Chloroquine is a drug belonging to the aminoquinoline family that is widely used for treating diseases such as lupus, cancer, and malaria. In this sense, the present work describes the development of a simple method based on electrogenerated chemiluminescence (ECL) and a screen-printed carbon electrode (SPE) modified with carbon black for chloroquine determination. The carbon black modified SPE was characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry and linear sweep voltammetry to obtain the ECL-potential curves. The ECL method is based on the chemiluminescence resulting from the interaction between chloroquine and the tris(2’2-bipyridyl) ruthenium(II) complex. Under optimized experimental conditions, the method showed a wide linear working range between 0.5 and 500 µmol L-1. The method presented good precision and accuracy in drug samples used in the treatment of malaria and artificial urine sample, showing recovery values from 100 to 103% and 99 to 103%, respectively.

The present work presents the development of a sensitive and selective amperometric sensor for the determination of hydrazine (HZ) in pharmaceutical formulations using a glassy carbon electrode (GCE) modified with a composite based on Co(Salophen), reduced graphene oxide (rGO) and deoxyribonucleic acid (DNA). The rGO/Co(Salophen)/DNA composite was characterized by using Fourier-transform infrared spectroscopy (FTIR), cyclic voltammetry, and amperometry. The proposed platform presented a well-defined voltammetric profile with a redox couple around 0.32 V vs. Ag/AgCl which showed excellent catalytic activity towards HZ oxidation. The peak current of HZ electrochemical oxidation on the proposed electrochemical platform have changed linearly with the HZ concentration in the range from 2 to 364 µmol L-1. The proposed platform presented sensitivity, limit of detection, and limit of quantification of 0.056 µA L µmol-1, 0.54 µmol L-1, and 1.64 µmol L-1 to HZ, respectively. The relative standard deviation for eight determinations using a solution of 50 µmol L-1 HZ was 0.85%. The proposed sensor was successfully applied for the determination of HZ in pharmaceutical formulations, and the recovery tests showed a good accuracy with recovery percentage between 99 and 101%.

This work presents a simple and fast method for colchicine (CO) determination in pharmaceutical formulations and urine by multiple pulse amperometry (MPA) with flow injection analysis (FIA) system using a boron-doped diamond electrode. In optimized conditions, it was possible to quantify CO in urine samples without interference of uric acid and ascorbic acid. The working linear range for CO quantification was achieved from 1.0 × 10-7 to 0.5 × 10-3mol L-1 with a low limit of detection of 2.14 × 10-8mol L-1. Furthermore, the proposed method showed high repeatability for 10 consecutive injections of 1.0 × 10-4mol L-1 CO (relative standard deviation = 1.28%) and good analytical frequency (30 determinations per hour). The addition and recovery studies in all pharmaceutical samples were approximately 100% and the results for CO determination were compared by high performance liquid chromatography (HPLC) with UV detection.

A novel and simple electroanalytical method for the determination of Cu2+ in biodiesel samples by stripping voltammetric analysis was developed. The method employs a carbon paste electrode (CPE) modified with Vulcan carbon, previouly functionalized with carbazone (CBZ). The CPE/Vulcan-CBZ sensor promoted a significant increase in the analytical signal obtained from copper as compared to unmodified CPE, and the CPE modified with Vulcan carbon (CPE/ Vulcan). Vulcan-CBZ, Vulcan and CBZ materials were characterized by Fourier transform infrared spectroscopy (FTIR) technique. The electrochemical behavior of the sensor was evaluated using cyclic voltammetry (CV) and square-wave anodic stripping voltammetric (SWASV) techniques. The CPE/Vulcan-CBZ modified electrode showed excellent response and was able to detect Cu2+ at nanomolar levels. The electrochemical method is based on preconcentration of Cu2+ ions on the CPE/Vulcan-CBZ at 0.35 V vs. Ag/AgCl(sat) in 0.2 mol L-1 ammonium sulfate solution ((NH4)2SO4), pH 3.5, during 120 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu2+ concentrations in the range from 6 to 190 nmol L-1 (r = 0.998), with a detection limit of 1.2 nmol L-1. The sensor was successfully applied for the determination of Cu2+ in biodiesel and the average recovery varied between 97.0 and 102.8% for the soybean biodiesel samples and between 109.6 and 111.0% for the babassu biodiesel samples showing a good accuracy for the proposed method.

The present work describes the development of a selective electrochemical sensor for urate based on tris(1,10-phenantroline)copper(II) bis(tetracyanoquinodimethanide) (Cu(phen)3(TCNQ)2) adsorbed on multi-walled carbon nanotubes (CNT). The composite material was characterized by infrared spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The composite material showed an excellent electrocatalytic activity toward oxidation of urate. The heterogeneous charge transfer rate constant (k’) between the analyte and the sensor was determined using linear sweep voltammetry experiments. The composite material shows a linear range from 5 up to 2500 µmol L-1 with limit of detection of 1.05 µmol L-1 and limit of quantification of 3.50 µmol L-1. The high sensitivity and selectivity of the sensor for urate was sufficient for its determination in biological fluids. Finally, the proposed sensor was successfully applied in urine samples.