Determinação de potássio por espectrometria de emissão atômica com chama em rochas silicáticas após decomposição ácida assistida por ultrassom

Abstract

This work presents the development of an analytical method for sample preparation aiming at the potassium determination in silicate rocks, following ultrasound digestion and analysis by flame atomic emission spectrometry (F AES). Three samples of silicate rocks that are sources of potassium (K), with different characteristics among each other, were studied, which were basalt, monzogranite and shale fines. Sample preparation using ultrasound (US) was optimized by using fractional factorial designs (factors: sample mass, volumes of HNO3, HCl and HF, and US time). After this optimization, the following optimal conditions were obtained for each silicate rock: 0.1 g of sample mass for any of the three samples, and volumes of HNO3, HCl and HF, respectively of 2.5, 0.8 and 2.5 mL for basalt; 3.5, 0.8 and 2.5 mL for monzogranite, and finally, 2.5, 1.0 and 2.0 mL for shale fines. Samples digestion were made using the ultrasound bath at room temperature for 1 hour. After this period, samples volume were made up to 50 mL with deionized water. The evaluated linear range was from 0.1 to 1.2 mg L-1 of K, with a correlation coefficient greater than 0.99 and limit of quantification of 0.006 mg L-1. The methodology accuracy was evaluated through the analysis of two certified reference materials, for which there was no statistical difference between the certified and the found K concentration values, Title: Determination of potassium by flame atomic emission spectrometry in silicate rocks after acid-assisted acid decomposition under the conditions of the present study, at a 95% confidence level. Additionally, the standard addition technique was applied for the three investigated rocks, and the recovery values ranged between 86,0 and 110%, with relative standard deviations lower than 5%. In conclusion, the developed procedures for the digestion of the three different silicate rocks presented accurate and reliable results for K determination by F AES, and the method has shown to be efficient, simple and safe, which are important features for the implementation of a methodology as a routine analysis.