Search

A paper spray tandem mass spectrometric (PS-MS/MS) method without column separation was developed for the rapid screening of clonidine in dietary supplements. PS-MS/MS provided acceptable performance compared to high-performance liquid chromatography – tandem mass spectrometry (HPLC-MS/MS) in terms of limits of detection and quantification, accuracy, and precision. To overcome ionization suppression of complicated plant-based pharmaceutical products, nizatidine, tizanidine, and apraclonidine were investigated as internal standards. A more similar structured internal standard is most suitable for matrix effect compensation. The developed method has advantages of simplicity and speed for the screening of clonidine in dietary supplements. [ABSTRACT FROM AUTHOR]

Hempseed cake is a byproduct of hempseed oil extraction and is potentially a useful source of protein and fiber for use in ruminant diets. However, data are lacking on the appearance and/or clearance of cannabinoids in tissues of animals fed hempseed cake. To this end, a rapid method for quantifying cannabinol (CBN), cannabidiol (CBD), cannabinolic acid (CBNA), cannabidiolic acid (CBDA), cannabigerolic acid (CBGA), cannabichromenic acid (CBCA), cannabidivarin (CBDV), cannabidivarinic acid (CBDVA), tetrahydrocannabinol (THC) and tetrahydrocannabinolic acid (THCA) in cattle tissues, plasma, and urine was developed using rapid screen electrospray ionization mass spectrometry (RS-ESI-MS). Regression coefficients of matrix-matched standard curves ranged from 0.9946 to >0.9999 and analyte recoveries averaged from 90.2 ± 15.5 to 108.7 ± 18.7% across all compounds. Limits of detection and quantification ranged from 0.05 to 2.79 ng · mL−1 and 0.17 to 9.30 ng · mL−1, respectively, while the inter-day relative standard deviation ranged from 5.1 to 15.1%. Rapid screening electrospray ionization mass spectrometry (RS-ESI-MS) returned no false positives for any cannabinoid in plasma, urine, and tissue (liver, skeletal muscle) samples from 6 non-dosed control animals (n = 90 samples; of which 72 samples were plasma or urine and 18 samples were tissues). Across-animal cannabinoid concentrations measured in 32 plasma samples of cattle dosed with ground hemp were quantified by RS-ESI-MS; analytical results correlated well (r2 = 0.963) with independent LC-MS/MS analysis of the same samples. [ABSTRACT FROM AUTHOR]

The bio-analytical method was developed and validated for simultaneous detection and quantification of paclitaxel (PAC) and erlotinib (ERL) in plasma samples. The sample preparation process was accomplished by liquid-liquid extraction technique. The dried and reconstituted samples were subjected to chromatography on Discovery -C18 (50 × 4.6 × 5µm) column and a mobile phase, composed of a mixture of 0.1% formic acid in water: acetonitrile (70:30, v/v), in isocratic mode at a flow rate of 0.6 mL/min. Liquid chromatography coupled to tandem mass spectrometry detection in positive ion mode was selected to provide optimal selectivity and sensitivity. The mass transitions of erlotinib, erlotinib13C6, Paclitaxel and docetaxel were m/z 394.5→278.4, m/z 400.4→284.5, m/z 876.6→308.4 and m/z 830.0→304.0 respectively. The linearity in the calibration curves was obtained in the concentration range of 3.6 − 1006.7 ng/ml (r ≥ 0.99) for erlotinib and 5.3 − 1500.0 ng/mL for paclitaxel with an LLOQ (lower limit of quantification) of 3.6 and 5.3 ng/ml respectively. The run time was achieved in 2.5 min only, for all the analytes. [ABSTRACT FROM AUTHOR]

A fast, straightforward, efficient, and high throughput reverse-phase high-performance liquid chromatography and electrospray ionization mass spectrometry method has been developed to analyze tea extracts containing polyphenols. The polyphenols detected in green tea (GT), black tea (BT), and paradise tropical tea (PTT) were separated in 18 min at wavelengths 254 nm, 260 nm, and 280 nm with a gradient elution on the RP-HPLC system. Our approach detected, identified, and quantified three catechins in the tea extracts analyzed, and the response at 280 nm wavelength was the best. The ESI-MS data confirmed the fragmentation patterns of the catechins detected in the tea extract. The validation data showed that the limit of detection (LOD) and limit of quantitation (LOQ) of catechins ranged from 5.26 ± 0.02 to 36.44 ± 0.02 ppb, and 17.52 ± 0.03 to 121.45 ± 0.16 ppb, respectively, for six catechins studied. The standard addition calibration approach used to quantify the catechin content in the tea extract simultaneously showed that PTT has a higher catechin content than GT and BT. The content of polyphenols in GT, BT, and PTT are summarized. This approach holds great promise for quality control studies to quantify polyphenols in nutritional products. [ABSTRACT FROM AUTHOR]

To the best of our knowledge, this is the first study on the effect of solvent (water, methanol, and ethyl acetate) upon phenolics extracted from Onosma mitis. The antioxidant capacities together with the enzyme inhibitory properties toward tyrosinase and α-amylase were also assessed. The yields of the extract were 2.62, 10.93, and 21.68% for ethyl acetate, methanol, and water, respectively. The concentrations of phenolic compounds were from 11.89 (ethyl acetate) to 2.66 mg gallic acid equivalent/g extract (methanol). Twenty-five molecules were identified and quantified by liquid chromatography – electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Significant differences were present between the extracts; methanol presented the highest number of compounds (25) while ethyl acetate provided the lowest (18). Chlorogenic acid, luteolin 7-glucoside, rosmarinic acid, and apigenin 7-glucoside were the major compounds regardless of solvent. Antioxidant and inhibitory enzyme assays showed that O. mitis exhibited interesting biological properties. The results illustrate the use of O. mitis as a promising source of biomolecules for industrial applications. [ABSTRACT FROM AUTHOR]

This study evaluated the association of urinary nitrate concentrations with cognition in older subjects enrolled in the NHANES study. We also explored whether associations between urinary nitrate and cognition were modified by cardiovascular risk, vitamin D status and vitamin C intake. Two NHANES cycles were merged (2011–2012 and 2013–2014) and a total of 1,015 adults aged 60–80 (69.4 ± 0.3) years were included. Cognition was assessed using the Word List Learning, Word List Recall, Animal Fluency and the Digit Symbol Substitution tests. Urinary nitrate was analysed using electrospray tandem mass spectrometry. Urinary nitrate concentrations were not associated with cognitive performance on any of the cognitive tests. Associations were also not significant in subjects at greater risk for cognitive impairment (i.e. high cardiovascular risk and non-optimal vitamin D status). Longitudinal analyses are needed to explore the associations of urinary nitrate concentrations with dietary nitrate intake and cognitive function. [ABSTRACT FROM AUTHOR]

To our knowledge, this is the first work on the influence of species upon the bioactive molecules, antioxidant properties, and enzyme inhibitory capacities against tyrosinase and α-amylase of Onosma polyantha and O. mollis. The levels of phenolic compounds were from 6.55 to 10.37 mg gallic acid equivalent/g extract. The concentrations of total flavonoids varied from 2.71 to 10.78 mg quercetin equivalent/g extract. Twenty-five compounds were quantified via liquid chromatography – electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Significant differences were found between the two species. Chlorogenic acid, rosmarinic acid, hesperidin, and luteolin 7-glucoside were the major compounds in both species. Four antioxidant assays together with two enzyme tests confirmed that O. polyantha and O. mollis extracts exhibited remarkable antioxidant and enzyme inhibitory capacities. Statistical analyses confirmed that the biological activities depend on the synergism between phenolic compounds and radicals. The results proposed O. polyantha and O. mollis species as potential sources of bioactive compounds for industrial application. [ABSTRACT FROM AUTHOR]

A method for determining seven microcystins and nodularin in surface water at nanogram per liter concentrations was developed based on on-line solid-phase extraction ultra-performance liquid chromatography – electrospray ionization tandem mass spectrometry (on-line SPE-UPLC-MS/MS). Aliquots of 5 mL water sample were directly injected into on-line SPE after passage through a membrane filter. The water sample was enriched and purified by a hydrophilic–liphophilic balance (HLB) polymeric column and eluted by mobile phase. The analytes were separated by Acquity BEH130 column, detected using tandem mass spectrometry, and quantified by external standardization. Under the optimized conditions, the method detection limits for all of the targets ranged from 1.4 to 3.3 ng/L with the recoveries from 85.5 to 121%. The precision of the method, indicated by the relative standard deviation, was 3.87 to 13.9%. The results of the analysis of surface water samples demonstrated that the proposed method has the ability to determine microcystins and nodularin without the need for complex manual pretreatment. [ABSTRACT FROM AUTHOR]

Mangroves were reported as a source of bioactive compounds that include subgroups of polyphenols with various therapeutic activities. A new, sensitive and selective ultra-high-performance liquid chromatography – electrospray ionization – tandem mass spectrometry (UPLC-ESI-MS/MS) method was developed and validated for the determination of phenolic acids and flavonoids in fourteen mangrove species. Furthermore, anti-Candida activities were evaluated for the mangroves and selected compounds. The selectivity and sensitivity provided by multiple reactions monitoring mode allowed the separation of analytes within 14 minutes using the optimized conditions. The method exhibited excellent linearity for all analytes with correlation coefficient (R2) values of at least 0.991. The limits of detection and quantification were between 0.24 and 15.62 ng/ml and 0.48 and 31.25 ng/mL. The intra- and inter-day precision values characterized by the relative standard deviation were from 3.27 to 8.05% and 3.02 to 8.83%. The corresponding accuracy values were from -6.81 to 9.49% and −4.07 to 7.99%, respectively. Among the selected polyphenols, chlorogenic acid was the dominant compound at concentrations between 8.13 ng/mg and 5690 ng/mg. The phenolic acid (p-coumaric acid, caffeic acid and ferulic acid), flavonol (quercetin, rutin, myricetin), flavanone (naringenin), and flavone (apigenin) concentrations varied as per the mangrove species. The mean recoveries of selected analytes were from 88.8% to 101.9%. Additionally, among the selected mangroves, the Sonneratia species showed potent anti-Candida effects while the flavonoids showed higher anti-Candida activity than the phenolic acids. The selected polyphenols were successfully identified and quantified by UPLC-ESI-MS/MS in mangroves and this method can be used for the analysis of other biological extracts. [ABSTRACT FROM AUTHOR]

To our knowledge, this is the first study on the influence of water, ethyl acetate and methanol as the extraction solvent upon the bioactive compound composition, antioxidant capacities and enzyme inhibitory activities of Marrubium lutescens isolates. The contents of the total phenolic compounds varied between 9.94 and 54.80 mg gallic acid equivalent/g extract and the level of total flavonoids were between 4.45 and 27.20 mg quercetin equivalent/g extract. Twenty-four compounds were identified using liquid chromatography – electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Rosmarinic acid, luteolin 7-glucoside, chlorogenic acid, caffeic acid and hyperoside were the primary compounds present for all of the used solvents. The most compounds (23) were detected in the methanol extract. Six antioxidant assays revealed that M. lutescens extracts showed interesting antioxidant activities with a significant variation between the extracts. The results revealed that the highest tyrosinase and α-amylase inhibitory activities was detected in the ethyl acetate extract. This work confirmed that the nature of solvent influenced the levels and the types of the extracted biomolecules. Moreover, the obtained results suggest that M. lutescens may be a source of bioantioxidants for industrial additives. [ABSTRACT FROM AUTHOR]

Three extraction methods, involving maceration, reflux, and ultrasonic extractions, were used to evaluate the phytochemical content and antioxidant activity of leaf extracts from Capparis spinosa L. collected from five localities in South Tunisia. The results showed that the maceration extract contained the highest content of phenolic acids and flavonoid compounds. The maceration extraction method exhibited the highest antioxidant activities using the reducing power assay, the azinobis (3-ethylbenzothiazoline)-6-sulfonic acid (ABTS+), and the 2,2-diphényl-1-picrylhydrazyle (DPPH°) radical scavenging activity. The determination of the phytochemicals in the extracts was carried out using a quadrupole mass spectrometer equipped with an electrospray ionization source that was operated in the negative ionization mode (LC–ESI–MS). The results allowed the detection of seven phenolic acids in the maceration extract and ultrasonic assisted extraction, but only six phenolic acids in the reflux extract. The major identified phenolic acids were quinic acid, gallic acid, and protocatchuic acid. Ten flavonoids were detected, and their concentrations varied according to the extraction method. Catechin was the most abundant flavonoid in all of the extracts. This investigation provides additional support for the use of caper leaves in medicinal and food applications. [ABSTRACT FROM AUTHOR]

A sudden increase in serum creatinine after paraquat intoxication has been reported in several clinical studies. However, this dramatic change of creatinine may be possibly due to an interconversion of creatine-creatinine in relation to paraquat toxicity. In order to investigate the creatine-creatinine relationship, a liquid chromatography tandem mass spectrometry in combination with electrospray ionization was developed and validated for simultaneous determination of creatine and creatinine in the serum. The chromatographic separation was achieved on a Gemini® C6-Phenyl column with a gradient elution consisting of 0.1% formic acid in ultrapure water and methanol as the mobile phase. The method yielded suitable levels of specificity and selectivity, and calibration curves of creatine and creatinine in serum were linear over the concentration range of 0.5–200 µg mL−1. The limit of quantification of both compounds was 0.5 µg mL−1, and the method was accurate within the recovery range of 96.23–102.75%, indicating the robustness of the method. The method was successfully applied to toxicological samples from paraquat-intoxicated patients, and the concentrations of creatine and creatinine were quantified. High creatine concentrations in serum samples were observed which may lead to high serum creatinine despite normal kidney function as creatine is converted to creatinine in proportion to its concentration. [ABSTRACT FROM AUTHOR]

Rapid analysis of pharmaceutical preparations is of great interest in clinical studies with benefits for identifying counterfeit drugs. In this study, droplet spray ionization tandem mass spectrometry (DSI-MS/MS) was developed for the rapid determination of adenine arabinoside monophosphate in pharmaceutical injections without complex sample pretreatment. The sample solution was loaded on the slip corner placed in front of the inlet of a mass spectrometer, and high voltage was applied to the solution to create a charged spray from the corner for MS analysis. The sample was loaded for analysis without additional sample preparation protocols, which greatly simplifies the operation. The limit of detection and limit of quantification were determined to be 2.7 and 9.1 ng/mL, respectively. The recoveries were in the range from 96% to 112%, and the calculated relative standard deviations were less than 7% for the DSI-MS/MS method. Three adenine arabinoside monophosphate pharmaceutical injection samples and a degraded sample obtained by acid treatment at 40 °C were successfully analyzed by directly dissolving and diluting the sample. Moreover, the sample-loading step required only 2 s. Together these capabilities indicate that the DSI-MS/MS is a simple and robust method and has promising applications in pharmacology studies without complicated sample pretreatment. [ABSTRACT FROM AUTHOR]

Phlebodium decumanum (P. decumanum), together with other tropical ferns commonly known as Calaguala, have been empirically applied since ancient times to ameliorate inflammatory disorders, skins diseases and even cancer. There are evidences of antineoplastic potential and anti-inflammatory, immunomodulatory and antioxidant properties of the extract. Preliminary studies have also shown direct antitumor activity of the extracts. In the present article, the phytochemical composition of a hydro-ethanolic extract of P. decumanum is investigated using high-performance liquid chromatography (HPLC) with ultraviolet–visible (UV–vis) diode array detection (DAD) and electrospray ionization (ESI) quadrupole time-of-flight tandem mass spectrometry (QTOF–MS/MS) detection. First, the chromatographic profile is established as a representative fingerprint of the compounds extracted from the fern. Then, a total of 122 chemicals, including 23 flavonoids, 47 phenolic acids (34 hydroxycinnamic acids and 13 hydroxybenzoic acids), 9 amino and amino-sugar derivatives, 24 organic acids and their derivatives, and other metabolites, have been characterized. Moreover, 12 unknown compounds were also detected, providing the first comprehensive characterization available on the phytochemical composition of the leaves of P. decumanum. [ABSTRACT FROM AUTHOR]

A rapid, simple, and sensitive UPLC-MS/MS method was developed and validated for the determination of etodolac in rat plasma using flurbiprofen as an internal standard (IS). Etodolac and IS were detected using electrospray ionization in negative ion multiple reaction monitoring mode by monitoring the transitions (precursor to product) m/z 286.2→212.1 and 243.2→199.2, respectively. The developed new extraction procedure for etodolac in rat plasma does not contain more than one stage. Chromatographic separation was performed on reverse phase C18 column with a gradient mobile phase, which consisted of methanol for solvent A and 5 mM ammonium formate in water solvent B percentages varying at a flow rate of 0.4 mL/min. The LLOQ for etodolac was determined as 1 ng/mL. The calibration curve for etodolac was linear (r > 0.996 for plasma) well within the range of 1-5000 ng/mL. Quantification of etodolac in rat plasma is possible in a short chromatographic run time (1.91 min) with this method. The proposed method was fully validated by determining specificity, linearity, LLOQ, precision and accuracy, recovery, matrix effect, and stability. The validated method was successfully applied to plasma samples obtained from rats. [ABSTRACT FROM AUTHOR]

Two polar aminoglycosides, kasugamycin and validamycin-A, were determined in cereals (brown rice, wheat and corn) by high-performance liquid chromatography-tandem mass spectrometry. The analytes were extracted from samples using methanol and water (70:30, v/v) at pH 5.5, purified using both a hydrophilic-hydrophobic-balanced cartridge and a strong cation-exchange cartridge, and then analysed using multiple reaction monitoring in positive electrospray ionisation mode with a special ReproSil 100 C18 high-performance liquid chromatography column. This newly proposed method yielded good sensitivity and excellent chromatographic performance. The limits of quantification for kasugamycin and validamycin-A were 4.1 µg/kg and 1.0 µg/kg, respectively. The recoveries for both compounds at three fortification levels (4, 100 and 500 µg/kg for kasugamycin; 1, 10 and 100 µg/kg for validamycin-A) ranged from 75% to 110%, and the relative standard deviations were below 15%. [ABSTRACT FROM AUTHOR]

Twelve 2,3′-bisindolylmethanes with various substituents were investigated using electrospray ionization quadrupole time-of-flight tandem mass spectrometry in positive ion mode. A retro-[3+2] reaction was observed in the collision-induced dissociation spectra of protonated 2,3′-bisindolylmethanes for the first time. The mechanism of retro-[3+2] reaction was concerted or stepwise. For the concerted pathway, carbon–carbon bonds of a protonated compound simultaneously cracked and the m/z 208 ion ([C15H10D2N]+) was observed with hydrogen–deuterium exchange labeling. The stepwise pathway goes through 1,3-hydrogen migration twice and the m/z 208 ion ([C15H10D2N]+) and m/z 207 ion ([C15H11DN]+) were detected with deuterium labeling. In the deuterium-labeled tandem mass spectrum for one compound, only the peak at m/z 208 was present at high abundance, suggesting that the concerted pathway is more likely. In addition, the substituents have no obvious trends on the ratios of the product intensity to the base intensity, further supporting the concerted pathway. [ABSTRACT FROM AUTHOR]

Voriconazole is used to prevent invasive pulmonary aspergillosis. However, little is known about the concentrations of voriconazole in human lung epithelial cells (A549), which is the target for preventing invasive pulmonary aspergillosis. The goal of this study was to develop a high-performance liquid chromatography–tandem mass spectrometry method to quantify voriconazole in A549 cells. A triple-quadrupole mass spectrometer in selected reaction monitoring mode was used with positive electrospray ionization. The total duration of each run was 5 min. The calibration curves fit a least squares model for the voriconazole concentration ranging from 0.625 to 160 ng/mL. Intraday and interday coefficients of variation were less than 10%. Recoveries at the concentrations of the quality control samples where greater than 85%, and the matrix effects showed that the ratios of the peak response exhibited a 15% suppression of the signal in the matrix compared to water. Voriconazole may penetrate A549 cells. However, the voriconazole uptake was slow in A549 cells, reaching a plateau at 2 h, where the dose-dependent intracellular voriconazole concentrations were 1.98 ± 0.38, 4.43 ± 0.54, and 8.14 ± 0.52 ng/mg protein for extracellular voriconazole concentrations of 5, 10, and 20 µg/mL, respectively. The uptake of voriconazole by A549 cells was linear at extracellular concentrations from 0 to 20 µg/mL. This study established a rapid and sensitive method suitable for determining voriconazole in A549 cells and described the kinetic properties of the absorption of voriconazole by A549 cells. [ABSTRACT FROM PUBLISHER]

A rapid and selective liquid chromatography-mass spectrometry (LC-MS) method was developed for the evaluation of amlodipine and atorvastatin in human plasma. Detection of analytes was assigned by tandem mass spectrometry with electrospray ionization interface in positive ion mode was applied under the multiple-reaction monitoring mode (MRM). Analytes were extracted from plasma by simple liquid-liquid extraction technique using ethyl acetate. The reconstituted samples were chromatographed on C18 column by pumping acetonitrile-water (10 mM CH3COONH4, pH 3.0) = 70:30 (v/v) at a flow rate of 0.15 mL/min. The standard curves were assigned to be linear in the range of 0.2-20 ng/mL for atorvastatin and 0.1-10 ng/mL for amlodipine with mean correlation coefficient of ≥0.999 for each analyte. The intra-day and inter-day precision and accuracy results were well within the acceptable limits. The urbanized evaluate method was successfully applied to validation of amlodipine and atorvastatin in human plasma. [ABSTRACT FROM AUTHOR]

A rapid liquid chromatographic-tandem mass spectrometric method was developed for the simultaneous determination of four natural and synthetic hormone residues (progesterone, testosterone, trenbolone acetate and zeranol) in animal tissue samples. Sample preparation was optimised to minimise time and solvent consumption. Meat samples were mechanically homogenised and digested in a procedure that gave similar recoveries to those enzymatically hydrolysed byHelix pomatia. Efficient extraction was achieved using acidified acetonitrile (1% acetic acid). Chromatographic conditions were optimised to minimise matrix effects. Analytes were separated using a C18 column with gradient elution using ammonium formate solution in methanol (MeOH)/water (1:9) and MeOH mobile phases. Finally, residues were qualitatively and quantitatively determined by electrospray ionisation tandem mass spectrometry in multiple reaction monitoring mode. Different parameters for LC-MS/MS (e.g., declustering potential and collision energy) were optimised using API 6500QT; all analytes were measured using positive-mode electrospray ionisation (ESI+) except zeranol which was measured in negative mode (ESI–). Due to LC-MS/MS signal enhancement/suppression, the determination of hormones was based on matrix-matched standard calculations. The method was validated for the four hormones on meat samples at different fortification levels and showed accepted performance criteria according to European Commission Decision 2002/657/EC. Decision limits and detection capabilities were estimated for all analytes. [ABSTRACT FROM PUBLISHER]

A series of mono-, di- and tri-substituted arylpentazoles were obtained via different synthetic routes. The effects of the number and position of the substituents on the arylpentazoles stability have been investigated at different temperatures. Investigators used electrospray ionization tandem mass spectrometry to infer the decomposition pathway of arylpentazoles. The article examines the relationship between the arylpentazole stability and the relative intensity of the generated pentazolate anion. [ABSTRACT FROM PUBLISHER]

To investigate the process of analyte adduct formation with the components of the mobile phase in the negative electrospray ionization mode and to answer the question if the strategy of adduct identification/fragmentation is applicable for a bigger number of drugs, which meet the appropriate ionization conditions and compare the detection of appropriate analyte adducts to deprotonated analytes with tandem mass spectrometry, ten drugs containing carboxyl groups capable of negative electrospray ionization were chosen for appropriate experiments. The continuous infusion of captopril, fenbufen, gabapentin, ibuprofen, ketoprofen, naproxen, ramipril, salicylic acid, tiaprofenic acid, and 11-nor-9-carboxy-delta-9-tetrahydrocannabinol made the adduct identification/fragmentation experiments possible. The results achieved show that the adduct formation/fragmentation process can be used for LC–MS/MS analysis of drugs that meet the appropriate ionization conditions like the presence of a carboxyl group. It was also demonstrated that signal intensities achieved by the fragmentation of deprotonated drugs are in most cases higher than the signals connected with the fragmentation of appropriate adducts. [ABSTRACT FROM AUTHOR]

Polyacrylate stir bar sorptive extraction (SBSE) of 2,6-dichlorobenzamide followed by liquid desorption and analysis by liquid chromatography–tandem mass spectrometry using electrospray ionization is presented. The parameters influencing the methods were optimized and included a stirring speed of 500 revolutions per minute, an extraction time of two hours, a sample volume of 15 milliliters, 30 percent NaCl, and liquid desorption using acetonitrile under ultrasonication for fifteen minutes. A reverse phase C18column was used with isocratic elution (50 percent acetonitrile and 50 percent 5 millimoles per liter aqueous ammonium acetate buffer at pH 2.4), a flow rate of 0.4 milliliter per minute, and an injection volume of 10 microliters. Quantitative analysis was carried out by multiple reaction monitoring using positive polarity. The developed method required low sample volume (15 milliliters) and provided satisfactory figures of merit with a limit of detection of 0.002 microgram per liter, a limit of quantification of 0.006 microgram per liter, and good precision (inter-day relative standard deviation below 10 percent). The polyacrylate Twister was employed for up to twenty-five extraction and liquid desorption cycles. The applicability of the method was assessed by analyzing ground water collected at five sites in North Italy. The concentrations of 2,6-dichlorobenzamide were between 0.070 and 0.282 microgram per liter. Preliminary results on the use of polar stir bars for the determination of other polar pesticides in water are also provided. [ABSTRACT FROM PUBLISHER]