Molybdate-antimony reagent

Molybdate-Antimony Reagent dissolve lOg of ammonium molybdate m 40ml of 2M sulphuric acid, dissolve 0 1 g of sodium antimony tartrate m 50 ml of 2M sulphuric acid Mix die two solutions and dilute to 500 m 1 with 2M sulphuric acid... 

Colorimetric methods Silicon is determined by the molybdenum blue spectrophotometric method after solubilization in H2O, in alkaline solutions or in concentrated HF. A flow analysis procedure for the measurement of soluble silicon with respect to the total Si concentration is used. The proposed method is applied to samples of rain water and of aerosols on filters [45]. Simultaneous determination of orthophosphate and silicate in brackish water is performed by the same technique. Molybdate/ antimony, ascorbic acid, and oxalic acid reagents are added to the samples and spectra are recorded in the wavelength range 410-820 nm after a total reaction time of 30 min [46]. 

The determination of the orthophosphate was carried out by using the automated systems described by the Technicon Instruments Corporation. The manifolds used are shown in Fig. 12.3. The procedures referred to below as methods I and II are Technicon industrial methods Nos. 94-70W and 155-71W, respectively. Method I includes ascorbic acid alone for the reduction of the molybdophosphoric acid whereas in method II the mixed reagents ascorbic acid, sulphuric acid, ammonium molybdate and antimony potassium tartrate are used. Method I is intended for use for high levels of phosphorus (up to lOpg ml4) and method II for low levels (less than 0.5pg ml4). The wetting agent (Levor IV) used in order to obtain a smooth bubble pattern, is present in the ascorbic acid reagent line for method I whereas it is added externally Fig. 12.3) in the water line (0.5pg ml4 of Levor) in method II. 

To prepare the colorimetric reagent, sulfuric acid (250 ml 2.5 M) is added to ammonium molybdate (75 ml) and mixed. Then, ascorbic acid (50 ml) is added and mixed, followed by antimony potassium tartrate (25 ml) and further thorough mixing. The volume is finally adjusted to 500 ml. 

The seawater sample is allowed to react with a composite reagent containing molybdic acid, ascorbic acid, and trivalent antimony. The resulting complex heteropoly acid is reduced in situ to give a blue solution thh extinction of which is measured at 8850 A. 

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