Chromatography-mass Spectrometry Determination Research Articles

Method Development and Validation in Water Matrix Employing Tandem Mass Spectrometry: Quantitative Analysis of 76 Multiclass Pesticides in Groundwater Samples Collected from Delhi Ncr Region by Quechers Based Liquid-liquid Extraction Method

A miniaturized, QuEChERS based, liquid–liquid extraction method followed by tandem gas chromatography–mass spectrometry determination was developed and validated for 76 pesticide residues determination in water using European SANTE/11312/2021 guideline and monitored the 70 ground water samples collected from Delhi NCR, India region for the determination of pesticide residues. The accuracy, precision, specificity, linearity, recovery, repeatability, reproducibility, robustness, limit of detection and limit of quantification of the method were evaluated. Uncertainty measurement was calculated for each analyte. The samples were extracted with dichloromethane using liquid-liquid extraction process. Each Pesticide was optimized in terms of different MS parameters and chromatographic conditions by GC-MS/MS using Multiple Reaction Monitoring (MRM) mode. In linearity regression co-efficient (R2) value of each pesticide was determined in the range of 0.9856-0.9997. The percent average recoveries were found from 87.98—119.99 at 1, 5 and 10 LOQ spiking level. The method performance complied with the regulatory requirements, and thus, can be implemented. LOD and LOQ of the pesticides were found 10µg/L and 30µg/L respectively. Expanded Measurement of uncertainty of all pesticides was below ±50 percent of mean recovery value as per SANTE 11312/2021. Organophosphorous, fungicides, and pyrethroids were the group of pesticides most frequently found. In this study, 12 pesticides were found above the MRL (EEC Council Directive 1980/778/EEC). Additionally, dieldrin, which is now banned by law in India, was found in samples of ground water. The method provided a high throughput analysis of multi-class pesticides with satisfactory selectivity, sensitivity, accuracy, and precision.

A novel multiwalled carbon nanotube–cyclodextrin nanocomposite for solid-phase microextraction–gas chromatography–mass spectrometry determination of polycyclic aromatic hydrocarbons in snow samples

Novel solid-phase microextractioncoatings based on the use of multiwalled carbon nanotube–cyclodextrin (MWCNT-CD) nanocomposites were developed for the determination of 16-priority polycyclic aromatic hydrocarbons at ultratrace levels in snow samples. The performance of both β- and γ-CD was tested to increase the detection capabilities towards the heaviest and most lipophilic compounds, i.e., five- and six-ring PAHs. To facilitate the interactions of MWCNTs with CDs, an oxidation procedure using both HNO3 and H2O2 was applied, obtaining superior results using MWCNTs-H2O2-γ-CD fiber. Detection and quantitation limits below 0.7 and 2.3 ng/L, RSD lower than 21%, and recoveries of 88(± 2)–119.8(± 0.4)% proved the reliability of the developed method for the determination of PAHs at ultratrace levels. The complexation capability of the γ-CD was also demonstrated in solution by NMR and fluorescence spectroscopy studies and at solid state by XRD analysis. Finally, snow samples collected in the ski area of Dolomiti di Brenta were analyzed, showing a different distribution of the 16 priority PAHs, being naphthalene, phenanthrene, fluoranthene, and pyrene the only compounds detected in all the analyzed samples.Graphical

Degradation dynamics of organophosphorus insecticides applied in stored soybean (Glycine max L.) during supervised trials.

During storage, soybean kernels can be attacked by insects, which are preventively controlled with insecticides. Information on the dissipation of insecticide residues is crucial to know their final concentrations in food and establish the waiting periods necessary for consumption without health risks, and to determine the minimum waiting period necessary to comply with national and international standards. The aims of this study were to quantify the residue levels of organophosphorus insecticides (dichlorvos, chlorpyrifos-methyl and pirimiphos-methyl) in stored soybean, establish the effect during the storage period, and model the dissipation dynamics. Insecticide residues in soybeans were analyzed at 2, 30, 60, 90 and 120 days after application. An analytical method based on QuEChERS extraction followed by gas chromatography mass spectrometry (GC-MS/MS) determination was validated, with mean recoveries of 82-105%, depending on the spiking levels. Residues decreased below 80% of the initial concentration at 60 days after application and below quantifiable levels at 120 days. Residues followed a pseudo-first-order dissipation dynamics [Ct = C0×exp(-k.t)], with the dissipation constant (k) and half-lives being 0.538 and 1.3 days for dichlorvos, 0.018 and 38.8 days for chlorpyrifos-methyl, and 0.023 and 30.1 days for pirimiphos-methyl, respectively. These results allow concluding that, at the recommended dosage, these insecticides are safe for use on soybean grains stored under standard conditions commonly nowadays used in Argentina.

Application of gas flow headspace liquid phase micro extraction coupled with gas chromatography-mass spectrometry for determination of 4-methylimidazole in food samples employing experimental design optimization.

Background4-Methylimidazole (4-MeI) or 4-methyl-1H-imidazole, a slightly yellowish solid with molecular formula C4H6N2, is a heterocyclic compound which supposedly does not exist as a natural product and is formed when carbohydrates are heating with ammonium compounds. This compound is used in pharmaceuticals, agriculture and photography chemicals, dyes and pigments, and rubber manufacturing. In the present study, a simple and efficient sample preparation method designated gas flow headspace liquid phase microextraction (GF-HS-SDME) was employed for the extraction and preconcentration of 4-methylimidazole (4-MeI) from food and beverage samples, before its determination by gas chromatography-mass spectrometry.ResultTo investigate the optimal conditions for the extraction process in GF-HS-SDME method, factors affecting extraction, including selection of extraction solvent, vial volume, extraction solvent ratio, position of extracting solvent, drop volume, sample volume, stirring speed, temperature, extraction time, sample pH, ionic strength of the sample solution and gas flow rate were optimized by utilizing both one-variable-at-a-time method and Plackett–Burman design. The investigation of protocol was carried out by using a standard solution containing 100.0 μg L−1 of 4-MeI in deionized water.ConclusionIn this study, a simple and green analytical method based on GF-HS-SDME was proposed for the extraction and preconcentration of 4-MeI from foodstuffs, followed by GC–MS determination. The main advantage of this method is its high preconcentration factor and fastness due to the application of an inert gas stream during microextraction.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13065-022-00823-z.

Metal-organic framework-based magnetic dispersive micro-solid-phase extraction for the gas chromatography–mass spectrometry determination of polycyclic aromatic compounds in water samples

A magnetic hybrid material based on the use of the mixed-ligand Metal-Organic Framework (MOF) PUM198 is proposed for the magnetic dispersive micro solid-phase extraction (MD-μSPE) of the 16 polycyclic aromatic hydrocarbons (PAHs) included in the US-EPA priority pollutants list. PUM198 is a thermally robust MOF characterized by a doubly interpenetrated microporous framework in which Zn2+ ions and carboxylate groups define 2D planes that are pillared by a bis-pyridine-bis amide ligand containing a biphenyl scaffold. PUM198 revealed to be ideal to adsorb PAHs efficiently through non-covalent interactions. A Plackett-Burman Design followed by a Central Composite Design and the multicriteria method of the desirability functions were applied to find the optimal conditions for the extraction of the investigated PAHs, resulting in a reduced solvent consumption, i.e., 50 μL of solvent per extraction for 5 mL of sample, approximatively 3–20 times lower than those reported in previous studies, thus satisfying the principles of green analytical chemistry. Method validation proved the reliability of the method for the determination of PAHs at trace level, obtaining detection limits in the 6.7–27 ng/L range, good precision with RSDs% lower than 19% and recovery rates in the 99 (±13)–126 (±8)% range near the quantitation limit. Finally, the applicability of the method was demonstrated by analyzing underground water samples taken from contaminated sites

Development and Validation of a U-HPLC-MS/MS Method for the Concurrent Measurement of four Immunosuppressants in Whole Blood.

This study aimed to develop and validate a U-HPLC-MS/MS method for simultaneous determination of four immunosuppressants in human whole blood. The method was based on the injection of 20 µL of calibrators and controls pretreated with the liquid phase extraction method for chromatography separation and mass spectrometry determination. LPE offline was performed by adding 0.1 mol/L ZnSO4 and acetonitrile, while separation of target compounds was achieved within 2.5 minutes by a Zorbax Eclipse XDB-C8 column using ammonium acetate and ACN mixed with formic acid as solvents. The assay offers ng/mL detection limits (from 1.1 to 12.4 ng/mL), accuracy (% deviation from -4.4% to 5.6%), precision (CV less than 15% at all QC levels), and linearity (from 23.4 to 948 ng/mL for CsA, from 2.11 to 45.5 ng/mL for TAC, SIR and EVR). The recovery and matrix results were acceptable, and the carryover was less than 1%. The results of method comparison show that IA-based methods overestimated the concentration of drugs compared with the MS-based method. Comparing our MS-based method with external LC-MS/MS showed that the results were within 2 SDs. We have developed a reliable assay for the analysis of CsA, TAC, SIR and EVR in whole blood using U-HPLC-MS/MS.

Application of curcumin as a green and new sorbent in deep eutectic solvent-based dispersive micro-solid phase extraction of several polycyclic aromatic hydrocarbons from honey samples prior to gas chromatography-mass spectrometry determination.

A green, simple, and efficient dispersive micro-solid phase extraction method was developed for the extraction of polycyclic aromatic hydrocarbons from honey samples. In this method, for the first time, curcumin was used as an efficient and green sorbent to extract the analytes from the sample. After that the adsorbed analytes were eluted using a deep eutectic solvent prepared by mixing tetrabutylammonium chloride: ethylene glycol and analyzed by gas chromatography-mass spectrometry. Important experimental factors affecting adsorption and desorption steps of the method were optimized and under optimal experimental conditions, low limits of detection (0.14-0.37ng/g) and quantification (0.49-1.3ng/g), wide linear range (1.3-500ng/g) with a coefficient of determination ≥0.994 were obtained. Relative standard deviation values for intra- and interday precisions were ≤7.5% for all of the analytes at a concentration of 2ng/g for each analyte (n=6). Extraction recovery of the method was in the range of 72-81%. Finally, 20 honey samples were analyzed and the analytes were successfully detected. The method is environment friendly because of the use of curcumin as a sorbent. Also, biodegradability of the used deep eutectic solvent components is another advantage of the method.

Thyroid disrupting effects of low-dose dibenzothiophene and cadmium in single or concurrent exposure: New evidence from a translational zebrafish model

Thyroid hormones (THs) are major regulators of biological processes essential for correct development and energy homeostasis. Although thyroid disruptors can deeply affect human health, the impact of exogenous chemicals and in particular mixture of chemicals on different aspects of thyroid development and metabolism is not yet fully understood. In this study we have used the highly versatile zebrafish model to assess the thyroid axis disrupting effects of cadmium (Cd) and dibenzothiophene (DBT), two environmental endocrine disruptors found to be significantly correlated in epidemiological co-exposure studies. Zebrafish embryos (5hpf) were exposed to low concentrations of Cd (from 0.05 to 2 μM) and DBT (from 0.05 to 1 μM) and to mixtures of them. A multilevel assessment of the pollutant effects has been obtained by combining in vivo morphological analyses allowed by the use of transgenic fluorescent lines with liquid chromatography mass spectrometry determination of TH levels and quantification of the expression levels of key genes involved in the Hypothalamic-Pituitary-Thyroid Axis (HPTA) and TH metabolism. Our results underscore for the first time an important synergistic toxic effect of these pollutants on embryonic development and thyroid morphology highlighting differences in the mechanisms through which they can adversely impact on multiple physiological processes of the HPTA and TH disposal influencing also heart geometry and function.

Extraction-Free, Direct Determination of Caffeine in Microliter Volumes of Beverages by Thermal Desorption-Gas Chromatography Mass Spectrometry.

An extraction-free method requiring microliter (μL) volumes has been developed for the determination of caffeine in beverages. Using a pyrolysis-gas chromatography mass spectrometry system, the conditions required for the direct thermal desorption-gas chromatography mass spectrometry (TD-GC/MS) determination of caffeine were optimised. A 5 μL aliquot was introduced to the thermal desorption unit, dried, and thermally desorbed to the GC/MS. The response was linear over the range 10 to 500 μg/mL (R2 = 0.996). The theoretical limit of detection (3 σ) was 0.456 μg/mL. No interferences were recorded from endogenous beverage components or from commonly occurring drugs, such as nicotine, ibuprofen, and paracetamol. Replicate caffeine determinations on fortified latte style white coffee and Pepsi Max® gave mean recoveries of 93.4% (%CV = 4.1%) and 95.0% (%CV = 0.98%), respectively. Good agreement was also obtained with the stated values of caffeine for an energy drink and for Coca-Cola®. These data suggest that the method holds promise for the determination of caffeine in such samples.

Sample preparation of soils and bottom sediments for gas chromatography–mass spectrometry determination of PAHS

Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds which have been known to be carcinogenic, teratogenic and mutagenic as well as act as pollutants of environmental objects. The determination of PAHs in complex matrices is difficult, and it is very important to use an efficient sample pretreatment technique. A sample preparation technique was developed involving extractive freezing-out and centrifugation of the samples for the determination of polycyclic aromatic hydrocarbons (PAHs) in soils and bottom sediments using gas chromatography – mass spectrometry (GC–MS). Sochi soils (The Imereti Lowlands), turf, sea bottom sediments (Azov Sea, The Temryuk Bay), river bottom sediment (Kurchansky estuary) and Caio Romano (Cuba) island sand were selected as the objects for the research. Soils and bottom sediments which contained no determined PAHs were used as model samples. The conditions of sample preparation have been optimized, and the extraction effects of acetonitrile with water on the PAHs recoveries have been investigated. It was found that for the determination of the compounds consisting from two to four fused aromatic rings such as naphthalene, 2-methylnaphthalene, acenaphthylene, biphenyl, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene, the extraction occurred when the extractive mixture contained 15% acetonitrile. The proposed method detection limits of individual compounds ranged from 0.83 to 0.92 µg/kg. The extractive mixture containing 50% acetonitrile was proposed for the determination of 20 PAHs such as naphthalene, 2-methylnaphthalene, acenaphthene, biphenyl, acenaphthylene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, triphenylene, benz[b]fluoranthene, benz[k]fluoranthene, benz[e]pyrene, benz[a]pyrene, indene[1,2,3–c,d]pyrene, dibenz[a,h]anthracene, benz[g,h,i]perylene. The extraction of PAHs in these conditions demonstrated the recoveries from 61% to 97%. As matter of fact, the lower recoveries of PAHs, that contained four or more fused aromatic rings, have been caused by the sorption in the cracks of the solid aqueous phase. The extraction, clear-up of extract and concentration were realized as one step of the sample pretreatment. As a result, the rapid and express technique of the sample preparation with combined GC-MS were proposed for the PAHs determination in soils and bottom sediments. This method’s limits of individual PAHs quantitation ranged from 1 to 5 µg/kg, and these were lower that the maximum permissible concentration.

Analytical methods for the routinely evaluation of pesticide residues in lemon fruits and by products

Citrus fruits and their by-products such as concentrated juices and essential oils are important intermediate by-products in the food industry that can selectively accumulate plant protection agrochemicals employed in their production. They are very difficult matrices for pesticide residue analysis due their high number and concentration of phytochemicals that could hamper the determinations. The fruit processing leads to the concentration/dilution or elimination of some of these natural products that change totally the nature of the matrix where the pesticides partition unevenly. Looking at the industrial process of the fruit, a unified vision for the pesticide residues analysis throughout the lemon fruit chain production, useful for the routine analysis of the above mentioned three matrices is presented. The driven concept is the minimization of matrix effects through sample dilution of the concentrated by-products, either after sample treatment or not. This approach will contribute to the maintenance of the whole instrumental system. QuEChERS AOAC 2007.01 was selected as the most suitable protocol for routine determination of, residues of 16 the pesticides most commonly used in the fruits during the citrus production through liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The same protocol was applied for pesticide residue analysis in concentrated juice after diluting 4 times the sample to minimize the matrix effects. For the analysis of lemon essential oils, the dilution and shoot procedure proved to be useful for LC–MS/MS and gas chromatography–mass spectrometry determination. The three methodologies were validated following SANTE guidelines, with quantitation limits below the established European Union and Codex Alimentarius maximum residue limits. The developed methodologies are useful tools for the routine control analysis of pesticide residues in lemon matrices, allowing high sample throughput and enhancing labs productivity.

Matrix-matched standards in the liquid chromatography–mass spectrometry determination of neonicotinoids in soil and sediment

The use of matrix-matched standards with a solid-liquid extraction and salting out without the addition of further cleanup steps or costly cleanup procedures associated with the quick, easy, cheap, effective, robust, and safe (QuEChERS) method was evaluated to address variations in ionization efficiency in the LC–MS/MS determination of neonicotinoid pesticides in complex environmental samples. Limits of detection (1.4–3.4 ng/g) and limits of quantitation (4.6–11.3 ng/g) for various neonicotinoid analogs were comparable to previously reported QuEChERS extraction methods. Mean recovery of standard neonicotinoid samples spiked with 10 ng/g was found to be 78.0–100.5%, while samples spiked with 100 ng/g were found to be 55.1–99.9%. Recovery of analytes was matrix dependent; the highest recovery was from sediment (86.2–100.5%) followed by laboratory sand (70.9–81.7%) and agricultural soil (55.5–102.6%), respectively. Optimization of this methodology resulted in the reduction of procedure time and cost, and can aid in environmental monitoring efforts of common neonicotinoid pesticides in soils and sediments.

The geochemical and organic petrological characteristics of coal measures of the Xujiahe formation in the Sichuan Basin, China

Upper Triassic coaly and lacustrine source rocks complicate efforts to determine the source of hydrocarbons in Sichuan Basin. Total organic carbon analyses, pyrolysis experiments, petrological examinations, and gas chromatography and gas chromatography–mass spectrometry determinations were conducted on coals, carbonaceous mudstones and mudstones collected from two outcrop sections and cores of nine wells. Results revealed that the abundant organic carbon content will prolong the hydrocarbon generation cycle for coals and then the hydrocarbon generating capacity of coals will be enhanced by salinization, thereby contributing bacteria and algae microorganisms into humic coal of the Xujiahe Formation. Compared with mudstone, coal with the same maturity has a stronger adsorption effect on free hydrocarbons. When Ro is greater than 1.35, coal still has a strong hydrocarbon generation ability. The stable water column stratification and euxinic bottom water conditions are evidenced from the lower Pr/Ph and the higher gammacerane indices. The mixing of sea water has been proven by the existence of 4α,23,24,-trimethylcholestanes.

Gas Chromatography–Mass Spectrometry Determination of Polycyclic Aromatic Hydrocarbons in Surface Water

The current status and problems of the determination of polycyclic aromatic hydrocarbons (PAHs) in surface waters are discussed. Sixteen unsubstituted PAHs, which are priority pollutants of aquatic ecosystems, are selected as analytes. Gas chromatography–mass spectrometry (GC–MS) ensures the identification of the majority of pollutants using an integrated spectral library and their determation at a level below the maximum permissible concentration (MPC). The conditions for the simultaneous determination of 16 unsubstituted PAHs by GC–MS with detection in the selected ion monitoring mode are optimized. PAHs were extracted from a 1-L water sample by ultrasound-assisted liquid–liquid extraction. The main performance characteristics of the procedure were estimated. The lower limit of the analytical range was from 0.5 ng/L (benzo(a)pyrene) to 50 ng/L (naphthalene); the upper limit of the analytical range was 250 ng/L for all PAHs. The procedure was tested in model systems and real samples.

Online Solid-Phase Extraction LC-MS/MS: A Rapid and Valid Method for the Determination of Perfluorinated Compounds at Sub ng·L−1 Level in Natural Water

In this research paper, we report a method able to detect perfluorinated compound at pg·L−1 levels in superficial and underground water samples. An online solid phase extraction HPLC-MS/MS method was developed for the analysis of 12 perfluoroalkyl acids (PFASs). The method is based on injection of 5000 µL of water sample in SPE online WAX column followed by chromatography separation and mass spectrometry determination. SPE online elution was performed by water + 0.05% NH4OH and methanol + 0.05% NH4OH, while separation of target compounds was achieved within 10 min by Gemini chromatographic column operating from 1 to 12 pH range and using a mixture of water-methanol + 0.05% NH4OH. Sub ng·L−1 method detection limits (from 0.2 to 5 ng·L−1), linearity (from 0.2 to 250 ng·L−1), accuracy (from 80 to 120%), and precision (RSD less than 15% at LOQs levels) were achieved. The method is capable of measuring PFAS at trace levels, but above all it can reach the limit of 200 pg·L−1 required by European regulation for PFOS determination in surface and underground waters. The method was validated for quantitative analysis of PFASs in real water samples.

Development of a single format membrane assisted solvent extraction-molecularly imprinted polymer technique for extraction of polycyclic aromatic hydrocarbons in wastewater followed by gas chromatography mass spectrometry determination

A technique that combines membrane assisted solvent extraction and molecularly imprinted polymer into a single step format has been successfully developed and evaluated for the extraction of the 16 US-EPA priority polycyclic aromatic hydrocarbons in wastewater samples followed by determination using gas chromatography coupled with time of flight mass spectrometry. The technique involves placing the polymer particles into a hydrophobic polypropylene membrane bag which is in contact with an aqueous donor phase. The technique was optimized for various parameters that include presence of an organic modifier in the donor phase, stirring rate and extraction time. The optimum conditions were 25% of dimethyl sulfoxide as an organic modifier and stirring at 1000 rpm for 120 min. The limits of detection using the technique were in the 0.01–0.45 ng mL−1 range. Linearity values determined in the 10–1 000 ng mL−1 calibration range were all above 0.9972. Extraction efficiencies of the sixt analytes calculated as averages for three spiking concentrations ranged from 62.8 to 96.8% (RSD = 3.1–12.3%). The optimized method was tested for the extraction of polycyclic aromatic hydrocarbons in wastewater samples in the presence of surrogate standards. The developed method showed great reproducibility with inter day repeatability values ranging from 0.6 to 24.9%. The analytes were quantified in the nanogram level showing that the developed technique is a viable alternative in the analysis of trace organic compounds in complex aqueous samples.

Fast and sensitive determination of per- and polyfluoroalkyl substances in seawater

In this work, a novel, fast, and sensitive method was developed for perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS) and PFOS precursor’s determination in seawater. The proposed method consists in a vortex-assisted liquid-liquid microextraction (VALLME) combined with liquid chromatography (LC) and LTQ-Orbitrap high resolution mass spectrometry (LTQ-Orbitrap HRMS) determination. Several parameters affecting both the HPLC-LTQ Orbitrap HRMS determination and the VALLME were studied, with special attention to blank contamination problem. The use of LTQ-Orbitrap-HRMS in full mode, quantifying the target analytes using the exact mass, provides a very powerful detection in terms of sensitivity and specificity maintaining all the information provided by the full mass spectra, allowing, also, the identification of non-target substances. The use of matrix-matched calibration, together with labelled surrogate standards, minimize matrix effects and compensate potential recovery losses, resulting in recoveries between 95 and 105%, with excellent sensitivity (quantitation limit between 0.7 and 6 ng L−1) and precision (4–10%). The proposed method requires only 35 mL of sample and 100 μL of extracting solvent, is fast and avoids the use of other solvents to obtain the dispersive cloudy solution, simplifying the procedure and improving the existing procedures for the determination of per- and polyfluoroalkyl substances (PFASs) in seawater in terms of green analytical chemistry. The method was successfully validated by participating in a proficiency test assay provided by the National Measurement Institute of the Australian Government for the determination of PFOA, total PFOS and linear PFOS in waters. A revision of the state of the art in the last twelve years of methods for the analysis of PFASs in seawater and other types of water was performed, and a critical comparison between the developed method and the previously published was included. Finally, the method was applied to the analysis of samples from Ría de Vigo, a sensitive and semiconfined coastal area located in the northwest of Spain. PFOS, N-methyl perfluorooctanesulfonamide (n-MeFOSA) and N-ethyl perfluorooctanesulfonamide (n-EtFOSA) were detected in samples at levels lower than the maximum allowable concentration (MAC) established by Directive 2013/39/EU, but above the annual average (AA) levels.

Gas chromatography–mass spectrometry determination of polycyclic aromatic hydrocarbons in baby food using QuEChERS combined with low-density solvent dispersive liquid–liquid microextraction

A sensitive GC–MS method is reported for the determination of twelve polycyclic aromatic hydrocarbons (PAHs) in baby food. The sample preparation involves QuEChERS extraction combined with low-density solvent dispersive liquid–liquid microextraction (LDS-DLLME) and ultra-low temperature (−80 °C). Plackett–Burman screening design was employed to identify the main sample preparation variables that affect the extraction efficiency, such as the volume of toluene used in LDS-DLLME. The suitability of proposed method was verified by analytical selectivity, linearity in solvent and matrix-matched calibration curves and adequate recoveries (72–112%) and precision (RSD values ≤11%), under repeatability and within-laboratory reproducibility conditions. High analytical sensitivity was achieved for the monitoring of PAHs at the strict limit of 1 µg kg−1 fixed by the European Commission for baby foods. The validated method was applied to thirty-two commercial baby food samples, and the investigated PAHs were not detected in any sample.

Homogeneous liquid-liquid microextraction via flotation assistance coupled with gas chromatography-mass spectrometry for determination of myclobutanil in cucumber, tomato, grape, and strawberry using genetic algorithm

ABSTRACTFacile and potent homogeneous liquid–liquid microextraction via flotation assistance method (HLLME-FA) combined with gas chromatography-mass spectrometry was proposed for determination of trace amounts of myclobutanil in fruit and vegetable samples. The paramount parameters, such as extraction and homogeneous solvent types and volumes, ionic strength and extraction time were studied. Under optimum conditions, the detection limit of 0.005 ng g−1, the linear range of 0.05–100 ng g−1, and the precision of 3.8% were acquired. A three-layer artificial neural network (ANN) model was used with 10 neurons and tan-sigmoid function at hidden layer and a linear transfer function at output layer were developed to predict the process. The results indicated that the proposed ANN model could perfectly predict the process with the mean square error of 0.89%. Then genetic algorithm was utilised to optimise the parameters. The proposed procedure showed satisfactory results for analysis of cucumber, tomato, grape, and strawberry.

Gas Chromatography–Mass Spectrometry Determination of Pregabalin in Human Plasma Using Derivatization Method

A gas chromatography–mass spectrometry method for the determination of pregabalin in human plasma is described. The procedure involves precipitation of protein, liquid–liquid extraction with ethylene glycol monomethyl ether, and derivatization with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide in the presence of N-hydroxysuccinimide as additive. Separation was attained on HP column (30 m × 0. 25 mm ID, 0.25 μm) coupled with mass spectrometric detector using electron impact selected ion monitoring. The assay showed an excellent linearity in the concentration range of 0.36–10 μg mL−1 with correlation coefficient (r2) values of 0.999. The intra- and inter-day assay variations for three different concentration levels were less than 10%. The limit of quantification was detected at 0.36 μg mL−1. The method is highly specific, precise, accurate, and reproducible and could also be applied for the determination of pregabalin in human plasma.