Gas-sampling technique for arsenic determination by atomic absorption spectrophotometry.

IN CONVENTIONAL atomic absorption spectrophotometry a solution of the sample is introduced into the flame as an aerosol by means of a nebulizer. However, commercial nebulizers are only about 5 efficient in forming fine droplets suitable for atomization by the flame ( I ) . Furthermore, a solution aspirated at a usual rate of 3-5 ml/min for about 10 sec produces a concentration signal extending over the length of aspiration. Theoretically, if the element were introduced into the flame rapidly-e.g., 1 second-with no loss, a high narrow signal should result and the detection limit should improve. Several devices aimed at improving the efficiency of atomic absorption sampling have been described in the literature. One scheme, developed by Brandenberger and Bader (2) was used to determine nanogram amounts of mercury. In their technique, mercury in solution was deposited on a copper wire and placed io the arm of a specially constructed cell with quartz windows. An electrical potential applied across the wire volatilized the mercury instantaneously. The mercury vapors were then swept through the cell with air and the atomic absorption signal was recorded as a function of time. The above “flameless” technique cannot be used to determine arsenic because of the high temperature required to maintain arsenic in its vapor state. Arsenic often needs to be determined in trace amounts, and an improvement in the present detectian limit of about 0.5 ppm would be desirable. This can be achieved if arsine is generated from the sample, collected in a cold trap such as liquid nitrogen, and then passed into the burner of an atomic absorption spectrophotometer, with the signal recorded cs. time.