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To the Editor:
Our laboratory developed procedures for the simultaneous measurement of ethylene glycol and glycolic acid by gas chromatography- flame ionization detection (GCFID)1 (1) and by GC-MS (2). The selection of a suitable structurally similar internal standard for glycolic acid proved problematic because of either coeluting interference during GC-FID or ion overlap of deuterated and nondeuterated di-tertbutyldimethylsilyl derivatives during GC-MS analysis. As a compromise, 1,3-propanediol (1,3-PD), an acceptable internal standard for ethylene glycol, was also selected as the internal standard for glycolic acid in the GC-MS procedure.
Considerable experience with the procedure has revealed a limitation of this structurally dissimilar internal standard for measuring glycolic acid. In the procedure, serum proteins are precipitated with acetonitrile containing 1,3-PD, the supernatant is dehydrated with a water scavenger, and the volume is reduced to <100 µL in a N,N-dimethylformamide (DMF)- trapping solvent (but not to dryness). Evaporation of DMF causes some presumed evaporative loss of ethylene glycol and a somewhat lesser loss of 1,3-PD (evaporation to dryness leads to severe loss of both and should be avoided). Thus, the use of 1,3-PD compensates reasonably well for any loss of ethylene glycol, so that the relative recovery and...