FRACTIONATION OF BORON IN GEOLOGICAL REFERENCE MATERIALS BY SEQUENTIAL EXTRACTION ICP-AES

A five-step sequential chemical-extraction scheme is described for the analysis of B in geological reference materials by ICP-AES. Each of t he chemical fractions is operationally defined as follows: 1) 0.1 M po tassium nitrate for the ion-exchange and adsorbed fraction; 2) 0.05,M ethylendiaminetetraacetic acid disodium salt (EDTA) for the EDTA solub le fraction; 3) a mixture of 0.025 M EDTA, 0.1 M ammonium oxalate, 0.1 M oxalic acid, 0.05 hi ascorbic acid and 0.005 M HCl for the oxide fr action; 4) a mixture of 6 M HNO3 and 1 M HCl for the HNO3-HCl soluble fraction; and 5) fusion with Na2CO3 for the residual fraction. The rel ative standard deviation for B at levels of 0.15 and 5 mu g were 20 an d 4%, respectively. The detection limit was approximately 0.8 ppm for a 0.1 g sample. Satisfactory agreement was observed between the sum of the B values from ion-exchange and adsorbed to residual fractions and the reported total B values. Analytical results of B for twenty five geological reference materials, such as igneous rocks, sedimentary roc ks, sediments, soils and coal fly ashes were tabulated, and geological and mineralogical features are discussed.