An Improved Thiocyanate Method for Determination of Molybdenum using Thioglycollic Acid as Reductant

An improved method for determination of Mo by thiocyanate has been standardized by employing thioglycollic acid, instead of currently employed stannous chloride, as reductant of Mo. The method ensures stability of the colored complex in aqueous acidic medium for about 3.5 hours which is otherwise unachievable and the color unstable while using stannous chloride. The method is linear over 0.5 to 15 ppm Mo in a 2 mL sample with regression estimate in units of absorbance value per μg Mo, b ± s.e., 0.0268 ± 0.0002 and r ± s.e., 0.9998 ± 0.0002 (n = 30). The detection limit can be further reduced to 0.1 ppm by using 8 mL sample and extracting the complex into an organic solvent: 3 mL diethyl ether and 1 mL petroleum ether. The method has been coupled to an extraction protocol employing 0.5M NaOH to extract added Mo from soil, and from water in presence of high metal load. Per cent recovery of added Mo has been 97.3 ± 0.8 (n= 30) with mean per cent accuracy (n=30) and COV (n=4) about 4 each. The method is suitable for monitoring Mo in environmental and other samples including biosolid wastes having toxicological implications.