Development of a headspace-gas chromatography (HS-GC-PID-FID) method for the determination of VOCs in environmental aqueous matrices: Optimization,verification and elimination of matrix effect and VOC distribution on the Fortaleza Coast,Brazil

An analytical protocol combining a headspace technique with gas chromatography and detection by photoionization detector and flame ionization detector (HS-GC-PID-FID) was developed. This procedure was used to measure volatile organic compounds (VOCs) in environmental aqueous matrices and was applied in determination of VOCs on the coast of Fortaleza, Brazil. At optimum operating conditions, analytical figures of merit such as linearity (R ranged from 0.9983 to 0.9993), repeatability (5.62 to 9.63% and 0.02 to 0.19% for the quantitative and qualitative analyses, respectively), detection limits (0.22 to 7.48 μg L⁻¹) and sensibility were estimated. This protocol favors a fast sampling/sample preparation (in situ), minimizes the use of laboratory material, eliminates the matrix effect from environmental samples, and can be applied to river, estuarine and oceanic waters. The advantage of detectors in series is that a low sensitivity in detection in one is compensated by the other. Toluene was the most abundant VOC in the studied area, with an average concentration of 1.63 μg L⁻¹. It was followed by o-xylene (1.15 μg L⁻¹), trichloroethene (1.08 μg L⁻¹), benzene (0.86 μg L⁻¹), ethylbenzene (0.74 μg L⁻¹), carbon tetrachloride (0.55 μg L⁻¹), m/p-xylene (0.48 μg L⁻¹) and tetrachloroethene (0.46 μg L⁻¹), compounds which are very commonly detected in urban runoff from most cities. The results of the VOC distribution showed that port activity was not the main source of VOCs along the Fortaleza Coast, but that the contribution from urban runoff seemed more significant.     

Simple derivatization of aldehydes with d-cysteine and their determination in beverages by liquid chromatography–tandem mass spectrometry

We describe a simple derivatization method to determine aldehydes. This method is based on derivatization with d-cysteine and consecutive liquid chromatography–tandem mass spectrometry (LC–MS/MS). The optimum derivatization conditions of aldehydes with d-cysteine were 10 min at 50 °C and pH 7.0. The formed alkyl thiazolidine-4-carboxylic acid derivatives were directly injected in LC–MS/MS. In the established condition, the method was used to detect eight aldehydes in beverages. The limit of detection (LOD) and limit of quantification (LOQ) of the aldehydes were 0.2–1.9 μg L⁻¹ and 0.7–6.0 μg L⁻¹ and the relative standard deviation was less than 2.0% at concentrations of 0.1 mg L⁻¹ and 1.0 mg L⁻¹ with the exception of octanal. All the beverage samples had detectable levels of methanal (0.033–0.145 mg L⁻¹), ethanal (0.085–2.12 mg L⁻¹), propanal (ND to 0.250 mg L⁻¹), butanal (ND to 0.003 mg L⁻¹), pentanal (ND to 0.471 mg L⁻¹), hexanal (ND to 0.805 mg L⁻¹), heptanal (0.019–3.91 mg L⁻¹) and octanal (0.029–0.118 mg L⁻¹).     

Evaluation of needle trap micro‐extraction and solid‐phase micro‐extraction: Obtaining comprehensive information on volatile emissions from in vitro cultures

Volatile organic compounds (VOCs) emitted from in vitro cultures may reveal information on species and metabolism. Owing to low nmol L⁻¹ concentration ranges, pre‐concentration techniques are required for gas chromatography–mass spectrometry (GC–MS) based analyses. This study was intended to compare the efficiency of established micro‐extraction techniques – solid‐phase micro‐extraction (SPME) and needle‐trap micro‐extraction (NTME) – for the analysis of complex VOC patterns. For SPME, a 75 μm Carboxen®/polydimethylsiloxane fiber was used. The NTME needle was packed with divinylbenzene, Carbopack X and Carboxen 1000. The headspace was sampled bi‐directionally. Seventy‐two VOCs were calibrated by reference standard mixtures in the range of 0.041–62.24 nmol L⁻¹ by means of GC–MS. Both pre‐concentration methods were applied to profile VOCs from cultures of Mycobacterium avium ssp. paratuberculosis. Limits of detection ranged from 0.004 to 3.93 nmol L⁻¹ (median = 0.030 nmol L⁻¹) for NTME and from 0.001 to 5.684 nmol L⁻¹ (median = 0.043 nmol L⁻¹) for SPME. NTME showed advantages in assessing polar compounds such as alcohols. SPME showed advantages in reproducibility but disadvantages in sensitivity for N‐containing compounds. Micro‐extraction techniques such as SPME and NTME are well suited for trace VOC profiling over cultures if the limitations of each technique is taken into account.     

Synthesis and application of imprinted polyvinylimidazole-silica hybrid copolymer for Pb determination by flow-injection thermospray flame furnace atomic absorption spectrometry

A novel ion imprinted polyvinylimidazole-silica hybrid copolymer (IIHC) was synthesized and used as a selective solid sorbent for Pb²⁺ ions preconcentration using an on-line solid phase extraction (SPE) system coupled to TS-FF-AAS. The ionic hybrid sorbent was prepared using 1-vinylimidazole and 3-(trimethoxysilyl)propylmethacrylate as monomers, Pb²⁺ ions as template, tetraethoxysilane as reticulating agent and 2,2′-azobis-isobutyronitrile as initiator. The best on-line SPE conditions concerning sorption behavior, including sample pH (6.46), buffer concentration (9.0 mmol L⁻¹), eluent (HNO₃) concentration (0.5 mol L⁻¹) and preconcentration flow rate (4.0 mL min⁻¹), were optimized by means of full factorial design and Doehlert matrix. The analytical curve ranged from 2.5 to 65.0 μg L⁻¹ (r = 0.999) with limit of detection of 0.75 μg L⁻¹; the precision (repeatability) calculated as relative standard deviation (n = 10) was 5.0 and 3.6% for Pb²⁺ concentration of 10.0 and 60.0 μg L⁻¹, respectively. From on-line breakthrough curve, column capacity was 3.5 mg g⁻¹. Preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were 128.0, 0.16 mL and 25.6 min⁻¹, respectively. The selective performance of the sorbent, based on relative selectivity coefficient, was compared to NIC (non imprinted copolymer) for the binary mixture Pb²⁺/Cd²⁺, Pb²⁺/Cu²⁺ and Pb²⁺/Zn²⁺. The results showed that ion imprinted polyvinylimidazole-silica hybrid polymer had higher selectivity for Pb²⁺ than NIC at 64.9, 16.0 and 8.8 folds. The developed method was successfully applied for highly sensitive and selective Pb²⁺ determination in different kinds of water samples, parenteral solutions and urine. Accuracy was also assessed by analyzing certified reference fish protein (DORM-3) and marine sediment (MESS-3 and PACS-2) with satisfactory results.     

Stripping voltammetric determination of Cd(II) based on multiwalled carbon nanotube functionalized with 1-(2-pyridylazo)-2-naphthol

The present work has focused on the modification of multiwalled carbon nanotube with a ligand,l-（2-pyridylazo）-2-naphthol, and its potential application for the development of a new,simple and selective modified glassy carbon electrode for stripping voltammetric determination of Cd（Ⅱ）.The analytical curve for Cd（Ⅱ） ions covered the linear range varying from 0.8 up to 220.4μgL^-1.The limit of detection was found to be 0.1μgL^-1,while the relative standard deviation（RSD） at 50.0μgL^-1 was 1.8%（n=5）.This modified electrode was successfully applied for determination of Cd（Ⅱ） in some water samples.     

Comparison of sample preparation methods for the ICP-AES determination of minor and major elements in clarified apple juices

Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of minor and major elements present in apple juices. Prior to ICP-AES measurement, samples were diluted with nitric acid or digested in a microwave assisted digestion system. The differences in the measured element concentrations after application of different types of sample preparation procedures are discussed. The direct measurement compared to closed microwave dissolution was found to be the best sample preparation procedure. Prior to the measurements the ICP-AES method was validated and optimized for the determination of elements in apple juices. For diluted apple juice samples the lowest limits of detection (LOD) were obtained for Ba and Cd (< 20 μg L^{− 1}), moderate ones for Cu, Mn, Ni, Fe, Ag, Ca, Cr, Zn, Mg, and Sr (20–100 μg L^{− 1}), and the highest LODs for K, Pb, Na, and Al (> 110 μg L^{− 1}). The results obtained for the repeatability (< 0.9%), the intermediate precision (< 4.5%), the day-to-day reproducibility (< 5.2%), and the overall uncertainty of measurement (approx. 4–7%) for all elements analyzed demonstrated the good applicability of the proposed method. Differences in major element content in fresh and commercial apple juice are discussed.     

Serum/plasma methylmercury determination by isotope dilution gas chromatography-inductively coupled plasma mass spectrometry

A method for the determination of methylmercury in plasma and serum samples was developed. The method uses isotope dilution with ¹⁹⁸Hg-labeled methylmercury, extraction into dichloromethane, back-extraction into water, aqueous-phase ethylation, purge and trap collection, thermal desorption, separation by gas chromatography, and mercury isotope specific detection by inductively coupled plasma mass spectrometry. By spiking 2 mL sample with 1.2 ng tracer, measurements in a concentration interval of (0.007–2.9) μg L⁻¹ could be performed with uncertainty amplification factors <2. A limit of quantification of 0.03 μg L⁻¹ was estimated at 10 times the standard deviation of concentrations measured in preparation blanks. Within- and between-run relative standard deviations were <10% at added concentration levels of 0.14 μg L⁻¹, 0.35 μg L⁻¹ and 2.8 μg L⁻¹, with recoveries in the range 82–110%. Application of the method to 50 plasma/serum samples yielded a median (mean; range) concentration of methylmercury of 0.081 (0.091; <0.03–0.19) μg L⁻¹. This is the first time methylmercury has been directly measured in this kind of specimen, and is therefore the first estimate of a reference range.     

Ultra-sensitive DNA assay based on single-molecule detection coupled with fluorescent quantum dot-labeling and its application to determination of messenger RNA

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 (R² = 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.     

Dispersive suspended microextraction

A novel sample pre-treatment technique termed dispersive suspended microextraction (DSME) coupled with gas chromatography-flame photometric detection (GC-FPD) has been developed for the determination of eight organophosphorus pesticides (ethoprophos, malathion, chlorpyrifos, isocarbophos, methidathion, fenamiphos, profenofos, triazophos) in aqueous samples. In this method, both extraction and two phases’ separation process were performed by the assistance of magnetic stirring. After separating the two phases, 1 μL of the suspended phase was injected into GC for further instrument analysis. Varieties of experiment factors which could affect the experiment results were optimized and the following were selected: 12.0 μL p-xylene was selected as extraction solvent, extraction speed was 1200 rpm, extraction time was 30 s, the restoration speed was 800 rpm, the restoration time was 8 min, and no salt was added. Under the optimum conditions, limits of detections (LODs) varied between 0.01 and 0.05 μg L⁻¹. The relative standard deviation (RSDs, n = 6) ranged from 4.6% to 12.1%. The linearity was obtained by five points in the concentration range of 0.1–100.0 μg L⁻¹. Correlation coefficients (r) varied from 0.9964 to 0.9995. The enrichment factors (EFs) were between 206 and 243. In the final experiment, the developed method has been successfully applied to the determination of organophosphorus pesticides in wine and tap water samples and the obtained recoveries were between 83.8% and 101.3%. Compared with other pre-treatment methods, DSME has its own features and could achieve satisfied results for the analysis of trace components in complicated matrices.     

Response surface optimisation applied to a headspace-solid phase microextraction-gas chromatography-mass spectrometry method for the analysis of volatile organic compounds in water matrices

A new method for the simultaneous determination of 12 volatile organic compounds (trans-1,2-dichloroethene, 1,1,1-trichloroethane, benzene, 1,2-dichloroethane, trichloroethene, toluene, 1,1,2-trichloroethane, tetrachloroethene, ethylbenzene, m-, p-, o-xylene) in water samples by headspace solid phase microextraction (HS–SPME)–gas chromatography mass spectrometry (GC–MS) was described, using a 100?µm PDMS (polydimethylsiloxane) coated fibre. The response surface methodology was used to optimise the effect of the extraction time and temperature, as well as the influence of the salt addition in the extraction process. Optimal conditions were extraction time and temperature of 30?min and ?20°C, respectively, and NaCl concentration of 4?mol?L^?1. The detection limits were in the range of 1.1?×?10^?3–2.3?µg?L^?1 for the 12 volatile organic compounds (VOCs). Global uncertainties were in the range of 4–68%, when concentrations decrease from 250?µg?L^?1 down to the limits of quantification. The method proved adequate to detect VOCs in six river samples.     

Determination of N-methylcarbamate insecticides in water samples using dispersive liquid–liquid microextraction and HPLC with the aid of experimental design and desirability function

A rapid and simple method for the extraction and preconcentration of N-methylcarbamates (NMCs) (carbofuran, carbaryl and promecarb) in water samples using dispersive liquid–liquid microextraction (DLLME) using chemometrics was developed. Influence variables such as volume of extracting (CHCl₃) and dispersing solvents (ACN), pH and ionic strength, extraction time and centrifugation time and speed were screened in a 2^7–4 Plackett–Burman design was investigated. The significant variables were optimized by using a central composite design (CCD) combined with desirability function (DF). At optimum conditions values of variables set as 126 μL chloroform, 1.5 mL acetonitrile, 1 min extraction time, 10 min centrifugation at 4000 rpm min⁻¹, natural pH, 4.7% (w/v) NaCl, the separation was reached in less than 14 min using a C₁₈ column and an isocratic binary mobile phase (acetonitrile: water (50:50, v/v)) with flow rate of 1.0 mL min⁻¹. At optimum conditions method has linear response over 0.001–10 μg mL⁻¹ with detection limit between 0.0001 and 0.0005 μg mL⁻¹ with relative standard deviations (RSDs) in the range 2.18–5.06% (n = 6).     

Enzyme-linked immunosensor based on super paramagnetic nanobeads for easy and rapid detection of okadaic acid

Okadaic acid (OA), a lipophilic phycotoxin highly toxic to humans is produced by toxigenic dinoflagellates. The need to develop high performing methods for OA analysis able to improve the traditional ones is evident. In this work, competitive indirect enzyme-linked electrochemical immunosensor based on super paramagnetic nanobeads has been developed for the detection of OA. Streptavidin-coated magnetic beads were used as support to immobilize the biotinylated OA. Preliminary, colorimetric tests were performed in order to optimize different experimental parameters. Electrochemical detection was carried out by differential pulse voltammetry (DPV). The limit of detection (LOD) (0.38 μg L⁻¹), the mid point value (IC₅₀) (3.15 μg L⁻¹) and the time needed (60 min) for analysis of a real sample validated the developed electrochemical immunosensor as a promising tool for routine use. The matrix effect and the recovery rate were also assessed, showing an excellent percentage of recovery.     

Fast and simultaneous determination of phenolic compounds and caffeine in teas, mate, instant coffee, soft drink and energetic drink by high-performance liquid chromatography using a fused-core column

A fast HPLC method with diode-array absorbance detector and fluorescence detector for the analysis of 19 phenolic acids, flavan-3-ols, flavones, flavonols and caffeine in different types of samples was developed. Using a C₁₈ reverse-phase fused-core column separation of all compounds was achieved in less than 5 min with an overall sample-to-sample time of 10 min. Evaluation of chromatographic performance revealed excellent reproducibility, resolution, selectivity and peak symmetry. Limits of detection for all analyzed compounds ranged from 0.5 to 211 μg L⁻¹, while limits of quantitation ranged between 1.5 and 704 μg L⁻¹. The developed method was used for the determination of analytes present in different samples, including teas (black, white, green), mate, coffee, cola soft drink and an energetic drink. Concentration of the analyzed compounds occurring in the samples ranged from 0.4 to 314 mg L⁻¹. Caffeine was the analyte found in higher concentrations in all samples. Phytochemical profiles of the samples were consistent with those reported in the literature.     

Application of an ultrasound-assisted surfactant-enhanced emulsification microextraction method for the analysis of diethofencarb and pyrimethanil fungicides in water and fruit juice samples

In this work, a simple, practical and environmentally friendly sample pre-treatment method, ultrasound-assisted surfactant-enhanced emulsification microextraction coupled with high performance liquid chromatography–diode array detector/electrospray ionisation mass spectrometry, was developed to determine diethofencarb and pyrimethanil residues in water and fruit juice samples. Tween 80 was used as an emulsifier and carbon tetrachloride was chosen as the extraction solvent, and no dispersive organic solvent was needed, which is typically required in common dispersive liquid–liquid microextraction methods. Several variables, such as the type and volume of extraction solvent and surfactant, extraction temperature and ultrasound extraction time were investigated and optimised. Under optimal conditions, the enrichment factors were 265 and 253 for diethofencarb and pyrimethanil, respectively. The limits of detection (LODs), calculated as three times the signal-to-noise ratio (S/N), were 0.01 μg L⁻¹ for both diethofencarb and pyrimethanil. The linearity of the method was obtained in the range of 0.05–2000 μg L⁻¹, with correlation coefficients of 0.9994–0.9998. The water (at fortified levels of 0.1 and 1.0 μg L⁻¹) and fruit juice samples (at fortified levels of 0.1 and 1.0 μg L⁻¹) were successfully analysed using the proposed method, and the relative recoveries were in the range of 88–114%, 93–111%, 86–117% and 94–101%, respectively.     

Application of porous membrane protected micro-solid-phase-extraction combined with gas chromatography-mass spectrometry for the determination of estrogens in ovarian cyst fluid samples

A cost effective and environmentally friendly extraction technique using porous membrane protected micro-solid phase extraction (μ-SPE) is described for the extraction of estrogens in cyst fluid samples obtained from cancer patients. A sorbent (ethylsilane (C2) modified silica) (20 mg) was packed in a porous polypropylene envelope (2 cm × 1.5 cm) whose edges were heat sealed to secure the contents. The μ-SPE device was conditioned with acetone and placed in a stirred (1:5) diluted cyst fluid sample solution (10 mL) to extract estrogens for 60 min. After extraction, the analytes were desorbed and simultaneously derivatized with a 5:1 mixture of acetone and N,O-bis(trimethylsilyl)-trifluoroacetamide. The extract (2 μL) was analyzed by gas chromatography–mass spectrometry. Various extraction, desorption and derivatization conditions were optimized for μ-SPE. With this simple technique, low limits of detection of between 9 and 22 ng L⁻¹ and linear range from the detection limits up to 50 μg L⁻¹ were achieved. The optimized method was used to extract estrogens from cyst fluid samples obtained from patients with malignant and benign ovarian tumors.     

Monoclonal antibody based electrochemical immunosensor for the determination of ochratoxin A in wheat

Competitive electrochemical enzyme-linked immunosorbent assays based on disposable screen-printed electrodes have been developed for quantitative determination of ochratoxin A (OTA). The assays were carried out using monoclonal antibodies in the direct and indirect format. OTA working range, I₅₀ and detection limits were 0.05-2.5 and 0.1-7.5 μg L⁻¹, 0.35 (±0.04) μg L⁻¹ and 0.9 (±0.1) μg L⁻¹, 60 and 100 μg L⁻¹ in the direct and indirect assay format, respectively. The immunosensor in the direct format was selected for the determination of OTA in wheat. Samples were extracted with aqueous acetonitrile and the extract analyzed directly by the assay without clean-up. The I₅₀ in real samples was 0.2 μg L⁻¹ corresponding to 1.6 μg/kg in the wheat sample with a detection limit of 0.4 μg/kg (calculated as blank signal −3σ). Within- and between-assay variability were less than 5 and 10%, respectively. A good correlation (r = 0.9992) was found by comparative analysis of naturally contaminated wheat samples using this assay and an HPLC/immunoaffinity clean-up method based on the AOAC Official Method 2000.03 for the determination of OTA in barley.     

Improvement of HS-SPME for analysis of volatile organic compounds (VOC) in water samples by simultaneous direct fiber cooling and freezing of analyte solution

The sensitivity and precision of headspace solid-phase micro extraction (HS-SPME) at an analyte solution temperature (T _as) of +35 °C and a fiber temperature (T _fiber) of +5 °C were compared with those for HS-SPME at T _as and T _fiber of −20 °C for analysis of the volatile organic compounds benzene, 1,1,1-trichloroethane, trichloroethylene, toluene, o-xylene, ethylbenzene, m/p-xylene, and tetrachloroethylene in water samples. The effect of simultaneous fiber cooling and analyte solution freezing during extraction was studied. The compounds are of different hydrophobicity, with octanol/water partition coefficients (Kow) ranging from 126 and 2511. During a first set of experiments the polydimethylsiloxane (PDMS) SPME fiber was cooled to +5 °C with simultaneous heating of the aqueous analyte solution to +35 °C. During a second set of experiments, both SPME fiber holder and samples were placed in a deep freezer maintained at −20 °C for a total extraction time of 30 min. After approximately 2 min the analyte solution in the vial began to freeze from the side inwards and from the bottom upwards. After approximately 30 min the solution was completely frozen. Analysis of VOC was performed by coupling HS-SPME to gas chromatography-mass spectrometry (GC-MS). In general, i.e. except for tetrachloroethylene, the sensitivity of HS-SPME increased with increasing compound hydrophobicity at both analyte solution and fiber temperatures. At T _as of +35 °C and T _fiber of +5 °C detection limits of HS-SPME were 0.5 μg L⁻¹ for benzene, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, 0.125 μg L⁻¹ for toluene, and 0.025 μg L⁻¹ for ethylbenzene, m/p-xylene, and o-xylene. In the experiments with T _as and T _fiber of −20 °C, detection limits were reduced for compounds of low hydrophobicity (Kow<501), for example benzene, toluene, 1,1,1-trichloroethane, and trichloroethylene. In the concentration range 0.5–62.5 μg L⁻¹, the sensitivity of HS-SPME was enhanced by a factor of approximately two for all compounds by performing the extraction at −20 °C. A possible explanation is that freezing of the water sample results in higher concentration of the target compounds in the residual liquid phase and gas phase (freezing-out), combined with enhanced adsorption of the compounds by the cooled fiber. The precision of HS-SPME, expressed as the relative standard deviation and the linearity of the regression lines, is increased for more hydrophobic compounds (Kow>501) by simultaneous direct fiber cooling and freezing of analyte solution. Background contamination during analysis is reduced significantly by avoiding the use of organic solvents.     

A novel solid-phase microextraction method based on polymer monolith frit combining with high-performance liquid chromatography for determination of aldehydes in biological samples

In this work, a polypropylene frit with porous network structure (20 μm pole size) was first utilized as the mould of polymer monolithic material, poly(methacrylic acid-co-ethylene glycol dimethacrylate) (MAA-co-EDMA) monolith was synthesized within channels and macropores of the frit. A simple and sensitive solid-phase microextraction method based on polymer monolith frit coupled with high-performance liquid chromatography (HPLC) was established and applied to analysis of hexanal and heptanal in biological samples (human urine and serum). In the method, small molecule metabolites (aldehydes) in biological samples derivatized with 2,4-dinitrophenylhydrazine (DNPH), and the formed hydrazones were extracted simultaneously on the monolithic frit and thereafter ultrasound-assisted desorbed with acetonitrile as elution solvent. The experimental parameters with regard to polymerization, derivatization and extraction were investigated. Under the optimal conditions, the linearity was in the range of 0.02–5.0 μmol L⁻¹ (r = 0.9994) for both hexanal and heptanal and the limits of detection (S/N = 3) were 0.81 nmol L⁻¹ for hexanal and 0.76 nmol L⁻¹ for heptanal. The relative standard deviations (RSDs, n = 5) were less than 6.5% for the same monolithic frit and less than 8.9% for the different monolithic frits. Satisfactory recoveries ranging from 70.71% to 88.73% were obtained for the urine samples. The method possesses many advantages including simple setup, fast analysis, low cost, sufficient sensitivity, good biological compatibility and less organic solvent consumption. The proposed method is a useful assistant tool in the clinical early diagnosis of lung disease by monitoring aldehyde biomarker candidates in complex biological samples.     

Simultaneous analysis of chlorophenols, alkylphenols, nitrophenols and cresols in wastewater effluents, using solid phase extraction and further determination by gas chromatography-tandem mass spectrometry

An analytical methodology has been developed for the simultaneous extraction of 13 phenolic compounds, including chlorophenols (CPs), nitrophenols (NTPs), cresols and alkylphenols (APs) in different types of wastewater (WW) effluents. A solid-phase extraction (SPE) method has been optimized prior to the determination by gas chromatography coupled to triple quadrupole tandem mass spectrometry (GC-QqQ-MS/MS). Due to the complexity of the matrix, a comparison study of matrix-matched-calibration (MMC) and standard addition calibration (SAC) was carried out for quantification purposes. The optimized procedure was validated using the SAC approach since it provided the most adequate quantification results (in terms of recovery and precision values). Recoveries were in the range 60-135% (0.5 μg L⁻¹), 70-115% (1 μg L⁻¹), and 78-120% (5 μg L⁻¹), with precision values (expressed as relative standard deviation, RSD) ≤30% (except for 2-nitrophenol) involving intra-day and inter-day precision studies. Limits of detection (LODs) and quantification (LOQs) were also evaluated, and LOQs ranged from 0.03 μg L⁻¹ to 2.5 μg L⁻¹. The proposed method was applied to the analysis of 8 real WW effluent samples, finding some phenolic compounds (e.g. 2-chlorophenol, 2,4,6-trichlorophenol and 4-tert-octylphenol) at concentrations higher than the established LOQs.     

Assisted inhibition effect of acetylcholinesterase with n-octylphosphonic acid and application in high sensitive detection of organophosphorous pesticides by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry

A simple and practical approach to improve the sensitivity of acetylcholinesterase (AChE)-inhibited method has been developed for monitoring organophosphorous (OP) pesticide residues. In this work, matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS) was used to detect AChE activity. Due to its good salt-tolerance and low sample consumption, MALDI-FTMS facilitates rapid and high-throughput screening of OP pesticides. Here we describe a new method to obtain low detection limits via employing external reagents. Among candidate compounds, n-octylphosphonic acid (n-Octyl-PA) displays assistant effect to enhance AChE inhibition by OP pesticides. In presence of n-Octyl-PA, the percentages of AChE inhibition still kept correlation with OP pesticide concentrations. The detection limits were improved significantly even by 10²–10³ folds in comparison with conventional enzyme-inhibited methods. Different detection limits of OP pesticides with different toxicities were as low as 0.005 μg L⁻¹ for high toxic pesticides and 0.05 μg L⁻¹ for low toxic pesticides. Besides, the reliability of results from this method to analyze cowpea samples had been demonstrated by liquid-chromatography tandem mass spectrometry (LC–MS/MS). The application of this commercial available assistant agent shows great promise to detect OP compounds in complicated biological matrix and broadens the mind for high sensitivity detection of OP pesticide residues in agricultural products.