Molybdenum phosphate dimers

The absorbance of the 12-MPA dimer may then be measured, or it may be reduced to form the highly colored PMB using a variety of reductants. The optimum wavelength and sensitivity are a function of both molybdate and acid concentrations [77. Because molybdenum blue may also form through direct reduction of Mo(VI) if the pH is <0.7, even in the absence of phosphorus, the acid concentration is kept within the range of 0.3-0.5 N [77]. The selectivity of this reaction for phosphate is also highly pH-dependent, and again the reaction acidity must be strictly controlled. 

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