USE OF BORIC-ACID TO IMPROVE THE MICROWAVE-ASSISTED DISSOLUTION PROCESS TO DETERMINE FLUORIDE FORMING ELEMENTS IN STEELS BY FLOW-INJECTION INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

The applicability of FI-ICP-MS combined with microwave sample digestio n far the simultaneous determination of trace amounts of La, Ce, Pr, N d, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu in iron and steel samples was investigated. The use of hydrofluoric acid in the sample dissolut ion process produced nearly invisible insoluble particles with the REE s, leading to erroneous quantification of these elements. The addition of boric acid, complexing HF, solved this problem. By monitoring the transient signals produced by the FI microsampling system, it was poss ible to evaluate the effectiveness of the sample dissolution procedure . Severe depressive matrix effects caused by the sample matrix were en countered when the signals were compared with those from HNO3 solution s; in contrast, no effects were observed with the addition of boric ac id. A highly alloyed steel, stainless steel certified reference materi al JK 37 (Sandvik Steel), was used to evaluate the effectiveness of th e dissolution procedure and to develop the method. The limits of quant ification (LOQ) calculated on the basis of 10 root 2s ranged between 0 .008 mu g g(-1) for Lu and 0.040 mu g g(-1) for Nd. The relative stand ard deviation for all the analytes was better than 3% (n = 4) for conc entrations above 10 times the LOQ.