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The most important species of chromium (VI) formed in water are anions such as CrO₄^2-, whereas chromium (III) is mainly present in the form of cationic species such as Cr(OH)₂⁺. Pure water and tap water samples were artificially contaminated with mixture of chromium (VI) and chromium (III) standard solutions. Sequential filtration through commercially available Whatman P81 cellulose phosphate paper and Whatman DE81 DEAE cellulose paper was employed for separation and preconcentration of chromium (III) and chromium (VI) in these water samples, respectively. The PIXE measurements of these filter paper samples were performed using 2-MeV proton beams delivered by a tandem pelletron accelerator at Research Laboratory for Nuclear Reactors, Tokyo Tech. The beam current and the measuring time for each sample were 1 nA and 10 minutes, respectively. Instrumental detection limits were 60 ng for chromium (VI) and 120 ng for chromium (III). Detectable range for chromium (VI) and chromium (III) in water were ≧ 10 ppb and ≧ 50 ppb, respectively. For chromium (VI), the detectable range was considerably lower than the maximum allowed concentration of 50 ppb for chromium (VI) in both the drinking water standards and the environmental quality standards in many countries.

Traces of vanadium, manganese, iron, cobalt, nickel, copper, and zinc were quantitatively extracted with diethyldithiocarbamate (DDTC) in benzene from a digested solution of biological materials and the metal-DDTC complexes were collected into a small amount of polystyrene foam produced by lyophilization of the benzene extract after addition of polystyrene. The polystyrene foam was dissolved in benzene and spread on Mylar film. After drying, a polystyrene film containing metal-DDTC complexes was produced on Mylar film, and then the polystyrene film was peeled from the Mylar film. This film was subjected to PIXE analysis. This method was applied to NBS SRM 1572 citrus leaves and a marine macroalgal sample, and 6 trace metals were simultaneously and accurately determined.

Recent studies were reviewed on the PIXE analysis of metal ions preseparated by means of capillary type isotachophoresis (ITP-PIXE). The principle was described of isotacho-phoresis which was one of electrophoretic methods with high separability and concentration ability. Some applications of ITP-PIXE were demonstrated on the investigation of the separation behavior of metal ions and the analysis of trace elements in a crude rare earth chloride from a monazite and a model mixture of a high level liquid waste. It was revealed that PIXE could be a powerful detection method for the fractions of isotacho-phoresis because of its high sensitivity and multielemental analyzability. Since the matrix effect in X-ray measurement was significantly reduced by such preseparation, the minor elements could be determined accurately.

PIXE technique has been applied to quantitative analysis of thorium and uranium ions in drainage from a radioisotope laboratory of Tohoku University. Two kinds of targets were prepared and analyzed with an in-air vertical PIXE system of 3 MeV protons. The concentrations of thorium and uranium higher than 40 ppb were easily determined by 3-μC irradiation on targets which are made from a 0.12-ml solution containing Ga-internal standard evaporated on a hand-made polycarbonate film. Uranium(VI) ions in a 25-ml sample were preconcentrated into a thin uniform target containing Zr or Pd as an internal standard by means of dibenzyldithiocarbamate complexation with subsequent condensation into dibenzylidene-D-sorbitol gels, and low concentration of 10 ppb was precisely determined by PIXE measurement. This method does not work for concentrating thorium ions. The PIXE analysis for these two kinds of targets has good sensitivity and precision enough to determine concentrations of thorium and uranium lower than their permissible concentration limits in drainage from a radioisotope laboratory.

A method has been developed and tested for PIXE analysis of soluble and insoluble constituents in a variety of water samples in our surroundings. Insoluble components were filtered on a Nuclepore filter of 0.4-μm pores. For soluble fractions, a target of major components was made from a 0.15-ml filtrate evaporated on a user-made polycarbonate film, and in turn heavy metals in trace amounts were preconcentrated in a PIXE-target through the use of a combination of dibenzyldithiocarbamate-chelation with subsequent condensation into dibenzylidene-D-sorbitol gels. These three kinds of targets were analyzed with a PIXE system of 3-MeV proton beams. The widespread concentrations (several tenths of ppb to a few tens of ppm) of ~24 elements from Na to Pb were determined simultaneously in a precision sufficient to reveal the elemental distribution between the soluble and insoluble fractions of various aqueous samples such as river water, rain water and water leaking from disposal sites of industrial wastes. Hence, the methodology for preparing three types of targets promotes the PIXE analysis to a truly effective means for monitoring a water-pollution problem in our surroundings.