Cathodic Adsorptive Stripping Voltammetric Determination of Molybdenum Using Mo (VI)-Cr (VI)-Pyrocatechol Violet Ternary Complex

Abstract

In this study a new selective method for determination of trace amounts of molybdenum
by adsorptive stripping voltammetry at pH= 4.5 is proposed. The method is based on adsorptive
accumulation of Mo-pyrocatechol violet (PCV) complex onto hanging mercury drop electrode
(HMDE) at accumulation potential of +0.10 V (vs Ag/AgCl), followed by reduction of adsorbed
species by voltammetric scanning in the potential range of -0.40 and 0.80 V (vs Ag/AgCl) in
differential modulation. The reduction peak current at -0.68 V (vs Ag/AgCl) is enhanced by
addition of dichromate. The effect of instrumental and chemical variable on the sensitivity of the
method were studied and optimized. In the optimum condition the limit of detection was found
0.050 ng mL-1
. The relationship between the peak current and molybdenum concentration is
linear in the range of 1.0 – 70.0 ng mL-1
. The relative standard deviations for ten replicate
determinations of 40.0 and 25.0 ng mL-1 Mo(VI) are 0.85 and 1.3%, respectively. The effects of
interferences ion were studied and it was found that the method is free from interferences of
some common cations. The procedure is applied to the determination of molybdenum in real
and synthetic samples with satisfactory recoveries (92.5-104%).