Determination of 35 Elements includings REEs, Ba, Th and Pb in Soil by Inductively Coupled Plasma-Mass Spectrometry with Four-Acid Ultrawave Digestion

The analysis of soil elements is of great significance to geological survey, resource exploration and other fields. However, the simultaneous digestion and analysis of multi-element single-process of metals and rare earth elements (REEs) often face the problems of incomplete digestion of insoluble elements (such as REEs, Ba, Th, etc.) and interference of complex matrix mass spectrometry. Although the traditional pressurized acid digestion method shows good recovery for elements like Li, Be, and Ti, the recovery rate of insoluble elements such as REEs is low (most ＜ 90%), which makes it difficult to meet the needs of simultaneous analysis of general elements and insoluble elements. In this paper, by comparing the digestion effects of 15 acid digestion systems composed of 4 mL of inverse aqua regia, different amounts of hydrofluoric acid and perchloric acid and two kinds of acid removal conditions on 37 elements of national soil standard materials, the ultrawave digestion-four acid system combined with ICP-MS/MS was established. The optimal conditions were determined as follows: 3 mL nitric acid + 1 mL hydrochloric acid + 2 mL hydrofluoric acid + 0.8 mL perchloric acid digestion system and multiple additions of nitric acid to strengthen the acid removal combination. This method effectively destroys silicate mineral structures, promotes the dissolution of refractory oxides, and through repeated acid addition and high-temperature acid driving, removes residual hydrofluoric acid, avoiding the formation of insoluble fluoride precipitates. The method was systematically verified using 8 national soil standard materials (including GBW07565, etc.) and root soil of typical crops (Xizang highland barley, Xinjiang tomato, Jiangxi rice). The results show that this method can accurately determine 35 target elements except Cd and Cr, with a method detection limit of 0.0005–3.410 mg/kg. The relative standard deviation (RSD) of all samples was 0.2%–14.1% and the recovery of actual samples was 81.6%–107.4%. The results show that the method has good stability and applicability. Compared with the traditional pressurized closed acid dissolution method, this method significantly improves the recovery rate of REEs, Ba, Th and other elements (mostly＞90%), and provides an efficient and reliable solution for multi-element analysis of different matrix soils.