SEQUENTIAL INJECTION PHOTOMETRIC-DETERMINATION OF MOLYBDENUM USING ORGANIC WETTING FILM EXTRACTION

Wetting film extraction was combined with colorimetry to determine nan ogram amounts of molybdenum(VI). The simple extraction procedure enhan ced sensitivity and selectivity while maintaining a high sample throug hput. Extraction and back extraction steps were exploited to exclude i nterference from the 31 metal species and 11 anions tested. In the fir st step, molybdenum(VI) was extracted into a toluene film as an ion pa ired complex. Molybdenum(VI) reacted with thiocyanate to form anionic molybdenum(V) and/or molybdenum(VI) thiocyanate complexes. The complex es were extracted into a toluene film containing tetraheptylammonium b romide as ion pairing reagent. The thiocyanate ligands were displaced by 1,5-diphenylcarbazone (DPC) to form a more intensely colored comple x (lambda(max) = 540 nm). DPC was introduced in the back extraction so lvent, methanol. The relative standard deviation was 2.5% for 50 ng ml (-1) of molybdenum(VI) (n = 10) at a rate of 25 samples h(-1). The det ection limit (3 X baseline noise) was 2.5 X 10(-8) M. (C) 1997 Academi c Press.