Abstract
Summary
Various protein precipitating agents were used to obtain protein-free filtrates for determination of free proline in serum. Recovery of proline from serum was 98–101% after precipitation of protein with 95% acidic ethanol; with 10% trichloracetic acid and 2.2% tungstic acid in 0.15 M sulfuric acid, recovery was 111–130%. Accuracy of the method was ± 3% when acidic ethanol was used as a precipitant. Lower maximal absorption values for the prolineninhydrin condensation product were obtained in aqueous standard solutions with trichloracetic acid and tungstic acid than with acidic ethanol, but rate of formation of the acid condensation product did not vary significantly in each system. Strong acid precipitants may alter physicochemical properties of proline itself or of the enol tautomer formed in the proline-ninhydrin condensation to produce the differences noted.
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