DETERMINATION OF CHROMIUM(VI) IN WATER BY PIXE ANALYSIS USING ION EXCHANGE PAPER — LIMIT OF DETECTION AND INTERFERENCE BY COEXISTING ANIONS

Abstract

Concerning the PIXE analysis of Cr ( VI ) in water using ion-exchange filters, the limit of detection (LOD) and the influence of matrix anions were investigated. In order to look for the experimental condition for obtaining the minimum LOD, we measured the Cr - K α X-ray counts and background counts under the K α X-ray peak as a function of the incident proton energy and the thickness of the Mylar absorber foil in front of the detector. To investigate the interference by coexisting anions, each of PO 43-, SO 42-, NO 3-, Cl -, and F - ions and Cr ( VI ) ions were mixed in aqueous solutions and adsorbed on DE81-DEAE cellulose paper, a weakly basic anion exchanger with diethylaminoethyl functional groups. Then the filter samples were measured by PIXE using 2.5 MeV proton beams. We obtained a LOD of 0.16 µg or 8 ppb for 20 mL samples at a proton energy of 2.5 MeV and a Mylar film thickness of 50 or 100 µm. The experimental results on the mixed solutions indicated that NO 3-, Cl -, and F - as coexisting ions didn't interfere significantly with determination of a 50 µ g / L Cr ( VI ) concentration for 40 mL total solution volume, despite the total amount of anions was about 90% of ion exchange capacity of a filter. On the other hand, slight interferences by PO 43- ions were observed. However, under the same condition, we found that if the total amount of SO 42- ions was higher than 20% of ion exchange capacity, they induced significant interferences in determining Cr ( VI ).