ION-CHROMATOGRAPHIC DETERMINATION OF FLUORIDE IN WELDING FUMES WITH ELIMINATION OF HIGH CONTENTS OF IRON BY SOLID-PHASE EXTRACTION

An ion chromatography (IC) procedure was developed for the determinati on of fluoride in fumes from are-electric welding of steels with basic electrodes. The interference of metal ions was eliminated by passing the sample solution through an on-line pre-column of a strong cation-e xchange resin. Both a strong acid (Hf form) resin and a strong chelati ng (Na+ form) resin were experimented for this purpose. Linear respons e was obtained from 0.02 to 1 mg of fluoride (in a 50-mu l loop), whic h corresponds to a concentration range from 0.15 to 7.5 mg/m(3) air (6 to 300% of the threshold limit value-time weighted average), for the experimental conditions used (2-h sampling periods, air flow-rate 17 l /cm(2).h, through a 1.2-mu m pore size cellulose nitrate filter, from which a l-cm diameter disk was attacked and analysed). The short-term (within 30 min) precision of the IC determination was <3% (7 determina tions). The accuracy of the procedure was evaluated by analysing both synthetic solutions and real samples. When several mixed standard solu tions of fluoride, iron(III) and aluminium(III), covering the ranges a nd ratios of concentration levels in real samples, were analysed, prac tically quantitative fluoride recovery (97-101%) was found. When 13 sa mples with 0.6-18 mg/l of fluoride were determined in parallel by IC ( 0.03-0.9 mu g injected) and a well established ion-selective electrode (ISE) procedure, no bias was found: a linear regression[IC] = 0.99 (/- 0.12) [ISE] + 0.9 (+/- 1.4) (confidence limits at 95% confidence le vel in parentheses) was obtained.