In the medium of surfuric acid and phosphoric acid(S-P) mixed in 1+1, containing p-bromo benzene hydroxyacetic acid(Br BHA),
EDTA, the polarographic currents observed at-0.50V(vs.SCE)
and -0.87V were not so sensitive. But in the presence of NaClO_3, the very sensitive catalytic currents appeared at -0.44V and -0.78V respectively.A possibility of these catalytic currents mentioned above further enhanced by protonated organic dyes or by cationic surfactants has been investigated. Among them the methylene blue (MB) was the best one, which has the lowest detection limit both for Mo (Ⅵ) (1× 10-9mol/L) and W (Ⅵ) (3×10~(-10)mol/L). After adding an appropriate amount of MB, the catalytic currents for Mo(Ⅵ) and W(Ⅵ) were further increased significantly, and Ep was shifted to -0.43V for Mo(Ⅵ) and to -0.83V for W(Ⅵ) respectively. The responses for Mo (Ⅵ) and for W(Ⅵ) were linear over the range of 2×10~(-9) to 4×10~(-7)mol/L and 5×10~(-10) to 2×10~(-8)mol/L respectively. Most coexisting ions(44 cations, 10 anions) studied did not interfere with the determination of Mo(Ⅵ) and W(Ⅵ), and the allowable proportion of Mo(Ⅵ) to W(Ⅵ) or in the reverse both was 1:25000. The proposed method has been applied to determine the molybdenum and tungsten in alloys simultaneously and directly with satisfactory results.