Optimized Eco-friendly Sample Preparation Methods for Determining Major and Minor Elements in Cheeses by ICP OES

This work describes the optimization and validation of sample preparation methods for determining major and minor elements in artisanal Brazilian cheese samples by inductively coupled plasma optical emission spectrometry. Three sample preparation methods were optimized and compared: microwave-assisted digestion, ultrasound-assisted extraction, and alkaline solubilization using tetramethylammonium hydroxide. A central composite design was used for the optimization using the R software. The optimal experimental conditions were achieved at 1.58 mL of HNO₃ 14 mol L⁻¹ and 0.570 g of sample mass for the microwave-assisted digestion (capable of determining Ca, Fe, K, Mg, Na, and P); 3.4 mol L⁻¹ of HNO₃, 0.91 mol L⁻¹ of HCl, and 2.5 min for the ultrasound-assisted extraction (capable of determining Ca, K, Na, and Zn); and 21.8% (w/w) of tetramethylammonium hydroxide, 50 °C, and 103 min for the AS method (capable of determining K, Na, and Zn). The optimized methods were validated and applied for the analysis of four kinds of artisanal Brazilian cheeses and compared with the dry-ashing method, using a paired t-test, where the means agreed with the dry-ashing method at a 95% confidence interval.