Reducing the Detection Limit for Tetraphenylborate in Tank 50H Waste

摘要

SRTC personnel are developing a technique that can determine the concentration of tetraphenylborate (TPB) at 300 grams in 100,000 gallons of salt solution (0.8 mg/L) in the presence of0.378 Ci/gal of Cs-137. The current High Performance Liquid Chromatography (HPLC) method of analysis can determine the TPB concentration at 5 mg/L and higher. The limit of quantitation was lowered by modification of the sample preparation steps. The HPLC sample preparation method currently used requires neutralization of the tank waste sample followed by extraction with acetonitrile. This method dilutes the tank waste sample 6.5 to 1 increasing the limit of quantitation. The method described in this report concentrates the sample two-fold lowering the limit of quantitation from 5 mg/L to 0.25mg/L. Researchers used solvent extraction of undiluted tank waste to isolate, and concentrate (two-fold) samples of tank supernate and Plant Inhibited Water (PIW) that simulated tank supernate at the cesium level of approximately 0.3 Ci/gal. The 137Cs content in the tank supernate measured 0.65 Ci/gal prior to a two-fold dilution with PIW. The concentration of the TPB was determined by HPLC on a reversed-phase HPLC column using methanol, acetonitrile, and buffered water as the mobile phase. Important Findings: The 0.8 mg/L quantitation limit was met in the presence of radioactive cesium. A 93 per cent reduction in activity in the acetonitrile layer was achieved. A five-mL acetonitrile aliquot from the extraction of a tank waste sample containing 0.378 Ci/gal of Cs-137 could be handled in a radiological hood and comply with the less than 5 mR/hr hood limit. This method is applicable to tank waste solutions of high ionic strength (greater than 2.0 M Na). The ionic strength of tank waste solutions of low ionic strength will need to be adjusted by the addition of NaOH or 5.6 M average salt solution to facilitate the formation of two layers (organic and aqueous). Increasing the ionic strength of tank waste samples by blending in a high ionic strength solution will raise the limit of quantitation.