Wavelength dispersion X-ray fluorescence spectrometry (WDXRF) is a non-destructive technique and therefore attractive for gunshot residues (GSR) analysis. It is well known for determination of inorganic constituents of samples. However, X-ray scattering region spectral data is not commonly used, although it may provide information about organic constituents and their interactions. This work employed X-ray scattering region and inorganic elements spectral data for a better characterization of GSR. Swabs containing residues collected from the hand of people who fired (shooters group) and also from the hands of people which did not fire (control group) with guns were analyzed directly by the WDXRF. Brake pad and people who perform activities that favor the accumulation of characteristic elements of GSR on their hands were chosen to compose the control group. Principal components analysis (PCA) discriminated the GSR according to the firearm/cartridge used. However, similar GSR clustering did not occur without X-ray scatter data, showing the importance of X-ray scattering spectrum for GSR evaluation. The k-nearest neighbors (k-NN) method correctly classified all samples from shooters and control groups, employing from 1 to 5 nearest neighbors. No anomalous behavior was detected by PCA and hierarchical cluster analysis (HCA).

This work proposes a new simple and fast spectrophotometric method for cephalexin determination in pharmaceutical formulations. The method is based on the charge transfer reaction between cephalexin and quinalizarin in dimethylsulfoxide medium. Several analytical parameters related to the system were optimized and the reaction was characterized in terms of stoichiometry. Also, association constant and apparent molar absorptivity of the product were determined. The method presented a limit of detection of 0.46 mg L-1 and a quantification limit of 1.5 mg L-1. It was successfully applied in the determination of cephalexin in two samples of commercial pharmaceutical formulations.

Neste trabalho é proposto um novo método para a determinação espectrofotométrica simples e rápida de azitromicina em formulações farmacêuticas. O método está baseado na reação de transferência de carga entre a azitromicina e a quinalizarina em meio de metanol. O efeito de diversas variáveis foi avaliado com o intuito de alcançar máxima sensibilidade analítica. A reação de transferência de carga foi caracterizada, sendo determinadas a estequiometria da reação, a absortividade molar aparente e a constante de associação. Melhores resultados foram obtidos em meio de metanol e com uma concentração de quinalizarina de 50 mg L-1. Nestas condições, o ânion radicalar (produto da reação de transferência de carga) foi formado imediatamente após a mistura dos reagentes, apresentando máxima absorção em 564 nm. O método apresentou um limite de detecção de 0,35 mg L-1 e um limite de quantificação de 1,2 mg L-1, sendo aplicado com sucesso na determinação de azitromicina em três amostras de medicamentos comerciais contendo azitromicina.

This paper proposes a new method for simple and fast spectrophotometric determination of azithromycin in pharmaceutical formulations. The method is based on the charge transfer reaction between the azithromycin and quinalizarin in methanol medium. In order to achieve maximum sensitivity the effect of some chemical variables such as the type of solvent, reagent concentration and reaction time were evaluated. The reaction was characterized in terms of stability of the product formed and its stoichiometry, and the apparent molar absorptivity and association constant were derived. Best conditions for the analytical determination of azithromycin were observed in methanol medium with a quinalizarin concentration of 50 mg L-1. At these conditions, the radical anion (absorbing specie) was formed in the medium immediately after mixing of the reagents and showed maximum absorption at 564 nm. The method presented a limit of detection of 0.35 mg L-1 and a limit of quantification of 1.2 mg L-1. It was successfully applied in the determination of azithromycin in three commercial pharmaceutical formulations of azithromycin and no matrix interferences were observed.