DETERMINATION OF TRACE AMOUNTS OF CU(II), NI(II), CO(II) AND CD(II) IN RIVER WATER BY PRECONCENTRATION OF THEIR RUBEANATES ON A MICRO-MEMBRANE FILTER AND ATOMIC-ABSORPTION DETECTION USING DIRECT ASHING METHOD

A new highly effective preconcentration method for Cu(II), Ni(II), Co( II) and Cd(II) in water samples which involved the collection of rubea nic acid complexes of these metal ions on a micro-membrane filter (MMF , cellulose nitrate, diameter: 4 mm, pore size: 0.20 mu m) was develop ed. It was possible to determine metal ions concentrated on a surface of the MMF by GFAAS in which the MMF was introduced directly into a cu p-type graphite cuvette. More than 95% of Cu(II), Ni(II), Co(II) and C d(II) were recovered by adding a salting out reagent (NaCl) and/or a c oprecipitant (excess Cu(II)). For the MMF direct ashing technique on t he GFAAS, an addition of 20 mu l of 5 vol% H2SO4/DMF was effective to reduce the variation of results. Only 5 ml of each samples of sub-ppb level of Cu(II), Ni(II), Co(II) and Cd(II) was enough for one analysis . The detection limits (3 x sigma of blank solution) for Cu(II), Ni(II ), Co(II) and Cd(II) are 80, 95, 50 and 1.6 ppt, respectively. An appl ication of the method for the determination of Cu(II), Ni(II) and Cd(I I) in river water was also described.