Abstract
An official method for the determination of fluorine in sediments and soils regulated by Ministry of the Environment of Japan in Soil Contamination Countermeasure Law has been examined, and some improvements are proposed. The improved method is as follows: 1.00 g solid sample was ashed in muffle furnace at 550°C, then mixed it thoroughly with 5.00 g mixture of Na2CO3+K2CO3 in platinum crucible and fused for 40 min, over a Teclu burner. The sample was cooled, then the crucible was transfered in a teflon beaker and 50 ml of distilled water was added to dissolve the soluble material. The sample was filtered and acidified using (1+1) sulfuric acid, the solution was transferred to a 100 ml volumetric flask and diluted to volume with water. Subsequently aliquot of 30 ml was taken out for steam distillation to separate fluoride from interfering substances, and then distilled until 260 ml of distillate was collected. Fluoride was determined by lanthanum-alizarine complexone spectrophotometric method.
Analytical results of 4 certified reference materials (CRMs: sediment) showed good agreement with the provisional or recommended values, but in spite of the improvement the results for 2 CRMs gave 10% lower values.
The precision of the determination of fluorine (relative standard deviation at 5 determinations) was 1.0-2.4 %.
The concentration of fluorine in river sediments in Kanagawa prefecture were detected in the range from 115-176 μg/g (average 150 μg/g) .
