Plasma lipid analysis by hydrophilic interaction liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A novel method for the analysis of endogenous lipids and related compounds was developed employing hydrophilic interaction liquid chromatography with electrospray ionization tandem mass spectrometry. A hydrophilic interaction liquid chromatography with carbamoyl stationary phase achieved clear separation of phosphatidylcholine, lysophosphatidylcholine, sphingomyelin, ceramide, and mono‐hexsosyl ceramide groups with good peak area repeatability (RSD% < 10) and linearity (R² > 0.99). The established method was applied to human plasma assays and a total of 117 endogenous lipids were successfully detected and reproducibly identified. In addition, we investigated the simultaneous detection of small polar metabolites such as amino and organic acids co‐existing in the same biological samples processed in a single analytical run with lipids. Our results show that hydrophilic interaction liquid chromatography is a useful tool for human plasma lipidome analysis and offers more comprehensive metabolome coverage.     

Rapid quantification of HIV protease inhibitors in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

HIV protease inhibitors are important antiretroviral drugs which have substantially reduced the morbidity and mortality associated with HIV-1 infection. Recent data have shown relationships between plasma concentrations of the protease inhibitors and clinical response, which makes therapeutic drug monitoring valuable. We have developed and validated an assay, using liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS), for the routine quantification of the six licensed protease inhibitors (amprenavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir) and the pharmacologically active nelfinavir metabolite M8 in plasma. The sample pretreatment consisted of protein precipitation with a mixture of methanol and acetronitrile using only 100 microl of plasma. Chromatographic separation was performed on an Inertsil ODS3 column (50 x 2.0 mm i.d., particle size 5 microm), with a quick stepwise gradient using an acetate buffer (pH 5) and methanol, at a flow rate of 0.5 ml min(-1). The analytical run time was 5.5 min. The use of a 96-well plate autosampler allowed batch sizes up to 150 patient samples. The triple-quadrupole mass spectrometer was operated in the positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over the concentration ranges 0.01-10 microg ml(-1) for indinavir and saquinavir, 0.1-10 microg ml(-1) for amprenavir, 0.05-10 microg ml(-1) for nelfinavir and ritonavir, 0.1-20 microg ml(-1) for lopinavir and 0.01-5 microg ml(-1) for M8. Saquinavir-d(5) and indinavir-d(6) were used as internal standards. The coefficients of variation were always <10% for both intra-day and inter-day precisions for each compound. Mean accuracies were also between the designated limits (+/-15%). The validated concentration ranges proved to be adequate in daily practice. This robust and fast LC/MS/MS assay is now successfully applied for routine therapeutic drug monitoring and pharmacokinetic studies in our hospital.     

Bromazepam determination in human plasma by high-performance liquid chromatography coupled to tandem mass spectrometry: a highly sensitive and specific tool for bioequivalence studies

A rapid, sensitive and specific method to quantify bromazepam in human plasma using diazepam as the internal standard (IS) is described. The analyte and the IS were extracted from plasma by liquid-liquid extraction using diethyl ether-hexane (80 : 20, v/v). The extracts were analyzed by high-performance liquid chromatography (HPLC) coupled to electrospray tandem mass spectrometry (MS/MS). Chromatography was performed isocratically on a Genesis C(18) analytical column (100 x 2.1 mm i.d., film thickness 4 microm). The method had a chromatographic run time of 5.0 min and a linear calibration curve over the range 5.0-150 ng ml(-1) (r(2) > 0.9952). The limit of quantification was 5 ng ml(-1). This HPLC/MS/MS procedure was used to assess the bioequivalence of two bromazepam 6 mg tablet formulations (bromazepam from Medley SA Indústria Farmacêutica as the test formulation and Lexotan from Produtos Roche Químico e Farmacêutico SA as the reference formulation). A single 6 mg dose of each formulation was administered to 24 healthy volunteers (12 males and 12 females). The study was conducted using an open, randomized, two-period crossover design with a 3 week washout interval. Since the 90% CI for C(max), AUC(last), AUC(0-240 h) (linear) and AUC((0- infinity )) ratios were all inside the 80-125% interval proposed by the US Food and Drug Administration, it was concluded that the bromazepam formulation from Medley is bioequivalent to the Lexotan formulation for both the rate and the extent of absorption.     

Characterization of tropane and cinnamamide alkaloids from Scopolia tangutica by high‐performance liquid chromatography with quadrupole time‐of‐flight tandem mass spectrometry

Scopolia tangutica is a traditional Chinese medicine used for antispasmodic, anesthesia, analgesia, and sedation. Its medicinal activity is associated to alkaloid constituents, including tropane and cinnamamide types. Low content of alkaloids in plant makes them difficult to be isolated and identified. The present work developed an effective method to quickly characterize alkaloids from Scopolia tangutica by high‐performance liquid chromatography coupled with quadrupole time‐of‐flight tandem mass spectrometry. Thirteen reference compounds were studied for their fragmentation pathways, including five tropane alkaloids and eight cinnamamide ones. Alkaloid constituent was analyzed by an optimized high‐performance liquid chromatography method and mass spectrometry analysis to achieve systematic characterization of alkaloids from Scopolia tangutica. As a result, 53 compounds were identified, including 21 tropane alkaloids (eight new ones), 18 caffeoyl ones (ten new ones) and 14 dicaffeoyl ones (seven new ones). It was important to provide rich information in phytochemical study and structure‐guided isolation of important compounds from this plant.     

Nevirapine quantification in human plasma by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry. Application to bioequivalence study

A rapid, sensitive and specific method to quantify nevirapine in human plasma using dibenzepine as the internal standard (IS) was developed and validated. The method employed a liquid-liquid extraction. The analyte and the IS were chromatographed on a C(18) analytical column, (150 x 4.6 mm i.d. 4 microm) and analyzed by tandem mass spectrometry in the multiple reaction monitoring mode. The method had a chromatographic run time of 5.0 min and a linear calibration curve over the range 10-5000 ng ml(-1) (r(2) > 0.9970). The between-run precision, based on the relative standard deviation for replicate quality controls was 1.3% (30 ng ml(-1)), 2.8% (300 ng ml(-1)) and 3.6% (3000 ng ml(-1)). The between-run accuracy was 4.0, 7.0 and 6.2% for the above-mentioned concentrations, respectively. This method was employed in a bioequivalence study of two nevirapine tablet formulations (Nevirapina from Far-Manguinhos, Brazil, as a test formulation, and Viramune from Boehringer Ingelheim do Brasil Química e Farmacêutica, as a reference formulation) in 25 healthy volunteers of both sexes who received a single 200 mg dose of each formulation. The study was conducted using an open, randomized, two-period crossover design with a 3 week washout interval. The 90% confidence interval (CI) of the individual ratio geometric mean for Nevirapina/Viramune was 96.4-104.5% for AUC((0-last)), 91.4-105.1% for AUC((0-infinity)) and 95.3-111.6% for C(max) (AUC = area under the curve; C(max) = peak plasma concentration). Since both 90% CI for AUC((0-last)) and AUC((0-infinity)) and C(max) were included in the 80-125% interval proposed by the US Food and Drug Administration, Nevirapina was considered bioequivalent to Viramune according to both the rate and extent of absorption.     

Quantitative liquid chromatography/time-of-flight mass spectrometry

Over the last decade, time-of-flight (TOF) instruments have increasingly been used as quantitation tools. In addition, because of their high resolving power, they can be used for verification of empirical formulas. Historically, TOF instruments have had limited quantitation capabilities because of their narrow dynamic range. However, recent advances have improved these limitations. This review covers the rationale for using TOF for LC detection, and describes the many methods currently in the literature for the quantitation of pharmaceuticals, environmental pollutants, explosives and many phytochemicals.     

Rapid confirmatory method for the determination of 11 nitroimidazoles in egg using liquid chromatography tandem mass spectrometry

A rapid confirmatory method has been developed and validated for the simultaneous identification, confirmation and quantitation of 11 nitroimidazoles in eggs by liquid chromatography tandem mass spectrometry (LC–MS/MS). The method is validated in accordance with Commission Decision 2002/657/EC and is capable of analysing metronidazole (MNZ), dimetridazole (DMZ), ronidazole (RNZ), ipronidazole (IPZ) and their hydroxy metabolites MNZ-OH, HMMNI (hydroxymethyl, methyl nitroimidazole), IPZ-OH. The method is also capable of analysing carnidazole (CRZ), ornidazole (ORZ), tinidazole (TNZ) and ternidazole (TRZ). MNZ, DMZ and RNZ have been assigned a recommended level (RL) of 3 μg kg⁻¹ by the Community Reference Laboratory (CRL) in Berlin. The developed method described in this study is easily able to detect all the nitroimidazole compounds investigated at this level and below. Egg samples are extracted with acetonitrile, and NaCl is added to help remove matrix contaminants. The acetonitrile extract undergoes a liquid–liquid wash step with hexane; it is then evaporated and reconstituted in mobile phase. The reconstituted samples are analysed by liquid chromatography tandem mass spectrometry (LC–MS/MS). The decision limits (CCα) range from 0.33 to 1.26 μg kg⁻¹ and the detection capabilities (CCβ), range from 0.56 to 2.15 μg kg⁻¹. The results of the inter-assay study, which was performed by fortifying hen egg samples (n = 18) on three separate days, show the accuracy calculated for the various analytes to range between 87.2 and 106.2%. The precision of the method, expressed as %CV values for the inter-assay variation of each analyte at the three levels of fortification (3, 4.5 and 6.0 μg kg⁻¹), ranged between 3.7 and 11.3%. A Day 4 analysis was carried out to examine species variances in eggs from different birds such as duck and quail and investigating differences in various battery and free range hen eggs.     

Analysis of amicarbazone and its two metabolites in grains and soybeans by liquid chromatography with tandem mass spectrometry

A sensitive, simple and reliable analytical method based on a modified quick, easy, cheap, effective, rugged, safe sample preparation and liquid chromatography with tandem mass spectrometry detection was developed for the simultaneous determination of amicarbazone and its two major metabolites desamino amicarbazone and isopropyl‐2‐hydroxy‐desamino amicarbazone residues in grains (rice, wheat, corn, buckwheat) and soybean. Several parameters, including liquid chromatography and tandem mass spectrometry conditions, extraction approaches and the adsorbents for clean‐up, which might influence the accuracy of the method, were extensively investigated. The established method was further validated by determining the linearity (R² > 0.99), fortified recovery (79–118%), precision (1–12%) and sensitivity (limit of quantification, 5 μg/kg for amicarbazone and desamino amicarbazone, and 10 μg/kg for isopropyl‐2‐hydroxy‐desamino amicarbazone). Finally, the established method was successfully applied to determine the residues of amicarbazone and its metabolites in 49 real samples of grain and soybean.     

In vivo and in vitro metabolism of aspirin eugenol ester in dog by liquid chromatography tandem mass spectrometry

Aspirin eugenol ester (AEE) is a promising drug candidate for treatment of inflammation, pain and fever and prevention of cardiovascular diseases with fewer side effects than its precursor, aspirin. Investigation into its metabolic process in target animal species will help to illustrate its mechanism of action and to establish its residual mark compound to formulate its dosage. Six beagle dogs were orally given a dose of 20 mg kg^?1 of AEE and one dog was used to prepare blank liver microsomes. Their liver microsomes were prepared for in vitro study and their plasma and urine were collected for in vivo metabolic analysis using liquid chromatography tandem mass spectrometry. In this study we identified 10 metabolites, M1, M2, M3, M4, M5 in phase I and M6, M7, M8, M9, M10 in phase II. Based on the metabolites of AEE, the pathways of AEE metabolism in dog were demonstrated. Copyright © 2014 John Wiley & Sons, Ltd.     

Isolation and characterization of flavonols from blackcurrant by high-performance counter-current chromatography and electrospray ionization tandem mass spectrometry

Blackcurrant is considered as a natural high-value food raw material and possesses a variety of therapeutic properties. The health benefits of blackcurrant have generally been credited to its high anthocyanin content; however, the therapeutic properties of other minor flavonoids constituents have not yet been investigated due the difficulties related to their isolation. Multiple steps of high-performance counter-current chromatography in combination with ESI tandem mass spectrometry (MS(n)) were successfully used for the preparative isolation of flavonols from blackcurrant extract, to study their electrospray ionization mass spectrometry fragmentation behavior. Seven flavonols, namely myricetin-3-O-rutinoside (145.5 mg), myricetin-3-O-hexoside (79.7 mg), myricetin-3-O-(6″-malonyl)-glucoside (17.4 mg), kaempferol-3-O-glucoside (20.5 mg), quercetin-3-O-rutinoside (55.1 mg), quercetin-3-O-hexoside (25.8 mg), and myricetin (129.1 mg) have been successfully isolated and their multistage MS(n) data were used for detailed structure characterization. The results of these experiments demonstrated that high-performance counter-current chromatography along with ESI-MS(n) is a sensitive, selective, and effective technology for isolation and characterization of minor constituents from a complex mixture.     

Free amino acids analysis by liquid chromatography with tandem mass spectrometry in several botanicals with antioxidant character

A novel method based on liquid chromatography with tandem mass spectrometry for the analysis of 19 amino acids in plant materials is described. For the analysis, the plant material is extracted with 0.1 N hydrochloric acid with internal standards present in the extraction solution. The filtered extracts are injected using no clean‐up into the liquid chromatographic system coupled with a triple‐quadrupole tandem mass spectrometer with an electrospray ionization source. The analytes are separated using ion pair chromatography on a reversed‐phase column. The detection is performed in multiple‐reaction monitoring positive‐ion mode. Quantitation is obtained using calibrations. The validated procedure has been applied for the analysis of amino acids in 18 samples of plant material including botanicals with antioxidant character. The analysis requires 16 min separation time, has excellent precision and accuracy allowing amino acid analysis in a wide range of concentrations.     

Separation of selenium species and their sensitive determination in rice samples by ion‐pairing reversed‐phase liquid chromatography with inductively coupled plasma tandem mass spectrometry

A highly sensitive method was developed for the simultaneous separation and determination of organic and inorganic selenium species in rice by ion‐pairing reversed‐phase chromatography combined with inductively coupled plasma tandem mass spectrometry. To achieve a good separation of these species, a comparison between anion‐exchange chromatography and ion‐pairing reversed‐phase chromatography was performed. The results indicated that ion‐pairing reversed‐phase chromatography was more suitable due to better separation and higher sensitivity for all analytes. In this case, a StableBond C18 column proved to be more robust or to have a better resolution than other C18 columns, when 0.5 mM tetrabutylammonium hydroxide and 10 mM ammonium acetate at pH 5.5 were used as the mobile phase. Moreover, an excellent sensitivity was obtained in terms of interferences by means of tandem mass spectrometry in the hydrogen mode. The detection limits were 0.02–0.12 μg/L, and recoveries of five selenium species were 75–114%, with relative standard deviations ≤ 9.4%. This method was successfully applied to the analysis of rice samples. Compared with previous studies, the proposed method not only gave comparable results when used for measuring selenium‐enriched rice, but it can provide greater sensitivity for the detection of low concentrations of selenium species in rice.     

Determination of paraquat and diquat in human body fluids by high-performance liquid chromatography/tandem mass spectrometry

Paraquat (PQ) and diquat (DQ) in human whole blood and urine were analyzed by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) with positive ion electrospray ionization (ESI). The compounds were extracted with Sep-Pak C18 cartridges from whole blood and urine samples containing ethyl paraquat as an internal standard. The separation of PQ and DQ was carried out using ion-pair chromatography with heptafluorobutyric acid in 20 mM ammonium acetate and acetonitrile gradient elution for successful coupling with MS. Both compounds formed base peaks due to [M-H]+ ions by HPLC/ESI-MS and the product ions produced from each [M-H]+ ion by HPLC/MS/MS. Selective reaction monitoring (SRM) showed much higher sensitivity for both body fluids. Therefore, a detailed procedure for the detection of compounds by SRM with HPLC/MS/MS was established and carefully validated. The recoveries of PQ and DQ were 80.8-95.4% for whole blood and 84.2-96.7% for urine. The calibration curves for PQ and DQ showed excellent linearity in the range of 25-400 ng ml(-1) of whole blood and urine. The detection limits were 10 ng ml(-1) for PQ and 5 ng ml(-1) for DQ in both body fluids. The intra- and inter-day precision for both compounds in whole blood and urine samples were not greater than 13.0%. The data obtained from the determination of PQ and DQ in rat blood after oral administration of the compounds are also presented.     

Rapid and sensitive detection of the phenoxy acid herbicides in environmental water samples by magnetic solid‐phase extraction combined with liquid chromatography–tandem mass spectrometry

Phenoxy acid herbicides are widely used herbicides that play an important role in improving the yield and quality of crops. However, some research has shown that this kind of herbicide is poisonous to human and animals. In this study, a rapid and sensitive method was developed for the detection of seven phenoxy acid herbicides in water samples based on magnetic solid‐phase extraction followed by liquid chromatography and tandem mass spectrometry. Magnetic amino‐functionalized multiwalled carbon nanotubes were prepared by mixing bare magnetic Fe₃O₄ nanoparticles with commercial amino‐functionalized multiwalled carbon nanotubes in water. Then the amino‐functionalized multiwalled carbon nanotubes were used to enrich phenoxy acid herbicides from water samples based on hydrophobic and ionic interactions. The effects of experimental variables on the extraction efficiency have been studied in detail. Under the optimized conditions, the method validation was performed. Good linearities for seven phenoxy acid herbicides were obtained with squared regression coefficients ranging from 0.9971 to 0.9989. The limits of detection ranged from 0.01 to 0.02 μg/L. The method recoveries of seven phenoxy acid herbicides spiked at three concentration levels in a blank sample were from 92.3 to 103.2%, with inter‐ and intraday relative standard deviations less than 12.6%.     

Determination of fungicides in wine by mixed-mode solid phase extraction and liquid chromatography coupled to tandem mass spectrometry

A novel procedure for the determination of nine selected fungicides (metalaxyl-M, azoxystrobin, myclobutanil, flusilazole, penconazole, tebuconazole, propiconazole, diniconazole and difenoconazole) in wine samples is presented. Sample enrichment and purification is simultaneously performed using mixed-mode, anion exchange and reversed-phase, OASIS MAX solid-phase extraction (SPE) cartridges. Analytes were determined by liquid chromatography coupled to tandem mass spectrometry using atmospheric pressure electrospray ionization (LC-ESI-MS/MS). Parameters affecting the chromatographic determination and the extraction-purification processes were thoroughly investigated. Under optimized conditions, 10 mL of wine were firstly diluted 1:1 with ultrapure water and then passed through the mixed-mode SPE cartridge at a flow of ca. 5 mLmin(-1). After a washing step with 5 mL of an aqueous NH(4)OH solution (5%, w:v), analytes were recovered with just 1 mL of methanol and injected in the LC-MS/MS system without any additional purification. The selective extraction process avoided significant changes in the ionization efficiency for red and white wine extracts in comparison with pure standards in methanol. Performance of the method was good in terms of precision (RSDs<11%) and accuracy (absolute recoveries>72%, determined against pure standards in methanol) reporting method LOQs in the range of 0.01-0.79 ngmL(-1) for target compounds, which are far below the EU maxima residue levels (MRLs) for fungicides in vinification grapes and wine. Several commercial wines from different geographic areas in Spain were analyzed. In most samples, metalaxyl-M and azoxystrobin were found at concentrations up to several ngmL(-1).     

Investigations on the degradation of aspartame using high-performance liquid chromatography/tandem mass spectrometry

Aspartame is a widely used sweetener,the long-term safety of which has been controversial ever since it was accepted for human consumption.It is unstable and can produce some harmful degradation products under certain storage conditions.A high-performance liquid chromatography/tandem mass spectrometry method was developed for the simultaneous analysis of aspartame and its four degradation products,including aspartic acid,phenylalanine,aspartyl-phenylalanine and 5-benzyl-3,6-dioxo-2-piperazieacetic acid in water and in diet soft drinks.Aspartame and its four degradation products were quantified by a matrix matched external standard calibration curve with excellent correlation coefficients.The limits of detection were 0.16–5.8 mg/L,which exhibited higher sensitivity than common methods.This method was rapid,sensitive,specific and capable of eliminating matrix interferences.It was also applied to the study of the degradation of aspartame at various pH and temperatures.The results indicated that aspartame was partly degraded under strong acidic or basic conditions and the extent of degradation increased with increasing temperature.     

Simultaneous analysis of indaziflam and its metabolites in pitaya using dispersive solid phase extraction coupled with liquid chromatography coupled with tandem mass spectrometry

A simple and efficient multiresidue method using dispersive solid phase extraction and liquid chromatography coupled with tandem mass spectrometry was developed for the targeted analysis of indaziflam and its five metabolites (indaziflam‐diaminotriazine, indaziflam‐carboxylic acid, indaziflam‐triazine indanone, indaziflam‐hydroxyethyl, and indaziflam‐olefin) in pitaya samples (including roots, plants, flowers, peels, pulp, and whole fruit). The analytes were extracted with acetonitrile, and the extracts were purified using multiwalled carbon nanotubes. The method was validated using pitaya samples spiked at 0.5, 5, and 50 µg/kg, and the average recoveries varied from 61.1 to 103.7% with relative standard deviations lower than 12.7% (n = 5). This method exhibited sufficient linearity within the concentration range of 0.1–100 µg/L. The limits of detection and quantification were in the ranges of 0.001–0.1 and 0.003–0.3 µg/kg, respectively. The method was successfully applied to analyze pitaya samples in Nanning, and no indaziflam or its metabolites were detected in the samples analyzed.     

A sensitive method for determination of allergenic fragrance terpene hydroperoxides using liquid chromatography coupled with tandem mass spectrometry

Different compositions of monoterpenes are utilized for their pleasant scent in cosmetics and perfumes. However, the most commonly used fragrance terpenes easily oxidize upon contact with air, forming strongly skin‐sensitizing hydroperoxides. Due to their thermolability and low UV absorbance, detection methods for hydroperoxides are scarce. For the first time, a simple and sensitive method using LC/ESI‐MS/MS was developed to quantitatively determine hydroperoxides from the common fragrance compounds linalool, linalyl acetate, and limonene. The method was applied to autoxidized petitgrain oil and sweet orange oil. A separation was accomplished using a C₃ column. The method LOD for the investigated hydroperoxides in the essential oils was below 0.3 μg/mL, corresponding to 0.3 ppm. For prevention purposes and according to EU regulations, concentrations in cosmetics exceeding 100 ppm in “rinse‐off” and 10 ppm in “stay‐on” products of linalool and limonene must be labeled. However, the products may still contain allergens, such as hydroperoxides, formed by oxidative degradation of their parent terpenes. The sensitivity and selectivity of the presented LC/MS/MS method enables detection of hydroperoxides from the fragrance terpenes linalool, linalyl acetate, and limonene. However, for routine measurements, the method requires further validation.     

Investigating the presence of pesticide transformation products in water by using liquid chromatography-mass spectrometry with different mass analyzers

Many pesticide transformation products (TPs) can reach environmental waters as a consequence of their normally having a higher polarity than their parent pesticides. This makes the development of analytical methodology for reliable identification and subsequent quantification at the sub-microgram per liter levels necessary, as required under current legislation. In this paper we report the photodegradation of several pesticides frequently detected in environmental waters from the Spanish Mediterranean region using the high-resolution and exact-mass capabilities of hybrid quadrupole time-of-flight mass spectrometry (QTOF MS) hyphenated to liquid chromatography (LC). Once the main photodegradation/hydrolysis products formed in aqueous media were identified, analytical methodology for their simultaneous quantification and reliable identification in real water samples was developed using on-line solid-phase extraction (SPE)-LC-tandem MS with a triple-quadrupole (QqQ) analyzer. The methodology was validated in both ground and surface water samples spiked at the limit of quantification (LOQ) and 10 x LOQ levels, i.e. 50 and 500 ng/l, obtaining satisfactory recoveries and precision for all compounds. Subsequent analysis of ground and surface water samples resulted in the detection of a number of TPs higher than parent pesticides. Additionally, several soil-interstitial water samples collected from the unsaturated zone were analyzed to explore the degradation/transformation of some pesticides in the field using experimental plots equipped with lisimeters. Several TPs were found in these samples, with most of them having also been detected in ground and surface water from the same area. This paper illustrates the extraordinary potential of LC-MS(/MS) with QTOF and QqQ analyzers for qualitative/structural and quantitative analysis, respectively, offering analytical chemists one of the most powerful tools available at present to investigate the presence of pesticide TPs in water.