Among the goals of lipidomics applied to triacylglycerols (TAGs) is identification of molecular species, degree and location of unsaturation, and positions of fatty acyl chains (i.e., identification of regioisomers). Toward those ends, we define one, two, and three “Critical Ratios” for Types I, II, and III TAGs that provided different aspects of the desired information. Critical Ratio 1, [MH]+/Σ[DAG]+, is correlated to the degree of unsaturation ([MH]+ is the protonated molecule and Σ[DAG]+ is the sum of diacylglycerol-like ions, [DAG]+); Critical Ratio 2, [AA]+/[AB]+ for Type II TAGs (“ABA/AAB/BAA”) and [AC]+/([AB]++[BC]+) for Type III TAGs (“ABC/CBA/BAC/CAB/ACB/BCA”), is correlated to identification of regioisomers; and Critical Ratio 3, [BC]+/[AB]+, provides information about those [DAG]+ from Type III TAGs. Furthermore, Critical Ratios are used in the Updated Bottom Up Solution (UBUS) to reproduce the mass spectra of TAGs by atmospheric pressure chemical ionization mass spectrometry applied to analysis of soybean oil in a dietary supplement gelcap. We present a new model for the [MH]+/Σ[DAG]+ ratio, quantify regioisomers using the [AA]+/[AB]+ ratio, and describe trends for [BC]+/[AB]+ that have never been reported before. The UBUS is also applied to other classes of molecules, i.e., vitamin D and DAGs. The amount of vitamin D3 in the gelcap fell from 2011 ± 22 when received to 1689 ± 33 just prior to expiration. The Critical Ratios constitute a compact data set that can provide structural information and also act as a library of mass spectra.
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The work of Dr. Robert Goldschmidt in assisting with some integration and reporting functions is gratefully acknowledged. This work was supported by the USDA Agricultural Research Service. Mention or use of specific products or brands do not represent or imply endorsement by the USDA.
Compliance with ethical standards
The author declares no potential conflicts of interest with respect to the performance of experiments, authorship, or publication of this article.
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