Location: Food Composition and Methods Development LaboratoryTitle: The updated bottom up solution applied to atmospheric pressure photoionization and electrospray ionization mass spectrometry
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/5/2015
Publication Date: 10/28/2015
Citation: Byrdwell, W.C. 2015. The updated bottom up solution applied to atmospheric pressure photoionization and electrospray ionization mass spectrometry. Journal of the American Oil Chemists' Society. 92:1533-1547.
Interpretive Summary: A new method for obtaining information about the structures of triacylglycerols (fats and oils) that was developed for one type of mass spectrometry has been expanded and proved to apply to two more types of mass spectrometry. The relative ratios of fragments of the fats are used to figure out structural information about the fats, in a process called 'lipidomics'. One ratio tells about whether they are saturated, monounsaturated or polyunsaturated fats. Another ratio tells about where the fats that make up the triacylglycerols are located within the fat, specifically, which fatty acid is in the middle position of the fat or oil, to determine if it is available for the body to digest and absorb. Another ratio provides information about the fatty acids on the left and right sides of the fats. Not only do these ratios provide information about the structure of the fats, but they also constitute a 'reduced data set' from which a library of mass spectra (plots of the masses of the fragments of the fat or oil) can be produced.
Technical Abstract: The Updated Bottom Up Solution (UBUS) was recently applied to atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) of triacylglycerols (TAGs). This report demonstrates that the UBUS applies equally well to atmospheric pressure photoionization (APPI) MS and to electrospray ionization (ESI) MS. Critical Ratio 1 (CR1), the [MH]+/'[DAG]+ ratio, does not exhibit the same strongly sigmoidal shape as it does by APCI-MS. CR1 varies more widely for APPI-MS than by APCI-MS, having a maximum value of 11.8, indicating a much greater effect of unsaturation on ion ratios in APPI-MS than APCI-MS. Critical Ratio 2, the [AA]+/[AB]+ ratio for Type II TAGs or [AC]+/([AB]++[BC]+) ratio for Type III TAGs, allows quantification of regioisomers of TAGs, and shows good agreement for APPI-MS to regioisomer quantification determined by APCI-MS. Critical Ratio 3 (CR3), the [BC]+/[AB]+ ratio for Type III TAGs, reveals new trends relating the degree of unsaturation by APPI-MS, and shows that structural assignments made by ESI-MS are in good agreement to APCI-MS data. In addition to providing valuable structural information, the Critical Ratios also constitute a reduced data set that allows APPI-MS or ESI-MS mass spectra to be reconstructed when processed through the UBUS. Quantification by APPI-MS of vitamin D in the analyzed dietary supplement gelcaps gave an average value of 42.90 ± 0.83 ug per capsule, or 1716 ± 33 international units, in good agreement to APCI-MS.