Determination of 23 Elements in Surface Ground Substrate Samples of Plain Areas by ICP-OES with Three Mixed Acid Digestion and Aqua Regia Extraction

The surface ground substrate is primarily composed of the agricultural tillage layer, with high organic matter content and significant compositional variations, which affect the accuracy of detection results. The industry standard DZ/T 0279.2-2016 adopts a four-acid digestion method, leading to differences between the standard curve established using standard solutions and that of processed samples due to matrix effects. On the basis of this standard method, a method for determining 23 elements in surface ground substrate samples from plain areas using three acid digestion followed by aqua regia extraction and inductively coupled plasma-optical emission spectroscopy (ICP-OES) has been optimized and established. In order to solve the problems of complete sample digestion and matrix matching, the strong decomposition ability of hydrofluoric acid on silicates was utilized to form a three-acid system with perchloric acid and nitric acid (hydrofluoric acid, nitric acid, and perchloric acid in a volume ratio of 5∶3∶1), which completely digested the sample under heating. The extraction efficiency of aqua regia at five different dosages was investigated, and 10mL was determined to be optimal. A standard curve was established using certified reference materials with varying concentration gradients to ensure matrix matching between the standard series and the samples, thereby eliminating matrix interference. The results indicate that the measured values for each element in the certified reference material are consistent with the certified values. The method precision (n = 12) is less than 10%, and the accuracy (ΔlogC) is not greater than 0.1. The method detection limits are lower than those specified in DZ/T 0258-2014, and the differences compared to XRF and ICP-MS detection results are not significant. Through verification with actual samples, this method improves the efficiency of simultaneously detecting multiple elements in surface ground substrate samples from plain areas and reduces analysis costs.