Analytical chemistry: phosphorus

Here is bench space arranged for measuring the phosphorus content of small samples. The samples are weighed and then digested with potassium persulfate (very reactive!) in an autoclave (under steam pressure). Then the pH of the samples is carefully adjusted, and a mixture of ammonium molybdate and ascorbic acid is added. The mixture turns the samples blue, and the shade of blue depends on the amount of phosphorus present. The color is measured with a spectrophotometer.

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