On-line sample preparation of paraquat in human serum samples using high-performance liquid chromatography with column switching

Sequential injection differential pulse voltammetric method based on screen printed carbon electrode modified with carbon nanotube/Nafion for sensitive determination of paraquat

The screen-printed carbon electrode (SPCE) modified with various nanoparticles has been studied for using as a working electrode in voltammetric technique. The electrochemical behavior of paraquat on different electrodes was studied by cyclic voltammetry (CV), and then differential pulse voltammetry (DPV) has been employed for trace analysis of paraquat based on redox reaction which the peak current was directly proportional to the concentration of paraquat in the solution. The SPCE modified with carbon nanotube dispersed in Nafion and ethanol (SPCE-CNT/Nafion) gave the best result. Sequential injection-differential pulse voltammetric (SI-DPV) method has been developed for more automated analysis and to reduce chemical consumption. The parameters affecting the SI-DPV system such as step potential, modulation amplitude, flow rate, and concentration of sodium chloride as an electrolyte were studied to improve the sensitivity. Under the optimum condition of the system, i.e., Nafion concentration of 1% (w/v), volume of CNT suspension of 2µL, flow rate of 100µLs^-1, step potential of 5mV, modulation amplitude of 100mV and concentration of sodium chloride of 1M, a linear calibration graph in the range of 0.54-4.30µM with a good R² of 0.9955 and a limit of detection of 0.17µM (0.03mgL^-1) were achieved. The proposed system shows high tolerance to some possible interfering ions in natural water, surfactant, and other pesticides. The relative standard deviation (RSD) was 4.2% for 11 replicate measurements with the same electrode. The reproducibility for the preparation of 7 modified electrodes was 2.3% RSD. Recoveries of the analysis were obtained in the range of 82-106%. The developed system can be conveniently applied for analysis without pretreatment of the samples.

Quantification of paraquat in postmortem samples by gas chromatography-ion trap mass spectrometry and review of the literature

Paraquat (PQ) is an herbicide implicated in numerous fatalities, mainly caused by voluntary ingestion. Several methods have been used to quantify PQ in plasma and urine samples of intoxicated humans as a predictor of clinical outcome. There is no validated method for the analysis of PQ in postmortem samples. Therefore, the aim of this study was to develop an analytical method, using gas chromatography-ion trap mass spectrometry (GC-IT/MS) after solid-phase extraction, to quantify PQ in postmortem samples, namely in whole blood, urine, liver, lung and kidney, to cover the routes of distribution, accumulation and elimination of PQ. The method proved to be selective as there were no interferences of endogenous compounds with the same retention time as PQ and ethyl paraquat (internal standard). The regression analysis for PQ was linear in the range 0-10 µg/mL. The detection limits ranged from 0.0076 µg/mL for urine to 0.047 µg/mL for whole blood, and the recoveries were suitable for forensic analysis. The proposed GC-IT/MS method provided an accurate and simple assay with adequate precision and recovery for the quantification of PQ in postmortem samples. The proof of applicability was performed in two fatal PQ intoxications. A review of the analytical methods for the determination of quaternary ammonium herbicides is also provided for a better understanding of the presently available techniques.

Analytical Methods of Biological Monitoring for Exposure to Pesticides: Recent Update

Extensive use of synthetic pesticides for agricultural and nonagricultural purposes began in the past 50 years. As a result of their wide and extensive application, exposure to hazardous pesticides is a concern to the general population and occupationally exposed persons. Robust methods are therefore needed for measuring markers of pesticide exposure. This article presents a review of the most recently published analytical methodologies and instrumentations developed for and applied to biological monitoring of exposure to pesticides of various classes. Most of the methods reviewed here are based on chromatography combined with mass spectrometry detection. This work clearly demonstrates that although gas chromatography still appears to be the most widely employed technique for pesticide analysis in various biological samples, recently a trend has been observed toward the use of liquid chromatography coupled with tandem mass spectrometry.

Rapid and Sensitive HPLC Method for the Simultaneous Determination of Paraquat and Diquat in Human Serum

A rapid and sensitive HPLC method for the simultaneous determination of paraquat and diquat in human serum has been developed. After deproteinization of the serum with 10% trichloroacetic acid, the samples were separated on a reversed-phase column, and subsequently reduced to their radicals with alkaline sodium hydrosulfite solution. These radicals were monitored with a UV detector at 391 nm. This method permitted the reliable quantification of paraquat over linear ranges of 50 ng - 10 microg/ml and 100 ng - 10 microg/ml for diquat in human serum. The within- and between-day variations are lower than 2.3 and 2.2%, respectively. This technique was also utilized to determine the paraquat and diquat serum levels in a patient who had ingested herbicide (Prigrox L) containing paraquat and diquat.

Column-switching high-performance liquid chromatographic analysis of fluvastatin in rat plasma by direct injection

A column-switching high-performance liquid chromatographic (HPLC) method has been developed and validated for quantification of fluvastatin in rat plasma. Plasma samples were diluted with an equal volume of mobile phase, i.e. acetonitrile-5 mM potassium phosphate buffer (pH 6.8) (15:85, v/v), and the mixture was directly injected onto the HPLC system. The analyte was enriched in a pre-treatment column, while endogenous components were eluted to waste. The analyte was then back-flushed onto an analytical column and quantified with fluorescence detection (lambdaex=305 nm; lambdaem=390 nm). The standard curve for the drug was linear in the range 0.5-100 ng mL(-1) in rat plasma. The limit of quantitation for plasma was found to be 0.5 ng mL(-1). This method has been fully validated and shown to be specific, accurate and precise. The method is simple and rapid because of a minimized sample preparation and appears to be useful for the pharmacokinetic study of fluvastatin.

Column-switching high-performance liquid chromatographic method for the determination of zaltoprofen in rat plasma

A direct injection column-switching high-performance liquid chromatography (HPLC) method was developed and validated for quantification of zaltoprofen in rat plasma. Following dilution with mobile phase A, i.e. acetonitrile-10mM potassium phosphate buffer (pH 6.8) (12:88, v/v) samples were directly injected to the pre-column without sample pre-purification step. After endogenous plasma components were eluted to waste, the system was switched and the analyte was eluted to the trap column. Zaltoprofen was then back-flushed to the analytical column for separation with mobile phase B, i.e. acetonitrile-10mM potassium phosphate buffer (pH 6.8) (35:65, v/v) and quantification with an ultraviolet detector at 230 nm. The calibration curve was linear in the concentration range of 40-5000 ngmL(-1). This method has been fully validated and shown to be specific, accurate and precise. The method is simple, rapid and the sample preparation is minimal and appears to be useful for the pharmacokinetic study of zaltoprofen.

A multi-analyte method for the quantification of contemporary pesticides in human serum and plasma using high-resolution mass spectrometry

We have developed a sensitive and accurate analytical method for quantifying 29 contemporary pesticides in human serum or plasma. These pesticides include organophosphates, carbamates, chloroacetanilides, and synthetic pyrethroids among others and include pesticides used in agricultural and residential settings. Our method employs a simple solid-phase extraction followed by a highly selective analysis using isotope dilution gas chromatography-high-resolution mass spectrometry. Our method is very accurate, has limits of detection in the low pg/g range and coefficients of variation of typically less than 20% at the low pg/g end of the method linear range. We have used this method to measure plasma pesticide concentrations in females living in an urban area. We found detectable concentrations of carbaryl/naphthalene, propoxur, bendiocarb, chlorpyrifos, diazinon, dicloran, captan and folpet or their metabolites in more than 20% of the plasma samples tested.

Development of a two-dimensional liquid chromatography system with trapping and sample enrichment capabilities

A two-dimensional HPLC system was developed where "heart-cutting" chromatography, in conjunction with cold temperature trapping, was used to isolate and concentrate specific sample analytes. Low molecular mass polystyrene oligomers were used as model compounds to illustrate the operation of the instrument and evaluate the performance of the trapping system. A critical factor in the operation of the trapping system was the relative degree of retention between the first column and the trapping column. The results of this study showed that up to 32 consecutive heart-cut fractions from the first separation dimension could be stored in a trapping column with good analyte recovery and without significant loss in resolution upon elution on the second separation dimension.

Narrowbore high-performance liquid chromatography for the simultaneous determination of sildenafil and its metabolite UK-103,320 in human plasma using column switching

A fully automated narrowbore high-performance liquid chromatography method with column switching was developed for the simultaneous determination of sildenafil and its active metabolite UK-103,320 in human plasma samples without pre-purification. Diluted plasma sample (100 microl) was directly introduced onto a Capcell Pak MF Ph-1 column (20x4 mm I.D.) where primary separation occurred to remove proteins and concentrate target substances using 15% acetonitrile in 20 mM phosphate solution (pH 7). The drug molecules eluted from the MF Ph-1 column were focused in an intermediate column (35x2 mm I.D.) by a valve switching step. The substances enriched in the intermediate column were eluted and separated on a phenyl-hexyl column (100x2 mm I.D.) using 36% acetonitrile in 10 mM phosphate solution (pH 4.5) when the valve status was switched back. The method showed excellent sensitivity (detection limit of 10 ng/ml), good precision (RSD < or = 2.3%) and accuracy (bias: +/-2.0%) and speed (total analysis time 17 min). The response was linear (r2 > or = 0.999) over the concentration range 10-1000 ng/ml.

Column-switching high-performance liquid chromatography-electrospray ionization mass spectrometry for identification of heroin metabolites in human urine

In order to prove heroin (DAM) use, a simple, rapid and sensitive analytical method has been established by combining semi-microcolumn HPLC, a column switching technique and electrospray ionization mass spectrometry (ESI-MS). Urine samples were directly introduced to the system, and endogenous urinary constituents were removed by using on-line column switching solid-phase extraction with a strong cation-exchange (SCX) cartridge column (2.0 mm I.D. x 10 mm). Heroin and its metabolites enriched on the top of the column were then successfully analyzed with excellent separation by use of a SCX semi-microcolumn (1.5 mm I.D. x 150 mm), accompanied by ESI mass spectral detection. The proposed conditions are as follows: mobile phase, 10 mM ammonium acetate (pH 6.0)-acetonitrile (30:70, v/v) (for main separation) and 30 mM ammonium acetate (for trapping); flow-rates, 120 microl/min (for main separation) and 200 microl/min (for trapping); capillary voltage, +4.5 kV; cone voltage, 50 V. Linear calibration curves were obtained in the selected ion monitoring (SIM) mode using protonated molecular ions (m/z 370 for DAM, m/z 328 for MAM and m/z 286 for MOR) over the concentration ranges from 10 to 1000 ng/ml for morphine (MOR) and 1-100 ng/ml for DAM and 6-acetylmorphine (MAM). The detection limits were 0.1-3 ng/ml. Upon applying the scan mode, 2-30 ng/ml were the detection limits. The present HPLC-ESI-MS method was successfully applied to the determination of opiates in users' urine samples.

Analysis of the enzymatic racemization of D-aspartic acid to L-aspartic acid by the on-line coupling of a solid-phase extraction column and a ligand-exchange high-performance liquid chromatography column

D-Aspartic acid can be enzymatically biotransformed with D-amino acid oxidase and aminotransferase to L-aspartic acid. The reaction was surveyed at three temperatures and a period of 3 days, however, L-aspartic acid can be produced only at the reaction temperature 90 degrees C. However, the separation of D-aspartic acid and L-aspartic acid by ligand-exchange chromatography showed matrix interference. Therefore, the column-switching technique by coupling a solid-phase extraction (SPE) column to the analytical ligand-exchange HPLC column was used to eliminate the matrix effect. The pretreatment of reaction samples with the SPE column was considered as a combination of size-exclusion chromatography and ion-pair chromatography. The ion-pair reagent was 0.005 M sodium 1-octanesulfonate aqueous solution adjusted to pH 2.2. Part of the first eluted peak from the SPE column was then switched through the ligand-exchange column and analyzed with a 0.25 mM Cu2+ aqueous mobile phase of pH 3.6. The quantitative analysis of D- and L-aspartic acids was performed by the standard addition method. Overall, the separation and analysis of D- and L-aspartic acids in the enzymic solution was convenient, fast, and successful with the developed on-line LC-LC column-coupling and column-switching system.

On-line trace enrichment for the simultaneous determination of microcystins in aqueous samples using high-performance liquid chromatography with diode-array detection

The need for a rapid, sensitive and reliable analytical method for cyanobacterial toxins, microcystins, has been emphasized by the awareness of toxic cyanobacteria as a human-health risk through drinking water. A new high-performance liquid chromatographic method with column switching was developed for the determination of microcystin-LR, -RR and -YR from water samples without pre-purification. The filtered water sample was passed through a Zorbax CN precolumn at a flow-rate of 3 ml/min for on-line trace enrichment. After valve switching, concentrated analytes were eluted in back-flush mode and separated on a Luna C18 column with a gradient of acetonitrile -20 mM phosphate buffer (pH 2.5). The method showed excellent precision, accuracy and speed with detection limits of 0.02 microgram/ml from 100 ml of surface water. The total analysis time per sample was about 90 min. This method improves reliability, sensitivity and sample throughput, and shortens the analysis time compared to analysis methods using off-line solid-phase extraction.

Microbore high-performance liquid chromatographic determination of cisapride in rat serum samples using column switching

For the determination of cisapride from serum samples, an automated microbore high-performance liquid chromatographic method with column switching has been developed. After serum samples (100 microl) were directly injected onto a Capcell Pak MF Ph-1 pre-column (10 x 4 mm I.D.), the deproteinization and concentration were carried out by acetonitrile-phosphate buffer (20 mM, pH 7.0) (2:8, v/v) at valve position A. At 2.6 min, the valve was switched to position B and the concentrated analytes were transferred from MF Ph-1 pre-column to a C18 intermediate column (35x2 mm I.D.) using washing solvent. By valve switching to position A at 4.3 min, the analytes were separated on a Capcell Pak C18 UG 120 column (250 x 1.5 mm I.D.) with acetonitrile-phosphate buffer (20 mM, pH 7.0) (5:5, v/v) at a flow-rate of 0.1 ml/min. Total analysis time per sample was 18 min. The linearity of response was good (r=0.999) over the concentration range of 5-200 ng/ml. The within-day and day-to-day precision (CV) and inaccuracy were less than 3.7% and 3.8%, respectively. The mean recovery was 96.5+/-2.4% with the detection limit of 2 ng/ml.