Banca de DEFESA: GABRIEL MARTINS VIEGAS

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : GABRIEL MARTINS VIEGAS
DATE: 22/12/2021
TIME: 09:00
LOCAL: https://conferenciaweb.rnp.br/webconf/jose-geraldo-rocha-junior
TITLE:

Spectrophotometric determination of antimony in samples of rifle bullets

KEY WORDS:

antimony, lead alloy, spectrophotometry, ANOVA, ammunition classification

PAGES: 94
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Química Analítica
SPECIALTY: Métodos Óticos de Análise
SUMMARY:

The analysis of the chemical composition of projectiles found at the scene of a crime is a useful tool to obtain information that aids in the investigation of cases involving rifle shooting, in which the integrity of the fired projectile is not preserved, and ballistic confrontation cannot be used. Antimony is normally present in rifle projectiles and has stood out as one of the key elements for their classification. The work proposes a methodology for the dissolution of rifle bullet samples for the determination of antimony by spectrophotometry, with the aim of using this result in the differentiation of these bullets, according to the manufacturers. The proposed method was used in the analysis of projectiles from three manufacturers, provided by the Civil Police of the State of Rio de Janeiro, and involved the dissolution of samples in HNO₃ 8 mol L^-1, at 150 °C. The lead ion was removed from the solution, as it interferes with the determination, through its precipitation as PbSO₄ and, later, centrifugation. The spectrophotometric determination of antimony was based on the formation of the tetraiodoantimonate(III) complex (λ = 425 nm) after the addition of a potassium iodide solution in an acidic medium and proved to be adequate for the analysis of the projectiles. The analytical curve showed excellent linearity (R² = 0.9998) and the detection limits (1.05 ± 0.02 mg L^-1) and quantification (3.49 ± 0.04 mg L-1) obtained were adequate, as the solutions produced by dissolving the samples presented a concentration (20 mg L^-1) well above these limits. The study of the absorbance of the antimony solutions produced by the proposed dissolution method, as well as the accuracy of the method, determined by the recovery studies, between 99.022 ± 0.003% and 109.719 ± 0.005%, were satisfactory, as they indicate that during the dissolution of the samples and PbSO₄ precipitation, there was no appreciable loss of antimony by volatilization or co-precipitation, respectively. ANOVA and Tukey's test was used to discriminate the projectiles by the manufacturer. By analyzing the fragments of the projectiles, it was possible to discriminate only one of the projectile manufacturers (CBC 7.62x51mm) from the others (Winchester .308, CBC .308) by its Sb content. When comparing projectiles from the same manufacturer, a significant difference was observed between the projectiles produced by only one of them (Winchester .308). No significant differences were observed in the Sb contents when analyzing the different sections of the same projectile, indicating that the Sb distribution is relatively homogeneous (considering the sample size and the number of replicates taken for the analysis), an interesting fact, as This method is intended for analyzing rifle bullets that, when found at crime scenes, are fragmented, or deformed. However, when comparing the manufacturers choosing specific sections of the projectiles, it was noticed that the sections at the ends of the projectiles presented a potential for the differentiation of the manufacturers, having differentiated the manufacturer's Winchester .308 e CBC 7.62x51mm.

BANKING MEMBERS:
Interno - 2626414 - JOSE GERALDO ROCHA JUNIOR
Externo ao Programa - 2630672 - FLAVIO COUTO CORDEIRO
Externo ao Programa - 387373 - OTAVIO RAYMUNDO LA
Externo à Instituição - CARLOS EDUARDO RODRIGUES DE PAULA - UFRJ
Externa à Instituição - VIVIANE GOMES TEIXEIRA - UFRJ