SELECTION OF INTERNAL STANDARDS FOR THE DETERMINATION OF MAJOR AND MINOR ELEMENTS IN SILICATE ROCKS AND LIMESTONES BY LASER-ABLATION INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

Use of contained and added internal standards has been compared in las er ablation ICP-AES of silicate rocks and limestones to improv e both precision and accuracy. Glass disks obtained by fusion of rocks with l ithium tetraborate were sampled by means of a Q-switched Nd:YAG laser (355 nm, 10 Hz, 10 mJ per shot) and analyzed with an ICP emission spec trometer equipped with a segmented charge-coupled device detector. The Si and Ca major elements of the silicate and limestone samples, respe ctively, were compared with the Li and B Bus elements for internal sta ndardization. A 2- to 5-times improvement in the percent relative stan dard deviation (%RSD) of the repeatability was found, irrespective of the internal standard, leading to a repeatability in the 1-2% RSD rang e. On the basis of the use of Li and B as internal standards, linear c alibration graphs were obtained for Si, Al, Ca, Mg, Fe, Ti, Na, and K by using reference geological materials. The possibility of using Bus elements overcomes the need to have prior knowledge of the concentrati on when a contained element is being used as an internal standard.