RESUMO
A fluorometric method was developed for simultaneous determination of Cr(VI) and Cr(III) ions using graphitic carbon nitride nanosheets (g-C3N4 NS) as a nanosized fluorescent indicator probe. The g-C3N4 NS were prepared using high-temperature carbonization of melamine followed by ultrasonication-assisted liquid exfoliation. The g-C3N4 NS display fluorescence with excitation/emission peaks located at 320 and 450 nm. The chromium speciation is based on the quenching of g-C3N4 NS fluorescence. The total concentration of chromium is determined after oxidation of Cr(III) to Cr(VI). The Cr(III) content was then calculated by subtracting the concentration of Cr(VI) from that of total chromium. The effects of pH value, probe amount, and contact time are optimized. Under optimum conditions, calibration plots are linear in the range in the 0.01 to 100 µM chromium concentration range. The limit of detection is 3 nM for for Cr(VI). The intra- and inter-day relative standard deviations (RSD) of the assay are 3.6-7.5% and 4.1-8.5%, respectively. The indicator probe was applied to the determination of chromium species in spiked water and food samples, and recoveries were satisfactory (93.9-107.0%). Graphical abstract Graphitic carbon nitride nanosheets are synthesized by melamine carbonization and employed for Cr speciation in water and food real samples. Total Cr(VI) and Cr(VI) are assessed based on the quenching of the fluorescence of nanosheets by Cr(VI).
RESUMO
BACKGROUND: Lidocaine hydrochloride (LH) is one of the most extensively used local anesthetics and peripheral analgesics. Availability of a simple and sensitive assay method for this analyte in pharmaceutical preparations as well as development of new voltammetric detectors that can be applied in chromatographic systems for determination of this analyte in biological samples are of great importance. OBJECTIVES: In this study, a square-wave voltammetric (SWV) determination of LH at a bare carbon-paste electrode (CPE) was reported. Moreover, the oxidation mechanism for LH molecule at this electrode was investigated. MATERIALS AND METHODS: The SW voltammogram of LH solution at CPE showed a well-defined peak between +0.80 and +0.88 V depending on a scan rate in potassium nitrate (KNO3) solution. Different chemical and instrumental parameters influencing the voltammetric response, such as the pH level and scan rate were optimized for LH determination. RESULTS: A linear range of 8.0 - 1000.0 µmol L(-1) (r(2) = 0.999) was obtained. The limit of detection (LOD) was 0.29 µmol L(-1). The relative standard deviations of 2.1% obtained for 0.8 800 µmol L(-1) solution of LH indicated a reasonable reproducibility of the method. CONCLUSIONS: The results of this study show that LH in different pharmaceutical preparations could be determined with good reliability. In addition, the results reveal that the equal numbers of electrons and protons are involved in the oxidation of LH and the irreversible oxidation of an analyte was performed via amine groups of LH molecule.