Application of matrix solid-phase dispersion to the determination of amitrole and urazole residues in apples by capillary electrophoresis with electrochemical detection.

A new method based on matrix solid-phase dispersion (MSPD) extraction was studied for the extraction of amitrole (3-amino-1,2,4-triazole), and its metabolite urazole (3,5-dihydroxy-1,2,4-triazole), in apple samples. The influence of experimental conditions on the yield of the extraction process and on the efficiency of the cleanup step was evaluated. Determination was carried out by capillary electrophoresis (CE) with electrochemical detection, demonstrating the compatibility between MSPD and CE techniques. The method has been successfully applied to different apple varieties. Recoveries in samples spiked at 1.6 and 1.7 microg g(-1) for amitrole and urazole were 88 and 82%, respectively. The limits of detection were 0.4 microg g(-1) for both compounds using electrochemical detection.

Determination of amitrole and urazole in water samples by capillary zone electrophoresis using simultaneous UV and amperometrical detection.

In this paper, capillary zone electrophoresis with amperometric detection (CZE-AD) was first applied to the simultaneous separation and determination of amitrole and urazole in water samples. A simple end-column electrochemical detector was used in combination with a commercially available capillary electrophoresis instrument with UV detection. The effects of several important factors were investigated to find optimum conditions. A carbon disk electrode was used as working electrode. Separation and determination of these compounds in water samples were performed in 0.030 mol l(-1) acetate buffers at pH 4.5, 25 kV as separation voltage and the samples were introduced by hydrodynamic mode for 1.5 s. Most of the studies realized showed that the direct electrochemical detection is more sensitive and selective than UV detection. Under the optimum conditions, excellent linearity was observed between peak amperometric signal and analyte concentrations in the range of 0.19-1.35 mg l(-1) for amitrole and 0.20-1.62 mg l(-1) for urazole. The detection limits were 63 and 68 microg l(-1) for amitrole and urazole, respectively. The utility of this method was demonstrated by monitoring water samples, and the assay results were satisfactory. The detection limits using a previous preconcentration step for amitrole and urazole in spiked mineral water samples were 0.6 and 1.0 microg l(-1) for amitrole and urazole, respectively.

Multiresidue analysis of phenylurea herbicides in environmental waters by capillary electrophoresis using electrochemical detection.

A rapid multiresidue method has been developed for the analysis of seven phenylurea herbicides in the presence of two s-triazines in environmental waters. A simple end-column electrochemical detector was used in combination with a commercially-available capillary electrophoresis instrument with UV detection. The determination of phenylurea pesticides using micellar electrokinetic capillary chromatography with electrochemical detection represents the first such determination that has been reported. In both detection systems, linear ranges were obtained for the seven phenylurea herbicides at concentrations lower than 2.0x10(-5) mol l(-1), in 0.020 mol l(-1) phosphoric acid at pH 7.0 and containing 0.020 mol l(-1) of sodium dodecylsulfate, in order to obtain selectivity in the additional separation by a micellar distribution process. Under these conditions a detection limit lower than 5.0x10(-6) mol l(-1) (0.25 pmol of pesticide) was achieved for most of them. The pesticides were resolved in less than 30 min.

Determination of 3-amino-1,2,4-triazole (amitrole) in environmental waters by capillary electrophoresis.

3-Amino-1,2,4-triazole (amitrole) is a widely used pesticide, with many difficulties to be analyzed at the regulatory level in drinking water, because its high solubility in water. This paper describes a simple and fast method for the simultaneous determination of amitrole and atrazin-2-hydroxy, principal degradation product of s-triazines, by capillary zone electrophoresis. Separation and determination of these herbicides in water samples was performed in 0.02 mol l(-1) phosphate buffer at pH 3.2. The method allows determination of the amitrole and atrazin-2-hydroxy in water samples in concentration lower than 100 mug l(-1). The detection limits using a previous preconcentration step of amitrole in Alberche River (Comunidad Autónoma de Madrid, Spain) and drinking water spiked samples was of 4 mug l(-1).

Determination of s-triazines with copper and glassy carbon electrodes. Flow injection analysis of aziprotryne in water samples.

The detection and determination of s-triazines, atrazine-desethyl and aziprotryne by cyclic voltammetry and an amperometric method using a metallic copper electrode and a glassy carbon electrode are described. The concentrations of atrazine-desethyl and aziprotryne in 0.1 M NaOH solutions were determined using the oxidation signal corresponding to the Cu(0)/Cu(I) redox process. The detection level calculated for these s-triazines were 0.3 and 0.5 microg/mL of analyte, respectively. The glassy carbon electrode was shown to give sensitive reduction response to aziprotryne in flow injection mode. No special activation was required for the glassy carbon electrode. A detection limit of 0.2 microg/mL (20 ng aziprotryne) was obtained for a sample loop of 0.1 mL at a fixed potential of -1.0 V (vs. Ag/AgCl) in 0.1 M HCl and a flow rate of 3.5 mL/min. Furthermore, the glassy carbon electrode showed stable response in such a system, and the relative standard deviation was only 2.7% using the same surface, and 6.3% using different surfaces. The method developed was applied to the determination of aziprotryne in environmental and tap water samples; using a prior solid-phase extraction step, aziprotryne concentrations lower than 1.0 ng/mL could be measured.

Direct determination of prolintane and its metabolite oxoprolintane in human urine by capillary zone electrophoresis and beta-cyclodextrin-modified micellar electrokinetic chromatography.

This paper describes a fast and simple method for the direct determination of the stimulant prolintane and its principal urinary metabolite, oxoprolintane, in human urine by capillary zone electrophoresis and beta-cyclodextrin-modified micellar electrokinetic chromatography. The determination was performed in phosphate buffer, pH 8.5, with UV detection at 211 nm. The effect of the ionic strength ratio between sample and running electrolyte, pH, sodium dodecyl sulphate and beta-cyclodextrin concentrations, and other factors, on the electrophoretic signals of these drugs was examined. This method can be applied for doping control. The determination limits are 1.0 microgram ml-1 for prolintane and 0.7 microgram ml-1 for oxoprolintane.

Direct determination of ephedrine and norephedrine in human urine by capillary zone electrophoresis.

This paper describes a simple and fast method for the simultaneous determination of ephedrine and norephedrine in urine by capillary zone electrophoresis. Separation and determination of these stimulants in human urine was performed in 50 mM phosphate buffer at pH 9.5, modifying the electroosmotic flow with acetonitrile. The method allows direct determination of the stimulants in urine in concentrations lower than 20.0 micrograms/ml, and has a limit of determination of 2.6 +/- 0.2 micrograms/ml for ephedrine and 2.3 +/- 0.2 micrograms/ml for norephedrine in urine and may be applied for doping control.

Voltammetric studies of a psychotropic drug with nitro groups. Determination of flunitrazepam in urine using HMDE.

The adsorption behaviour of flunitrazepam at the hanging mercury drop electrode was studied by staircase voltammetry and by adsorptive stripping differential pulse voltammetry. Flunitrazepam is adsorbed in the whole potential range, from the most positive values up to the reduction potential. Flunitrazepam reduction product is also adsorbed. The time dependence of the voltammetric response proves that a diffusion-controlled adsorption takes place. Flunitrazepam can be determined (down to nanomolar levels) by using adsorptive preconcentration prior to the differential pulse voltammetric scan. An application of such a method to flunitrazepam determination in human urine is described. The detection limit was 30 ng per milliliter of urine with a 20-sec accumulation time; the mean relative standard deviation was lower than 3.2% and the mean recovery 97.8%.

Measurement of nanomolar levels of psychoactive drugs in urine by adsorptive stripping voltammetry.

Adsorptive stripping voltammetry was used to determine nanomolar levels of the benzodiazepines pinazepam, camazepam, bromazepam and thienodiazepine (BrTDO) in urine. Measurements were made by differential pulse voltammetry at a hanging mercury drop electrode. The influences of various operational conditions on the stripping response were examined. The optimum accumulation potentials and accumulation times were -0.40 V and up to 60 sec for pinazepam, -0.60 V and up to 40 sec for camazepam, -0.40 V and up to 30 sec for bromazepam and -0.60 V and up to 60 sec for BrTDO, respectively. The effects of various urine components on the voltammetric response were also studied, and preliminary separation of the drugs was found necessary because of interference by creatinine and uric acid. The proposed method is appropriate for the determination of the four drugs in urine up to the 1000 ng/ml level with short accumulation periods (10-60 sec). The relative standard deviation for the 500 ng/ml level of the drugs in urine (30-sec accumulation) was less than 3%.