Determination of Co, Cr, Mn and Ni traces in fluorine containing materials for optical fibers using laser enhanced ionization techniques with flame and rod-flame atomizers

Abstract

Two fluorine-containing materials (NH 4F and NaF) for optical fiber production have been analyzed with respect to their contents of Co, Cr, Mn and Ni using two different laser enhanced ionization (LEI) techniques, one using a rod-flame as an atomization-ionization system and one using a flame as the atomizer. One advantage of the rod-flame system is that it can separate the evaporation and atomization steps which thereby leads to a reduction of the influences of matrices. Another advantage is that it can be used for analysis of both solid and liquid samples. The NH 4F sample was analyzed as a solid and also as a solution (dissolved to 50 or 100 g/l in water). In the flame atomizer the NH 4F matrix created a non-selective ionization background giving detection limits in the order of tens of ng/g (concentrations in the solid sample). Using the rod-flame system, however, it was found that Cr, Mn, and Ni could be determined in the NH 4F sample down to a few ng/g by analysis of the sample solutions without any need for preconcentration procedures. Direct analysis of solid samples, without any sample preparation, could also be done using the rod-flame system with a ten-fold improvement in detectability. The detection limits for analysis of the solid samples were estimated to be the following: Co, 1 ng/g; Cr, 0.2 ng/g; Mn, 0.3 ng/g; and Ni, 0.08 ng/g. The NaF sample was more complicated to analyze. When using the flame, a significant ionization background was obtained even for solutions diluted down to 0.2 g/l. However, using the rod-flame system, analysis of the elemental content of the NaF sample could be performed. Detection limits in the range of tens of ng/g could be obtained from diluted solutions (≤20 g/l). It was found that the NH 4F and NaF material contained the following concentrations of impurities (HN 4F: Cr, 70 ± 5 ng/g; Mn, 88 ± 6 ng/g; and Ni, 56 ± 5 ng/g. NaF: Cr, 290 ± 70 ng/g; Mn, 40 ± 15 ng/g; and Ni 2200 ± 400 ng/g). For the case of Co, only an upper limit could be assessed (<1 ng/g for NH 4F and <70 ng/g for NaF).