Abstract
A method for the determination of micro-amounts of fluoride in ambient air was developed, in which fluoride ion was converted to trimethylfluorosilane (TMFS) by trimethylchlorosilane (TMCS) and determined by head space gas chromatography.
Fluoride in ambient air was collected on the membrane filter for fluoride particulates and on the alkali filter paper impregnated with 1% Na2CO3 solution for gaseous fluoride at a rate of 20l/min for 1-2 h. The sample on each filter paper was extracted with 20ml of distilled water on water bath. The sample solution was filtered off and diluted to 25ml with distilled water.
The sample solution containing up to 0.3 μg of fluoride was taken into a 50-m1 vial. Then 20ml of HCI was added and diluted to 50 ml with distilled water. The vial was sealed quickly after adding 1ml of HCI saturated with TMCS. The mixture was allowed to stand for 30 min at 30°C. The head space gas of TMFS in the vial was sampled and was in jected into gas chromatograph equipped with FID. A good linear relationship was obtained between peak height of TMFS and concentration over the range 0-3 μg of fluoride. The relative standard deviation for 10 results at the 0.1 μg of fluoride level was 2.4%. The method was simple and sensitive, and also relatively free from interferences.
Satisfactory results were obtained when the method was applied to ambient air. The detection limit of fluoride was 0.01 μg/m3.
