Quantitation of natural triacylglycerols by reversed-phase liquid chromatography with direct liquid inlet mass spectrometry.
Using acetonitrile and propionitrile as eluting solvents and reagent gases the yields of both quasi-molecular and fragment ions were found to vary with the molecular weight, degree of unsaturation and positional distribution of the fatty acids in the triacylglycerol molecule, and appropriate calibration factors were necessary for accurate quantitation. In the absence of pure structural isomers and mixed acid standards, preliminary calibration factors have been determined for total ion and specific ion current responses by comparing the peak area ratios obtained by liquid chromatography-mass spectrometry with the proportions of the molecular species known to be present in randomized oils and in natural oils of known chemical composition. Although the derived factors include both chromatographic and mass spectrometric effects and are obtained with a gradient of reagent gases, they appear to be generally applicable. It was shown that positional isomers affected the yield of the (MH-RCOOH)+ ions over a 1-3-fold range of intensities, while the nature of the fatty acid affected it over a range of 1.25-fold. After suitable calibration of the relative ion responses it was possible to determine the identities and amounts of the individual molecular species in natural fats and oils.
Utilization of direct liquid inlet LC/MS in studies of pharmacological and toxicological importance.
The temperature of the droplets produced at the tip of the direct liquid inlet liquid chromatography/mass spectrometry (DLI LC/MS) probe decreases to about -70 degrees during the adiabatic evaporation of the droplet in the vacuum of the mass spectrometer. Broadening of peaks eluting from the probe is acceptable, being about 80 microL in volume, as shown by the DLI LC/MS analysis of cortisone, dexamethasone, and corticosterone in both the positive and the negative chemical ionization (PCI and NCI) modes. The minimum amount of sample which can be injected is about 10 ng in the scanning mode and about 100 pg in the selected ion monitoring (SIM) mode as shown by the analysis of bromocriptine and bromocriptinine. Other thermally-labile and/or non-volatile compounds analyzed by this system in the PCI and/or the NCI modes included ergotamine, esculin, sulfamethazine, chloramphenicol, erythromycin, alpha-tocopherol, cocaine, 8-chloro-theophylline, and dicophol. Non-ultraviolet absorbing carbohydrates were also analyzed, including sucrose (NCI), permethylated maltotriose, and partially hydrolyzed, derivitized lichenan and starch. By a flow switching technique, bromocriptine in a Pariodel tablet, ergot alkaloids in a Hydergine drop solution, and bromocriptine and bromocriptinine in whole urine could be analyzed without prior extraction.
THE IRON-ACETOCARMINE METHOD OF FIXING AND STAINING CHROMOSOMES
A short description of this procedure was given in Vol. 55 of the American Naturalist, pp. 573â€”574. The method has now been used almost daily for five years, and certain improvements have suggested themselves. The solution can be prepared by mixing about equal volumes of glacial acetic acid and water. To this is added powdered carmine in excess. The liquid is then â€ ? just brought to boil, cooled, and decanted. To the red solution there are then added a few drops of a solution of ferric hydrate in 50 per cent. acetic acid, to act as a mordant. The amount of iron varies with different objects. Too much produces a precipitate in a short time. The more