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

Two fluorine-containing materials (NH4F and NaF) for optical fiber pro duction have been analyzed with respect to their contents of Co, Cr, M n and Ni using two different laser enhanced ionization (LEI) technique s, one using a rod-flame as an atomization-ionization system and one u sing a flame as the atomizer. One advantage of the rod-flame system is that it can separate the evaporation and atomization steps which ther eby leads to a reduction of the influences of matrices. Another advant age is that it can be used for analysis of both solid and liquid sampl es. The NH4F sample was analyzed as a solid and also as a solution (di ssolved to 50 or 100 g/l in water). In the flame atomizer the NH4F mat rix created a non-selective ionization background giving detection lim its 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 NH4F sample down to a few ng/g by analysis of the sample solutions without any need for preconcentration procedu res. Direct analysis of solid samples, without any sample preparation, could also be done using the rod-flame system with a ten-fold improve ment 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 t o analyze. When using the flame, a significant ionization background w as 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 sa mple could be performed. Detection limits in the range of tens of ng/g could be obtained from diluted solutions (less than or equal to 20 g/ l). It was found that the NH4F and NaF material contained the followin g concentrations of impurities (HN4F: 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 lim it could be assessed (<1 ng/g for NH4F and <70 ng/g for NaF).