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 laser ablation ICP-AES of silicate rocks and limestones to improv e both precision and accuracy. Glass disks obtained by fusion of rocks with lithium 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 spectrometer equipped with a segmented charge-coupled device detector. The Si and Ca major elements of the silicate and limestone samples, respectively, were compared with the Li and B Bus elements for internal standardization. A 2- to 5-times improvement in the percent relative standard deviation (%RSD) of the repeatability was found, irrespective of the internal standard, leading to a repeatability in the 1-2% RSD range. On the basis of the use of Li and B as internal standards, linear calibration 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 concentration when a contained element is being used as an internal standard.