Abstract
The determination of trace amounts of phosphorus in high-purity silicon has been investigated. A sample was decomposed by a mixed acid vapor of hydrofluoric acid and nitric acid in a pressure bomb. The presence of 0.5ml of sulfuric acid prevented the loss of phosphorus during the decomposition. Phosphorus in the residue was converted to molybdophosphate and collected on a polycarbonate filter as an ion pair with dodecyltrimethylammonium bromide (DTMAB). The molybdophosphate-DTMAB ion pair was dissolved in 0.2ml of conc. sulfuric acid, and diluted to 510ml with water. The molybdenum in the solution was determined by isotopic dilution/ICP-MS, which resulted in the determination of phosphorus. The interference with silicon, aluminium, and iron was almost negligible up to a concentration as high as 1001000 times that of phosphorus ; also, a μg g-1 level of arsenic in silicon materials did not interfere with the phosphorus determination. The lower limit of detection was under 0.01μg g-1 in silicon based on 3σ of blank values.
