Matrix-matched Calibration Curves Research Articles

An integrated calibration strategy for the development and validation of an LC-MS/MS method for accurate quantification of egg allergens (Gal d 1–6) in foods

Accurate determination of egg allergens in food is vital for allergen management and labeling. However, quantifying egg allergens with mass spectrometry poses challenges and lacks validation methods. Here, we developed and validated an LC-MS/MS method for quantifying egg allergens (Gal d 1–6) in foods. Sample extraction, enzymatic digestion, purification, proteins/peptides selection, and calibration curves were optimized. VMVLC[+57]NR (Gal d 1) and GTDVQAWIR (Gal d 5) exhibited outstanding sensitivity and stability, serving as quantitation markers for egg white and yolk. Using a matrix-matched calibration curve with allergen ingredients as calibrants and labeled peptides as standards, we achieved highly accurate quantitation. Validation involved spiking egg protein into egg-free foods, showing excellent sensitivity (LOQ: 1–5 mg/kg), accuracy (62.4 %–88.5 %), and reproducibility (intra-/inter-day precision: 3.5 %–14.2 %/8.2 %–14.6 %). Additionally, we successfully applied this method to commercial food analysis. These findings demonstrate optimal allergen selection, peptides, and calibration strategy are crucial parameters for food allergen quantification via MS-based methods.

Determination of Tilmicosin in Bovine, Swine, Chicken, and Turkey Tissues by Liquid Chromatography With Tandem Mass Spectrometry, Single-Laboratory Validation.

An LC-MS/MS method was developed for determination and confirmation of tilmicosin in bovine, swine, chicken, and turkey tissues (liver, kidney, muscle, and skin/fat) and bovine milk. The method was subjected to single-laboratory validation to establish method performance parameters. Animal tissues and bovine milk were fortified at four concentrations ranging from 0.5 times the lowest maximum residue limit (MRL) or tolerance to 2 times the highest MRL or tolerance considering the Codex and EU MRLs and the US tolerances in the various tissues and milk studied. Incurred tissues were analyzed to verify the precision of the method. The data demonstrated linearity of matrix-matched calibration curves using a weighted (1/×) regression. Recoveries varied from 83.3 to 107.1%. Repeatability precision (RSDr) ranged from 0.465 to 13.4% and intermediate precision (RSDi) ranged from 2.24 to 14.7% in fortified tissue. Repeatability of the method was verified in incurred tissues, ranging from 3.41 to 16.0%. The limits of detection and quantitation of the method are presented and vary by matrix. One confirmatory transition ion was examined across all matrixes and met US and EU criteria for mass spectrometry confirmation. The method was shown to be robust when small changes in method parameters were made, and stability of the analyte in fortified tissues, extracts, standard solutions, and matrix-matched standards was estimated. The data satisfy the requirements of the AOAC Stakeholder Panel for Veterinary Drug Residue Methods for single-laboratory validation studies and the U.S. Food and Drug Administration Center for Veterinary Medicine Guidance for Industry #208 (VICH GL49). The LC-MS/MS method was demonstrated to be suitable for determination and confirmation of tilmicosin residues in bovine, swine, chicken, and turkey tissues and bovine milk based on Codex and EU MRLs and US tolerances.

Deep eutectic solvent-based dispersive liquid–liquid microextraction for determination of organochlorine pesticides in water and apple juice samples

In this work, we developed a deep eutectic solvent-based dispersive liquid–liquid microextraction (DES-based DLLME) method for the extraction and preconcentration of organochlorine pesticides (OCPs) from water and apple juice samples. Different DESs were synthesized by mixing menthol with carboxylic acids such as acetic, formic, and lactic acids. Among them, DES synthesized by mixing menthol with formic acid at a molar ratio of 1:1 showed the highest extraction efficiency for the target OCPs compared to other DESs. Various parameters affecting the method's extraction efficiency, including volume of DES, ionic strength, and centrifugation rate and time, were optimized. Under optimum conditions, matrix-matched calibration curves were separately constructed using water and apple juice samples. The obtained calibration curves have exhibited wide linearity ranges for both matrices. The limits of detections (LODs) and quantifications (LOQs) of the method ranged from 0.01 to 0.04, and 0.10–0.14 ng mL−1 for water and 0.05–0.09 and 0.22–0.41 ng mL−1 for apple juice samples, respectively. Similarly, the trueness of the method studied by spiking the samples at three concentration levels showed recovery values ranging from 80.1 to 112.5 % for both water and apple juice matrices. The findings demonstrated that the proposed DES-based DLLME method is rapid, simple, and environmentally benign. Thus, it could be used as an alternative method for determining OCPs in water, apple juice, and other related matrices.

Determination of glyphosate and aminomethylphosphonic acid residues in Finnish soils by ultra‐high performance liquid chromatography–tandem mass spectrometry

Glyphosate [N-(phosphonomethyl) glycine] (GLY) adsorbs strongly in Finnish soils. A new method for GLY and its main degradation product, aminomethylphosphonic acid (AMPA) residues in clay soils (Protovertic Luvisol) was developed and validated. A new method was necessary because the previous one required laborious cleaning pre-treatments, and its recovery was quite poor (<40%–70%). In the new method, the earlier method's extraction solvent, 0.1 M potassium hydroxide (KOH), was replaced by more effective 0.6 M KOH. The old post-column high-performance liquid chromatography and fluorescence (HPLC-FLD) method was replaced by the ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) method. Compounds were identified as their fluorenyl methyl chloroformate (FMOC) derivatives by a multiple reaction monitoring (MRM) technique and quantified by an internal standard method utilising multipoint matrix-matched calibration. Glufosinate-ammonium (GLUF) was used to monitor the effectiveness of extraction with good recovery (80–119%). All calibration curves were found to be linear (R2 ≥ 0.98) in the studied calibration range (0.01–3.31 mg kg−1 in fresh soil). The repeatability and reproducibility were 25% and 28% for GLY, and 20% and 24% for AMPA in real research soil samples. The method was effective throughout the calibration range in all the studied Finnish agricultural soils.•An improved method was created to analyse glyphosate (GLY) and AMPA in Finnish clay soil.•The challenge caused by strong GLY adsorption on soil was solved by using multipoint matrix-matched calibration curve samples which were prepared identically with the research samples.•The method performed well in all tested clay, loam and sandy loam soils.

Simultaneous Determination of 54 Pesticides in Proso Millet Using QuEChERS with Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS).

To assess the potential risks posed to the environment and human health, analyzing pesticide residues in proso millet is important. This paper aimed to develop a modified QuEChERS method with liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the analysis of 54 pesticide residues in proso millet. Parameters including the mobile phase of the instrument, the acidity of the extraction solvent, and the type of absorbents were optimized to provide satisfactory performance. The method was validated concerning linearity, limit of quantification (LOQ), matrix effect, accuracy, and precision. In detail, the linearity of the matrix-matched calibration curve was acceptable with correlation coefficients (R2) higher than 0.99. The mean recovery was in the range of 86% to 114% with relative standard deviations (RSDs) ≤ 20% (n = 5). The LOQ was determined to be 0.25-10 μg/kg. The developed method was feasible for the determination of multiple pesticide residues in proso millet.

Determination of 80 pesticide residues in milk using NH_2-MWNTs by liquid chromatography-time of flight mass spectrometry

A method for the determination of 80 pesticide residues in milk by liquid chromatography-time-of-flight mass spectrometry(LC-QTof-MS) was developed. The target compounds in milk were extracted with acetonitrile-methanol(9∶1, V/V) containing 1% acetic acid, and purified by aminated multi-walled carbon nanotubes(NH_2-MWNTs). The chromatographic column was Waters Acquity UPLC BEH C_(18 )(100 mm×2.1 mm, 1.7 μm). The 80 pesticides were detected by liquid chromatography-time-of-flight mass spectrometry and quantified using an external standard method by matrix matched calibration curve. The purification method showed a good linearity(r~2≥ 0.99) over the concentration range from 5 to 100 μg/L for the 80 pesticides in this study. The limits of detection(LODs) and quantification(LOQs) of the 80 pesticides in milk ranged from 0.01 to 0.50 μg/L and 0.03 to 1.50 μg/L, respectively. The mean recoveries of the three spiked levels ranged from 71.5% to 116.9% with the relative standard deviation ranging from 1.2% to 18.1%, indicating that the accuracy and precision of the method were good. Among the milk samples, no residues of the 80 pesticides in this study were found after screening. The method has good linearity, good sensitivity, accuracy and precision and is suitable for the simultaneous and rapid determination of 80 pesticide residues in milk.

Simultaneous determination of 36 mycotoxins in fruits by QuEChERS coupled with ultra performance liquid chromatography-tandem mass spectrometry

Mycotoxins are secondary metabolites produced by toxigenic fungi under specific environmental conditions. Fruits, owing to their high moisture content, rich nutrition, and improper harvest or storage conditions, are highly susceptible to various mycotoxins, such as ochratoxin A (OTA), zearalenone (ZEN), patulin (PAT), Alternaria toxins, etc. These mycotoxins can cause acute and chronic toxic effects (teratogenicity, mutagenicity, and carcinogenicity, etc) in animals and humans. Given the high toxicity and wide prevalence of mycotoxins, establishing an efficient analytical method to detect multiple mycotoxins simultaneously in different types of fruits is of great importance. Conventional mycotoxin detection methods rely on high performance liquid chromatography (HPLC) coupled with mass spectrometry (MS). However, fruit sample matrices contain large amounts of pigments, cellulose, and minerals, all of which dramatically impede the detection of trace mycotoxins in fruits. Therefore, the efficient enrichment and purification of multiple mycotoxins in fruit samples is crucial before instrumental analysis. In this study, a reliable method based on a QuEChERs sample preparation approach coupled with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was established to determine 36 mycotoxins in fruits. In the optimal extraction method, 2.0 g of a sample was extracted with 10 mL of acetic acid-acetonitrile-water (1∶79∶20, v/v/v) in a 50 mL centrifuge tube, vortexed for 30 s, and ultrasonicated for 40 min. The mixture was then salted out with 2.0 g of anhydrous MgSO4 and 0.5 g of NaCl and centrifuged for 5 min. Next, 6 mL of the supernatant was purified using 85 mg of octadecylsilane-bonded silica gel (C18) and 15 mg of N-propylethylenediamine (PSA). After vigorous shaking and centrifugation, the supernatant was collected and dried with nitrogen at 40 ℃. Finally, the residues were redissolved in 1 mL of 5 mmol/L ammonium acetate aqueous solution-acetonitrile (50∶50, v/v) and passed through a 0.22 μm nylon filter before analysis. The mycotoxins were separated on a Waters XBridge BEH C18 column using a binary gradient mixture of ammonium acetate aqueous solution and methanol. The injection volume was 3 μL. The mycotoxins were analyzed in multiple reaction monitoring (MRM) mode under both positive and negative electrospray ionization. Quantitative analysis was performed using an external standard method with matrix-matched calibration curves. Under optimal conditions, good linear relationships were obtained in the respective linear ranges, with correlation coefficients (R2) no less than 0.990. The limits of detection (LODs) and quantification (LOQs) were 0.02-5 and 0.1-10 μg/kg, respectively. The recoveries of the 36 mycotoxins in fruits ranged from 77.0% to 118.9% at low, medium, and high spiked levels, with intra- and inter-day precisions in the range of 1.3%-14.9% and 0.2%-17.3%, respectively. The validated approach was employed to investigate mycotoxin contamination in actual fruit samples, including strawberry, grape, pear, and peach (15 samples of each type). Eleven mycotoxins, namely, altenuene (ALT), altenusin (ALS), alternariol-methyl ether (AME), tenuazonic acid (TeA), tentoxin (Ten), OTA, beauvericin (BEA), PAT, zearalanone (ZAN), T-2 toxin (T2), and mycophenolic acid (MPA), were found in the samples; three samples were contaminated with multiple mycotoxins. The incidence rates of mycotoxins in strawberry, grape, pear, and peach were 27%, 40%, 40%, and 33%, respectively. In particular, Alternaria toxins were the most frequently found mycotoxins in these fruits, with an incidence of 15%. The proposed method is simple, rapid, accurate, sensitive, reproducible, and stable; thus, it is suitable for the simultaneous detection of the 36 mycotoxins in different fruits.

A pH-dependent CT sensitive method for detection of trace Mn in milk by UV-spectrophotometry

In this study, a new method was developed for the extractive pre-concentration/detection of trace Mn in milk prior to analysis by UV-spectrophotometry. The method is based on the pH-controlled intra-ligand charge transfer (ICT) complexation of modifier, 2-HBT in presence of trace Mn (II), and then the extraction of the complexes, where the hydrazine and hydrazone tautomers are predominant at pHs of 2.0/ 3.0, and pH 6.0 because of CT at pH 4.0. The free Mn (II) and total Mn levels of the samples were detected at 269 nm by UV-spectrophotometry. For total Mn, the method was validated by analysis of two certified milk samples. The results were statistically in good agreement with the certified values, and the precision was lower than 6.4%. After a pre-concentration of 62.5-fold, the limits of detection were 1.45/1.92 and 1.54/2.12 μg L−1 in range of 5–165 and 5–150 µg L−1 from the solvent-based and matrix-matched calibration curves, respectively. There is not a matrix effect from comparison of the calibration curves’s slopes. The method was successfully applied to analysis of milk samples. In terms of speciation, the free Mn (II) and total Mn levels in milk were in the range of 7.65–30.4 μg L−1, and 10.2–34.7 and 10.7–35.5 μg L−1 after the microwave and ultrasound assisted extraction.

In-syringe cotton fiber solid-phase extraction coupled with stable-isotope-dilution liquid chromatography-tandem mass spectrometry for the determination of zearalenone

Here, an in-syringe cotton fiber solid-phase extraction (CF-SPE) method for the effective pretreatment of zearalenone (ZEA) in cereal crops and traditional Chinese medicines was developed. In this method, a syringe tube is packed with degreasing cotton, which serves as the normal-phase adsorbent for extracting ZEA from the nonpolar solvent extract of samples. The entire extraction process, including activation, sampling, washing, and elution steps, can be conveniently performed by employing a series of pull–push operations to force the solution to pass through the degreasing cotton. Optimal extraction recoveries were achieved using 200 mg of degreasing cotton as the adsorbent, a 3 mL volume of sampling solution, a desorption solution consisting of 2 mL of acetonitrile, and 4 pull–push times for both sampling and desorption. Coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS), quantification of ZEA in corns was achieved by validating matrix-matched calibration curves in the range of 0.1–100.0 ng/g with satisfactory linearity (R2 = 0.9996). The limit of detection (LOD) was calculated to be 0.025 ng/g with a signal-to-noise ratio (S/N) of 3. The intra-/inter-day relative recoveries and relative standard deviations were calculated to be in the ranges of 93.8%–110.4% and 3.2%–9.3%, respectively, which were satisfactory for quantitative analysis. The proposed in-syringe CF-SPE-LC-MS/MS method is simple, cheap, and labor/time-saving.

In-house validation of an LC-MS method for the multiplexed quantitative determination of total allergenic food in chocolate.

Mass spectrometry has been widely accepted as a confirmatory tool for the sensitive detection of undeclared presence of allergenic ingredients. Multiple methods have been developed so far, achieving different levels of sensitivity and robustness, still lacking harmonization of the analytical validation and impairing comparability of results. In this investigation, a quantitative method has been validated in-house for the determination of six allergenic ingredients (cow's milk, hen's egg, peanut, soybean, hazelnut, and almond) in a chocolate-based matrix. The latter has been produced in a food pilot plant to provide a real and well-characterized matrix for proper assessment of method performance characteristics according to official guidelines. In particular, recent considerations issued by the European Committee for Standardization have been followed to guide a rigorous single-laboratory validation and to feature the main method performance, such as selectivity, linearity, and sensitivity. Synthetic surrogates of the peptide markers have been used both in native and labelled forms in matrix-matched calibration curves as external calibrants and internal standards, respectively. A two-order of magnitude range was investigated, focusing on the low concentration range for proper assessment of the detection and quantification limits (LOD and LOQ) by rigorous calibration approach. Conversion factors for all six allergenic ingredients have been determined for the first time to report the final quantitative information as fraction of total allergenic food protein (TAFP) per mass of food (µgTAFP/gfood), since such areporting unit isexploitable in allergenic risk assessment plans. The method achieved good sensitivity with LOD values ranging between 0.08 and 0.2 µgTAFP/gfood, for all ingredients besides egg and soybean, whose quantitative markers reported a slightly higher limit (1.1 and 1.2 µgTAFP/gfood, respectively). Different samples of chocolate bar incurred at four defined concentration levels close to the currently available threshold doses have been analyzed to test the quantitative performance of the analytical method, with a proper estimate of the measurement uncertainty from different sources of variability. The sensitivity achieved resulted in compliance with the various threshold doses issued or recommended worldwide.

Optimization and validation of an extraction method for the analysis of multi-class emerging contaminants in soil and sediment

Analytical methods for the determination of multi-class emerging contaminants are limited for soil and sediment while they are essential to provide a more complete picture of their distribution in the environment and to understand their fate in different environmental compartments. In this paper, we present the development and optimization of an analytical strategy that combines reliable extraction, purification and the analysis using ultra-pressure liquid chromatography triple quadrupole mass spectrometry (UPLC-MS/MS) of 90 emerging organic contaminants including pesticides, pharmaceuticals and personal care products, flame retardants, per- and polyfluoroalkyl substances (PFASs) and plasticizers in soil and sediment. To extract a wide range of chemicals, the extraction strategy is based on the QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) approach. A number of different options were investigated (buffer, acidification, addition of EDTA, different types and combinations of dispersive SPE etc.) and the effectiveness of the chemical extraction procedure and the clean-up was assessed for two matrices: soil (organic matter content of 9%) and sediment (organic matter content of 1.9%). The method was fully validated for both matrices, in terms of accuracy, linearity, repeatability (intra-day), reproducibility (inter-day), method limits of detection and quantification (LODs and MLOQs, respectively). The final performance showed good accuracy and precision (mean recoveries were between 70 and 120% with relative standard deviations (RSD) less than 20% in most cases), low matrix effects, good linearity for the matrix-matched calibration curve (R2≥0.991) and MLOQs ranged from 0.25 and 10 µg/kg. To demonstrate the applicability and suitability of the validated method, soil and sediment samples from Vietnam, France, Sweden and Mexico were analyzed. The results showed that of the 90 target compounds, a total of 33 were quantified in the sediment and soil samples analyzed. In addition to multi-target analysis, this strategy could be suitable for non-target screening, to provide a more comprehensive view of the contaminants present in the samples.

A miniaturized sample preparation method for routine elemental determination in whole blood using volumetric absorptive micro-sampling by ICP-QQQ.

Volumetric absorptive micro-sampling (VAMS) has emerged as a simple and safe tool for collecting and storing blood samples in clinical and bioanalytical fields. This study presents a novel method for determining essential and non-essential trace elements (As, Be, Cd, Cs, Cu, Fe, Mg, P, Pb, S, Sb, Se, Tl, V, U) in VAMS-collected blood samples using microwave-assisted digestion with diluted acid as sample preparation method and an inductively coupled plasma triple quadrupole mass spectrometry (ICP-QQQ) as determination technique. While certain elements posed challenges due to VAMS tip background issues (Al, Ti, Cr, Mn, Co, Ni, Sn, Mo, Ba), the method demonstrated high precision and accuracy for the targeted analytes. It was demonstrated that 4.5mol L-1 HNO3 plus 100 µL H2O2 30% (w/w) was suitable for an efficiency of digestion for further elemental determination using micro-analysis (spending less than 300 µL analytical solution) by ICP-QQQ, given that the residual carbon content (RCC) after the digestion procedure was lower than 5%. All the results higher than limit of quantification (LOQ) were in agreement with reference values for all analytes. Accuracy was assessed through reference material analysis and recovery tests using spiked samples. Moreover, suitable agreements (p > 0.05) between this method (VAMS-M) and the comparative method (liquid sampling method) were obtained for all analytes >LOQ. Furthermore, all results >LOQ showed good precision according to precision requirements (Horwitz equation). In this way, with the use of dilute acid, low dilution factor (30-fold), and excellent digestion efficiency (>95%), the proposed method was able to achieve an excellent detection limit, precision, and accuracy for 15 elements: As, Be, Cd, Cs, Cu, Fe, Mg, P, Pb, S, Sb, Se, Tl, V, and U using ICP-MS/MS, without the need for matrix-matched calibration curves. This research showcases an innovative analytical approach using VAMS for blood samples, offering biosafety, practicality, sensitivity, versatility, and robustness. This method contributes to the advancement of trace element analysis in biomedical research and clinical applications.

Monitoring residue levels of multiple types pesticides in chrysanthemum (Chrysanthemum morifolium Ramat) and its residue pattern in diet consumption

In this study, a modified preparation method named "Quick, Easy, Cheap, Effective, Rugged and Safe" (QuEChERS) was designed to detect six pesticide residues (fenthion, pendimethalin, trifloxystrobin, bifenazate, pyridaben, and pyraclostrobin) in 25 chrysanthemum (Chrysanthemum morifolium Ramat) samples by the gas chromatography-mass spectrometry (GC-MS) analysis. Prior to GC-MS analysis, extraction was performed using acetonitrile-2.5 % formic acid with European standard (EN) QuEChERS method extraction salts, and the matrix was purified with a combination of sorbent primary secondary amine/graphitized carbon black/octadecylsilane (PSA/GCB/C18). The limits of detection and quantification were then measured by applying matrix-matched calibration curves (R2 ≥ 0.999) in the ranges of 0.35–3.25 and 1.04–9.76 μg·kg−1, respectively. By quantitative analysis, the recoveries of pesticides ranged from 80.14 % to 98.57 % with the relative standard deviations < 10 % at the spiked levels of 0.01, 0.05 and 0.10 mg·kg−1. The transfer rates of pyraclostrobin in chrysanthemum to its infusion ranged from 11.38 % to 25.75 %. According to the favorable results, the method may be suitable for the quantitative detection of six chemical pesticides in chrysanthemums. Additionally, with a hazard quotient of 1.43 %, pyraclostrobin posed a negligible risk to human health.

Determination of cortisone and cortisol in human scalp hair using an improved LC-MS/MS-based method.

Human scalp hair is an easily available but complex matrix for determination of cortisone and cortisol, and has been shown to reflect long-term glucocorticoid exposure. Hair glucocorticoid analysis has been used to detect hypo- and hypercortisolism. In this study, we describe the development and validation of a LC-MS/MS method for quantification of cortisone and cortisol in human scalp hair, and provide a novel approach for analysis and interpretation of the results. Improved sample preparation using pulverization and solid phase extraction allowed for low sample volumes (10 mg). Baseline chromatographic separation without matrix interference was achieved by reversed phase chromatography and MRM measurement in negative ion mode. Run-to-run time was 8 min. Mixed model analyses were performed to create individual patterns of cortisone and cortisol concentrations. Matrix matched calibration curves showed excellent linearity up to 100 pg (analyte)/mg (hair) for both cortisone and cortisol (R2>0.995). LLOQ was 1.5 and 1.0 pg/mg for cortisone and cortisol, respectively. Matrix effect was negligible for hair color (recoveries 95-105 %). Cortisone and cortisol concentrations decreased from proximal to distal hair segments, following a predictable, but subject-specific pattern, with less individual variation for cortisone than for cortisol. This improved LC-MS/MS method is able to accurately quantify cortisone and cortisol in human hair with minimum matrix interference. This new way of data analysis and interpretation including individual patterns of cortisone and cortisol will be of help with detection of pathological concentrations in both the high- and the low ranges of glucocorticoids.

Simultaneous Determination of Multiple Contaminants in Chicken Liver Using Dispersive Liquid-Liquid Microextraction (DLLME) Detected by LC-HRMS/MS

Simultaneous determination of a mixture of food contaminants, including pesticides, sulphonamides, fluoroquinolones, anthelmintics, and aflatoxin B1, in solid biological samples (chicken liver) by dispersive liquid-liquid microextraction/liquid chromatography-high resolution mass spectrometry (DLLME/LC-HRMS) is presented. Previous work focused on the application of DLLME to single-class contaminants. In this work, the DLLME extraction method has been extended to complex multiresidues in the biological matrix. The first part of this study was the selection of an appropriate solvent that enabled the dissolution of analytes from the chicken livers. The matrix-matched calibration curves showed good linearity in the range 0.5–50.0 µg kg−1 for aflatoxin B1 and 50–500 µg kg−1 for pesticides, fluoroquinolones, sulphonamides, and anthelmintics, with a coefficient of determination (R2) values of 0.9916–0.9967. The mean recoveries were in the range of 80.4–96.3%, and the relative standard deviation (RSD) values were in the range of 1.53–8.98%. The limit of detection (LOD) and the limit of quantification (LOQ) values were 0.03 µg kg−1 and 0.09 µg kg−1, respectively, for aflatoxin B1, and for pesticides, fluoroquinolones, sulphonamides, and anthelmintics, they were in the range of 0.011–1.197 µg kg−1 and 0.150–2.579 µg kg−1, respectively. The developed method was compared with the standard solid phase extraction (SPE) method, and there was no significant difference between the two methods.

Effervescence-assisted dispersive liquid-liquid microextraction for extraction and preconcentration of organochlorine pesticides in water samples

ABSTRACT. In this paper, effervescence-assisted dispersive liquid-liquid microextraction method has been developed for the extraction and preconcentration of organochlorine pesticides in water samples before their determination by gas chromatography-mass spectrometry. The method involves in-situ generation of CO2 bubbles to induce dispersion of the extraction solvent in the aqueous sample. Different parameters affecting the extraction efficiency of the method including the type and concentration of the effervescent agents as well as the type and volume of extraction solvent were optimized. Under optimum conditions, matrix matched calibration curves were constructed at eight concentrations ranging from 0.6–4.0 ng/mL showed good linearity with coefficient of determinations of ≥ 0.9961. The limits of detections and quantifications ranged from 0.2–0.4 and 0.6–1.0 ng/mL, respectively. The intra- and inter-day precisions studied at two concentration levels had below 5% relative standard deviation values. Similarly, recoveries investigated at two concentration levels ranged from 80.7–117.4%. The findings demonstrated that proposed method is simple, rapid, and efficient to be used as alternative method for analysis of organochlorine pesticides from environmental water and other similar matrices.&#x0D; &#x0D; KEY WORDS: Effervescence agents, CO2 bubbles, Organochlorine pesticides, Water samples, gas chromatography-mass spectroscopy&#x0D; &#x0D; Bull. Chem. Soc. Ethiop. 2023, 37(5), 1109-1122. &#x0D; DOI: https://dx.doi.org/10.4314/bcse.v37i5.4

Optimizing Linear Ion-Trap Data-Independent Acquisition toward Single-Cell Proteomics.

A linear ion trap (LIT) is an affordable, robust mass spectrometer that provides fast scanning speed and high sensitivity, where its primary disadvantage is inferior mass accuracy compared to more commonly used time-of-flight or orbitrap (OT) mass analyzers. Previous efforts to utilize the LIT for low-input proteomics analysis still rely on either built-in OTs for collecting precursor data or OT-based library generation. Here, we demonstrate the potential versatility of the LIT for low-input proteomics as a stand-alone mass analyzer for all mass spectrometry (MS) measurements, including library generation. To test this approach, we first optimized LIT data acquisition methods and performed library-free searches with and without entrapment peptides to evaluate both the detection and quantification accuracy. We then generated matrix-matched calibration curves to estimate the lower limit of quantification using only 10 ng of starting material. While LIT-MS1 measurements provided poor quantitative accuracy, LIT-MS2 measurements were quantitatively accurate down to 0.5 ng on the column. Finally, we optimized a suitable strategy for spectral library generation from low-input material, which we used to analyze single-cell samples by LIT-DIA using LIT-based libraries generated from as few as 40 cells.

Determination of 13 halobenzoquinone disinfection by-products in drinking water using solid phase extraction-ultra performance liquid chromatography-triple quadrupole mass spectrometry

Disinfection of drinking water is critical to prevent waterborne diseases. An unexpected consequence of water disinfection is the formation of disinfection by-products by the interaction of disinfectants with organic matter (natural or anthropogenic) and halides, which present significant toxicological effects and carcinogenic risks. As an emerging disinfection by-product, halobenzoquinones (HBQs) have attracted increasing attention owing to their severe toxicity and high detection rates. The credible determination of HBQs is essential for further studies on their occurrence, toxicity, and control measures; however, HBQs are usually detected in drinking water at trace levels. Therefore, accurate and efficient analytical techniques are critical for HBQ determination and quantitation. In this study, a method based on solid phase extraction (SPE) combined with ultra performance liquid chromatography-triple quadrupole mass spectrometry (UPLC-MS/MS) was developed to determine 13 HBQs, including six chlorobenzoquinones, six bromobenzoquinones, and one iodobenzoquinone, in drinking water. One-liter water samples were added with 2.5 mL of formic acid, and 500 mL of each sample was collected for further enrichment. Pretreatment optimization mainly focused on the SPE column, washing solvent, and nitrogen blowing temperature. After extraction using Plexa SPE columns (200 mg/6 mL), the samples were washed with ultrapure water containing 0.25% formic acid combined with 30% methanol aqueous solution containing 0.25% formic acid, eluted with 6 mL of methanol containing 0.25% formic acid, and then nitrogen blown at 30 ℃. The UPLC-MS/MS parameters were optimized by comparing the results of two reversed-phase columns (BEH C18 and HSS T3) and various concentrations of formic acid in the mobile phase, as well as by establishing the best instrumental conditions. The separation of 13 HBQs was performed using an HSS T3 column (100 mm×2.1 mm, 1.8 μm) via gradient elution with a mixture of 0.1% formic acid aqueous solution and methanol as the mobile phase for 16 min. The 13 HBQs were detected using a triple quadrupole mass spectrometer equipped with a negative electrospray ionization source (ESI-) in multiple reaction monitoring (MRM) mode. Matrix-matched calibration curves were used to quantify the HBQs owing to intense matrix inhibitory effects. The results reflected the good linear relationships of the 13 HBQs and yielded correlation coefficients (r) greater than 0.999. The method detection limits (MDLs, S/N=3) were 0.2-10.0 ng/L, while the method quantification limits (MQLs, S/N=10) were 0.6-33.0 ng/L. The recoveries of the 13 HBQs were 56%-88% at three spiked levels (10, 20, 50 ng/L), and the relative standard deviations (RSDs, n=6) were less than or equal to 9.2%. The optimization method was applied to analyze HBQs in five drinking water samples. Four HBQs, namely, 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), 2,5-dibromo-1,4-benzoquinone (2,5-DBBQ), 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ), and 2,6-dibromo-3,5-dimethyl-1,4-benzoquinone (2,6-DBDMBQ), were detected in the samples with detection rates of 100%, 20%, 80%, and 20%, respectively. The most frequently detected HBQ, 2,6-DCBQ, also exhibited the highest content (15.0-56.2 ng/L). The method showed high sensitivity, stability, accuracy, and efficiency, rendering it suitable for the analysis of 13 HBQs in drinking water. Compared with previous methods that mainly focused on 2,6-DCBQ and 2,6-DBBQ, the developed method achieved higher throughput and enabled the simultaneous analysis of 13 HBQs. The method presented in this study provides an opportunity to explore different types and concentrations of HBQs in drinking water, offers a deeper understanding of the occurrence of HBQs, and facilitates further studies on the health risks and control measures of these compounds.

Rapid determination of five halobenzoquinones in aquatic products by QuEChERS-ultra performance liquid chromatography-tandem mass spectrometry

Halobenzoquinones (HBQs), which are emerging chlorinated disinfection byproducts (DBPs), have attracted increasing attention because they are frequently detected in treated tap water, entrainment water, etc. These compounds are mainly generated during the water treatment process using chlorine, chloramine, and chlorine dioxide as disinfectants, and display more toxic effects than regulated DBPs, such as trihalomethane and haloacetic acid. HBQs have been recognized as potential bladder carcinogens and are harmful to the nervous system. Additionally, they can exert genotoxic effects and cause oxidative damage to DNA and proteins. The risk of HBQs in aquatic products is expected to rise because the disinfection of public facilities has significantly increased in recent years. Therefore, developing a sensitive and accurate analytical method to detect HBQs in aquatic products is of great importance. Several analytical methods, including gas chromatography, gas chromatography-mass spectrometry, electrochemical methods, liquid chromatography, and liquid chromatography-tandem mass spectrometry, can be used to identify and quantify HBQs in water. However, to the best of our knowledge, no reports on the determination of HBQ levels in aquatic products are yet available. Further, pretreatment is essential for HBQ determination because of the complex matrix effects of aquatic products. Herein, a sensitive and accurate method based on the QuEChERS technique coupled with ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for the simultaneous determination of five HBQs in aquatic products. For the QuEChERS procedure, the pretreatment conditions, such as the extraction solvent and adsorbent species, were systematically optimized. The sample was extracted with 10 mL of 10% methanol acetonitrile solution (containing 0.1% formic acid), dehydrated, and centrifuged with sodium chloride and anhydrous magnesium sulfate. The supernatant was purified using a QuEChERS packing material consisting of 50 mg N-propylethylenediamine (PSA), 30 mg of graphitized carbon black (GCB), and 30 mg of neutral alumina (Al2O3), dried with nitrogen, and concentrated. The five HBQs were separated on a Waters ACQUITY UPLC BEH C18 column (100 mm×2.1 mm, 1.7 μm) using 0.25% acetonitrile formate solution and 0.25% formic acid aqueous solution as the mobile phase under a gradient elution program and then detected using UPLC-MS/MS with negative electrospray ionization (ESI-) under multiple reaction monitoring (MRM) mode. Quantitative analysis was performed using a matrix-matched external standard method. The five HBQs achieved rapid separation within 6 min, indicating that the proposed method has a much shorter separation time compared with previous studies. The matrix effect was evaluated by establishing a matrix-matched calibration curve. The results showed that 2,5-dichloro-1,4-benzoquinone (2,5-DCBQ) presented a matrix-enhancing effect, whereas the other HBQs displayed matrix-inhibiting effects. In particular, tetrachlorobenzoquinone (TCBQ) exhibited strong inhibitory effects. Under the optimized experimental conditions, the five HBQs demonstrated good linear relationships in the range of 1.0-50.0 μg/L, with correlation coefficients (r)≥0.9992. The detection limits of the method were 0.15-0.8 μg/kg, and the recoveries of the target compounds were 85.9%-116.5%. The relative standard deviations were 1.4%-8.2%, which indicates good reproducibility. The proposed method was successfully applied to actual sample detection, and 2,6-dichloro-3-methyl-1,4-benzoquinone (2,6-DCMBQ) was detected in grass carp. The proposed method is convenient, sensitive, accurate, and suitable for the simultaneous determination of five HBQs in aquatic products. Moreover, the developed method provides a reliable reference for the routine monitoring of trace HBQs in food samples.

Method development and validation for accurate and sensitive determination of terpenes in bio-based (citrus) oils by single quadrupole gas chromatography-mass spectrometry (GC/MS)

Studies for the utilize of valuable components such as terpenes in essential oils of citrus and similar valuable wastes to the environment have been progressively proceeding in recent years. This study presented the method development and validation studies for simple, accurate and sensitive determination of twenty-four terpenes in bio-based (citrus) oils by gas chromatography/mass spectrometry (GC/MS). The validation study covered the parameters of linearity of the matrix-matched calibration curve, sensitivity (the limit of detection (LOD) and the limit of quantification (LOQ)), accuracy (recovery), precision, matrix effect, and measurement uncertainty. In the method development, all terpenes had the best chromatographic conditions at 250 °C inlet temperature, 1:15 split ratio, and 2 µL injection volume with a few exceptions. The measurement range had dynamic linearity between 0.50 mg/L and 100 mg/L in the calibration curves possessing a higher than 0.996 correlation coefficient for all terpenes. The LODs for all terpenes were obtained to be in the range of 0.08 mg/L and 0.16 mg/L, and the ranges of LOQ for terpenes were determined from 0.24 mg/L to 0.48 mg/L. Recoveries for accuracy ranged from 80.86% to 93.17% with relative standard deviations (RSDs) below 15% (3.28–10.19%). In precision, acceptable recovery (average: 86.13%, ranging from 79.84% to 97.29%) and RSD values (average: 7.14%, ranging from 1.70% to 13.90%) were obtained for all terpenes at three different concentrations. D-Limonene (58.56–78.08%), Myrcene (8.19–17.21%), Valencene (0.09–5.91%), Linalool (0.45–2.99%), Beta-Ocimene (0.36–2.86%), Nerol (0.19–7.98%), and Alpha-Pinene (0.38–1.47%)are the most abundant terpenes in real samples. These results indicate that this method represents an effective, reliable, and lower cost alternative to current-use analysis methods for terpenes in bio-based (citrus) oil samples.