Determination of phosphorus content in steels using flow injection into an argon-water carrier for Inductively Coupled Plasma Mass Spectrometry

This paper describes a methodology for the determination of phosphorus in steels using argon-water carrier, in flow injection with Inductively Coupled Plasma Mass Spectrometry. P-31 is a monoisotopic element and its determination, at very low levels, is very difficult due to contamination problems and interference inherent in the plasma and solvents. These unduly raise the background being necessary a sample pretreatment step to achieve the required contents. To dissolve the samples in this study, a microwave digestion system was applied to minimize the sample preparation time, the quantities of reagents and the risk of contamination. A mercury cathode electrolysis was used for performing a rapid matrix removal/analyte enrichment. The use of an argon-water stream as carrier yielded an enhancement in sensitivity and the detection limit was improved by a factor of approximately 2.5 when compared with that experienced using flow injection into an all-water carrier. Optimization of the operating conditions for the argon-water flow injection and for Inductively Coupled Plasma Mass Spectrometer, were selected with respect to the peak height sensitivity and were found to be dependent on the nebulizer gas flow-rate, the radio frequency power, the sample injection volume and the carrier flow-rate. The detection limit based on a sample rate of 0.02 g m/(-1) was 0.4 mu g.g(-1) and the relative standard deviations at 100 and 10 mu g./(-1) P solution were 2.0 and 15% respectively. Data are presented for 3 Standard Reference Materials: JSS 003-2, (from Japanese Iron and Steel Certified Reference Materials); and ECRMs 285-1 and 278-1 (from Bureau of Analysed Samples LTD).