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100-ppb concentration range in a continuous fashion can be achieved using the FPD detector and the calibration/monitoring procedure developed and tested in this work.With the exception of Son, the sulfur gases studied can be successfully separated and quantitated in the low ppb concentration range by the use of a cold trap, followed by GC analysis with a specially treated Porapak QS column and an FPD detector. ACKNOWLEDGMENTThanks are due to S. Guerin and R. Grozelle for their technical assistance and to J. MacMillan, S. Prahacs, R.Wostradowski, and B. Fleming for their very helpful suggestions during the course of this project.Radiotracers were used to evaluate a variety of procedures for concentrating selenium for its determination with the heated graphite atomizer (HGA) atomic absorption technique. The concentration procedures studied included extraction, internal electrolysis, coprecipitation, and hydride generation. Although hydride generation using sodium borohydride was chosen as the best method for concentrating and introducing samples into the HGA, the data in this report indicate that published procedures may liberate as little as 10% of the total inorganic selenium from the solution. Optimization of the hydride generation step as well as the other steps necessary for the determination of selenium resulted in a procedure which is sensitive, straightforward, and free from interference.