A Comparative Study of Methods Used for Analysis of Specific Precipitates in Quantitative Immunochemistry

Abstract

A comparison of the sensitivity and precision of the biuret, ultraviolet absorption, Folin-Ciocalteu and ninhydrin methods for the analysis of specific precipitates has been made, and the uses and limitations of each have been discussed. The ultraviolet absorption of samples in 0.25 N acetic acid and the biuret methods were found to be simple and accurate, the limits of 2 S. D. being ±5 to 10%. The former may be used for samples containing as little as 5 μg nitrogen whereas the lower limit of the latter is about 20′ μg nitrogen. The Folin-Ciocalteu method may be used for samples as small as 5 μg nitrogen and 2 S.D. equals ±15%. The ninhydrin method has a sensitivity making it capable of determining as little as one microgram of protein nitrogen but for reproducible results should probably not be employed without the use of a standard.