Selective determination of TNT in soil extracts by sequential injection spectrophotometry

A rapid sequential injection spectrophotometric method for the selective de termination of 2,4,6-trinitrotoluene (TNT) in soil samples is presented. Th e method is based on a derivatization reaction of TNT with sodium sulfite i n a basic acetone medium. The reaction conditions, namely the percentage of acetone used in the reaction, the sample and reagent volumes, the mixing c oil volume, and the reaction time, were optimized. The reaction was found t o be particularly sensitive to the concentration of acetone; an acetone/wat er medium of 88% (v/v) acetone was found to be optimal. A study of the resp onse of the method to other explosives demonstrated that the method is sele ctive for TNT, In particular, it was shown that the method had little (<2%) or no response to other secondary explosives such as 2,4- or 2,6-dinitroto luene (DNT). An average precision of 6.1% RSD was established for five soil samples (n = 4). The limit of detection was 0.5 mu g mL(-1) for aqueous st andards and 80 mu g g(-1) for similar to 300 mg soil samples. analysis time was approximately three minutes per sample. Quantitative results from the determination of TNT in authentic contaminated soil samples compared favora bly to those obtained using a standard method. The extension of the method to water samples and the means by which samples can be preconcentrated on-l ine using solid-phase extraction (SPE) techniques are discussed.