Avaliação da extração por ponto nuvem para a especiação e pré-concentração de arsênio em material particulado atmosférico

Abstract

Particulate materials may come from natural or artificial sources. They interfere with air quality and may impair visibility, affect the dispersion and absorption of solar radiation, cause acidification of clouds and rain, and may cause damage to human health, such as respiratory diseases. Arsenic is present in nature in different chemical forms, and one of the means of human exposure to high levels of inorganic arsenic is through inhalation of contaminated air. Inorganic arsenic is more toxic than its organic forms, detaching the importance of monitoring it in atmospheric particulate matter. A cloud point extraction method was proposed for inorganic arsenic speciation in atmospheric particulate matter samples and detection by UVVis spectrophotometry. The parameters related to cloud point extraction were optimized (n = 2) and the best results obtained were: pH 1.5; 0.8 mmol L-1 ammonium molybdate; 0.06% v v1 of Triton X-114; 0.05 mmol L-1 of antimony potassium tartrate and 0.2 mmol L-1 of ascorbic acid. The accuracy for this study was shown to be adequate (RSD: 3-10%). A interference study was performed and the phosphate proved to be the main interferent. The linear regression model in the range of 0.04 - 0.12 mg L-1 was evaluated by the 95% confidence ANOVA. There was no evidence of heteroscedasticity of data (Ccalculated = 0.3989 < Ctabulated = 0.6838) and lack of normality (Wcalculated = 0.971 > Wtabulated = 0.874). There was no evidence of lack of fit for the obtained model (Fcalculated = 1.41 < Ftabulated (3;10) = 3.71) and therefore can be used for predictions. The limits of instrumental detection and quantification were LOD = 0.012 mg L-1 and LOQ = 0.04 mg L-1 , respectively. Selectivity was evaluated and the method proved to be selective for As (V). The oxidation of As (III) to As (V) was done with KMnO4. To determine the As levels in the samples, an ultrasound-assisted extraction method was established, using 6 mol L-1 hydrochloric acid. The addition to recovery tests, on two levels (n = 3), showed unsatisfactory recovery values for the samples (44 - 49%). The calibration was performed by standard addition method, confirming the existence of matrix effect. Phosphate interference was suspected, and an attempt was made to precipitate calcium phosphate, without success. The method was applied to a sample of atmospheric particulate matter, and quantification made by standard addition method. However, the levels of As were high and their quantification in the sample was not conclusive.