Gas chromatographic determination of glutamine in the presence of glutamic acid in biological fluids

The gas chromatographic determination of glutamine and glutamic acid in biological samples has so far presented considerable difficulties due to rapid conversion of glutamine to glutamic acid during derivatization. Quantitation of glutamine can be based on an intermediate in the above reaction, i.e. pyrrolidone carboxylic acid. However, the percentage formed is strongly dependent on reaction conditions, rendering quantitation unreliable. To overcome this problem d-glutamine, the optical isomer to the natural l-glutamine, is added as internal standard. The enantiomers are chemically identical and form the cyclic derivative to the same extent. The enantiomers of pyrrolidone carboxylic acid ester can easily be separated on a capillary coated with the chiral stationary phase Chirasil-Val. No extra derivatization step is required and quantitation is based merely on the ratio of the peak areas of both enantiomers.