Development and validation of an analytical method for the extraction and quantification of soluble sulfates in red clay

Desenvolvimento e validação de um método analítico para a extração e quantificação de sulfatos solúveis em argilas vermelhas

Abstract

In this work a fast and environmentally friendly method for the extraction and quantification of soluble sulphates in red clay using microwave assisted extraction (MAE) and determination by turbidimetry was developed and validated. The favorable conditions for the extraction of soluble sulphates in red clay by MAE were: 1 g of sample, with particle size of 63μm, dissolved in 50 mL of distilled water, it was extracted using a microwave oven with 70% of power during 5 min, later the sample was centrifuged during 5 min and then filtered. The soluble sulphates in red clays were quantified at 420 nm. The procedure proposed showed linear behaviour in the tested rank (5-7000 mg SO₄ ^2-/kg of clay) with R² 0.9993. The limits of detection and quantification were 4.30 and 14.33 mg/kg, respectively, with a variation coefficient of 1.41%. The method proposed in this work allows to determine soluble sulphates in red clay with a recovery of 94%.

Keywords:
red clay; soluble sulphates; microwave assisted extraction (MAE); turbidimetry