Correction of the sensitivity difference in atomic absorption spectrophotometry of chromium

Abstract

The sensitivity difference of four different chromium compounds and a method for eliminating it were studied. A Nippon Jarrell-Ash model AA-1 atomic absorption/flame emission spectrophotometer was used fitted with a slit burner for air-acetylene flame and a HETCO total consumption burner for air-hydrogen flame under the conditions shown in Table 1. As shown in Fig. 1, the four chromium compounds gave the same sensitivity at an acetylene flow-rate of 1.7 1/min or less. At faster acetylene flow-rates, each chromium compound gave the different sensitivity. As shown in Fig. 2, the sensitivity difference as also recognized at any hydrogen pressure in an air-hydrogen flame. The relative sensitivities were as follows: (NH4) 2CrO4> K2Cr2O7> CrCl3> K2CrO4 (air-acetylene flame) and K2Cr2O7> (NH4) 2CrO4> K2CrO4> CrCl3 (air-hydrogen flame). A method for eliminating such sensitivity difference was studied by the addition of ammonium chloride which yields an intensive enhancement interference on chromium. As shown in Fig. 3, with 0.02 M (air-acetylene flame) and 0.005 M (air-hydrogen flame) ammonium chloride, the absorbance became a substantially constant values. As shown in Figs. 4 and 5, at any acetylene flow-rate and hydrogen pressure, each chromium compound gave the same absorbance in the presence of ammonium chloride. These facts open up the possibility of using any chromium compound as a standard. Also the accurate estimation of the total amount of chromium in a sample solution containing various chromium compounds becomes possible by the additon of ammonium chloride to both the sample and standard solutions. Examples of analytical results are shown in Table 2. © 1975, The Japan Society for Analytical Chemistry. All rights reserved.