Electrothermal atomic absorption spectrometry (ET-AAS) determination of heavy metal impurities in fluoride salts for fiber optics manufacturing. Optimization of sample pretreatment, dissolution, matrix effect removal

This paper describes analytical methods optimized for the determination of iron, cobalt, nickel, copper, zinc, manganese and chromium impurities in a series of fluorides, namely NaF, LiF, AlF₃, YF₃, HfF₄, LaF₃ and ZrF₄ at trace levels with electrothermal atomic absorption spectrometry (ET-AAS) with and without matrix modifiers. Such fluorides are the basic components employed for the synthesis of 'fluoride glasses' which are used in the production of optical fibers for IR signal transmission. The transition metal impurities were determined after dissolution of the samples with an acid mixture in a microwave oven or after removal of the sample matrix. The paper compares several procedures for the dissolution of fluorides, matrix effects on transition metal determinations and their reduction, and the use of matrix modifiers. A comparison of the available purities of commercial fluorides is reported.