No abstract

In this work, the electrochemical behavior of hydrochlorothiazide and pyridoxine on the ethylenediamine-modified glassy carbon electrode were investigated by differential pulse voltammetry. In pH 3.4 Britton-Robinson (B-R) buffer solution, both hydrochlorothiazide and pyridoxine had a pair of sensitive irreversible oxidation peaks, that overlapped in the 1.10 V to 1.20 V potential range. Under the optimum experimental conditions, the peak current was linearly related to hydrochlorothiazide and pyridoxine in the concentration range of 0.10–2.0 μg/mL and 0.02–0.40 μg/mL, respectively. Chemometrics methods, including classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS), were introduced to resolve the overlapped signals and determine the two components in mixtures, which avoided the troublesome steps of separation and purification. Finally, the simultaneous determination of the two components in commercial pharmaceuticals was performed with satisfactory results.

In this paper, 2,3-naphthalenedialdehyde (2,3-Nda) was selected as color reagent with colorimetric and fluorometric assay for detecting melatonin in human saliva. 2,3-naphthalenedialdehyde reacted with melatonin under the catalysis of hydrochloric acid and Fe 3+ , which the color change was observed sensitively from colorless to yellow with the naked eye. On the other hand, the product of the reaction had a large conjugate structure with strong fluorescence for the fluorometric analysis. Under optimized experimental conditions, a concentration range of melatonin was 2.5-37.5 µM (R 2 = 0.998) by colorimetry with the limit of detection for 1.288 µM (S/N = 3), and 0.01-0.1 µM (R 2 = 0.997) by fluorometry with the limit of detection for 0.004 µM (S/N = 3). The two assays were successfully applied to the determination of melatonin in human saliva, which average recoveries were 97.80% and 95.96%, respectively, which has the potential in fast clinical examination of melatonin in human saliva.