Isolation of choline and choline esters from Krebs-Ringer solution for gas chromatographic determination

A simple and efficient novel method for isolating picomole amounts of choline and choline esters in milliliter volumes of Krebs-Ringer solution has been developed. The procedure is based on the observation that the solubility of choline esters in acetonitrile is 10(4)-10(5) times higher than that of the inorganic salt constituents of Krebs-Ringer solution. The glucose content of the medium, which prevented the one-step isolation of choline esters based on acetonitrile extraction from its lyophilizate, was removed using Amberlite CG-50 column chromatography. Bound compounds to the column were eluted in 0.25 N HCl and lyophilized. The lyophilizate was extracted with acetonitrile, which was then decanted and eliminated by evaporation to dryness. The resultant glucose and salt-free residue can be assayed by gas chromatography. Total recoveries of added choline and choline esters over the entire isolation procedure, measured isotopically and/or gas chromatographically, were 93 and 97%, respectively. Due to the high and close-to-equal recoveries of choline esters, and the high purity of the final product, this procedure is suitable for estimating acetylcholine and choline in neural tissue perfusates by gas chromatography, as was demonstrated by this method using hippocampal slices.