Technology Description

A highly sensitive, robust, and inexpensive benchtop colorimetric bioassay was developed under SERDP project ER-1530 for the determination of parts per billion (ppb) or μg/L-1 perchlorate. The bioassay uses the partially purified perchlorate reductase enzyme from Dechloromonas agitata to detect perchlorate with the redox active dye phenazine methosulfate and nicotine adenine dinucleotide. By using a specific addition scheme and covering all reactions with mineral oil, the reaction could be performed on the benchtop, with a lower detection limit of 200 ppb. When combined with perchlorate purification and concentration by solid phase extraction (SPE), the detection limit was reduced to 2 ppb. Perchlorate is eluted from the SPE column using a solution of 2 M NaCl and 200 mM morpholine propane sulfonic acid (pH 12.5). By applying this assay with the method of standard additions, the efficacy of the bioassay was demonstrated by analyzing perchlorate samples (2 - 17,000 ppb) in tap water and contaminated groundwater. A simple handheld spectrophotometer is commercially available for use with this assay. The presence of perchlorate is identified by the change in absorbance at 340 nm as the primary electron donor (NADH) for the reaction is depleted in proportion to the perchlorate concentration.