Determination of organic colorants in cosmetic products by high-performance liquid chromatography

Summary High-performance liquid chromatography (HPLC) with UV-vis detection was used for the determination of organic colorants in cosmetic products. 126 colorants were characterized by their retention times in an ion-pair reversed-phase HPLC system with gradient elution, and by their UV-vis spectra, recorded with a diode array detector (DAD). The method is rapid and efficient, as is demonstrated by the analysis of 45 cosmetic samples.     

Determination of 1,4-dioxane in cosmetic products by high-performance liquid chromatography

A rapid high-performance liquid chromatographic procedure has been developed for the assay of 1,4-dioxane in cosmetic products. After solid-phase extraction, using Bond Elut CN and Bond Elut C18 cartridges, samples were analysed directly on a LiChrospher CH-8 reversed-phase column with spectrophotometric detection at 200 nm and acetonitrile - water as eluent. Recovery of 1,4-dioxane from different cosmetic matrices was between 81.5 and 90.1% in the 30-90 microgram g(-1) range. The minimum quantifiable amount was 6.5 microgram g(-1). The method is simple, reproducible and specific and is suitable for routine analyses of commercial cosmetics.     

Determination of diclofenac in plasma by high-performance liquid chromatography with electrochemical detection

A reversed-phase high-performance liquid chromatographic method with electrochemical detection for the quantitative determination of diclofenac potassium in plasma was developed. Naproxen was used as the internal standard. The drug and internal standard were isolated from plasma by extraction with dichloromethane and 2 M hydrochloric acid. Chromatographic separation was performed on a C18 column with methanol-water (68:32, v/v) adjusted to pH 3.2 with phosphoric acid as mobile phase. The oxidation potential for detection was established by constructing a voltammogram for diclofenac. The quantification limit for diclofenac in plasma was 5 ng mL(-1). Linearity of the method was confirmed in the range 5-2000 ng mL(-1), correlation coefficient 0.9998. Within-day relative standard deviations (RSDs) ranged from 0.66 to 14.00% and between-day RSDs from 0.59 to 15.78%. The method was successfully applied for the determination of pharmacokinetic parameters after ingestion of a 50 mg dose of diclofenac. Studies were performed on 18 healthy volunteers of both sexes.     

Determination of thiamazole in serum by high-performance liquid chromatography with electrochemical detection

A simple and sensitive method for the determination of thiamazole in serum by high-performance liquid chromatography with electrochemical detection is described. Thiamazole in serum was quantified without an extraction procedure at concentrations down to 10 ng/ml. This method was applied to determine the serum concentration of the drug in two healthy volunteers given a single oral dose of 10 mg of thiamazole. The concentration of the drug reached a maximum at 3-4 h after the oral dose and two elimination phases were observed.     

Determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with electrochemical detection.

The cyclic voltammetric behavior of acetaldehyde and the derivatized product with 2,4-dinitrophenylhydrazine (DNPHi) has been studied at a glassy carbon electrode. This study was used to optimize the best experimental conditions for its determination by high-performance liquid chromatographic (HPLC) separation coupled with electrochemical detection. The acetaldehyde-2,4-dinitrophenylhydrazone (ADNPH) was eluted and separated by a reversed-phase column, C18, under isocratic conditions with the mobile phase containing a binary mixture of methanol/LiCl(aq) at a concentration of 1.0 x 10(-3) M (80:20 v/v) and a flow rate of 1.0 mL min(-1). The optimum condition for the electrochemical detection of ADNPH was +1.0 V vs. Ag/AgCl as a reference electrode. The proposed method was simple, rapid (analysis time 7 min) and sensitive (detection limit 3.80 microg L(-1)) at a signal-to-noise ratio of 3:1. It was also highly selective and reproducible [standard deviation 8.2% +/- 0.36 (n = 5)]. The analytical curve of ADNPH was linear over the range of 3-300 mg L(-1) per injection (20 microL), and the analytical recovery was > 99%.     

Determination of sugars, sugar degradation products and alcohols by high-performance liquid chromatography with electrochemical detection

Summary The use of an electrochemical, amperometric detector with nickel as a working electrode for the determination of carbohydrates and alcohols after separation by high-performance liquid chromatography (HPLC) is discussed. In order to get sensitive and stable signals pretreatment experiments were carried out and the combination of this detector with polymer-based cation-exchange columns as well as reversed phase columns is described.     

Determination of triazine pesticides by high-performance liquid chromatography with swept-potential electrochemical detection

A swept-potential electrochemical detector, operating in the square-wave voltammetric mode, is used to detect a mixture of five triazine pesticides separated on a reverse-phase resin column. Limits of detection are below 1 ng injected. Two compounds, not completely separated by the column, are resolved on the potential axis.     

Determination of platelet monoamine oxidase activity by high-performance liquid chromatography with electrochemical detection.

A procedure for determining human platelet monoamine oxidase (MAO) with dopamine (DA) as substrate is described. High-performance liquid chromatography (HPLC) with electrochemical detection (ED) was used to separate and detect components of the reaction mixture. The method for platelet preparation was also improved and only 2 ml of blood were required. Following a 10-min incubation of the platelet preparation with DA in 0.1 M Tris buffer (pH 9.0), excess DA substrate was removed by adsorption on a cation-exchange resin. The reaction product, 3,4-dihydroxyphenylacetaldehyde, was adsorbed on acid-washed alumina, eluted with 0.1 M perchloric acid and analyzed by HPLC. Simple, clean chromatograms were obtained with good reproducibility using 3,4-dihydroxybenzylamine as an internal standard. The within-sample, between-samples and between-day relative standard deviations were 0.9, 3.7 and 6.1%, respectively. The apparent Michaelis constant and maximum velocity were 0.10 mM and 0.37 nmol/min.mg protein, respectively. This HPLC-ED method offers a good alternative to methods using radioactivity.     

Determination of urinary 5-S-cysteinyldopamine by high-performance liquid chromatography with electrochemical detection

Summary 5-S-Cysteinyldopamine, a new metabolite of dopamine, was determined in urine by high-performance liquid chromatography with electrochemical detection. The catechol was detected in 14 of 21 melanoma patients and 7 of 21 normal subjects; the highest values were 657 μg/day for melanoma patients and 44 μg/day for normal subjects. These results suggest that the cysteine conjugate may arise from autoxidation of dopamine but tyrosinase may also participate in the oxidation.     

Determination of glutathione in biological material by high-performance liquid chromatography with electrochemical detection

Glutathione in biological samples is extracted by perchloric acid and separated by ion-paier chromatography on a RP-18 phase. In a post-column reaction, glutathione is converted to an isoindole derivative by reaction with o-phthalaldehyde and detected at a galssy carbon electrode at 800 mV v. Ag/AgCl/3 M KCl. The detection limit is 40 pmol of glutathione injected.     

Determination of bisphenol A in air by high-performance liquid chromatography with electrochemical detection

An air-sampling method for bisphenol A utilizing 13-mm glass fibre filters was developed. The collection efficiency and desorption characteristics were determined. Liquid chromatographic conditions were optimized for the electrochemical detection of bisphenol A. Detection under acidic and alkaline conditions is discussed. The detection minimum is 25 ng/m3 for a 60-1 sample.