No abstract

Wall-jet/thin-layer amperometric electrochemical detection (ECD) coupled with high-performance liquid chromatography (HPLC) was used here for the simultaneous analysis of dopamine (DA) and homovanillic acid (HVA) at a glassy carbon electrode. Compared with the conventional thin-layer mode and wall-jet mode, the presented wall-jet/thin-layer ECD has the advantages of enhanced capture of electroactive DA and HVA on the working electrode to give enhanced responses and more convenient washing/refreshment of the working electrode surface. Under optimized conditions, the HPLC-ECD calibration curves show good linearity from 0.01 to 100 μM for DA and HVA, and the limits of detection (LODs) obtained were 1.1 nM for DA and 0.7 nM for HVA which are lower than those obtained with an UV-vis detector and a commercial electrochemical detector. The method was tested on human urine with satisfactory results. The balance of response-signal, signal-background and noise level for our HPLC-ECD system is also discussed. In addition, a demethylation electrooxidation mechanism for HVA is suggested through potentiostatic bulk electrolysis, electrospray ionization-mass spectrometry, fluorescent spectrophotometry and cyclic voltammetry studies.

No abstract

No abstract

High-performance liquid chromatography (HPLC) with gradient elution was coupled to a glassy carbon electrode (GCE)-based wall-jet/thin-layer electrochemical detector (ECD) for the simultaneous analysis of isoniazid (isonicotinyl hydrazide, INH) and rifampicin (RIF). The simultaneous HPLC-ECD analysis of INH and RIF was performed using a reversed phase C18 column (150 mm  4.6 mm, 5 mm) using a gradient elution program at a flow rate of 1.0 mL min À1 , and an HPLC-Ultraviolet (UV) detector at a wavelength of 268 nm and the HPLC-ECD at a working potential of 0.9 V vs. SCE were used. Linear calibration plots for INH and RIF were obtained in the range of 0.01-100 mM for INH and RIF. Our walljet/thin-layer ECD gave limits of detection (LODs) of 0.3 and 0.5 nM (S/N ¼ 3) for INH and RIF, respectively, which are lower than those obtained with the UV detector and a commercial ECD. Our method was successfully applied for the simultaneous determination of INH and RIF in an antitubercolosis drug and urine substrate samples.