Antimony potassium tartarate hemihydrate is often used for quantification of phosphate using ammonium molybdate method with ascorbic acid as a reducing agent. We are recording significant decline in absorption maxima in presence of antimony compared to what we record in its absence. I am unable to uderstand why antimony is used? Amongst reducing agents [used so far by various research teams], we find ascorbic acid to be better.
Antimony potassium tartrate and ammonium molybdate react in an acid medium with dilute solutions of phosphorus to form an antimony-phosphomolybdate complex. This complex is reduced to a blue-colored complex by ascorbic acid. The color is proportional to the phosphorus concentration (Only orthophosphate forms a blue color in this test).
Thank you. Ammonium molybdate itself can react with phosphomolybdate under acidic conditions [better at pH ranging between 0.9 to 1.4] to form phosphomolybdic acid, which can be reduced to form stable blue coloured complex. Although, antimony is being used to probably stabilize the colour [or increase intensity and hence sensitivity], we have been repeatedly recording decrease in the intensity of blue colour [hence, reduction in OD values]. Recently, we have come across a publication that also reflects reduction in intensity of blue colour by antimony [please see Fig. 9 in Nagul et al. Analytica Chimica Acta 890: 60-82]. But, antimony is still preferred by few research teams. That is the precise reason, why I am keen in understanding the basic reason behind the use of antimony in phosphate estimation. My basic question is - if reduced phosphomolybdic acid gives higher OD values compared to reduced antimony-phosphomolybdic acid [with the same specific concentration of phosphate] [under similar pH conditions], why should we use antimony salt?
Hi Pardha_Saradhi
Am currently putting up a protocol for analysis phosphorus levels in plant tissues, Will you be kind enough to share your protocol for the analysis of Pi without the use of antimony potassium tartrate wiith me on [email protected]? I will be most grateful
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Article A Colorimetric Dip Strip Assay for Detection of Low Concentr...
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