Gas-liquid chromatographic measurement of guanidino acids

We present a method for separating and measuring guanidino acids by gas-liquid chromatography. Compared to ion-exchange techniques, this system is faster, more sensitive, requires smaller sample volumes, is independent of colorimetric reactions, and permits simultaneous determination of both amino and guanidino acids. N-Trifluoracetyl-n-butyl esters are formed and then are separated by using a column containing a mixed silicone liquid phase coated on Chromosorb W-HP. Analytical recoveries from plasma ranged from 86 to 112% and were done without prior protein precipitation. Speculations as to the cause of this interference by protein include coprecipitation, protein-binding, and cyclization of the guanidines in the acids used for denaturation. Evidence presented suggests that all three occur: ultrafiltrability is diminished in the presence of protein and nuclear magnetic resonance demonstrates cyclization of some of these esters.