A Comparison Of Measurement of Homovanillic Acid in Brain Tissue by Gas Chromatography Mass Spectrometry and Liquid Chromatography with Electrochemical Detection

Abstract

A comparison of liquid chromatography with electrochemical detection (LCEC) and gas chromatography mass spectrometry (GCMS) has been made for analysis of homovanillic acid (HVA) in rat brain tissue. The LCEC procedure gave slightly higher average values of HVA in the samples measured; however, the HVA content determined by both methods related significantly. Rat brain meostriatum was used as representative samples for comparison of the two analytical procedures.     

局部麻醉药的反相色谱安培法检测

本文系统研究了普鲁卡因,利多卡因,丁卡因等3种局部麻醉药的液相色谱安培法检测行法,并与液相色谱光度法检测结果进行了比较。     

Determination of glutathione in human plasma using high-performance liquid chromatography with electrochemical detection with a carbon-epoxy resin composite electrode chemically modified with cobalt phthalocyanine

High-performance liquid chromatography with electrochemical detection (LCEC), incorporating a novel carbon-epoxy resin working electrode modified with cobalt phthalocyanine, has been employed for preliminary studies directed towards the determination of normal circulating levels of reduced glutathione (GSH) in human plasma. The mobile phase consisted of 0.05 M phosphate buffer (pH 3) containing 0.1% m/m ethylenediaminetetraacetic acid (EDTA); the calibration graph was linear in the range 0.24-30.7 ng of GSH injected. The mean recovery of GSH added to a control serum over the physiological concentration range (0.38-3.07 ng ml-1) was 99%; this was achieved following a simple sample pre-treatment method, prior to LCEC, involving chelation of divalent cations with EDTA and subsequent acidification with orthophosphoric acid. Using the LCEC method, the mean circulating level of GSH in plasma, found in three normal subjects, was 2.69 microM, GSH; this indicates that the method might be applicable to the determination of depressed circulating levels of GSH.     

Amperometric detection of catecholamines with liquid chromatography at a novelly constructed prussian blue chemically modified electrode

A novel Prussian blue chemically modified electrode (CME) was constructed and characterized for liquid chromatography electrochemical detection (LCEC) of catecholamines. Both anodic and cathodic peaks could be obtained by monitoring at constant applied potential at anodic and slightly cathodic potential ranges (0.3-0.7 and -0.2-0.1 V vs. SCE), respectively. When arranged in a series configuration, using the modified electrodes as generating and collecting detectors, extremely high effective collection efficiencies of 0.91 (for norepinephrine) and 0.58 (for dihydroxyphenylacetic acid) were achieved in dual-electrode LCEC for catecholamines; and a linear response range over 3 orders of magnitude and a detection limit of 10 pg were obtained with a downstream CME as the indicating detector.     

Amperometric Methods for Oxidoreductase Enzymes Based on Liquid Chromatography with Electrochemical Detection. Alcohol Dehydrogenase

Abstract

Nicotinamide adenine dinucleotide (NAD) is an important cofactor in a number of oxidoreductase enzyme systems. The detection and quantitation of its reduced form (NADH) is the basis for a number of methods which determine both substrates and enzyme activity. Although electrochemical techniques have shown promise in this area, they have suffered from a lack of selectivity. Liquid chromatography with electrochemical detection (LCEC) provides the selectivity and the sensitivity required. The use of alcohol dehydrogenase (ADH) for blood alcohol detection is investigated as a model system.     

Quantitative determination of epinephrine and norepinephrine in the picogram range by flame ionization gas-liquid chromatography.

A gas-liquid chromatographic method has been developed using the hydrogen flame detector to determine epinephrine (E) and norepinephrine (NE) in blood plasma, red blood cells, serum, and urine. The chromatographic method presents several advantages over other existing techniques. The derivatives enable separation of E and NE and are stable at room temperature with no signs of decomposition. The detection limit for the catecholamines with the hydrogen detector was approximately 0.1 pg. The catecholamines can be determined simultaneously from the same gas-liquid chromatogram. Purification of the catecholamines using the conventional procedure of chromatographing on alumina has been eliminated. With this gas chromatographic method, no by-products are formed that interfere with E and NE determinations. Dopamine, which constitutes the major source of interference in the commonly used fluorometric methods, does not interfere with the E and NE determinations. Norepinephrine and epinephrine values for several physiological fluids are given with the analysis expanded to include red blood cells, the contents of which have not been previously reported.     

Determination of Ascorbic Acid and Dehydroascorbic Acid in Blood Plasma Samples

Abstract

Following the stabilization of the plasma samples with HClO₄ and EDTA, the samples could be directly analyzed by HPLC using electrochemical detection and reversed-phase columns. The accuracy and precision of the method was evaluated using plasma samples spiked with ascorbic acid (10 μg/ml) and the results were also compared to the classical colorimetric procedure. Dehydroascorbic (5 μg/ml) was determined in plasma samples using UV detection following derivatization at room temperature for 45 minutes with o-phenylenediamine.     

Derivatization and Post-Column Reactions for Improved Detection in Liquid Chromatography/Electrochemistry

Abstract

A summary Is provided of most of Che reported derlvatizations that have been used for improved analyte detection in liquid chromatography with electrochemical detection (LCEC). These approaches include pre-column derivatizations and postcolumns chemical, photochemical or enzymatic reactions for oxidative EC detection. This review covers the literature up to early 1985, and includes information gathered from books, technical articles, previous reviews and scientific journal publications. Specific reagents, methods and instrumentation are described for those classes of compounds studied by derlvatization-LCEC, and suggestions for future experiments are included, where applicable. It is concluded that the future will likely Include the development of a great number of derivatizations which may be used in conjunction with LCEC for trace analysis.     

Determination of cabergoline in plasma and urine by high-performance liquid chromatography with electrochemical detection.

A sensitive and selective high-performance liquid chromatographic method for the determination of cabergoline in plasma and urine has been developed. After buffering plasma and urine samples, cabergoline was extracted with a methylene chloride-isooctane mixture, back-extracted into 0.1 M phosphoric acid, then analysed by reversed-phase high-performance liquid chromatography. Quantitation was achieved by electrochemical detection of the eluate. The linearity, precision and accuracy of the method were evaluated. No interference from the biological matrices (human plasma and urine) was observed. The assay was still inadequate in terms of sensitivity for the quantitation of cabergoline plasma concentrations after a single oral dose of 1 mg of the drug to humans, but was successfully used in the determination of the urinary excretion of the drug.     

Analysis of 3-Methoxy-4-Hydroxyphenylglycol in Human Cerebrospinal Fluid by Gas Chromatography Mass Spectrometry and Electrochemical Detection Liquid Chromatography

Abstract

Gas chromatography mass spectrometry [GCMS] and liquid chromatography with electrochemical detection [LCEC] have been compared in simultaneous determination of 3-methoxy-4-hydroxy-phenylglycol [MHPG] in human cerebrospinal fluid [CSF]. Both free and sulphate conjugated MHPG have been measured in these samples. By Spearman Rank Correlation non-parametric analysis both instrumental techniques related significantly for all quantitated samples.     

Determination of the endocannabinoid anandamide in human plasma by high-performance liquid chromatography

Anandamide (N-arachidonylethanolamine) is an endogenous cannabinoid receptor ligand that has been implicated in various physiological and pathophysiological functions. In the present study, a liquid-liquid extraction-based reversed-phase HPLC method with fluorometric detection was validated and applied for the analysis of anandamide in human plasma. Following derivatization with the fluorogenic reagent 4-(N,N-dimethylaminosulfonyl)-7-(N-chloroformylmethyl-N-methyl-amino)-2,1,3-benzoxadiazole (DBD-COCl), the analyte was separated using an acetonitrile-water gradient at a flow rate of 0.8 mL/min, and spectrophotometric detection at 560 nm with an excitation wavelength of 450 nm. The retention times for anandamide and R+-methanandamide (internal standard) were 27.1 and 30.7 min, respectively. The validated quantification range was 1-15 ng/mL. The developed procedure was applied to determine anandamide levels in human plasma following a 24 h incubation of human whole blood at 37 degrees C in the presence or absence of phenylmethylsulfonyl fluoride, an inhibitor of the anandamide-degrading enzyme fatty acid amide hydrolase. Anandamide levels determined under both conditions were within the validated concentration range with anandamide levels being 2.3-fold higher in plasma from PMSF-treated blood.     

Paper-based Potentiometric Biosensor for Monitoring Galactose in Whole Blood

A filter paper sputtered with a layer of Pt and subsequently coated with a Nafion® membrane is used as working electrode. The mixed potential of the Pt electrode allows the detection of H₂O₂ generated by the oxidation of galactose in the presence of the galactose oxidase enzyme. This provides a simple and mediator-free approach method. The system shows sensitivity values of −62.8±9.4 mV/decade of galactose in the range from 0.3 to 31.6 mM, well within the clinical relevant range. MnO₂ nanoparticles were added to decrease the interference from ascorbic acid so that validation of the sensor in whole blood samples was performed with good recovery.     

Determination of 4-nonylphenol and 4-octylphenol in human blood samples by high-performance liquid chromatography with multi-electrode electrochemical coulometric-array detection

Alkylphenols can affect human health because they disrupt the endocrine system. In this study, an analytical method for determining trace amounts of 4-nonylphenol (NP) and 4-octylphenol (OP) in human blood samples was developed. Reversed-phase HPLC with multi-electrode electrochemical coulometric-array detection was used for the determination of NP and OP in plasma and serum samples prepared with a solid-phase extraction method. The separation was achieved using an isocratic mobile phase of 0.7% phosphoric acid-acetonitrile with a C18 reversed phase column. The detection limits of NP and OP were 1.0 and 0.5 ng ml-1, respectively. The recoveries of NP and OP added to human plasma samples were above 70.0% with a relative standard deviation of less than 15.5%. The method was found to be applicable to the determination of NP and OP in various human blood samples such as serum and plasma.     

A Method for the Measurement of total Drug Convertible to Cysteamine: Application to Pharmacokinetic Experiments with Ethiofos

Abstract

An analytical method has been developed for the quantification of cysteamine (2-aminoethanethiol) in plasma. A reductive sample pretreatment is used to convert disulfide-bound cysteamine to the free thiol which is subsequently separated by HPLC and detected by electrochemical detection (LCEC). The method was developed to follow drug disposition after administration of ethiofos (WR-2721, S-2-(3-aminopropylamino) ethyl phosphorothioic acid) and WR-1065 (2-(3-aminopropylamino)ethanethiol). Standard calibration curves were linear over the range 0.01- to 25.0 /μg/mL (0.130-324 μM) and a minimum detectable quantity of 0.01 μg/mL was calculated at a signal-to-noise ratio of 3. Assay precision over the same range averaged 2% (coefficient of variation) and relative recovery, used as a measure of accuracy, was 100Z. Stability of cysteamine in plasma, relative to an internal standard (2-aminopropanethiol, WR-186) was good; stored samples were found to contain an average of 94.6 ± 10.4z of the original cysteamine concentration following 28 days at -75 °C.

This method was successfully applied in dosing experiments with rhesus monkeys in which ethiofos was administered into the cephalic vein (IV), portal vein (P) and duodenum. In IV experiments total VR-1065 plasma concentrations greatly exceeded total cysteamine concentrations. While results indicate formation of free and bound cysteamine is not a major metabolic pathway of ments total VR-1065 plasma concentrations greatly exceeded total cysteamine concentrations. While results indicate formation of free and bound cysteamine is not a major metabolic pathway of ethiofos, increased levels of bound cysteamine were observed.     

Enhancement of LCEC Response by Use of Rectrochemically Pretreated Glassy Carbon Electrodes

Abstract

A simple electrochemical pretreatment procedure has been shown to increase the selectivity of LCEC detection by lowering the required operating potential compared to that needed at conventional untreated glassy carbon. The effect of a conditioning procedure consisting of sequential application of brief positive and negative potentials to a polished glassy carbon surface was examined for a group of model LCEC analytes including p-hydroquinone, dopamine, dihydronicotinamide adenine dinucleotide (NADH), ascorbic acid, and hydrazine. The lowering of the potential required for detection of these species was greatest for the irreversibly oxidized systems which exhibit the largest overvoltage at untreated glassy carbon–natnely, NADH, ascorbic acid, and hydrazine. For these species at pretreated electrodes, comparable detector response was achieved using potentials 0.2 to 0.5 V less than that otherwise needed for optimum response. The improved performance of the electrochemically pretreated electrodes was maintained over a wide range of pH conditions and mobile phase compositions and dramatically facilitated the determination of the latter set of compounds in physiological matrices.     

HPLC determination of plasma taurine

Summary The taurine content in plasma was determined by high performance liquid chromatographic analysis of its dansyl derivative with fluorometric detection. After the reaction with dansyl chloride, the derivative was extracted from an aqueous mixture by using tetrabutylammonium as a counter-ion. The influences of different tetrabutylammonium salts and of the eluent mixture composition were studied. Omotaurine, added as the internal standard to the plasma samples, assured good reproducibility. The procedure was applied to the determination of taurine in specimens from different mammalian species.     

Liquid chromatographic method with electrochemical detection for determination of cisapride in serum

A sensitive liquid chromatographic (LC) method using electrochemical detection was developed for the identification and quantitation of cisapride in serum. The serum samples were deproteinized by a simple acetonitrile precipitation technique followed by n-hexane extraction. Cisapride in the deproteinized serum was separated by an isocratic elution with an ODS Hypersil LC column (150 x 4.6 mm) using a mobile phase consisting of 0.05M Na2HPO4-acetonitrile (60 + 40), pH 8.4. Cisapride eluted from the column was detected by a Coulochem II electrochemical detector. The precision of this assay method was determined by intra- and inter-day analyses of cisapride-free fetal bovine serum samples that were spiked with 25, 50, and 100 ng/mL cisapride. For the intra-day assay, recoveries were 94.3 +/- 1.4, 90.1 +/- 2.9, and 103.2 +/- 9.2%, respectively. This electrochemical detection LC method could be very useful in monitoring plasma levels of cisapride.     

Rapid determination of acetaminophen in physiological fluids by liquid chromatography using SDS mobile phase and ED detection

Acetaminophen is determined in serum and urine samples by a rapid, sensitive, and precise chromatographic method without any pretreatment step in a C18 column using a pure micellar mobile phase of 0.02M sodium dodecyl sulfate at pH 7. Acetaminophen is eluted in less than 5 min with no interference of the protein band. The use of electrochemical and UV detection is compared. Linearities (r > 0.999), as well as intra- and interday precision, are studied in the validation of the method. Limits of detection (LOD) are also calculated to be 0.56, 0.83, and 0.74 ng/mL in micellar solution, serum, and urine using electrochemical detection. The developed micellar liquid chromatographic method is useful for the quantitation of acetaminophen in serum and urine. Recoveries in the biological matrices are in the 98-107% range and results are compared with those obtained using a reference method. Drug excretion (in urine) and serum distribution are studied in several healthy volunteers, and no interference from metabolites is found. The developed procedure can be applied in routine analyses, toxicology, and therapeutic monitoring.     

Determination of 3-hydroxykynurenine in human brain and plasma by high-performance liquid chromatography with electrochemical detection. Increased concentrations in hepatic encephalopathy

A simple and specific method was developed for the determination of 3-hydroxykynurenine in brain tissue and blood plasma using high-performance liquid chromatography with electrochemical detection. This involved an extraction procedure using strong cation-exchange columns and also permitted the determination of 3-hydroxyanthranilic acid in brain tissue. The method was applied to the investigation of post mortem brain tissue from patients with hepatic encephalopathy. Cortical 3-hydroxykynurenine concentrations were substantially increased in such patients above control values, providing evidence for a dysfunction of tryptophan metabolism in this disease.     

An improved HPLC-ED method for monitoring plasma levels of clozapine and its active metabolites in schizophrenic patients

Summary An HPLC method with electrochemical detection has been developed for the determination of clozapine and its main metabolites, desmethylclozapine and clozapine N-oxide, in human plasma. An accurate pretreatment of the biological samples was implemented by means of solid phase extraction (SPE) on HLB cartridges. This improved pretreatment, together with a new mobile phase, allows for the accurate determination of clozapine N-oxide, which could not be quantitated by a previous method. The method uses only 100 μL of plasma for one complete analysis and shows good recovery values for all three analytes. The eluates from the SPE procedure were chromatographed in a reversed phase C18 column using a mobile phase composed of phosphate buffer, acetonitrile and methanol. Clozapine, desmethylclozapine and clozapine N-oxide were eluted in less than 10 minutes, without any interference from the biological matrix. Linearity was observed over the 2.50–150 ng mL⁻¹ (clozapine and desmethylclozapine) or 1.25–75 ng mL⁻¹ clozapine N-oxide) range for the three analytes, with satisfactory repeatability values. The limit of detection was 0.3 ng mL⁻¹ for clozapine and desmethylclozapine, samples of patients treated with Leponex gave good results. No interference from other common central nervous system drugs was found. This method seems to be a useful tool for pharmacokinetic studies and for clinical monitoring, because of its need for small plasma samples and its high sensitivity and selectivity.