Determination of Gallium, Germanium and Indium in Coal by Inductively Coupled Plasma-Mass Spectrometry with Ashing Acid Digestion

BACKGROUNDThe accurate determination of gallium, germanium and indium in coal provides an important basis for geochemical exploration of the scattered elements in coal, and is of great economic significance for the comprehensive utilization of the scattered metals. The ashing conditions of germanium are strict, and the analytical results of germanium are greatly influenced by the ashing temperature. Due to the different ashing temperatures of gallium (Ga), germanium (Ge) and indium (In), the three elements could not be processed and determined simultaneously using existing analytical methods.

OBJECTIVESTo develop a method for the analysis of Ga, Ge and In simultaneously, avoid the loss of Ge in the ashing and digestion processes, and to eliminate the interference in determination.

METHODSA sensitive and efficient analysis method of ashing acid digestion method combined with Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for determining Ga, Ge and In in coal was established by using the optimum ashing temperature of 625℃, selecting suitable acid solution conditions and mass spectrometry determining conditions. Using nitric acid-sulfuric acid-hydrofluoric acid to dissolve ash and 8 mol/L nitric acid for reconstitution, the volatilization loss of niobium was avoided. By optimizing the instrumental working conditions and interference experiments, ¹⁰³Rh was used as the internal standard element, and ⁷¹Ga, ⁷⁴Ge and ¹¹⁵In were selected as the determined isotopes, eliminating the interference of various elements.

RESULTSThe linear correlation coefficients of the standard curves of Ga, Ge and In are all above 0.9999. The detection limits of Ga, Ge and In are 0.004, 0.003 and 0.002 μg/L, respectively. The precisions range from 1.17% to 3.15%, and the sample recoveries are from 96.6% to 102.0%. The determination results of GBW07363, GBW07457 and GBW07428 are in agreement with the certified values.

CONCLUSIONSCompared to traditional analytical methods of Ga, Ge and In in coal, the proposed method is simpler, faster, and has a lower detection limit with simultaneous determination of multiple elements.