Two-Dimensional Chromatography to Evaluate Amino Acid Excretion

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COLLECTIVELY, amino acids may be determined quantitatively in terms of the α-amino nitrogen normally excreted in the urine. The amounts excreted show diurnal variation, and are affected by diet, by age of the person, and by disease. The purpose of this paper is to describe the chromatographic technic used for clinical screening of patients for abnormal amino acid excretion, to present results, and to discuss the usefulness of this technic as a clinical tool.

The term ‘free α-amino nitrogen’ has various meanings depending upon the method used to determine the concentration in a specimen and the interpretation placed upon it. As we use the term, it constitutes the collective group of compounds in an unhydrolyzed physiologic colorless specimen which upon reacting with ninhydrin become purple. It is assumed that the reacting amino radical of each of the compounds in this series yields the same color value. Although the color values differ considerably, such an analytic determination does furnish a clinically useful measurement. Included in the measurement are free amino acids, substituted free amino acids, and certain amino acid derivatives in which the amino group remains free. The free α-amino nitrogen is not to be confused with another entity generally known as the ‘total α-amino nitrogen,’ which has never been precisely defined, but empirically is the free α-amino nitrogen plus the extra yield of free α-amino nitrogen that appears after acid hydrolysis of the sample.

Material and Technic

From January, 1963, to March, 1964, the amino acid excretion of 168 subjects . . .



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