Manuel H. Blanco

Determination of copper(II) with a carbon paste electrode modified with an ion-exchange resin

The determination of copper(II) was studied using a carbon paste electrode modified with an ion-exchange resin (Dowex 50W-X8) using differential-pulse voltammetry. The conditions necessary for the preconcentration of copper were determined in an open circuit by ion exchange; copper levels down to 18 nM were determined. The method was applied to the determination of copper in pharmaceutical products.

Analysis of promazines in bovine livers by high performance liquid chromatography with ultraviolet and fluorimetric detection.

Fluorimetric and UV methods of detection for liquid chromatographic determination of phenothiazines (chlorpromazine, acetopromazine and propionylpromazine) were developed. The effects of several experimental parameters on the separation and the sensitivity of the methods were evaluated. The detection limits ranged from 31 to 350 ngml(-1). Optimized methods were successfully applied to determination of the promazines in bovine liver samples.

Determination of flunitrazepam by differential-pulse voltammetry using a bentonite-modified carbon paste electrode

A method is described for the determination of flunitrazepam using a bentonite-modified carbon paste electrode. Flunitrazepam is adsorbed on the electrode in an open circuit (pH 3.8) and determined in 0.5 M KNO3 by differential-pulse voltammetry.The calibration is linear for values between 0.2 and 4.0 µg ml–1. The detection and determination limits were about 0.04 and 0.13 µg ml–1 of flunitrazepam, respectively. The measurements have a relative standard deviation of 1.8% and a relative error of 1.6%. It is possible to determine directly 1.5 µg ml–1 of flunitrazepam in serum and urine with a relative standard deviation of <6.0% when compared with the same determination in a solution without serum.

Voltammetric determination of nitrobenzene with a chemically modified carbon paste electrode. Application to wines, beers and cider

SummaryA method for the determination of nitrobenzene with a sepiolite modified carbon paste electrode is presented. Nitrobenzene is adsorbed on the electrode at open circuit (pH 3.5), and determined by differential pulse voltammetry and cyclic voltammetry at pH 5.5 in 0.5 mol/l KNO3. The calibration is linear up to 0.4 μg × ml−1. The method was applied to the determination of nitrobenzene in wines, beers and cider. The error was ±2% and the standard deviation 5%.

Determination of nitrazepam and flunitrazepam by flow injection analysis using a voltammetric detector

Nitrazepam and flunitrazepam were determined by flow injection analysis using a glassy carbon electrode as a voltammetric detector. The sample solution (200 µl 5.6–28.1 µg ml–1 and 6.3–31.3 µg ml–1 for nitrazepam and flunitrazepam, respectively) was injected into the carrier stream, which was a 0.1 M phosphate buffer solution (pH 7.0) containing 10%V/V of methanol. Nitrazepam and flunitrazepam were determined by reduction at the glassy carbon electrode; a 70 cm delay coil (0.58 mm i.d.) was incorporated before the detector and a flow-rate of 4 ml min–1 was used. The system was applied to the determination of 5 and 2 mg of nitrazepam and flunitrazepam, respectively, giving concentrations of 5.1 ± 0.25 and 1.9 ± 0.08 mg (n= 5).

Highly Sensitive Methods for Determination of Fluoride in Biological Samples

Abstract A total of 40 samples of shell ashes from chicken eggs and 15 samples of chicken plasma have been investigated for amounts of fluoride. Two different methods have been applied. Egg samples were analysed with a spectrophotometric method (Alizarin:cerium:fluoride complex with detection at λ = 620 nm), following prior distillation of the samples in sulfuric media. Plasma samples were analysed by suppressed ion chromatography (IC) with conductivity detection. In this case, it was necessary to develop a cleaning method for the samples before their injection into the chromatographic system. The detection limits obtained were 25 ng mL−1 for the colorimetric method and 50 ng mL−1 in the case of the chromatographic method. Both methods were successfully applied to the analysis of the samples, and the obtained results were in accordance with the results obtained with the ion selective electrode (ISE) method. On the other hand, the proposed methods turn out to be a sensitive alternative when problems with sample size or cationic interferences are present.

Determination of Dihydrozeatin and Dihydrozeatin Riboside by Cathodic Stripping Voltammetry

The present study develops methods to quantify the phytohormones dihydrozeatin (DHZ) and dihydrozeatin ridoside (DHZR) using cathodic stripping and differential pulse voltammetry (DPS). Employing a supportive electrolyte with 0.04 M acetic/acetate buffer pH 4.5 and 40 s accumulation time at –0.60 V, the detection and determination limits for DHZ were 5.5 and 8.0 ng mL–1, respectively. For DHZR using a 0.04 M acetic/acetate buffer pH 4 with a 50 s accumulation time at –0.95 V the detection limit was 16.0 ng mL–1 with a determination limit of 24.0 ng mL–1. Both methods were successfully applied to determine minute amounts of cytokinins in apples.

ANALYSIS OF PHARMACEUTICAL RESIDUES IN BOVINE LIVER BY HPLC

A reversed-phase high performance liquid chromatographic method has been developed for the simultaneous analysis of a group of pharmaceuticals including corticoids (dexamethasone and betamethasone acetate) and major tranquillizers (chlorpromazine, acetopromazine, propionyl promazine, xylazine, and haloperidol) in bovine livers using U.V detection. Next to a fractionated liquid-liquid extraction, the total separation was carried out using a Kromasil C18 column and a mixture of methanol:water (80:20, v/v) as mobile phase. All the compounds were detected at 240 nm. The detection limits ranged from 21 ng·mL−1 to 298 ng·mL−1.

Determination of clonazepam by flow injection analysis

Clonazepam was determined by flow injection analysis using voltammetric (glassy carbon electrode) and spectrophotometric detectors. The sample solution (200 µl of 6.3–31.5 µg ml–1 and 250 µl of 0.6–31.5 µg ml–1 for voltammetric and spectrophotometric detection, respectively), was injected into the carrier stream, which was 0.1 M phosphate buffer solution (pH 7.0) containing 10%V/V of methanol. Sampling rates of 120 per hour were achieved, with high reproducibility of measurements (relative standard deviations below 1.1%). The systems were applied to the determination of clonazepam in pharmaceutical formulations and human urine.

Isomeric Transformation Of 4-Aminobiphenyl by U.V. Radiation and its Influence on the Determination by Flow Injection Analysis with Amperometric and Spectrophotometric Detection.

Abstract Two flow-injection methods for the determination of 4-aminobiphenyl by amperometry (glassy carbon electrode) and spectrophotometry are proposed. A sample volume of 200 or 400 μl containing an analyte concentration of 0.1–1.0 μg ml−1 or 0.8–24.0 μg ml−1 for amperometric or spectrophotometric detection, respectively, is injected into a carrier stream containing 0.04 or 0.02 M Britton-Robinson buffer at pH 10.0 or 8.0, respectively. The throughput thus achieved is 200 (amperometry) and 240 samples/h (spectrophotometry) and the relative standard deviation less than 2.5% and 4.2% respectively. Both methods were applied to the determination of 4-aminobiphenyl in commercially available, legally permitted food colouring additive.