Determination of chlorthalidone in plasma, urine and red blood cells by gas chromatography with nitrogen detection

A sensitive and selective gas chromatographic method is described for determining the diuretic and antihypertensive drug chlorthalidone in plasma, urine and erythrocytes. Use is made of an alkali flame ionization detector (nitrogen detector), and the chlorthalidone and internal standard are chromatographed as methyl derivatives. Down to 10 ng of drugs in the biological sample can be measured accurately, with a standard deviation of 5%. Because the concentration of chlorthalidone found in erythrocytes is 50-100 times higher than that in plasma, the influence of haemolysis on the plasma concentration has been investigated. In addition, a pharmacokinetic study with human volunteers revealed that the apparent concentration of the drug found in plasma can be much too low (by more than 50%), if the plasma is not separated from the erythrocytes immediately after venipuncture. Precautions to be observed to ensure correct handling of blood samples (so that results for plasma concentrations will be reliable) are stressed. The findings have application in kinetic studies on chlorthalidone.     

Determination of xylitol in human urine by gas-liquid chromatography.

A rapid and specific method for the quantitative determination of xylitol in human urine has been developed. The method consists of the gas-liquid chromatographic analysis of the acetate ester derivative of the alditol in deionized urine using dulcitol as an internal standard. As little as 20 ng xylitol can be detected. At concentrations ranging from 25 to 400 micrograms/ml urine, the accuracy is +/- 4.0%.     

Simultaneous determination of chloroquine, amodiaquine and their metabolites in human plasma, red blood cells, whole blood and urine by column liquid chromatography

A column liquid chromatographic method for the simultaneous determination of chloroquine, amodiaquine and their monodesethyl metabolite in human plasma, red blood cells, whole blood and urine is described. The drugs and internal standard were extracted as bases with methylene dichloride and then re-extracted into an acid aqueous phase. Separation was obtained using a reversed-phase column and a mobile phase of phosphate buffer (pH 3.0)-acetonitrile (88:12). The absorbance of the drugs was monitored at 340 nm with a sensitivity limit of 10 pmol/ml. No endogenous compound interfered at this wavelength. The mean overall recovery from each biological fluid was greater than 75%. This method can be applied to therapeutic, pharmacokinetic and epidemiological studies. The metabolism of these two amino-4-quinolines in humans is compared.     

Estimation of disaccharides in plasma and urine by gas-liquid chromatography

A technique for the estimation of disaccharides in plasma and urine using gas-liquid chromatography is described. The procedure involves the formation of trimethylsilyl derivatives followed by injection of the reaction mixture directly onto the column. The method is precise, linear over a wide range and gives recoveries of 93--99%. The limit of sensitivity is 80 micrograms per 100 ml, but with modification of the volumes used, levels of 40 micrograms per 100 ml may be quantitated.     

Rapid micro-method for the measurement of ethchlorvynol in blood plasma and in urine by gas-liquid chromatography

A rapid gas-liquid chromatographic method has been developed for use in the measurement of the hypnotic drug ethchlorvynol in small (50 microliter) volumes of either blood plasma or urine. Neither solvent transfer nor evaporation steps are used in the procedure and sources of interference have proved to be minimal. The method has been applied primarily to the analysis of specimens obtained from patients who had ingested an overdose of this drug. However with slight modification, the technique may be used in the measurement of the plasma concentrations of ethchlorvynol attained during therapy.     

Determination of brodimoprim and its hydroxy metabolite in human plasma, blood and urine by high-performance liquid chromatography.

A high-performance liquid chromatographic method was developed to measure the concentration of brodimoprim and its metabolite, hydroxybrodimoprim, in small volumes of blood, plasma and urine. The procedure involved a simple extraction step with chloroform, followed by chromatographic separation on a short reversed-phase column deactivated for the analysis of basic compounds. The column effluent was monitored by fluorescence (excitation wavelength 290 nm, emission wavelength 340 nm). The recoveries of both compounds were similar in all three biological fluids, and averaged 84 and 72%, respectively. The detection limit for both compounds reached 5 ng/ml. No endogenous compound interfered in the assay. The linearity of the method and its within- and between-day precision were analytically satisfactory.     

Determination of salbutamol in human plasma and urine by high-performance thin-layer chromatography

A rapid, accurate and sensitive method for the determination of salbutamol in plasma and urine is described. Salbutamol is extracted using solid-phase techniques and converted to an indoaniline dye by reaction with dimethyl-p-phenylenediamine. The indoaniline is separated using high-performance thin-layer chromatography and quantified by absorption microdensitometry at 650 nm. The method is sensitive down to 20 ng/ml in urine and to 1 ng/ml in plasma and provides data in good agreement with that obtained by gas chromatography--mass spectrometry. The method can be used for analysis of pharmacokinetic studies.     

Determination of trichlormethiazide in human plasma and urine by high-performance liquid chromatography

Summary This paper describes a high-performance liquid chromatographic (HPLC) assay method for the determination of trichlormethiazide (TCM) in human plasma and urine. After extraction and separation on an ODS column TCM from plasma was detected by oxidation in an electrochemical detector (ECD) by a porous graphite electrode. The sensitivity was better than HPLC with UV detection, enabling the determination of 2 ng ml^–1 TCM in human plasma. This method also allows determination of TCM at higher concentrations by exchanging the UV for the electrochemical detector. To study the pharmacokinetics, TCM in plasma and urine was assayed with coefficients of variation in the range 2–3%. The method has the advantages of high sensitivity for plasma assay and high precision with a simple procedure for both plasma and urine samples. Small samples of 0.5 ml plasma per assay also reduced the total volume of plasma needed.     

Determination of clorazepate and its major metabolites in blood and urine by electron capture gas-liquid chromatography.

A sensitive and specific blood level method employing differential extraction was developed for the determination of clorazepate and its N-desmethyldiazepam metabolite by electron capture gas-liquid chromatography (GLC-ECD). The assay requires the initial extraction of N-desmethyldiazepam, the major metabolite, into benzene-methylene chloride (90:10) from the biological sample made alkaline with 0.1 N NaOH. The samples is then acidified with 2 N HCl to decarboxylate clorazepate to N-desmethyldiazepam, which is then extracted into benzene-methylene chloride (90:10) after adjusting the pH to 12.8 with NaOH. The two extracts are evaporated and the residues are dissolved in benzene which contains griseofulvin as the reference standard. These solutions are assayed by GLC-ECD. The overall recovery and sensitivity limit of the assay for clorazepate is 60+/-5% (S.D.) and 4.0 ng/ml blood, respectively, while that for N-desmethyldiazepam is 95+/-5% (S.D.) and 4.0 ng/ml blood, respectively. The urinary excretion of clorazepate was determined by the measurement of the levels of N-desmethyldiazepam and oxazepam, the major urinary metabolites of clorazepate, both prior to and after enzymatic deconjugation. These methods were applied to the measurement of clorazepate and its metabolites in blood and urine following a single 15-mg dose of clorazepate dipotassium.     

Determination of indomethacin in serum and urine by electron-capture gas-liquid chromatography.

A specific and sensitive method for the quantitative determination of indomethacin in serum and urine is described. The drug is extracted at pH 5.0 with 1,2-dichloroethane and a portion of the organic extract is concentrated and made to react with diazoethane in diethyl ether. The ethyl ester derivative is analyzed by electron-capture gas-liquid chromatography, quantitation being achieved by comparison of peak areas for samples and standards, which are prepared in serum or urine and treated in the same manner as the samples. The limit of sensitivity is 50 ng/ml and the relative standard derivation for repeat determinations on the same sample is about 3%.     

Determination of cocaine adulterants in human urine by dispersive liquid-liquid microextraction and high-performance liquid chromatography

Analytical and Bioanalytical Chemistry - This study aimed to determine simultaneously five major street cocaine adulterants (caffeine, lidocaine, phenacetin, diltiazem, and hydroxyzine) in human...     

Determination of picotamide in human plasma and urine by high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of picotamide in human plasma and urine is described. After addition of an internal standard (bamifylline), the plasma and urine samples were subjected to liquid-liquid extraction and clean-up procedures. The final extracts were evaporated to dryness and the resulting residues were reconstituted in 100 microliters of methanol-water (50:50, v/v) and chromatographed on a LiChrosorb RP-SELECT B reversed-phase column coupled to an ultraviolet detector monitored at 230 nm. Chromatographic analysis takes about 10 min per sample. The assay was linear over a wide range and has a limit of detection of 0.005 and 0.1 micrograms/ml in plasma and urine, respectively. It was selective for picotamide, accurate and robust and thus suitable for routine assays after therapeutic doses of picotamide.