FLAME PHOTOMETRY OF PHOSPHORUS VAPORIZED FROM A SILICA-TREATED GRAPHITE-FURNACE

Phosphorus is determined by flame photometry in a fuel-rich H2-air flame using a graphite furnace to vaporize samples prior to introduction into the flame. When untreated graphite tubes are used, calcium and other metals depress phosphorus emission. However, impregnating tubes with SiCI4 followed by hydrolysis to SiO2 leads to a substantial reduction in the interference for the lifetime of the furnace. The resulting analytical system has a detection limit of 1 ng phosphorus. Response is linear in the absence of calcium and almost linear in the presence of a large excess of calcium. Evidence is presented to show that the Si02 forms a SiC coating on the graphite. This coating prevents reduction of phosphate to PO. As a result, metal phosphates are vaporized at furnace temperatures high enough to cause substantial decomposition to the elemental phosphorus. © 1979, American Chemical Society. All rights reserved.