BACKGROUNDTotal boron in geological samples is determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) with acid digestion. The key steps are preventing the loss of boron during the sample digestion stage and reducing matrix interference, spectral interference and memory effect during measurement.

OBJECTIVESTo establish a method for the determination of boron in geological samples by ICP-OES with low-pressure closed digestion.

METHODSUsing HF-HNO₃-HClO₄-H₃PO₄ to digest samples in a low-pressure closed sample tank, the dissolved boron element is fully complexed with a small amount of phosphoric acid to prevent the volatilization loss of boron. The standard curve was calibrated using the geological solid standard material with similar concentration of matrix and major components to effectively match and reduce the matrix interference of the sample. The operating software provided by the instrument was used to observe and analyze the interference of other elements near the spectral line and to determine the best position and width of background subtraction to reduce the spectral interference in the ICP-OES measurement. 10% Aqua regia was used as the rinsing liquid of the sample introduction system, which effectively reduced the memory effect during measurement.

RESULTSWhen the dilution factor was 200, the detection limit (3SD) was 1.2μg/g, and the quantitative limit (10SD) was 4.0μg/g. The precision and accuracy were analyzed and verified by using the national first-class standard substances in rock, soil and river sediment, the relative standard deviations (n=11) were from 1.8% to 7.9%, and the relative errors were from -3.6% to 6.3%. Compared with the results of external tests, the relative error of boron content above the quantitative limit ranged from -9.3% to 12.5%.

CONCLUSIONSThe method is suitable for the accurate measurement of boron above 4.0μg/g in geological samples.