Average mass approach to the isotopic analyses of compounds exhibiting significant interfering ions

Abstract

Kalinoski, H. T.; Udwth, H. R.; Smith, R. D. HRC CC, J.High Resolut. Chromatogr . Chromatogr . Commun . 1988, 9 , 145-153. 23. 192-199. . .of the oligosaccharides. The mode of splitless injection used in this work is a step toward making SFC-MS a quantitative, trace analysis technique. Injection technology being developed in a number of laboratories which will allow the splitless injection of solutes present in microliter volumes will strengthen the standing of SFC and SFC-MS in this area. Capillary supercritical fluid chromatography-mass spectrometry using an unmodified C02 mobile phase as presented here is limited to relatively nonpolar solutes. The use of modified and more polar mobile phases should extend the range of solute polarities which SFC-MS can handle (28). As the high-mass performance of quadrupole mass analyzers improves and as problems in interfacing SFC to mass spectrometer ion sources operating at high voltage are overcome ( 1 7 ) SFC-MS and SFI-MS will become even more powerful tools in characterizing mixtures containing high molecular weight, less volatile species. ACKNOWLEDGMENTStrife for guidance and useful discussions. The authors thank T. L. Chester, T. Keough, and R. J. Registry No. Methyl arachidate, 1120-28-1; tristearin, 555-43-1. LITERATURE CITED (1) Markides, K. E.; Fields, S. M.: Lee, M. L. J. Chromatogr. Sci. 1986, 2 4 , 254-257.(2) Chester, T. L.; Innis, D. P. HRC CC, J. High Resoluf. Chromatogr. Chromatogr. Commun. 1988, 9 , 209-212. (3) Gouw, T. H.; Jentoft, R. E.; Gallegos, E. J. J. High Pressure Scl. Techno/. AIRAPT Conf. 6th 1979, 583-592.

Fatty Acid Cycling in Human Hepatoma Cells and the Effects of Troglitazone

“…This is achieved by dividing the intensity of each peak by the sum of intensities of all relevant peaks of that compound. The expression of spectral data as molar fraction allows the determination of average mass (or average molecular weight) by the sum of the products of molar fraction and mass over the relevant mass range (8). 4 Since the chance of [ 13 C]acetyl-CoA condensing to form uniformly labeled fatty acids is almost zero, the sum of individual fractions of ions in the clusters corresponding to the uniformly labeled fatty acids gives the fraction of molecules converted by chain elongation or shortening.…”

“…The distribution of these mass isotopomers has previously been shown to conform to that of a binomial distribution (10,11). Thus, the acetyl-CoA enrichment can be obtained from the consecutive mass isotopomer ratio m 4 /m 2 according to the formula: m 4 /m 2 ϭ (n Ϫ 1)/2 p/q or 3.5 p/q, where n is 8, the number of acetyl units in palmitate, p is the enrichment of [1,[2][3][4][5][6][7][8][9][10][11][12][13] C]acetyl-CoA, and q the unenriched acetyl-CoA. Once the precursor enrichment is determined, fractional synthesis can be calculated by dividing the observed to the predicted mass isotopomer (m 2 ) fraction (10).…”

“…The presence of 12 C resulted in the formation of m ϩ 17 peaks in the spectra of [U- 13 C]stearate and oleate. The 13 C enrichment of these labeled compounds can be determined as the change in average molecular weight using the average mass approach (8 (Fig. 4).…”

Fatty Acid Transport and Utilization for the Developing Brain

“…To quantify deuterium recycling, ion clusters around the molecular ions of the methyl esters of palmitate, stearate, and oleate reduced to stearate were measured by selected ion monitoring (Lee et al, 1991). Deuterium incorporation was determined using the average mass approach (Blom et al, 1987;Blom, 1988) on ion groups m/z 269-274 for palmitate and m/z 296-302 for stearate and oleate reduced to stearate. This approach allows for the calculation of the total isotopic content of a fatty acid methyl ester from its mass spectrometrically determined average mass, in this instance the content of deuterium over the natural abundance of stable isotope in the molecules.…”

“…In the de novo biosynthesis of fatty acids, the deuterium-labeled ketone bodies will be incorporated into the newly synthesized fatty acid molecules, giving rise to new deuterated species (m + I and m + 2) of the corresponding fatty acids. The amount of deuterium incorporated, as determined by the average mass approach (Blom et al, 1987;Blom, 1988), would be proportional to the fraction of fatty acids that are new. Evidence for active de novo biosynthesis was observed (Table 1) by comparing the increase in deuterium content over the natural abundance for mass isotopomers, m + 1 and m + 2, of the ion cluster at m/z 270 for palmitate, at m/z 298 for stearate as methyl stearate derived from oleate (fraction 2), and at m/z 298 for stearate (fraction 3).…”