Conversion to alkyl or alkylether phosphoric acids

The phosphate esters are converted to the free acid form, if they are present as salts, and determined by alkali titration. Monoesters have one weakly acidic and one strongly acidic proton. Diesters are strongly acidic. 

Sokolov et al. [26] have reported successful analysis of a mixture of pure sodium dodecyl sulphate and pure sodium dodecyl phosphate (mono- or diester not specified) by this method, and Ivanov et al. [27] analysed alkyl phosphates by titration of the column effluent with alkali to bromocresol green. 

Dry a 1 g sample and extract the organic matter by boiling with dry propan-2-ol as in section 5.13.1. 

Cool and dilute with one-third volume of water. 

Pass through a column of a strongly acidic cation exchanger in the free acid form and wash the column free of solute, using propan-2-ol or ethanol (about three bed-volumes). Collect the effluent and washings in the same beaker. 

---