Deuterium enrichment of retinol in humans determined by gas chromatography electron capture negative chemical ionization mass spectrometry

Abstract

A new application of electron capture negative chemical ionization mass spectrometry method has been developed for detecting vitamin A enrichment in human serum. Octadeuterated all-trans retinyl acetate 1.5 mg was fed to a volunteer and blood samples were collected over a period of 32 days. Serum samples were extracted and isolated by high performance liquid chromatography to collect the fraction containing retinol. The retinol fraction was derivatized to a trimethylsilyl ether, which was analyzed by gas chromatograph (GC)/mass spectrometry using a capillary column coated with DB-1 followed by methane electron capture negative chemical ionization/mass spectrometry (ECNCI-MS). Although ECNCI-MS of derivatized retinol produced no molecular ion, it produced a single negatively charged fragment ion at m/z 268 for natural retinol (m/z 276 for octadeuterated retinol) due to loss of the silyl group. The serum enrichment of labeled retinol was detectable at 7 hours, reached a maximum of 2.6% at 24 hours, and declined thereafter but was still at 0.07% at 32 days. In 200 μL of serum, the minimum detectable enrichment of retinol- d 8 was 0.01%. The GC/ECNCI-MS method for detecting retinol in serum is at least 10 times more sensitive than any previously published mass spectrometry method.