Journal of Radioanalytical and Nuclear Chemistry, Vol. 220, No. 1 (1997) 31-35 Determination of monobutyl phosphate and dibutyi phosphate in mixed hazardous wastes by ion-pair chromatography K. E. Grant, G. M. Mong, S. A. Clauss, K. L. Wahl, J. A. Campbell* Advanced Organic Analytical Methods Group, Pacific Northwest National Laboratory, Richland, WA 99352, USA (Received September 5, 1996) Ion-pair chromatography was tested for its applicability in determining monobutyl phosphate (MBP) and dibutyl phosphate (DBP), which are degradation products of tributyl phosphate, in Hartford tank wastes. In tests with simulant waste mixtures, tetrahexylammonium bromide, an ion-pairing agent, was used to complex with all three phosphate species. Recovery studies indicated that ion-pairing chromatography is quantitative for detemaining the analytes in spiked samples. Initial results demonstrated that DBP could be detected easily and was fairly well separated from other peaks, but MBP was frequently lost due to large negative peaks. Then a preconcentration column procedure was used to clean up the waste-sample matrix, and the negative peaks disappeared. Results indicated that 80% of MBP and 90% of DBP could be recovered. Most of the radioactivity was t~wnoved from actual waste tank samples so that additional sample preparation could be performed safely in a fume hood rather than a hot cell. Dibutyl phosphate was identified in an actual tank waste, but MBP was not found; this result was confirmed by ion chromatography with conductivity detection. Introduction a method for determining DBP and MBP in simulant and actual waste mixtures by ion-pair chromatography with Radioactive mixed hazardous wastes stored in 177 tanks at the Hanford Site in southeastern Washington contain substantial amounts of tri-n-butyl phosphate (TBP), 1,2 which was used as a metal extractant to separate uranium, plutonium, and thorium in the reprocessing of spent nuclear fuel. Both thermal decomposition and radiolysis of Na4EDTA 76.0412 TBP have generated dibutyl phosphate (DBP), monobutyl Stcaricacid 54.1017 Citric acid 54.1132 phosphate (MBP), and butanol. The chemistry of these TBP 53.2622 processes has been described in great detail.3,4 Dibutyl DBP 42.0007 phosphate has been of particular interest in terms of waste Hexone 20.0403 tank safety because of its high enthalpy. Dodecane 34.0598 Numerous analytical methods involving gas Na3PO4 81.959D NaNO 2 507.7 chromatography, several different types of liquid NaNO 3 417.5241 chromatography, infrared, visible, and ultraviolet Na2CO3 178.0422 spectroscopy, nuclear magnetic resonance, titrimetry, etc. Na2SO 4 18.9207 exist to determine TBP.5 However, analytical methods for NaCI 0 MBP and DBP have proven to be more elusive in the NaF 0.0103 complex matrix found in the waste tanks. BOCEKet al.6 Ce(NO3)3 2.6926 Ca(NO3) 2 4.3549 have used high-speed isotachophoresis, a form of capillary KNO3 26.9705 electrophoresis with conductivity detection, to analyze for ZnfNO3) 2 0.2007 the degradation products of TBP in solutions containing CsNO3 0.0698 nitrates and nitrites. MtaamR et al. 7 have determined trace Sr(NO3)2 0.0034 NaOH 188.1429 amounts of DBP and TBP in nuclear fuel reprocessing Cr(NO3)3 100.9953 solutions by liquid chromatography, WmKi~SOr~ and Fe(NO3)3 6.4608 WILLIAMS 8 determined DBP and MBP by direct titration of Ni(NO3) 2 2.381 irradiated TBP samples, and KRISI-IRAMURTIaY and RuCl4 0.0717 SAMPATHKUMAR 9 have used titrimetry to determine Rh(NO3)3 0.062 Mn(NO3) 2 3.6022 dibutylphosphoric acid and monobutylphosphoric acid as Pb(NO3) 2 6.6808 degradation products in the two-component TBP-nitric Zr(citrate) 4.5111 acid system. AgNO3 0.004 Better methods are needed to separate and detect DBP Pd(NO)2 0.4893 and MBP in the highly basic complex waste mixtures NaAIO2 408.9299 found in radioactive waste storage tanks. Here we describe H20 1039 Table 1. Composition of simulant waste samples (from Reference 10) Component Weight, g mg/g 22.81 16.23 16.23 1~.98 12.60 6.012 10.218 24.59 152.3 125.3 53.41 5.676 0.0 0.0031 0.8078 1.31 8.091 0.06021 0.02094 0.001 56.44 30.30 1.938 0.7146 0.022 0.019 1.081 2.004 1.353 0.001 0.146 122.7 311.7 *Author for correspondence. 0236--5731/97/USD 17.00 9 1997 Akad~miai Kiadr, Budapest All rights reserved Elsevier Science B.V., Amsterdam Akad~miai Kiadr, Budapest