Detection of hydrazine, methylhydrazine, and isoniazid by capillary electrophoresis with a palladium-modified microdisk array electrode

Flow-injection determination of isoniazid using sodium dichloroisocyanurate- and trichloroisocyanuric acid-luminol chemiluminescence systems

A chemiluminescent (CL) method for the determination of isoniazid is described. The method is based on the CL generated during the oxidation of luminol by sodium dichloroisocyanurate (SDCC) and trichloroisocyanuric acid (TCCA) in alkaline medium. It was found that isoniazid greatly enhances this CL intensity when present in the luminol solution. Based on this observation, a new flow-injection CL method for the determination of isoniazid has been proposed in this paper. The detection limits were 2 and 3 ng ml(-1) isoniazid for the SDCC-luminol and TCCA-luminol CL systems, respectively. The relative CL intensity was linear with the isoniazid concentration in the range of 4-100 and 100-200 ng ml(-1) for the SDCC-luminol CL system, and 6-200 and 200-1000 ng ml(-1) for the TCCA-luminol CL system. The results obtained for the assay of pharmaceutical preparations compared well with those obtained by the official methods and demonstrated good accuracy and precision.

Electrochemical behavior of the antituberculosis drug isoniazid and its square-wave adsorptive stripping voltammetric estimation in bulk form, tablets and biological fluids at a mercury electrode

Isoniazid, pyridine-4-carboxylic acid hydrazide, is an antituberculosis-agent, which is used to prevent the development of clinical tuberculosis. A validated square-wave adsorptive cathodic stripping voltammetric procedure for the trace determination of the bulk drug at the hanging mercury drop electrode (HMDE) has been developed. Under the optimized conditions, (accumulation potential=-0.9 V, accumulation time=50-300 s, scan increment=8 mV, pulse-amplitude=25 mV, frequency=120 Hz and acetate buffer at pH 5.5) isoniazed generated two irreversible cathodic peaks. The first peak current showed a linear dependence with the drug concentration over the range 5 x 10(-10)-21 x 0(-6) M. The mean percentage recoveries, based on the average of five replicate measurements, for 7 x 10(-9) and 5 x 10(-8) M isoniazid were 97.71+/-2.93 and 99.76+/-0.77, respectively. The achieved limits of detection (LOD) and quantitation (LOQ) were 1.18 x 10(-10) and 3.93 x 10(-10) M isoniazid, respectively. The procedure was applied to the assay of the drug in tablets (Isocid and T.B. Zide), spiked human serum and urine with mean percentage recoveries of 97.81+/-1.49, 97.45+/-2.09, and 97.08+/-1.06, respectively. The limits of detection of 1.47 x 10(-9) and 2.4 x 10(-8) M, and quantitation of 4.9 x 10(-9) and 8 x 10(-8) M drug in human serum and urine, respectively, were achieved. The mean values of the various pharmackinetic parameters of isoniazid (C(max), T(max), t(1/2), AUC, and K(e)), estimated from analysis of plasma of two volunteers by means of the proposed procedure were similar to literature values.

Evaluation of a sol-gel derived carbon composite electrode as an amperometric detector for capillary electrophoresis

In this paper, we report the construction and application of a sol-gel derived carbon composite electrode (CCE) as an amperometric detector for capillary electrophoresis. The electrochemical properties were characterized and compared with those of conventional carbon fiber and carbon paste electrode (CPE). Experimental results show that peak-to-peak noise of CCE was about 20% of CPE and electrode capacitance was comparatively low. When applied to the detection of dopamine and epinephrine, the optimal detection potential for CCE was 0.1 V lower than CPE under the same separation conditions; CCE with diameter of 75 and 100 microm could achieve a low detection limit of 3 x 10(-8) and 6 x 10(-8) M for the detection of epinephrine, which approaching that of the 33-microm diameter carbon fiber electrode. Also, the linearity for epinephrine at CCE was more than two orders of magnitude, which was slightly wider than that of carbon fiber electrode. Applications to real sample analysis were tested by the determination of betahistine dihydrochloride in tablets and human urine. Using CCE with diameter < or = 100 microm as an amperometric detector after capillary electrophoresis separation, a low detection limit and a wide linear range combined with excellent reproducibility were obtained. This CCE possesses of many advantages, namely, convenience, ease of fabrication, low cost and high stability.

Flow injection determination of isoniazid using N-bromosuccinimide- and N-chlorosuccinimide-luminol chemiluminescence systems

A chemiluminescent method for the determination of isoniazid is described. Method is based on the chemiluminescence (CL) generated during the oxidation of luminol by N-bromosuccinimide (NBS) and N-chlorosuccinimide (NCS) in alkaline medium. It was found that the isoniazid could greatly enhance this CL intensity when present in the luminol solution. Based on this observation, a new flow-injection CL method for the determination of isoniazid is proposed in this paper. The detection limits were 4 and 3 ng ml(-1) isoniazid for the NBS- and NCS-luminol CL systems, respectively. The relative CL intensity was linear with the isoniazid concentration in the range of 8-600 and 600-5000 ng ml(-1) for the NBS-luminol CL system, and 6-200 and 200-2000 ng ml(-1) for the NCS-luminol CL system. The results obtained for the assay of pharmaceutical preparations compared well with those obtained by the official method and demonstrated good accuracy and precision.

Applications of a copper microparticle-modified carbon fiber microdisk array electrode for the simultaneous determination of aminoglycoside antibiotics by capillary electrophoresis

A copper microparticle-modified carbon fiber microdisk array electrode was fabricated and employed in capillary electrophoresis for the simultaneous determination of the five aminoglycoside antibiotics (AGs) including netilmicin, tobramycin, lincomycin, kanamycin and amikacin. The array electrode exhibited high catalytic activity for AGs, good reproducibility and stability. Under the optimum separation conditions (separation voltage of 6.2 kV, electrophoretic medium of 125 mM NaOH), the five AGs above were baseline separated within 20 min. At a working electrode potential of 0.7 V (versus saturated calomel electrode), the calibration curves were linear over two orders of magnitude of concentration, and the detection limits (SIN=3) were below 2 microM except for lincomycin (6.7 microM). The developed method was successfully employed for the simultaneous determination of the five AGs studied in pharmaceutical injections. The feasibility of this method for the simultaneous determination of lincomycin, kanamycin and amikacin in urine sample was also demonstrated.

Formation of Palladium Complex at Carbon Paste Surface in Chloride Solution as Studied by Cyclic Voltammetry

The deposition and dissolution of palladium at non-modified carbon paste electrode (CPE) is studied by cyclic voltammetry in chloride solutions (c ≥ 0.5 M KCl and pH 3 to 6). The Pd0 is deposited from tetrachloropalladate solution by potential cycles from E ≥ 0 V (vs Ag/AgCl) or positive potentials up to -0.5 V or by potentiostatic treatment at E ≤ 0 V. Oxidation peaks appear during potential sweep to positive direction after the preceding deposition of Pd. The appearance of two anodic peaks depends mainly on the amount of Pd0 deposited. The peak at about +0.1 V is caused by the dissolution of a palladium mono- or submonolayer, whereas the oxidation peak at more positive potentials is attributed to the dissolution of Pd from a palladium multilayer. After palladium deposition and potential sweep to positive potentials E > +0.8 V (or potentiostatic treatment at E > +0.8 V), a cathodic peak appears at about 0 V and corresponding anodic peak at +0.1 V. It is concluded that these peaks are caused by reduction and oxidation of the chloropalladate surface complex formed during preceding application of anodic potentials. Reaction schemes of PdII/Pd0 and chloropalladate complex are discussed.

Miniaturized thin-layer radial flow cell with interdigitated ring-shaped microarray electrode used as amperometric detector for capillary electrophoresis

A chip-type thin-layer radial flow cell was developed as an amperometric detector for capillary electrophoresis. We fabricated a carbon film-based interdigitated ring-shaped array (IDRA) microelectrode with a 2 microm bandwidth and an almost 1 microm gap on a glass plate and used it as a working electrode. A fused-silica capillary was arranged above the IDRA electrode using a guide hole drilled through the acryl plate that formed the flow cell lid. A flow channel for use in connecting the outlet capillary was also fabricated in the acryl plate. We characterized the analytical performance of the IDRA electrode in the microchip flow cell in terms of linear concentration range, sensitivity and concentration detection limit. We achieved a collection efficiency and catechol redox cycle at the IDRA microelectrode of 65% and 1.71, respectively, and thus a high sensitivity and low detection limit of 392.9 pA/microM and 15 nM for dopamine hydrochloride. We examined the reproducibility of the detector and found that the run-to-run and detector-to-detector relative standard deviations were both less than 10%.

Detection of hydrazine, methylhydrazine and isoniazid by capillary electrophoresis with a 4-pyridyl hydroquinone self-assembled microdisk platinum electrode

Capillary electrophoresis (CE)/electrochemical detection (EC) for the simultaneous detection of hydrazine, methylhydrazine, and isoniazid has been developed with a 4-pyridyl hydroquinone self-assembled microdisk platinum electrode. Such an electrode has very high catalytic ability for hydrazines and they could be detected even at 0.0 V. The responses for hydrazine, methylhydrazine, and isoniazid are linear over 3 orders of detected concentration and of magnitude of 0.2-400 microM, 0.2-400 microM, 0.5 microM-2 mM, with correlation coefficients of 0.9998, 0.9991, and 0.9982, respectively. And they could be detected to levels of 0.1, 0.1 and 0.2 microM, respectively. This modified electrode was found to be very stable and reproducible when continuously used as detector for capillary electrophoresis for period of at least 4 weeks with no apparent loss of response.

Analysis of antibiotics by capillary electrophoresis

The broad category of antibiotics encompasses some of the most widely prescribed pharmaceuticals in the world. As is the case with any pharmaceutical, an antibiotic must be characterized in terms of its potency or activity, and the presence and quantity of impurities. Additionally, any residue or metabolite that may be present as a result of its use must be monitored. Many capillary electrophoretic techniques have been utilized in the analysis of antibiotics, addressing the various aspects of their quantitation, profiling, and monitoring. Some of the more recent applications are summarized in this review article.