HIGH-SENSITIVITY LIQUID-CHROMATOGRAPHY COMBUSTION ISOTOPE RATIO MASS-SPECTROMETRY OF FAT-SOLUBLE VITAMINS

The sensitivity of high-precision liquid chromatography/combustion iso tope ratio mass spectrometry (LC/C-IRMS) was improved by more than two orders of magnitude by modifications which permit optimization of flo ws, The lower limits for high precision are about 3 mu g of analyte on -column for flow injection and LC modes. Pneumatic aerosol spray coati ng was implemented and compared with simple dip coating. The signal en hancement for aerosol compared with dip coating is up fourfold at high er levels but drops to less than twofold at lower levels, while the dy namic range is extended at higher levels by fourfold at high sample lo ad levels. LC separations for underivatized tocopherols, retinyl aceta te and ergocalciferol are demonstrated with precision and accuracy of about delta(13)C < 2.5 parts per thousand for replicates. This work de monstrates sensitivity useful for a wide range of LC analyses and exte nds high-precision LC/C-IRMS to the determination of several fat-solub le vitamins.