On the estimation of organic phosphorus

Abstract

In attempting to use the methods of Bloor and Bell and Doisy for estimating liopoid phosphorus, difficulty was experienced in securing uniform results. A study of these methods was therefore made using pure inorganic phosphate solutions. Complete recovery was rarely possible and the apparent losses were quite variable. After excluding other steps in the processes as possible causes of error, attention was given to the ashing process, modifications of the Neumann ashing process being used. In this method, which had given satisfaction for the macro estimation of phosphorus for a long time, two possible sources of error were discovered.

Although when heated alone, phosphoric acid does not volatilize until a temperature of about 260° C. is reached, when it is heated with sulphuric acid at 180°-200° C. it volatilizes slowly in the vapors of sulphuric acid—a fact which the writer subsequently found had been demonstrated by Hillebrand and Lundell. This source of loss was found to occur both in the Bloor and Bell and Doisy methods. In addition, when the latter method of ignition was used, some conversion of ortho to pyrophosphoric acid was usually found to occur because of the very small amount of sulphuric acid used.

The fact that volatilization occurs under the conditions present in the Bell and Doisy and Bloor ashing processes was demonstrated as follows:

One c.c. of a phosphate solution containing 1.0 mg. of P was placed in the bottom of a pyrex test tube 8×1 and to it were added a few washed quartz pebbles, 8 drops of sulphuric acid and 1 c.c. of nitric acid as suggested by Bell and Doisy, or 1.5 c.c. of a mixture of equal parts of sulphuric and nitric acids as Bloor uses.