Compensation for matrix effects in gas chromatography–tandem mass spectrometry using a single point standard addition

System stability and signal enhancement with analyte protectants: Gas chromatography analysis of oxygenated-polycyclic aromatic hydrocarbons

Matrix effects can affect detection limits, precision, and accuracy and lead to signal enhancement or suppression effects in gas chromatography analysis. Analyte protectants, such as shikimic acid and gluconolactone, can imitate the effect of matrix components and reduce the differences in matrix effect between samples. This study aimed to investigate the ability of analyte protectants to enhance gas chromatography detector signals of different oxygenated-polycyclic aromatic hydrocarbons. Addition of 100 μg L-1 shikimic acid and 200 μg L-1 gluconolactone effectively enhanced detector response of the investigated target compounds. Addition of a higher content of analyte protectants did not result in any further enhancement. It was found that between four and eleven consecutive injections of a standard solution with analyte protectants were required to obtain a stable compound response. The long-term signal stability was then maintained with subsequent injections, though an overall negative drift of the system was observed over the sequence of 200 investigated injections. Analysis of the actual sample matrix instead of standards in pure solvent, as presented in this study, could also be a way to minimize the required number of injections. Shikimic acid and gluconolactone were first and foremost able to enhance signals of oxygenated-polycyclic aromatic hydrocarbons with similar functional groups (hydroxyl) in their molecular structure. It can be relevant to consider alternative analyte protectants with different functional groups according to the type of target compounds investigated.

Standard addition method for rapid, cultivation-independent quantification of Legionella pneumophila cells by qPCR in biotrickling filters

Cultivation-independent molecular biological methods are essential to rapidly quantify pathogens like Legionella pneumophila (L. pneumophila) which is important to control aerosol-generating engineered water systems. A standard addition method was established to quantify L. pneumophila in the very complex matrix of process water and air of exhaust air purification systems in animal husbandry. Therefore, cryopreserved standards of viable L. pneumophila were spiked in air and water samples to calibrate the total bioanalytical process which includes cell lysis, DNA extraction, and qPCR. A standard addition algorithm was employed for qPCR to determine the initial concentration of L. pneumophila. In mineral water, the recovery rate of this approach (73%-134% within the concentration range of 100-5000 Legionella per mL) was in good agreement with numbers obtained from conventional genomic unit (GU) calibration with DNA standards. In air samples of biotrickling filters, in contrast, the conventional DNA standard approach resulted in a significant overestimation of up to 729%, whereas our standard addition gave a more realistic recovery of 131%. With this proof-of-principle study, we were able to show that the molecular biology-based standard addition approach is a suitable method to determine realistic concentrations of L. pneumophila in air and process water samples of biotrickling filter systems. Moreover, this quantification strategy is generally a promising method to quantify pathogens in challenging samples containing a complex microbiota and the classical GU approach used for qPCR leads to unreliable results.

Simultaneous Analysis of 272 Pesticides in Agricultural Products by the QuEChERS Method and Gas Chromatography with Tandem Mass Spectrometry

The aim of this study is to develop a rapid and accurate method for simultaneous analysis of multi-residue pesticides and conduct pesticide monitoring in agricultural products produced by the production and distribution stage in Korea. The representative agricultural products were selected as brown rice, soybean, potato, mandarin, and green pepper and developed using gas chromatography with tandem mass (GC-MS/MS) for the analysis of 272 pesticide residues. The experimental samples were extracted by the QuEChERS-EN method and then cleaned up by using d-SPE, including MgSO4 and primary secondary amine (PSA) sorbents. The established method was validated in accordance with Codex CAC-GL/40, and the limit of quantitation (LOQ) was determined to be 0.01 mg/kg. A total of 243 pesticides satisfied the guidelines in five samples at three levels with values of 60 to 120% (recovery) and ≤45% (coefficient of variation, CV). The remaining 29 pesticides did not satisfy the guidelines, and these pesticides are expected to be used as a screening method for the routine inspection of agricultural products. As a result of analyzing 223 agricultural products in South Korea by applying the simultaneous analysis method, none of the detected levels in the samples exceeded the standard values based on maximum residue limits (MRLs). The developed method in this study will be used to inspect residual pesticides in agricultural products, and it is anticipated to contribute to the distribution of safe agricultural products to consumers.

Matrix Effect Evaluation in GC/MS-MS Analysis of Multiple Pesticide Residues in Selected Food Matrices

Multi-analyte methods based on QuEChERS sample preparation and chromatography/mass spectrometry determination are indispensable in monitoring pesticide residues in the feed and food chain. QuEChERS method, even though perceived as convenient and generic, can contribute to sample matrix constituents' introduction to the measuring system and possibly affect analytical results. In this study, matrix effects (ME) were investigated in four food matrices of plant origin (apples, grapes, spelt kernels, and sunflower seeds) during GC-MS/MS analysis of >200 pesticide residues using QuEChERS sample preparation. Data analysis revealed considerable analyte signal enhancement and suppression: strong enhancement was observed for the majority of analytes in two matrices within the commodity groups with high water content-apples, and high acid and water content-grapes (73.9% MES and 72.5% MEA, and 77.7% MES and 74.9% MEA, respectively), while strong suppression was observed for matrices within the commodity groups with high starch/protein content and low water and fat content-spelt kernels, and high oil content and very low water content-sunflower seeds (82.1% MES and 82.6% MEA, and 65.2% MES and 70.0% MEA, respectively). Although strong matrix effects were the most common for all investigated matrices, the use of matrix-matched calibration for each sample type enabled satisfactory method performance, i.e., recoveries for the majority of analytes (up to roughly 90%, depending on the fortification level and matrix type), which was also externally confirmed through participation in proficiency testing schemes for relevant food commodity groups with the achieved z-scores within acceptable range ≤ |2|.

Organochlorine pesticides in vegetable oils: An overview of occurrence, toxicity, and chromatographic determination in the past twenty-two years (2000-2022)

Organochlorine pesticides (OCPs) are used globally to control pests in the food industry. However, some have been banned due to their toxicity. Although they have been banned, OCPs are still discharged into the environment and persist for long periods of time. Therefore, this review focused on the occurrence, toxicity, and chromatographic determination of OCPs in vegetable oils over the last 22 years (2000-2022) (111 references).Literature search shows that OCPs kill pests by destroying endocrine, teratogenic, neuroendocrine, immune, and reproductive systems. However, only five studies investigated the fate of OCPs in vegetable oils and the outcome revealed that some of the steps involved during oil processing introduce more OCPs. Moreover, direct chromatographic determination of OCPs was mostly performed using online LC-GC methods fitted with oven transfer adsorption desorption interface. While indirect chromatographic determination was favored by QuEChERS extraction technique, gas chromatography frequently coupled to electron capture detection (ECD), gas chromatography in selective ion monitoring mode (SIM), and gas chromatography tandem mass spectrometry (GC-MS/MS) were the most common techniques used for detection. However, the greatest challenge still faced by analytical chemists is to obtain clean extracts with acceptable extraction recoveries (70-120%). Hence, more research is still required to develop greener and selective extraction methods toward OCPs, thus improving extraction recoveries. Moreover, advanced techniques like gas chromatography high resolution mass spectrometry (GC-HRMS) must also be explored. OCPs prevalence in vegetable oils varied greatly in various countries, and concentrations of up to 1500 µg/kg were reported. Additionally, the percentage of positive samples ranged from 1.1 to 97.5% for endosulfan sulfate.

Optimization of a Multi-Residue Analytical Method during Determination of Pesticides in Meat Products by GC-MS/MS

In this study, a multi-residue analysis was developed for 32 compounds, including pesticides and metabolites, in five meat products using gas chromatography-tandem mass spectrometry (GC-MS/MS). The validation of the developed analytical method was also evaluated in accordance with Codex Alimentarius guidelines. Aminopropyl (NH2), C18, and florisil solid phase extraction (SPE) cartridges were used to evaluate and optimize the cleanup procedure of the tested samples prior to GC-MS/MS analysis. Based on the analytical performance, the C18 SPE cartridge was deemed to be the most suitable among the examined SPE cartridges. The optimized method demonstrated that 29 out of 32 tested compounds acquired good linearity (R2 ≥ 0.99), and 25 tested compounds displayed the method limit of quantification (MLOQ) ≤ 0.01 mg/kg. Out of the 32 tested compounds, only 21 compounds met the acceptable analytical criteria for the lard and tallow samples, compared to 27 compounds in the beef, pork, and chicken samples that falls within the acceptable standards for recovery (70-120%) and analytical precision (relative standard deviation RSD ≤ 20%). The average matrix effect was widely varied (20.1-64.8%) in the studied meat samples that were affected by either ion enhancement or suppression. In particular, in the lard sample, 13 compounds showed poor recovery and analytical precision due to ion suppression. Thus, the matrix effect (ME) was considered a critical factor during multi-residue pesticide analysis in different meat products. In conclusion, this developed analytical method can be used as a routine monitoring system for residual pesticide analysis in livestock products with acceptable analytical standards. Further meticulous analytical studies should be optimized and validated for multi-residue pesticide analysis in diversified meat products.

Protein Albumin Manipulation and Electrical Quantification of Molecular Dielectrophoresis Responses for Biomedical Applications

Research relating to dielectrophoresis (DEP) has been progressing rapidly through time as it is a strong and controllable technique for manipulation, separation, preconcentration, and partitioning of protein. Extensive studies have been carried out on protein DEP, especially on Bovine Serum Albumin (BSA). However, these studies involve the usage of dye and fluorescent probes to observe DEP responses as the physical properties of protein albumin molecular structure are translucent. The use of dye and the fluorescent probe could later affect the protein's physiology. In this article, we review three methods of electrical quantification of DEP responses: electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and capacitance measurement for protein BSA DEP manipulation. The correlation of these methods with DEP responses is further discussed. Based on the observations on capacitance measurement, it can be deduced that the electrical quantifying method is reliable for identifying DEP responses. Further, the possibility of manipulating the protein and electrically quantifying DEP responses while retaining the original physiology of the protein and without the usage of dye or fluorescent probe is discussed.

Speciation and Semiquantification of Nitrogen-Containing Species in Complex Mixtures: Application to Plastic Pyrolysis Oil

Plastic pyrolysis oil is of particular interest for waste management in the current context of a circular economy. Due to their uncontrolled origin, these oils may contain significant amount of unwanted compounds such as nitrogen-containing species. These compounds are known to be catalyst poisons during refining processes. Therefore, the removal of these species is crucial, and their characterization from structural and quantification points of view is essential for this purpose. This study presents a method to specify and quantify nitrogen-containing classes in a plastic pyrolysis oil by direct infusion mass spectrometry. Two steps were used, namely structural characterization to select suitable standards and semiquantification. The structural speciation of nitrogen-containing compounds was first performed by electrospray ionization Fourier transform mass spectrometry, followed by tandem mass spectrometry using high-resolution mass isolation and infrared multiphoton dissociation fragmentation. A semiquantification is then performed by the standard addition method, which is very appropriate for such complex matrices. Aromatic cores such as quinoline and quinoxaline were evidenced for both N₁ and N₂ classes, allowing 2-methylquinoxaline and 2-butylquinoline to be proposed as standards for the semiquantification of N₂- and N₁-containing compounds, respectively. The amount of nitrogen detected from the sum of the individual species was consistent with the bulk analysis. The reported methodology can be applied to numerous other families of compounds in various other complex matrices.

Oleamide as analyte protectant in GC analysis of THC and its metabolites in blood

Methods for the analysis of cannabinoids in bio-matrices are continually being developed, to achieve a proper sensitivity required for their detection and accuracy in their quantification. The presented paper shows that the analytical sensitivity of GC-MS to THC and its metabolites in blood samples can be significantly increase by oleamide (OLA) addition to the examined sample, which evokes the matrix effect of transient character. The magnitude of signal increment resulting from oleamide presence in the examined sample is the greatest for THC metabolites and depends on oleamide concentration in the examined sample. The use of transient matrix effect to increase the sensitivity of the analysis can be applied not only in QuEChERS procedure, which is applied in the described experiments, but also in other blood sample preparation methods. Evoking the transient matrix effect by means of OLA in the experimental analytical quantitation of THC and its metabolites in blood allowed to lower limit of detection (LOD) approximately by 20.5%, 87.6% and 90.1% in the case of THC, THC-OH and THC-COOH, respectively.

Improving the sensitivity of estimating CBD and other xenobiotics in plasma samples: Oleamide-induced transient matrix effect

The paper discusses the matrix effect evoked by oleamide (OLA), a compound frequently found in samples processed and/or stored in lab polypropylene vials or disposable syringes. In the case of many substances a higher response for their samples containing OLA than for net solutions is observed. The analyte signal gain resulting from OLA presence in the examined sample depends on the ratio of OLA concentration to analyte concentration. A characteristic feature of the matrix effect evoked by oleamide is its short duration, which makes the chromatographic data (retention value and signal magnitude of examined compound) repeatable and reproducible. The identified "transient matrix effect" may significantly increase the sensitivity of many analytical procedures employing GC. Evoking the transient matrix effect by means of OLA in the experimental analytical quantitation of cannabidiol in plasma allowed to lower its limit of detection (LOD) by more than 50 %.

Sandwich injection and analyte protectants as a way to decrease the drift due to matrix effect between bracketing calibration in GC-MS/MS: A case study

In pesticide residues analysis, the drift is the difference between the concentration of two bracketing calibrations in the same batch. According to the SANTE/12682/2019 guideline a criterion of ±30% must be met or positive samples should be reanalyzed. This study aimed to investigate, for the first time, the efficiency of using analyte protectants (Aps) and the sandwich injection approach (SIA) to eliminate the drift between bracketing matrix matched-calibrations taking strawberry as an example. The strawberry samples were prepared according to the citrate-buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure, followed by solvent exchange from acetonitrile to n-hexane:actone (9:1). Two batches were injected with the same sequence on GC-MS/MS, the only difference was that the first batch was without Aps and the second was with Aps. The sequence of the batch was as follows: blank solvent injection, 5 strawberry matched-calibrations at 0.05 μg/ml, separated by 20 blank strawberry injections after each strawberry matched-calibration injection. The drift was measured by considering the results of the first calibration as 100% and comparing the rest 4 injections with it. After 20 injections, out of the studied 219 pesticides, more than half of the pesticides fell out of criteria when analyte protectants were not used, and by the end of the samples batch 95% of the analytes were out of criteria. Only 8% of the studied analytes were out of criteria for the Aps batch after 20 injections. In the end of the 80 samples batch, 17% were out of criteria. Furthermore, at the end of the protected matrix-matched calibration batch, 90% of the pesticides had an RSD less than 15% in comparison with only 5% of the analytes for the non-protected batch. Moreover, the non-protected batch had an obvious negative drift in comparison with the protected batch. For example, the number of pesticides that had a lower result in the second matrix matched-calibration for the non-protected batch was more than twice the number in the protected batch (194 compared to 91 out of 219 pesticides for both experiments).

Electrochemically generated standard additions for gas chromatography: case study of O2 and H2 analysis

The method of standard additions with electrochemically generated spikes was elaborated and demonstrated on examples of O₂ and H₂ chromatographic analysis in standard mixtures. While oxygen portions may be generated directly in a stream of inert gas by solid-state electrolysis, a standard hydrogen-containing mixture is introduced into the electrochemical cell followed by controlled electrochemical consumption of hydrogen. In both cases the analysis characteristics are similar: the recovery is 90-120% and exhibits a slight sensitivity towards the flow rate of the analyzed oxygen-containing gas. The relative error associated with the non-ideal proportionality between the spike and chromatograph signal is within 10-15% for operation in the optimum concentration region. The major factors affecting the accuracy of the analysis are associated with detector characteristics, particularly influenced by the sample dilution, precision of flow controllers and linearity of the function "signal vs. spike." The lowest errors of determination were found to be for the analyte content range 1-5% while at oxygen and hydrogen concentrations below 0.5% the interference of the signal associated with other components may lead to overestimated results. Graphical abstract Scheme of the gas line used for oxygen determination with electrochemically generated standard additions (method 2). Inset shows an example of oxygen content calculation using the dependency "chromatographic signal vs. current."

Sorbent-excluding sample preparation method for GC-MS pesticide analysis in apple peel

Apple peel is frequently exposed to pesticides, especially in the last stages of the pesticide treatment practice. For a certain period, peel retains most of the applied pesticides, which precisely indicates the presence of pesticide residues. This study was conducted to establish and evaluate the method for the residue analysis of pyrimethanil, cyprodinil, trifloxystrobin, bifenthrin and boscalid by GC-MS in peel of Granny Smith, Golden Delicious and Idared varieties. The method consisted of few steps, without the routine usage of sorbents, and resulted in efficient removal of waxes, targeted as main interferences in GC-MS analysis. The matrix effect, boscalid selectivity issue, trend of lower trueness for bifenthrin in all matrices and for all analytes in Granny Smith matrix were in some way associated with the waxes. Finally, the method was applied to the analysis of three varieties of apple orchard samples, after 9 and 5 months of treatment with commercial formulations that contain pyrimethanil, cyprodinil and boscalid as active ingredients. Since the developed method consisted of few steps and used nontoxic and economic reagents, it could be implemented as a fast, economic and reliable screening method.

Determination of twenty pharmaceutical contaminants in soil using ultrasound-assisted extraction with gas chromatography-mass spectrometric detection

In this paper, an analytical method for the simultaneous determination of twenty pharmaceuticals (eight non-steroidal anti-inflammatory drugs, five oestrogenic hormones, two antiepileptic drugs, two β-blockers, and three antidepressants) in soils was developed. The optimal method included ultrasound-assisted extraction, a clean-up step on a silica gel column, derivatization using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and 1% trimethylchlorosilane (TMCS) in pyridine and ethyl acetate (2:1:1, v/v/v) for 30 min at 60 °C, and determination by gas chromatography-mass spectrometry working in the selected ion monitoring mode. This affords good resolution, high sensitivity and reproducibility, and freedom from interferences even from complex matrices such as soils. The method detection limits ranged from 0.3 to 1.7 ng g^-1, the intra-day precision represented as RSDs ranged from 1.1 to 10.0%, and the intra-day accuracy from 81.3 to 119.7%. The absolute recoveries of the target compounds were above 80%, except for valproic acid and diethylstilbestrol. The developed method was successfully applied in the analysis of the target compounds in soils collected in Poland. Among the 20 pharmaceuticals, 12 compounds were detected at least once in the soils. The determination of antiepileptic drugs, β-blockers, and antidepressants was also performed for the first time.

The detection of drugs of abuse and pharmaceuticals in drinking water using solid-phase extraction and liquid chromatography-mass spectrometry

Pharmaceuticals and drugs of abuse including novel psychoactive substances (NPS) are emerging as newer contaminants in the aquatic environment. The presence of such pollutants has implications on the environment as well as public health and therefore their identification is important when monitoring water quality. This research presents a new method for the simultaneous detection of 20 drugs of abuse and pharmaceuticals in drinking water, including 15 NPS, three traditional illicit drugs and two antidepressants. The developed method is based on the use of solid-phase extraction (SPE) followed by liquid chromatography-mass spectrometry (LC-MS). The SPE recoveries for the majority of target analytes ranged between 62 and 107%. The method detection and quantification limits ranged between 0.01 and 1.09 ng/L and 0.02-3.64 ng/L respectively. Both instrumental and method precisions resulted in relative standard deviations <15.04%, with an accuracy of < ±8.66%. The results show that LC-MS can be an alternative to the more popular technique of liquid chromatography-tandem mass spectrometry for the analysis of drugs of abuse and pharmaceuticals in drinking water. This newly developed simultaneous detection method has been applied to drinking water collected from the East Anglia region of the UK. Citalopram, cocaine, fluoxetine, ketamine, mephedrone, methamphetamine and methylone were detected at the range of 0.14 and 2.81 ng/L. This is the first time that the two NPS mephedrone and methylone, have been detected in UK drinking water.

Validation Including Uncertainty Estimation of a GC⁻MS/MS Method for Determination of Selected Halogenated Priority Substances in Fish Using Rapid and Efficient Lipid Removing Sample Preparation

A rapid method is proposed for the determination of selected H₂SO₄ stable organic compounds—eight organochlorines (OCs; hexachloro-1,3-butadiene, pentachlorobenzene, hexachlorobenzene, hexachlorocyclohexane—HCH—isomers, heptachlor) and six polybrominated diphenyl ethers (PBDEs; BDE-28, 47, 99, 100, 153, 154)—in fish samples. In the method, a modified QuEChERS (quick, easy, cheap, effective, rugged and safe) sample preparation using pH-tuned dispersive liquid–liquid microextraction (DLLME) and H₂SO₄ digestion fish extract clean-up is followed by gas chromatography–triple quadrupole tandem mass spectrometry (GC–QqQ-MS/MS) analysis. The method was validated in terms of linearity, limits of the method, recovery, accuracy, analysis of standard reference material (NIST SRM 1946), and estimation of combined uncertainty of the measurement (top-down approach). For validation, chub composite samples were used, and subsequently, the method was successfully applied to analysis of real samples of eight fish species. Finally, the method passed the analytical Eco-Scale evaluation as “an acceptable green analysis method”, and showed its advantages (simplicity, rapidity, low cost, high extract clean-up efficiency, good sensitivity) when compared to other reported QuEChERS based methods.

Quantification of folpet and phthalimide in tea and herbal infusions by LC- high-resolution MS and GC-MS/MS

Two methods based on a modified QuEChERS sample preparation and either LC coupled to atmospheric pressure ionisation and high-resolution MS or GC coupled to electron ionisation and tripled quadrupole MS have been assessed for the quantification of folpet and phthalimide in tea and other dry herbal infusions. Both methods have been fully validated in green tea and further checked in black tea, verbena and rooibos, and they performed according to the SANTE/11813/2017 criteria at the target LOQ concentration level (50 µg/kg). These methods allow the accurate quantification of folpet in the selected matrices according to the new EU residue definition, which includes phthalimide. Phthalimide is the main metabolite and degradation product of folpet, although according to recent studies, it could be generated from different sources than folpet breakdown, such as food processing or analysis by GC.

Gas chromatography-isotope dilution mass spectrometry method validation for target pesticides in soybeans

The production of certified reference materials requires the application of highly accurate methods for characterisation. A gas chromatography-isotope dilution mass spectrometry method, setting ambitious performance criteria, was developed for eight selected pesticides in soybeans. Pressurised liquid extraction was followed by automated gel-permeation chromatography and solid-phase extraction clean-up. Pesticides identification respected a Commission Decision and guidelines of the Directorate General for Health and Food Safety (DG SANTE). Reliable quantification involved stable isotopically labelled analogues as internal standards. Validation, according to ISO/IEC 17,025 and DG SANTE guidelines, assessed linearity, LOD/LOQ, trueness, selectivity, precision, stability and robustness. Mean recoveries ranges (83-109%, relative standard deviations < 3%), repeatability (2.2-4.8%), day-to-day variation (0.6-4.2%) and combined uncertainty (1.2-4.2%) were fit for purpose. The method is highly accurate and suitable for certification of the selected pesticides in soybean matrix reference material. Chemical compounds studied in this article: Diazinon (PubChem CID: 3017); malathion (PubChem CID: 4004); chlorpyrifos (PubChem CID: 2730); captan (PubChem CID: 8606); endosulfan (PubChem CID: 3224); tebuconazole (PubChem CID: 86,102); iprodione (PubChem CID: 37,517); cypermethrin (PubChem CID: 2912).

Combined use of a modifier gas generator, analyte protectants and multiple internal standards for effective and robust compensation of matrix effects in gas chromatographic analysis of pesticides

In the analysis of pesticides performed with gas chromatography, the quantitative performance of measurements can be severely compromised by phenomena known as matrix effects. In seeking a solution to the problem of matrix effects, the application of a modifier gas generator (MGG) was investigated in this study, together with analyte protectants and multiple internal standards. Ethylene glycol (EG) was used as modifier gas and matrix effects in GCMS analysis were then evaluated by using the extracts of various food commodities. MGG was used in combination with other known methods of matrix effect compensation and its performance in reducing matrix effects tested. We have found that by combining MGG with conventional analyte protectants, matrix effects were substantially reduced for most of pesticides. Use of EG was especially effective for organophosphate pesticides and those with amino groups. Using this approach, the shortcomings of conventional analyte protectants were remedied. Although neither EG nor analyte protectants could sufficiently reduce the matrix effects for certain classes of pesticides, this limitation could be overcome with the use of multiple internal standards (IS) in the analysis. Finally, it was shown that the method we developed could achieve better analytical performance than the matrix-matched calibration method. Our method was robust with respect to the variation of food matrix components, so its application to real-world analyses would be practical and promising.

Evaluation of Matrix Effects in Quantifying Microbial Secondary Metabolites in Indoor Dust Using Ultraperformance Liquid Chromatograph-Tandem Mass Spectrometer

Background

Liquid chromatography-tandem mass spectrometry (LC-MSMS) for simultaneous analysis of multiple microbial secondary metabolites (MSMs) is potentially subject to interference by matrix components.

Methods

We examined potential matrix effects (MEs) in analyses of 31 MSMs using ultraperformance LC-MSMS. Twenty-one dust aliquots from three buildings (seven aliquots/building) were spiked with seven concentrations of each of the MSMs (6.2 pg/μl-900 pg/μl) and then extracted. Another set of 21 aliquots were first extracted and then, the extract was spiked with the same concentrations. We added deepoxy-deoxynivalenol (DOM) to all aliquots as a universal internal standard. Ten microliters of the extract was injected into the ultraperformance LC-MSMS. ME was calculated by subtracting the percentage of the response of analyte in spiked extract to that in neat standard from 100. Spiked extract results were used to create a matrix-matched calibration (MMC) curve for estimating MSM concentration in dust spiked before extraction.

Results

Analysis of variance was used to examine effects of compound (MSM), building and concentration on response. MEs (range: 63.4%-99.97%) significantly differed by MSM (p < 0.01) and building (p < 0.05). Mean percent recoveries adjusted with DOM and the MMC method were 246.3% (SD = 226.0) and 86.3% (SD = 70.7), respectively.

Conclusion

We found that dust MEs resulted in substantial underestimation in quantifying MSMs and that DOM was not an optimal universal internal standard for the adjustment but that the MMC method resulted in more accurate and precise recovery compared with DOM. More research on adjustment methods for dust MEs in the simultaneous analyses of multiple MSMs using LC-MSMS is warranted.

Identification and characterization of matrix components in spinach during QuEChERS sample preparation for pesticide residue analysis by LC-ESI-MS/MS, GC-MS and UPLC-DAD

In this article matrix components in spinach were investigated in detail. The samples were prepared using two QuEChERS (quick, easy, cheap, effective, rugged and safe) methods, AOAC and CEN. Liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS), gas chromatography-mass spectrometry (GC-MS) and ultra performance liquid chromatography-diode array detector (UPLC-DAD), were applied for component identification. The strategies of identification by LC-ESI-MS/MS include accurate mass spectra of the parent ion, comparison with previous literature data and investigation of the mass spectral decomposition pattern. Overall, fourteen components were identified by LC-ESI-MS/MS in each methods of AOAC and CEN, which were phytosteroids, flavonoids, fatty acids and fatty acid amides. Fifty components using AOAC method and fifty-seven components using CEN method were identified in GC-MS by comparing mass data with the National Institute of Standards and Technology (NIST, U.S.) database. The results indicate that the major components of the matrix are terpenoids, fatty acids and fatty acid esters. Moreover, three pigments (neoxanthin, violaxanthin and lutein) in the AOAC method and eight pigments (neoxanthin, violaxanthin, zeaxanthin, lutein, chlorophyll a, chlorophyll b, pheophytin a and beta-carotene) in the CEN method that gave a characteristics peak at 440 nm were identified by the UPLC-DAD. According to the sample preparation condition using different amounts of graphitized carbon black (GCB) in this study, the AOAC method had higher matrix component removal efficiency than the CEN method. A better understanding of matrix components would increase the current knowledge for improvement of existing QuEChERS methodology, as well as contribute to new method developments.

Analytical features of microwave plasma-atomic emission spectrometry (MP-AES) for the quantitation of manganese (Mn) in wild grape (Vitis coignetiae) red wines: Comparison with inductively coupled plasma-optical emission spectrometry (ICP-OES)

The analytical features of MP-AES for the determination of Mn in wine were studied as compared with ICP-OES. The optimum spectral line (403.076 nm) of MP-AES was different from that (259.373 nm) of ICP-OES. Significant matrix effect was observed with MP-AES, but not with ICP-OES. A simple and cost-effective MP-AES for the quantitation of Mn in wild grape (Vitis coignetiae) red wines were developed and validated. A standard addition method was used to compensate the matrix effects. The sensitivity of MP-AES was comparable to that of ICP-OES. MP-AES was sensitive, precise, accurate and reliable. The Mn concentration in the wild grape wines was in the range of 502-3627 μg L^-1. MP-AES had a distinct drawback of low matrix tolerance. However, MP-AES had a clear advantage of the low running cost due to the use of nitrogen gas generated from air with a nitrogen generator.

Compensation for matrix effects in GC analysis of pesticides by using cucumber extract

Matrix effects (MEs) can adversely affect quantification in pesticide residue analysis using GC. Analyte protectants (APs) can effectively interact with and mask active sites in the GC system, and are added individually or in combination to sample extracts and calibration solutions to minimize errors related to MEs. Unfortunately, APs cannot sufficiently compensate for MEs in all cases. Plant extracts, containing a broad range of natural compounds with AP properties, can also be used for this purpose. In this study, the applicability of cucumber extract as a natural AP mixture was investigated both alone and in combination with traditional APs. Extracts of two selected difficult matrices (onion and garlic) were prepared according to the citrate-buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure. ME values of 40 representative GC-amenable pesticides were compared when calibrating against standards in pure solvent and in cucumber extract, with and without the addition of APs. Using a GC system with a contaminated inlet liner, the use of a cucumber-based calibration solution decreased MEs remarkably. The combination of APs with cucumber raw extract further decreased MEs, resulting in more than 85% of the tested pesticides showing ≤ 10% ME in onion and ≤ 20% ME in garlic. These results demonstrate that the preparation of calibration standards based on cucumber extracts (with or without the addition of APs) is a very useful and practical approach to compensate for MEs in pesticide residue analysis using QuEChERS and GC-MS/MS. The use of various internal standards is furthermore critically discussed.

Inorganic arsenic contents in infant rice powders and infant rice snacks marketed in Korea determined by a highly sensitive gas chromatography-tandem mass spectrometry following derivatization with British Anti-Lewisite

Toxic inorganic arsenic (iAs) has been reported to be present in high quantity in rice and rice-based products. The inorganic arsenic contents in infant foods (n = 59) of ready-to-cook infant rice powders and infant rice snacks marketed in Korea were determined by a highly sensitive gas chromatography-tandem mass spectrometry (GC-MS/MS). The mean iAs contents in the infant rice powder and infant rice snacks were 65.6 and 54.0 μg/kg, respectively. The percentages of rice powders and rice snack containing iAs over the maximum level (100 μg/kg) set by EU for the infant foods were found to be 21, and 6%, respectively. This result clearly suggested that regulation regarding the maximum limit of iAs levels for the baby rice products is urgently needed to be set in Korea. This represents the first report on the iAs levels in ready-to-cook infant rice powder products and infant snacks marketed in Korea.

Current state of bioanalytical chromatography in clinical analysis

Chromatographic methods have become popular in clinical analysis in both routine and research laboratories.

Inorganic arsenic contents in ready-to-eat rice products and various Korean rice determined by a highly sensitive gas chromatography-tandem mass spectrometry

Rice and rice products have been reported to contain high contents of toxic inorganic arsenic (iAs). The inorganic arsenic contents in microwavable ready-to-eat rice products (n=30) and different types of Korean rice (n=102) were determined by a gas chromatography-tandem mass spectrometry (GC-MS/MS). The method showed low limit of detection (0.015pg), high intra- and inter-day repeatability (<7.3%, RSD), and recovery rates (90-117%). The mean iAs content in the ready-to-eat rice products was 59μgkg^-1 (dry weight basis). The mean iAs contents in polished white, brown, black, and waxy rice were 65, 109, 91, and 66μgkg^-1, respectively. The percentages of ready-to-eat rice products, white, brown, black, and waxy rice containing iAs over the maximum level (100μgkg^-1) set by EU for the infant foods were 17, 4, 70, 36 and 0%, respectively.

Matrix Effects and Interferences of Different Citrus Fruit Coextractives in Pesticide Residue Analysis Using Ultrahigh-Performance Liquid Chromatography-High-Resolution Mass Spectrometry

The matrix effects of ethyl acetate extracts from seven different citrus fruits on the determination of 80 pesticide residues using liquid chromatography coupled to high-resolution time-of-flight mass spectrometry (UHPLC-(ESI)-HR-TOF) at 4 GHz resolution mode were studied. Only 20% of the evaluated pesticides showed noticeable matrix effects (ME) due to coelution with natural products between t_R = 3 and 11 min. Principal component analysis (PCA) of the detected coextractives grouped the mandarins and the orange varieties, but separated lemon, oranges, and mandarins from each other. Matrix effects were different among species but similar between varieties, forcing the determination of pesticide residues through matrix-matched calibration curves with the same fruit. Twenty-three natural products (synephrine, naringin, poncirin, glycosides of hesperitin, limonin, nomilin, and a few fatty acids, among others) were identified in the analyzed extracts. Twelve of the identified compounds coeluted with 28 of the pesticides under study, causing different matrix effects.

Dilution standard addition calibration: A practical calibration strategy for multiresidue organic compounds determination

Among calibration approaches for organic compounds determination in complex matrices, external calibration, based in solutions of the analytes in solvent or in blank matrix extracts, is the most applied approach. Although matrix matched calibration (MMC) can compensates the matrix effects, it does not compensate low recovery results. In this way, standard addition (SA) and procedural standard calibration (PSC) are usual alternatives, despite they generate more sample and/or matrix blanks consumption need, extra sample preparations and higher time and costs. Thus, the goal of this work was to establish a fast and efficient calibration approach, the diluted standard addition calibration (DSAC), based on successive dilutions of a spiked blank sample. In order to evaluate the proposed approach, solvent calibration (SC), MMC, PSC and DSAC were applied to evaluate recovery results of grape blank samples spiked with 66 pesticides. Samples were extracted with the acetate QuEChERS method and the compounds determined by ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). Results indicated that low recovery results for some pesticides were compensated by both PSC and DSAC approaches. Considering recoveries from 70 to 120% with RSD <20% as adequate, DSAC presented 83%, 98% and 100% of compounds meeting this criteria for the spiking levels 10, 50 and 100μgkg(-1), respectively. PSC presented same results (83%, 98% and 100%), better than those obtained by MMC (79%, 95% and 97%) and by SC (62%, 70% and 79%). The DSAC strategy showed to be suitable for calibration of multiresidue determination methods, producing adequate results in terms of trueness and is easier and faster to perform than other approaches.

One step derivatization with British Anti-Lewsite in combination with gas chromatography coupled to triple-quadrupole tandem mass spectrometry for the fast and selective analysis of inorganic arsenic in rice

We developed a new fast and selective analytical method for the determination of inorganic arsenic (iAs) in rice by a gas chromatography - tandem mass spectrometry (GC-MS/MS) in combination with one step derivatization of inorganic arsenic (iAs) with British Anti-Lewsite (BAL). Two step derivatization of iAs with BAL has been previously performed for the GC-MS analysis. In this paper, the quantitative one step derivatization condition was successfully established. The GC-MS/MS was carried out with a short nonpolar capillary column (0.25 mm × 10 m) under the conditions of fast oven temperature ramp rate (4 °C/s) and high linear velocity (108.8 cm/s) of the carrier gas. The established GC-MS/MS method showed an excellent linearity (r(2) > 0.999) in a tested range (0.2-100.0 μg L(-1)), ultra-low limit of detection (LOD, 0.08 pg), and high precision and accuracy. The GC-MS/MS technique showed far greater selectivity (22.5 fold higher signal to noise ratio in rice sample) on iAs than GC-MS method. The gas chromatographic running time was only 2.5 min with the iAs retention time of 1.98 min. The established method was successfully applied to quantify the iAs contents in polished rice. The mean iAs content in the Korean polished rice (n = 27) was 66.1 μg kg(-1) with the range of 37.5-125.0 μg kg(-1). This represents the first report on the GC-tandem mass spectrometry in combination with the one step derivatization with BAL for the iAs speciation in rice. This GC-MS/MS method would be a simple, useful and reliable measure for the iAs analysis in rice in the laboratories in which the expensive and element specific HPLC-ICP-MS is not available.

Determination of matrix effects occurred during the analysis of organochlorine pesticides in agricultural products using GC-ECD

Matrix effects observed during the multiresidue analysis of seven organochlorine pesticides in six different agricultural products with GC-ECD were assessed. The presence of matrix coextractives, a major cause of observed matrix effects, directly and/or indirectly influenced the chromatographic responses of some pesticides. Two types of external calibrations, solvent calibration (SC) and matrixmatched calibration (MC), were used to assess matrix effects. Greater matrix effects were observed at the lower concentrations of each pesticide. The extent of matrix effects varied unpredictably with matrix type. Among the analyzed pesticides, iprodione, cyhalothrin, and cypermethrin exhibited greater matrix effects (>150%) for almost all matrices. The pesticide recovery rates obtained with MC were not statistically different from a 100% recovery rate in most samples, which indicates that MC may diminish the overestimates occurred due to matrix effects in GC analysis.