Surrogate and Matrix Spike Recoveries in Chlorinated Samples Using Sodium Thiosulfate, Sodium Arsenite and L-Ascorbic Acid as Dechlorinating Agents

摘要

Chlorine reacts with various organics in environmental samples to produce undesirable artifacts. These artifacts can cause false positives to be reported, and other compounds actually present to be reported as not detected. The NPDES method (EPA Method 625) for base/neutral and acid compounds states that residual chlorine should be determined in the field. Effluents must be dechlorinated before acidification to prevent the chlorination of compounds present in the effluent. The study examined the suitability of three dechlorinating agents: sodium thiosulfate, L-ascorbic acid and sodium arsenite. The three dechlorinating reagents were also tested using the separatory funnel technique. The authors are currently using continuous extraction as the routine method of extraction for water samples. This method has been found to generally produce higher recoveries of all compounds when compared to separatory funnel extraction. The higher recoveries are due to the fact that the extraction solvent is constantly being re-distilled. This essentially results in numerous, repeated extractions using fresh solvent for each extraction.