BACKGROUNDThere are many kinds of mass spectral interferences when inductively coupled plasma-mass spectrometry (ICP-MS) is used to determine trace amounts of cadmium in geological samples. Usually, on-line or off-line equations are used for correction. When the sample has high tin content, traditional fixed coefficient correction equations can easily lead to significant deviations in the results, and even negative results.

OBJECTIVESTo develop a method for the determination of low-level Cd in high-Sn samples.

METHODSThe system of hydrofluoric acid-perchloric acid-nitric acid digestion and nitric acid compound solvent were applied to analyze the cadmium isotopes, ¹¹¹Cd, ¹¹³Cd and ¹¹⁴Cd for high-tin samples. The influence of interference elements, Sn, In, Zr and Mo on the determination of cadmium was studied.

RESULTSResults showed that there was a non-simple positive correlation between cadmium concentration and the concentration variations of interference sources. The interference increment value increased gradually with the concentration of interference elements. The interference coefficient of ¹¹⁴Sn on ¹¹⁴Cd ranges from 0.0272 to 0.0222, and that of ¹¹³In on ¹¹³Cd was 0.0670 to 0.0412. Cadmium suffers from different degrees of Zr and Mo based oxide/hydroxide mass spectrometry interferences. By measuring the cadmium interference value produced by a single standard solution close to the concentration of the interference source in the sample, the interference coefficient (γ) was corrected on-line to establish an accurate correction equation. The method has been verified by a series of certified standard substances with high accuracy and precision of 6.57%-9.94% (n=7). The method had the Cd detection limit of 0.03mg/kg, which met the requirements of geological sample analysis.

CONCLUSIONSThe method provides a feasible basis for the determination of low-content cadmium in high-Sn geological samples.