and cancerous cell cultures.

A method based on time domain nuclear magnetic resonance for the forensic differentiation of latex gloves by Michele Mauri; Lucio Mauri; Valerio Causin; Roberto Simonutti (pp. 1802-1809).

Latex gloves are employed by felons who want to avoid shedding fingermarks or biological traces, and are sometimes discarded on the crime scene or nearby. Comparison between the gloves found at the crime scene and those seized in the suspect's premises can provide useful information to investigators. This paper proposes the use of ¹H time domain nuclear magnetic resonance (TD-NMR) as a method for performing such a comparison. Two parameters can be quantified by this technique: the proton weight fraction, which is correlated to the chemical nature and formulation of the material, and the relaxation time T2, which is a measure of polymer chain dynamics. Both these features can be ultimately associated to differences in raw materials, formulation and processing of the gloves, thereby offering a means to discriminate items which are indistinguishable by visual examination. TD-NMR, without sample preparation and preserving the integrity of the specimen, allows differentiating 88% of the possible pairs of samples in a population of 20 latex gloves. TD-NMR data are complementary to those coming from thermal analysis.

Electrocatalytic oxidation and determination of epinephrine in the presence of uric acid and folic acid at multiwalled carbon nanotubes/molybdenum(vi) complex modified carbon paste electrode by Hadi Beitollahi; Iran Sheikhshoaie (pp. 1810-1814).

A novel modified carbon paste electrode was fabricated by incorporation of carbon nanotubes and a novel molybdenum(vi) complex (MC). The characterization of the modified electrode was carried out by cyclic voltammetry. The apparent charge transfer rate constant, ks, and transfer coefficient, α, for electron transfer between MC and CNT paste electrode were calculated. Furthermore, the modified electrode showed an excellent electrocatalytic effect on the oxidation of epinephrine (EP). Using differential pulse voltammetry (DPV), the peak currents of EP recorded in pH 7.0 solution were linearly dependent on their concentrations in the range of 0.09–750.0 μM. The limit of detection was 49 nM for EP. Then the modified electrode was used to determine EP in an excess of uric acid (UA) and folic acid (FA) by difference pulse voltammetry. Finally, this method was used for the determination of EP in EP ampoule.

Simultaneous analysis of phthalate esters and pyrethroid insecticides in water samples by temperature-controlled ionic liquid dispersive liquid-phase microextraction combined with high-performance liquid chromatography by Qingxiang Zhou; Xiaoguo Zhang; Guohong Xie (pp. 1815-1820).

A simple, rapid and efficient method is described for the simultaneous pre-concentration and determination of phthalate esters and pyrethroid insecticides in water samples by temperature controlled ionic liquid dispersive liquid phase microextraction in combination with high performance liquid chromatography. In this procedure, only ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate [C8MIM][PF6] was used for the enrichment. The proposed method successfully overcomes the disadvantages of conventional single drop liquid phase microextraction and dispersive liquid-liquid microextraction such as the instability of the suspending drop and the use of toxic solvents, and requires a smaller extraction volume. Factors such as volume of [C8MIM][PF6], sample pH, extraction time, centrifugation time, and temperature and salting-out effect were systematically investigated and optimized. The detection limits obtained for phthalate esters and pyrethroid insecticides were in the range of 0.23–0.47 μg L⁻¹ and the precisions were in the range of 2.2–5.9% (n = 6). Real water samples were used for validating the proposed method and satisfactory results were achieved.

Simultaneous determination of five quinoxaline-1,4-dioxides and two major metabolites in surface water by on-line solid phase extraction coupled to high-performance liquid chromatography by Zhenjuan Duan; Guozhen Fang; Mingfei Pan; Jianghua Yi; Lipeng Fan; Wei Liu; Shuo Wang (pp. 1821-1827).

Veterinary antibiotics are environmental contaminants of recent concern, so this study was designed to develop an analytical method of simultaneous determination for quinoxaline-1,4-dioxides (QdNOs) and their metabolites in the aqueous environment at trace levels. The new method is based on on-line solid phase extraction (SPE) using cigarette filter (CGFR) as the sorbent coupled to high-performance liquid chromatography (HPLC). Five QdNOs (carbadox, olaquindox, cyadox, mequindox, quinocetone) and two major metabolites (quinoxaline-2-carboxylic acid and methyl-3-quinoxaline-2-carboxylic acid) were detected in the surface water. The cleaned CGFR precolumn selectively retained target analytes when untreated water samples were upload by a flow-inject pump. Then the enriched extracts were subsequently eluted by HPLC mobile phase to the analytical column for chromatographic analysis. The on-line setup was uncomplicated and automated. The on-line SPE conditions were optimized in detail including sample pH, sample loading flow rate, sample volume, eluent, elution time and sorbents. Under the optimal experimental conditions, the enrichment factors were 33.3–630.0 by preconcentrating 25.0 mL of water samples. Limits of detection (S/N = 3) ranged from 1.6 to 24.3 ng L⁻¹. Satisfactory recoveries were obtained and ranged from 87.1 to 107.5% at two spiked levels in real water samples with high precision (RSD, 1.3–3.8%). The on-line SPE-HPLC method is simple, rapid, reliable, sensitive and could be applied for multiresidue determination of the QdNOs and their metabolites in water samples.

Application of ion mobility spectrometry in analytical support of drug substance development by Hong Gao; Xiujuan Jia; Rong Xiang; Xiaoyi Gong; Christopher J. Welch (pp. 1828-1837).

An investigation into the use of ion mobility spectrometry (IMS) for analytical support of drug substance development is reported. A group of thirty compounds including drug substances, starting materials and intermediates were analyzed by IMS, with 87% of the compounds affording a usable signal. The technique was further evaluated for single component quantification and multiple component quantification. A sub-ppm detection limit and a linearity range of 10 to 20 fold were obtained for most compounds tested, with the consecutive injection precision at less than 10% (RSD). Significant matrix effects on instrument response were observed when real reaction mixtures were analyzed. A spike/limit-testing method with a pre-established standard was developed for quick end of reaction monitoring. General advantages and limitations of the use of the IMS technique for drug substance development support are discussed, and some applications in areas such as starting material identification, high throughput screening and end of reaction monitoring are recommended.

Nitrite/nitrate speciation through arsenomolybdenum blue complex at trace level: application to biological and environmental samples by M. Pandurangappa; Y. Venkataramanappa (pp. 1838-1844).

A novel and simple method has been proposed for the estimation of nitrite/nitrate based on the reduction of arsenomolybdic acid to arsenomolybdenum blue using ascorbic acid. The obtained arsenomolybdenum blue complex has been oxidized by the addition of nitrite and the decrease in the absorbance of blue color is directly proportional to the nitrite quantity. The absorbance of the arsenomolybdenum blue complex has been measured at 840 nm. All the reaction variables have been optimized and Beer's law has been obeyed in the concentration range 2–10 μg in 25 mL of aqueous phase with a molar absorptivity 4.37 × 10⁴ L mol⁻¹ cm⁻¹. The relative standard deviation of the method has been found to be 1.7% for five measurements with a detection limit of 0.003 μg mL⁻¹. The method has been applied to determine nitrite/nitrate levels in biological samples as well as environmental samples.

A resonance light scattering amplification system for determination of trace amounts of benzidine in surface water by Zhanguang Chen; Guomin Zhang; Xi Chen; Yurui Peng; Yuejuan Lin; Simin Lu (pp. 1845-1850).

In this contribution, a novel resonance light scattering (RLS) amplification system was developed based on the enhanced RLS signals of the ammonium molybdate (AM)–cetyl trimethyl ammonium bromide (CTMAB) system upon the addition of benzidine (BD). It was found that in the presence of CTMAB, trace amounts of BD in surface water induced a remarkable change in RLS intensity of the AM–CTMAB system. Moreover, in the range of 0.005–1.0 μg mL⁻¹, there was a good linear relationship between the enhanced RLS intensity and the concentration of BD with a detection limit of 0.08 ng mL⁻¹. Three kinds of surface water sample were determined by this assay, and the interaction mechanism between AM and BD as well as several influencing factors were also investigated. Compared with conventional assays for the determination of BD in water, this assay has the advantages of simplicity, high sensitivity and it is more suitable for the determination of trace amounts of micromolecules.

Rapid and sensitive determination of Sudan dyes in hot chilli products by solid-phase extraction directly combined with time-of-flight mass spectrometry by Ming-Ming Zheng; Jian-Hong Wu; Yu-Qi Feng; Feng-Hong Huang (pp. 1851-1858).

A novel method based on combination of a solid-phase extraction (SPE) with humic acid-bonded silica (HAS) as sorbent with electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF MS) was developed for rapid and sensitive determination of four Sudan dyes in hot chilli products. A SPE procedure was optimized for the improvement of extraction efficiency and the removal of the matrix interferences such as the pigments and lipophilic compounds from hot chilli products. Under the optimum conditions, the desorbed analytes from the SPE sorbent allowed direct analysis by ESI-QTOF MS without time-consuming chromatographic separation. In the positive ion mode and MS/MS mode, linearities for concentration ranges of two orders of magnitude were obtained with the correlation coefficients (R²) greater than 0.9990; the limit of detection (LOD) and limit of quantification (LOQ) for four Sudan dyes were in the ranges of 1.1–4.3 and 3.8–14.3 ng g⁻¹ depending on matrices, respectively. The recoveries of four Sudan dyes in two matrices ranged from 85.6 to 119.7%, with relative standard deviations (n = 4, 3) less than 11.3% and 11.6%. The developed method was successfully applied for the determination of Sudan dyes in six hot chilli products and the positive samples were confirmed with a high number of identification points (IPs) according to IPs system defined by Commission Decision 2002/657/EC.

Development and validation of a competitive indirect enzyme-linked immunosorbent assay for the determination of mercury in aqueous solution by Huan He; Fan Wu; Minjie Xu; Shaogui Yang; Cheng Sun; Yonghua Yang (pp. 1859-1864).

A competitive indirect enzyme-linked immunosorbent assay (ELISA) was developed and successfully applied in a dissolved mercury assay. For mercury quantification, factors including the concentration of chelator EDTA, pH, ionic strength, and blocking solution were optimized in this study. Generally the detection limit of the ELISA was standardized as 0.459 μg L⁻¹, with an IC50 value of 13.09 μg L⁻¹ and linear range of 1 to 500 μg L⁻¹; whereas a cross-reactivity study showed that the immunoassay was quite specific for mercury, compared with nine other metal ions. The recovery of the method was evaluated by spiking ultrapure water, tap water and surface water of Taihu Lake with mercury at 1, 10, 50, 100 μg L⁻¹. The precision of the method was evaluated by spiking ultrapure water with mercury at 1, 10, 50, and 100, 500 and 1000 μg L⁻¹. The coefficients of variation of intra- and inter-assay were below 10% in most cases, and recoveries were 94.3–123.5%, 91.9–117.9%, and 92.3–115.6% for ultrapure water, tap water and surface water of Taihu Lake, respectively. Therefore, the developed method is able to determine mercury at levels below the maximum residue limits of water quality standards for drinking water sources of China.

Selection of PCB binding phages as potential biorecognition elements for food and environmental monitoring by Bieke Van Dorst; Jaytry Mehta; Elsa Rouah-Martin; Wim De Coen; Valery Petrenko; Ronny Blust; Johan Robbens (pp. 1865-1871).

Classification of vinegar samples based on near infrared spectroscopy combined with wavelength selection by Wei Fan; Hongdong Li; Yang Shan; Huiying Lv; Huaxiu Zhang; Yizeng Liang (pp. 1872-1876).

In this paper, near infrared spectroscopy combined with a wavelength selection method was used to identify fermented vinegar and blended vinegar. Competitive adaptive reweighted sampling (CARS) method was employed to select the key wavelengths. For classification of different vinegars, 11 wavelengths were selected and a PLS-DA model was calculated based on these selected wavelengths. The average error rate (AER) obtained by repeated double cross validation (RPCV) was 6.95%. The results indicated that NIR spectroscopy combined with a wavelength selection method could be applied as a fast alternative method for the identification of different vinegars.

Determination of volatile organic compounds in environmental water samples using three solid-phase microextraction fibers based on sol–gel technique with gas chromatography–flame ionization detector by Ali Sarafraz-Yazdi; Mehdi Mosadegh; Amirhassan Amiri (pp. 1877-1886).

Sol–gel technology was applied for the preparation of three solid-phase microextraction (SPME) fibers for the extraction of volatile organic compounds (VOCs) from environmental water samples using the gas chromatography-flame ionization detector (GC–FID). The compounds studied were methyl tert-butyl ether (MTBE), tetrahydrofuran (THF), benzene, n-heptane, methyl isobuthyl ketone (MIBK), toluene, tetrachloroethylene, ethylbenzene and o-xylene. These fibers were prepared from different coating polymers including poly(dimethylsiloxane) (PDMS), poly(ethylene glycol) (PEG) and PEG reinforced with multi-walled carbon nanotubes (MWCNTs). Important parameters influencing the extraction efficiency such as extraction temperature, extraction time, stirring speed, salt effect and desorption temperature were investigated and optimized for each fiber. Under the optimal conditions, the dynamic linear range with PDMS, PEG and PEG/CNTs fibers were 0.05–2000, 0.004–2000 and 0.002–2000 ng mL⁻¹ and the detection limits (S/N = 3) were 0.02–10, 0.002–1 and 0.001–0.5 ng mL⁻¹, respectively. The relative standard deviations (RSD) for one fiber (Repeatability) (n = 3) were obtained from 3.23 up to 7.57% and between fibers or batch to batch (n = 3) (Reproducibility) in the range of 2.91–8.91% for three fibers. However, PEG/CNTs fiber was the best one and the efficiency of PEG/CNTs was approximately 3 times and twice more than PDMS and PEG at the same conditions for most analytes respectively.

Preparation and measurement of standard organic gases using a diffusion method and a NASICON-based CO2 sensor combined with a combustion catalyst by Tetsuya Kida; Min-Hyun Seo; Shotaro Kishi; Yuichi Kanmura; Kengo Shimanoe (pp. 1887-1892).

The development of new analytical methods for the detection of volatile organic compounds (VOCs) requires the preparation of standard gases at various concentrations. In this study, using a diffusion method where liquid samples were heated and vaporized under a carrier gas flow, we prepared standard organic gases containing acetone or 2,6-diisopropylphenol (propofol), which are breath markers for diabetes and anesthesia depth, respectively. A Pt/Al2O3 combustion catalyst was used in conjunction with a NASICON (Na3Zr2Si2PO12; Na⁺ conductor)-based CO2 sensor for the continuous determination of organic concentrations in the sample gas streams; the catalyst allowed for conversion of ppm concentrations of acetone or propofol to CO2. The results demonstrate that the present system is feasible for the preparation and concentration determination of standard VOC gases.

Comparison of dispersive liquid–liquid microextraction and the modified QuEChERS method for the determination of fipronil in honey by high performance liquid chromatography with diode-array detection by Débora Tomasini; Maicon R. F. Sampaio; Liziane V. Cardoso; Sergiane S. Caldas; Ednei G. Primel (pp. 1893-1900).

Two methods, based on dispersive liquid–liquid microextraction (DLLME) and Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS), have been developed, validated and critically compared in order to analyze the insecticide fipronil in honey by high performance liquid chromatography coupled with diode array detection. Parameters that affect the extraction have been investigated for both methods. In optimal conditions, the limits of quantification were 0.03 and 0.6 mg kg⁻¹ for DLLME and modified QuEChERS, respectively. The relative recoveries were between 70.7–101.1% and 76.3–87.7% for DLLME and QuEChERS, with relative standard deviations in the range of 7.1–11.2% and 5.9–10.8%, respectively. Both methods were found to be simple, fast and inexpensive. By comparison with the modified QuEChERS, the advantages of the DLLME technique were the preconcentration factor and the lower amount of solvent. However, the modified QuEChERS method was demonstrated to be more robust and more suitable for the determination of pesticides in complex samples.

Calibration of a Fourier transform infrared spectrometer for hydrogen peroxide vapour measurement by Nicholas St Hill; Guy Turner (pp. 1901-1905).

A new method is described to calibrate a Fourier transform infrared (FTIR) spectrometer for the measurement of hydrogen peroxide (H2O2) vapour. A stream of nitrogen gas is bubbled through a 90% weight-to-weight solution of aqueous H2O2 to create a stream of vapour comprising of nitrogen, water and hydrogen peroxide. The vapour exiting the H2O2 bubbler is then measured by the FTIR spectrometer and then bubbled through a water bubbler which captures the H2O2, enabling the average concentration of the H2O2 vapour leaving the H2O2 bubbler to be determined. The average concentration obtained using the FTIR spectrometer is compared to the average concentration obtained from the H2O2 stored in the water bubbler to obtain a scaling factor and create a valid reference spectra at a known concentration. An advantage of using the average concentration to determine a scaling factor is that a stable concentration of H2O2 vapour is not required to obtain a valid reference spectra, which makes the calibration more robust and therefore more repeatable. The approach also has the advantage of being recursive, in that the initial reference spectra can be used to obtain new improved reference spectra. Calibration results are presented for H2O2 vapour concentrations in the range of 20–500 ppm. A good linear calibration curve was obtained with a coefficient of determination (R²) of 0.9998, and results which suggest an achievable resolution of ±3% of the reference vapour concentration.

Trace beryllium determination in polyvinyl alcohol wipes by extraction and fluorescence detection: interlaboratory analysis by Kevin Ashley; Tamara J. Wise; David Marlow; Anoop Agrawal; John P. Cronin; Lori Adams; Elizabeth Ashley; Paul A. Lee (pp. 1906-1909).

In the occupational hygiene field, polyvinyl alcohol (PVA)-based wipe materials are used extensively for beryllium (Be) sample collection and analysis. Hence there is a need for validated methods to determine trace Be in such sampling media. In this work an interlaboratory study was carried out to evaluate the performance of an extraction and fluorescence method for determining trace Be in PVA wipes containing refractory beryllium oxide (BeO). The method entails heated extraction with dilute ammonium bifluoride (NH4HF2), followed by fluorescence measurement of extracted Be in extract aliquots after reaction with the high quantum-yield fluorophore, hydroxybenzoquinoline sulfonate (HBQS). Certified BeO-spiked PVA wipe materials were prepared at six different levels ranging from 0.030 to 5.6 μg Be per wipe. Dry wipe materials and wipes wetted with 0.5 mL of deionized water were spiked as above. Duplicates of these materials, plus media blanks, were distributed to eight participating laboratories; spiking levels were unknown to the volunteers. Each participant was requested to carry out extraction and fluorescence measurement in accordance with an ASTM International standard test method, ASTM D7202, and to report their results in units of μg Be per wipe sample. Interlaboratory precision, as estimated by percent relative standard deviations (RSDs), ranged between 4.5% and 16%. Estimated percent Be recoveries were 90–99% for dry wipes and between 87 and 93% for wetted wipe materials after volume correction for water content.

Tissue imprint imaging by desorption electrospray ionization mass spectrometry by Demian R. Ifa; Amitava Srimany; Livia S. Eberlin; Hemanta R. Naik; Vasudeva Bhat; R. Graham Cooks; T. Pradeep (pp. 1910-1912).

Cross-sections of Myristica malabarica (Lam) seed and mouse brain tissue were imprinted on such ordinary surfaces as printer paper and TLC plates, and successfully imaged by desorption electrospray ionization mass spectrometry (DESI-MS) at 250 μm resolution. Chemical images representing the distribution of the alkaloid malabaricone C in the seed substructures and individual lipids in the substructures of the brain were obtained. Practical implications include analysis of irregular or soft materials, easy recording, transportation and storage of the latent image, and posterior analysis of the samples by different techniques without the requirement of addition of matrices or use of specific types of surfaces.

Back cover (pp. 1913-1914).

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Analytical Methods (v.3, #8)