No abstract

This study introduces modified carbon paste electrodes with carbon nitride nanosheets (CNNS) and outlines their application for the determination of hydroxychloroquine sulfate (HCQ) in tablets and synthetic urine samples. CNNS were synthesized by hydrothermal route (200°C, 10 h) using melamine and citric acid as their precursors. The carbon nitride nanosheets-based electrode (CNNS/E) presented a linear dynamic range for HCQ (LDR), ranging from 10.0 nmol l À 1 to 6.92 μmol l À 1 , and detection (LOD) and quantification limits (LOQ) of 0.16 nmol l À 1 and 0.52 nmol l À 1 , respectively. LOD and LOQ were calculated by the equations: LOD = 3(S d /b), and LOQ = 10(S d /b). The modified sensor presented excellent relative standard deviations for parameters such as repeatability (2.39 % and 1.87 %) and reproducibility (3.22 % and 2.32 %) in HCQ oxidation peaks (1 and 2). The CNNS/E has not shown significant variations in its anodic signal intensity in the presence of some organic and inorganic substances. It is worth bearing in mind that CNNS/E can be easily manufactured and the sensor has the lowest HCQ detection limits reported so far. The proposed sensor was successfully applied for HCQ determination in tablets and synthetic urine, showing good recovery values and an error of 0.60 % about comparative method in tablet samples, assuring the quality of the method.

The modified electrode with 1,3-bis(4-butyl-1H-1,2,3triazol-1-yl)propan-2-ol ligand (CPE/BT) was applied to determinate Cu(II) ions in cabbage cultivated with the use of Bordeaux syrup. The parameters optimization resulted in better analytical signals in B-R buffer solution at pH 5.00, potential of-0.4 V for 900 s on preconcentration, scan rate of 10 mV s-1 and amount of modifier of 5%. Under the electroanalytical method obtained linear behavior in the range of 1.00 x 10-8 to 1.30 x 10-7 mol L-1 , with a correlation coefficient of 0.994. The limit of detection (LOD) and the limit of quantification (LOQ) for determination of copper were with 1.67 x 10-9 mol L-1 and 5.05 x 10-9 mol L-1 , respectively. The electrode was successfully applied in the determination of Cu 2+ on cabbage ("couve") cultivated with Bordeaux syrup and the quantity of copper found was 8.05 µg kg-1 , which is within the standards stipulated by ANVISA.