Comparison of radioimmunological determinations with gas chromatography mass spectrometry dosage. A study of PGE2 and PGF2α in gastrointestinal fluids

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Abstract
The reliability of radioimmunoassays for determination of PGE2 and PGF2α in gastrointestinal fluids was checked by two gas chromatographic mass spectrometric methods. Analyses were performed on samples of gastric juice from dogs and man (healthy volunteers), jejunal fluids from patients with celiac disease, mucous discharge from a villous adenoma of rectum, and bathing solutions from the Ussing chamber containing human jejunal mucosa. The radioimmunoassays included extraction and Sephadex LH‐20 chromatography as a preliminary purification before quantification was carried out. Gas chromatographic mass spectrometric analysis of PGE2 was performed by monitoring the molecular ion of the trimethylsilyl ether of PGB2 methyl ester, m/z 420 and m/z 424 for the protium and the deuterium form, respectively, while PGF2α was quantified as the triacetyl derivative of the methyl ester, using the ion pair (M‐3 × 60) i.e. m/z 314 and m/z 318. Recovery of immunoreactive PGE2 relative to gas chromatographic mass spectrometric dosage was 88.5% ± 6.5 (mean ± SEM; n = 13), while the amount of PGF2α in the same sample volume was at the borderline of sensitivity for the gas chromatographic mass spectrometric method used, with a recovery of 114% ± 19 (mean ± SEM; n = 4).