This paper compares the dichromate method with the photoelectrochemical method (PeCOD), with regards to the influence of chloride and turbidity with chemical oxygen demand (COD) determination. Whereas the upper limits of chloride concentration are well established for both techniques, the influence of turbidity and the combined interference of underdosing chlorides and turbidity together have never been reported. When only potassium hydrogen phthalate or sorbitol were analyzed, the results show no significant difference in either method when 607 mg Cl- L-1 or 230 NTU of turbidity were added to the samples within the range of 100-900 mg L-1 COD. However, a combined effect of these two interferents leads to significantly different results, mainly for low COD range, as evidenced by the Student's t-test for paired samples (p = 0.05).

This paper presents a quality assurance and quality control protocol in order to ensure the reliability of analytical results for the determination of acid volatile sulfides in environmental samples by potentiometry. The monitoring of the ion selective sensor readings must be realized continually and particularly in this situation where the analyte is susceptible to transformation and volatilization. Potentiometry with the standard addition was presented as a rapid, accurate, precise, feasible as well as a low cost technique. Concentrations of the analyte in the range of 0.49 to 1.02 mg L-1 were tested with percentage recoveries varying from 89 to 113%.

This paper discusses the historical and methodological fundaments of the dynamics and quantification of acid volatile sulfides (AVS) and simultaneously extracted metals (SEM) in aquatic sediments. It also discusses the SEM/AVS relationship, which involves several controversial aspects such as sulfide stability, sulfide-organic matter interaction, and the inability to predict the toxicity of organic compounds in the environment. This relationship is an important tool for the inference of metal bioavailability. The use of ecotoxicological tests with target organisms regulated by international standards is also a relevant aspect.

This paper proposes a methodology for spectrophotometric determination of hexamethylenetetramine (HMT) by using chromotropic acid in a phosphoric acid media employing a domestic microwave oven as a source of heating. The reddish-purple soluble product is quantitatively formed after 30 s of irradiation and obeys the Beer´s law in the range between 0.1-1.2 mg L-1 HMT (r = 0.99925). The method was applied successfully in commercial pharmaceutical preparations containing dyes in their composition. The results showed that the method proposed is feasible for simplicity, speed, low cost, precision and accuracy when compared with United States Pharmacopeia official method.

O presente artigo descreve uma metodologia espectrofotométrica para a análise de paraformaldeído presente em amostras de saneantes comerciais e industriais, utilizando-se ácido cromotrópico (ACT), ácido clorídrico concentrado e peróxido de hidrogênio, produzindo um composto púrpura - avermelhado (lambda max = 575 nm). A lei de Beer é obedecida numa faixa de concentração de 0,8 - 4,8 mg L-1 em formaldeído, apresentando excelente coeficiente de correlação (r = 0,9999). Os valores obtidos nas análises concordaram muito favoravelmente com os obtidos pelo procedimento padrão recomendado pelo NIOSH (National Institute for Occupational Safety and Health).

This paper describes a spectrophotometric method for the paraformaldehyde analysis in industrial and commercial disinfectant samples using chromotropic acid, concentrated hydrochloridric acid and hydrogen peroxide. The reaction produces a violet-red compound (lambda max = 575 nm). The method permits the determination of paraformaldehyde over a concentration range of 0.8-4.8 mg L-1 and the results obtained by the proposed method compared very favorably with those obtained by NIOSH’s standard procedure.

No presente trabalho desenvolveu-se metodologia simplificada para análise de hexametilenotetramina em medicamentos que apresentam corantes em sua formulação (azul de metileno, Ponceau Red, Bordeaux Red, acriflavina) seguida por titulação ácido-base usando indicador. O método foi aplicado com sucesso a amostras comerciais e os resultados obtidos foram comparados com aqueles encontrados por titulação potenciométrica, apresentando muito boa concordância. Recobrimentos situaram-se na faixa de 101,3 - 104,2%, com desvios padrão de 0,1 - 2,1.

In the present work a simplified methodology for hexamethylenetetramine analysis in pharmaceutical formulations in the presence of dyes (methylene-blue, ponceau Red, bordeaux Red, acriflavine), followed by acid-base titration using indicators is proposed. The proposed method was applied to commercial samples and the analytical results obtained for these products compared favorably with the results obtained by means of potentiometric titration. Recoveries were within 101,3 - 104,2 %, with standard deviations ranging from 0,1 to 2,1%.