Green sample preparation of medicinal herbs in closed digester block for elemental determination by ICP OES

Abstract

This work presents a simple, cost-effective, and environmentally friendly digestion method employing inductively coupled plasma optical emission spectrometry (ICP OES) for the determination of As, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, P, Pb, Sr, and Zn in medicinal herbs. A fractional factorial design uses a multivariate strategy to optimize the experimental parameters. At 180 ºC and 120 min of sample digestion, the optimal condition for a closed block digester was achieved with a mixture consisting of 1.38 mL of HNO₃ 65% m m^-1, 1.00 mL of H₂O₂ 30% m m^-1, and 2.62 mL of deionized water, using a mass of 0.10 g medicinal herb sample. The optimized procedure resulted in low dissolved organic carbon content and residual acidity concentration. The values of limits of detection (LOD) and of quantification (LOQ) ranging from 0.06 (Cd) to 1.9 (P) mg kg^-1 and 0.2 (Cd) to 6.3 mg kg^-1 (P), respectively. Accuracy was confirmed through the analysis of three certified reference materials, where agreement ranged from 83 (Sr) to 116% (As) for all analytes. The AGREE metric has confirmed the greenness of the proposed method. Twenty-seven medicinal herbs samples were used to assess the applicability of the developed procedure. Principal component analysis (PCA) was applied to inorganic constituent concentration data to classify the medicinal herbs, an excellent tool for classifying samples.

Keywords: Elemental composition; Fractional factorial design; ICP OES; Medicinal herbs; Sample preparation.