Microcolumn liquid chromatography with thermionic detection of the enantiomers of O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX)

An improved interface for the on-line coupling of microcolumn liquid chromatography (micro-LC) with thermionic detection (TID) is described. Modifications have been made to enable separate adjustment of the eluent introduction and the detector flame temperature in order to improve the sensitivity and ease of use of the system. The micro-LC-TID was used for the chiral separation of the nerve agent O-ethyl S-2-diisopropylaminoethyl methylphosphonothioate (VX). Baseline separation for the enantiomers of VX was obtained on Chiralcel OD using 1% isopropanol in hexane as the eluent. The detection limit of VX using 60 nl injections is ca. 5 μg/ml (ppm range). However, when using large-volume injections (10 μl) the detection limit is ca. 25 ng/ml (ppb range).     

Separation of organophosphorus pesticides by using nano-liquid chromatography

In the present research, the separation of a series of organophosphorus pesticides (fensulfothion, fenamiphos, profenofos, fonofos, isofenphos, dialifos, sulprofos and prothiofos), by using nano-liquid chromatography (nano-LC) with UV detection is described. Three 100 μm ID capillary columns, packed with different silica-based stationary phases (CN, C₁₈, and phenyl), were investigated. Among these, the phenyl column offered the best results in terms of chromatographic performance, and was selected for pesticide analyses. Parameters, such as sample dilution solvent, injection volume, mobile phase composition and flow rate, were optimized in order to define the ideal experimental conditions. With the aim of improving sensitivity, on-column focusing of large injection volumes was applied: a sensitivity increase of circa 100-fold was attained, with limits of detection (LODs) and quantification (LOQs) within the 4.4–37.5 and 14.5–125.0 ng/mL ranges, respectively. The method was validated, with satisfactory results, through the measurement of the following parameters: limits of detection and quantification, precision, linearity and recovery. Finally, five different baby foods, previously fortified with a solution of the eight aforementioned pesticides, and then subjected to liquid–liquid extraction and solid-phase extraction clean-up, were analyzed.     

High-performance liquid chromatographic assay of phosphate and organophosphorus pesticides using a post-column photochemical reaction and fluorimetric detection

A sensitive method for the post-column reaction detection of organophosphorus pesticides is described. The method relies on photolysis of the organocompounds by irradiation with a low-pressure mercury lamp (main spectral line, 254 nm) in the presence of peroxydisulfate. The resultant orthophosphate was reacted with molybdate to form molybdophosphoric acid, which subsequently reacted with thiamine to generate thiochrome. Finally, the fluorescence intensity of thiochrome was measured at 440 nm with excitation at 375 nm. Factors affecting the rate of these reactions were optimized so that its contribution to the total band-broadening was negligible.

This detection system was used for the determination of phosphate, acephate and methamidophos, which were separated on an ODS column by isocratic reversed phase chromatography with acetonitrile–water as the mobile phase. A linear relationship between analyte concentration and peak area was obtained within the range 0.016–7.0 μg ml⁻¹ with correlation coefficients greater than 0.9995 and detection limits between 4 and 12 ng ml⁻¹. Intra- and inter-day precision values of about 1.2% R.S.D. (n = 10) and 2.1% R.S.D. (n = 30), respectively, were obtained.

Pesticide residues below ng ml⁻¹ levels could be determined in environmental waters when a preconcentration device was coupled on-line with the HPLC system. Detection limits as low as 0.01 ng ml⁻¹ were achieved for only 250 ml of sample. In the analyses of vegetables and grains, the detection limit was about 1 μg kg⁻¹.     

Analytical and semipreparative separation of the enantiomers of new acetylcholinesterase inhibitors by high-performance liquid chromatography

Summary The resolution of the enantiomers of new acetylcholinesterase inhibitors by high-performance liquid chromatography (HPLC) was investigated on stationary phases containing cellulose tris-(3,5 methylphenylcarbamide) (Chiralcel OD). The effects of the mobile phase on retention, enantioselectivity and resolution were also studied. Ethanol and isopropanol were tested as organic modifiers and the influence of diethylamine was investigated. The effect of temperature on chiral separations was also studieded.     

On-line determination of organophosphorus pesticides in water by solid-phase microextraction and gas chromatography with thermionic-selective detection

This paper describes the extraction of 49 organophosphorus pesti-cides (OPPs) from water samples using solid-phase microextraction (SPME). Three fibers, including a 15-μm XAD-coated fiber, a 85-μm polyacrylate-coated fiber, and a 30-μm polydimethylsilox-ane-coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate-coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD- and polyacrylate-coated fibers. With some exceptions, the XAD- and polyacrylate-coated fibers performed better than the PDMS-coated fiber. The superiority of the XAD-nd polyacrylate-coated fiber. The superiority of the XAD- and polyacrylate-coated fibers over the PDMS-coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber.     

Ultrapreconcentration and determination of organophosphorus pesticides in water by solid‐phase extraction combined with dispersive liquid–liquid microextraction and high‐performance liquid chromatography

Solid‐phase extraction coupled with dispersive liquid–liquid microextraction was developed as an ultra‐preconcentration method for the determination of four organophosphorus pesticides (isocarbophos, parathion‐methyl, triazophos and fenitrothion) in water samples. The analytes considered in this study were rapidly extracted and concentrated from large volumes of aqueous solutions (100 mL) by solid‐phase extraction coupled with dispersive liquid–liquid microextraction and then analyzed using high performance liquid chromatography. Experimental variables including type and volume of elution solvent, volume and flow rate of sample solution, salt concentration, type and volume of extraction solvent and sample solution pH were investigated for the solid‐phase extraction coupled with dispersive liquid–liquid microextraction with these analytes, and the best results were obtained using methanol as eluent and ethylene chloride as extraction solvent. Under the optimal conditions, an exhaustive extraction for four analytes (recoveries >86.9%) and high enrichment factors were attained. The limits of detection were between 0.021 and 0.15 μg/L. The relative standard deviations for 0.5 μg/L of the pesticides in water were in the range of 1.9–6.8% (n = 5). The proposed strategy offered the advantages of simple operation, high enrichment factor and sensitivity and was successfully applied to the determination of four organophosphorus pesticides in water samples.     

Optimized separation of pesticide enantiomers by chiral high-performance liquid chromatography

Summary A computer-assisted method is described for optimization of multi-component, mobile phase selection for separating enantiomers of four pesticides in normal-phase HPLC. The method is based on the triangle, solvent-selection concept using a statistical scanning method. The optimization of the separation over the experimental region is based on a special polynomial estimation from seven experimental runs, and resolution (R_s) is used as the selection criterion. Excellent agreement was obtained between predicted and experimental data.     

Direct resolution of the enantiomers of new diphosphine and diphosphine oxide ligands by high-performance liquid chromatography

Summary Resolution of the enantiomers of new racemic diphosphines, which are very useful ligands for stereoselective catalysts, and of the corresponding phosphine oxides has been investigated by high-performance liquid chromatography (HPLC) on four different chiral stationary phases (CSP)—Chiralpak AD, Whelk-01, and Supelcosil naphthylurea and phenylurea columns. The mobile phases were optimized to achieve separation of the enantiomers. α andR _S values ranged from 1.05 to 5.17 and from 0.37 to 6.57, respectively, for the Chiralpak AD and (R,R)-Whelk-01 columns. For the Supelcosil LC-(R)-phenylurea and Supelcosil LC-(S)-naphthylurea columns α values ranged from 1.05 to 1.62 andR _S from 0.35 to 3.61.     

Extraction and determination of organophosphorus pesticides in water samples by a new liquid phase microextraction-gas chromatography-flame photometric detection

A rapid, sensitive and efficient liquid phase microextraction (LPME) method was developed to determine trace concentrations of some organophosphorus pesticides in water samples. This method combines liquid phase microextraction with gas chromatographic (GC) analysis in a simple and inexpensive apparatus involving very little organic solvent consumption. It involves exposing a floated drop of an organic solvent on the surface of aqueous solution in a sealed vial. Experimental parameters which control the performance of LPME such as type of organic solvent, organic solvent and sample volumes, sample stirring rate, sample solution temperature, salt addition and exposure time were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated by the water samples spiked with organophosphorus pesticides. Using optimum extraction conditions, very low detection limits (0.01-0.04 μg L⁻¹) and good linearities (0.9983 < r² < 0.9999) were achieved. The LPME was performed for determination of organophosphorus pesticides in different types of natural water samples and acceptable recoveries (96-104%) and precisions (3.5 < R.S.D.% < 8.9) were obtained. The results suggested that the newly proposed LPME method is a rapid, accurate and effective sample preparation method and could be successfully applied for extraction and determination of organophosphorus pesticides in water samples.     

Microcolumn liquid chromatography on carbon sorbents

Summary The retention volume dependences on the molar volume were found for aromatic compounds using liquid microcolumn chromatography. The contributions of the functional groups in molecules of these compounds to the total retention value were calculated from the capacity factor values. The comparison of capacity factor values for carbon sorbents and octadecyl-silicagel has shown that for several microcolumn separations the carbon sorbent column has a better selectivity and resolution than the octadecyl-silicagel column.     

Separation of the enantiomers of pyrethroic acids and their esters by high-performance liquid chromatography on a polysaccharide-derived chiral stationary phase

Summary The liquid-chromatographic separation of the enantiomers of pyrethroic acids and their esters has been investigated on a polysaccharide-derived chiral stationary phase (CSP), Chiralpak AS. Good separation of the enantiomers of underivatized pyrethroic acids was achieved on the column, and the enantiomers of pyrethroic acid methyl and ethyl ester derivatives were also resolved.     

Residue analysis of organophosphorus pesticides in food with two-dimensional gas chromatography using capillary columns and flame photometric detection

Two-dimensional gas chromatography with two capillary columns of different polarity (SP 2100 and OV 225) is used for pesticide residue analysis in food samples. By means of “live chromatography” applying pneumatic switching technique according to Deans, unequivocal identification of 57 organophosphorus pesticides in food samples is achieved at trace concentrations. The instrument is equipped with only one injection port and one flame photometric detector. On-line data processing is very helpful, especially in calibration and checking the system's reliability with the multitude of test compounds. The complete pesticide residue analysis including clean-up of about six food samples can be completed by one person in 8 hours.     

Microcolumn liquid chromatography with inductively-coupled plasma atomic emission spectronometric detection

Summary An ICP detector is described which is compatible with microcolumn liquid chromatography. The total column effluent is concentrically nebulized and aspirated into a plasma flame. The carbon compounds are selectively detected by monitoring the characteristic emission line at 247.9 nm using water or aqueous solutions as the mobile phase. The detection limit for carbon is 500 ng or less, and the response is linear over at least two decades. The potential of this system is illustrated by a few applications.     

Polyol‐enhanced dispersive liquid–liquid microextraction coupled with gas chromatography and nitrogen phosphorous detection for the determination of organophosphorus pesticides from aqueous samples,fruit juices,and vegetables

Polyol‐enhanced dispersive liquid–liquid microextraction has been proposed for the extraction and preconcentration of some organophosphorus pesticides from different samples. In the present study, a high volume of an aqueous phase containing a polyol (sorbitol) is prepared and then a disperser solvent along with an extraction solvent is rapidly injected into it. Sorbitol showed the best results and it was more effective on the extraction recoveries of the analytes than inorganic salts such as sodium chloride, potassium chloride, and sodium sulfate. Under the optimum extraction conditions, the method showed low limits of detection and quantification within the ranges of 12–56 and 44–162 pg/mL, respectively. Enrichment factors and extraction recoveries were in the ranges of 2799–3033 and 84–92%, respectively. The method precision was evaluated at a concentration of 10 ng/mL of each analyte, and relative standard deviations were found to be less than 5.9% for intraday (n = 6) and less than 7.8% for interday (n = 4). Finally, some aqueous samples were successfully analyzed using the proposed method and four analytes (diazinon, dimethoate, chlorpyrifos, and phosalone) were determined, some of them at ng/mL level.     

毛细管电泳在有机磷类除草剂检测中的应用进展

近年来,随着抗草甘膦转基因作物的发展,草甘膦用量逐年增大,大量草甘膦制剂的介入严重影响了土壤、水质及生态环境,危害人类身体健康。如何快速准确检测环境样品中的残留有机磷类除草剂已成为人们关注的焦点问题之一。本文从衍生方法、检测器、离线及在线富集技术等几个方面出发,总结了目前毛细管电泳在检测有机磷类除草剂方面的研究工作,并展望了未来的主要发展方向。     

Application of continual injection liquid‐phase microextraction method coupled with liquid chromatography to the analysis of organophosphorus pesticides

A liquid‐phase microextraction coupled with LC method has been developed for the determination of organophosphorus pesticides (methidation, quinalphos and profenofos) in drinking water samples. In this method, a small amount (3 μL) of isooctane as the acceptor phase was introduced continually to fill‐up the channel of a 1.5 cm polypropylene hollow fiber using a microsyringe while the hollow fiber was immersed in an aqueous donor solution. A portion of the acceptor phase (ca. 0.4 μL) was first introduced into the hollow fiber and additional amounts (ca. 0.2 μL) of the acceptor phase were introduced to replenish at intervals of 3 min until set end of extraction (40 min). After extraction, the acceptor phase was withdrawn and transferred into a 2 mL vial for a drying step prior to injection into a LC system. Parameters that affect the extraction efficiency were studied including the organic solvent, length of fiber, volume of acceptor and donor phase, stirring rate, extraction time, and effect of salting out. The proposed method provided good enrichment factors of up to 189.50, with RSD ranging from 0.10 to 0.29%, analyte recoveries of over 79.80% and good linearity ranging from 10.0 to 1.25 mg/L. The LOD ranged from 2.86 to 82.66 μg/L. This method was applied successfully to the determination of organophosphorus pesticides in selected drinking water samples.     

Packed-capillary supercritical fluid chromatography of pesticides using phosphorus-selective detection

Summary Packed-capillary, supercritical fluid chromatography using carbon dioxide modified with methanol or 2-propanol as mobile phase, was coupled with a thermionic detector for phosphorus-selective detection. Optimum conditions for thermionic detection were established for a number of hydrogen flow rates by adjusting the air flow rate and bead position. Using the mentioned modifiers, a series of organophosphorus pesticides of varying polarity could be separated within 8 min. An optimum sensitivity of 55–128 fg P/s and linearity over four orders of magnitude were obtained. The detector showed good selectivity for phosphorus over carbon and nitrogen, viz., 9·10⁴ g C/g P and 75 g N/g P, respectively. This was demonstrated by determining pesticides such as phoxim, dimethoate and azinphos-methyl in onion and tomato extracts.     

Use of enantioselective liquid chromatography for preparation of pure atenolol enantiomers

The study reported here shows a practicable preparation of pure atenolol enantiomers using enantioselective liquid chromatography. The successful separation of enantiomers of the final atenolol and the intermediate ester and the good peak shapes could not have been obtained without diethylamine as a component of the mobile phase. That makes difficult the recycling of the three-component mobile phase, an unavoidable step in simulated moving bed chromatography separation technology. The only suitable methodology for preparation of atenolol enantiomers proved to be synthesis from its N-benzyl-N-isopropyl precursor and the chiral stationary phase Chiralpak AD was found to be very convenient for preparative separation of these enantiomers. The enantiomeric purities and recovery of separated enantiomers of this N-benzyl-N-isopropyl precursor were very high, allowing high enantiomeric purities of the final products, ee's 99.3% for S- and 99.0% for R-atenolol. The chromatographic separation parameters, as well as solubility of racemate in the mobile phase, are good bases for the further examination of possible scale-up resolution of compound 6.     

Microanalysis of dialkylphosphorus metabolites of organophosphorus pesticides in human blood by capillary gas chromatography and by phosphorus-selective and ion trap detection

A procedure for the determination of dialkyphosphorus metabolites of organophosphorus pesticides in human blood has been worked out. Dimethyl and diethyl phosphates, phosphorothioates and phosphorodithioates, extracted with diethyl ether from plasma acidified with hydrochloric acid, were methylated with diazomethane and analysed by capillary gas chromatography with an alkali flame ionization detector and an ion trap detector. The extraction of metabolites was preceded by n-hexane extraction of parent organophosphorus pesticides without a negative effect on the efficiency of metabolite extraction. If plasma samples, containing 2 μ/ml of each metabolite, were not saturated with sodium chloride before extraction, only dialkyl phosphorothioates were recovered by more than 80%. The recoveries of other metabolites were less than 25%. The extraction of plasma samples saturated with sodium chloride resulted in higher recoveries of all metabolites. At concentrations ranging from 0.2 to 2.8 μg/ml the accumulation effeciencies (%±S.D.) of dimethyl and diethyl phosphorothioates were 92±20 and 97±11, and those of corresponding phosphorodithiotes 79±7 and 71±4. A significantly lower recovery (36±12%) was determined for dimethyl phosphate at concentrations in plasma below 2 μg/ml. The recovery of diethyl phosphate was dependent on the initial metabolite concentration in plasma being 31±5% at concentrations lower than 0.5 μg/ml, 51±12% at concentrations ranging from 0.7 to 1.7 μg/ml and 97±3% at concentrations at or above 2 μg/ml. Detection limits of metabolites in plasma using the phosphorus selective detector were 150 ng/ml for dimethyl phosphate and 50 ng/ml for other metabolites. Those values were for dialkyl phosphates and phophorothioates three to five times lower and for diakyl phosphorodithiotes even 30 times lower than detection limits achieved by the use of ion trap detector. The procedure was applied for the evidence and confirmation of human poisoning with organophosphorus pesticides.     

Determination of some organophosphorus pesticides in water and watermelon samples by microextraction prior to high-performance liquid chromatography

A novel method based on simultaneous liquid-liquid microextraction and carbon nanotube reinforced hollow fiber microporous membrane solid-liquid phase microextraction has been developed for the determination of six organophosphorus pesticides, i.e. isocarbophos, phosmet, parathion-methyl, triazophos, fonofos and phoxim, in water and watermelon samples prior to high-performance liquid chromatography (HPLC). Under the optimum conditions, the method shows a good linearity within a range of 1-200 ng/mL for water samples and 5-200 ng/g for watermelon samples, with the correlation coefficients (r) varying from 0.9990 to 0.9997 and 0.9986 to 0.9995, respectively. The limits of detection (LODs) were in the range between 0.1 and 0.3 ng/mL for water samples and between 1.0 and 1.5 ng/g for watermelon samples. The recoveries of the method at spiking levels of 5.0 and 50.0 ng/mL for water samples were between 85.4 and 100.8%, and at spiking levels of 5.0 and 50.0 ng/g for watermelon samples, they were between 82.6 and 92.4%, with the relative standard deviations (RSDs) varying from 4.5-6.9% and 5.2-7.4%, respectively. The results suggested that the developed method represents a simple, low-cost, high analytes preconcentration and excellent sample cleanup procedure for the determination of organophosphorus pesticides in water and watermelon samples.