Determination of Trace Amounts of Selenium in Wastewaters by Carbon Rod Atomization R. B. Baird, Soloukid Pourian, and S. M. Gabrielian San Jose Creek Water Quality Laboratory, The County Sanitation Districts of Los Angeles County, 2101 Workman Mill Lane, Whittier, Gal$
INCREASED EMPHASIS on the analysis of natural waters and wastewaters for trace metal pollution has created the need for more rapid, sensitive, and reliable analytic procedures. Past methods for the determination of selenium in the environment have included colorimetric procedures ( I ) , atomic absorption spectrometry ( 2 , 3), and, more recently, fluorometric techniques ( 4 ) . The method described in the thirteenth edition of “Standard Methods of Analysis” for selenium is based upon a colorimetric determination using 3,3 ’-diaminobenzidine (5, 6), and employs a classical bromine distillation step to separate selenium (as the oxyhalide) from interferences. The procedure is tedious and has exhibited erratic data in replicate analyses of many samples. The determination of selenium by atomic absorption spectrometry is well known, having been studied by many investigators. The primary difficulties encountered in the past, which hamper atomic absorption detection limits, arise from the relatively low intensity and poor stability exhibited by selenium hollow cathode lamps as well as from the high flame background and noise levels at resonances below 200 nm. Attempts to overcome these problems have been outlined elsewhere (3), but they all, more or less, suffer from the same difficulties. Major chemical interferences were eliminated, however, using a nitrogen-shielded nitrous oxide-acetylene flame (3). The method of analysis proposed here employs a flameless atomic absorption determination which utilizes a “carbon rod” attachment manufactured by Varian Techtron (7, 8). The carbon rod is designed around the principles of the graphite furnaces described by L’vov (9), Massman (IO), and West (11). The type employed in these experiments is the so-called “Mini-Massman” rod developed by Varian. The obvious advantages to this mode of atomic absorption analysis reside in the absence of the usual high levels of flame background normally responsible for the decreased sensitivity in selenium detection. The relatively small sample volume (
