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The Bottom Up Solution to the Triacylglycerol Lipidome Using Atmospheric Pressure Chemical Ionization Mass Spectrometry


W.C. Byrdwell, Florida Atlantic University, USA.


Reference: Lipids, 40:383-417 (2005).


Presented here is an approach to representing the data from atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) of triacylglycerols (TAG) using a set of one, two or three Critical Ratios.  These Critical Ratios may be used directly to provide structural information concerning the regioisomeric composition of the TAG, and about the degree of unsaturation in the TAG.  An ‘AAA’-type, or Type I, TAG has only one Critical Ratio, the ratio of the protonated molecule, [M+H]+, to the diacylglycerol fragment ion, [AA]+.  The Critical Ratio for a Type I TAG is [MH]+/ S[DAG]+, and the mass spectrum of a Type I TAG can be reproduced from only this one ratio.  An ‘ABA/AAB/BAA’, or Type II, TAG has two Critical Ratios, the [MH]+/S[DAG]+ ratio and the [AA]+/[AB]+ ratio.  The [AA]+/[AB]+ ratio for a single TAG or TAG mixture can be compared to the [AA]+/[AB]+ ratios of pure regioisomeric standards and the percentage of each regioisomer can be estimated.  The abundance of the protonated molecule and the abundances of the two [DAG]+ fragment ions can be calculated from the two Critical Ratios for a Type II TAG.  To calculate the abundances, the Critical Ratios are processed through the Bottom Up Solution to the triacylglycerol lipidome.  First, Critical Limits are calculated from the Critical Ratios, and then, the Critical Ratios are classified into Cases, by comparison to the Critical Limits.  Once the Case classification is known, the equation for the abundance of each ion in the mass spectrum is given by the Bottom Up Solution.  A Type III TAG has three different FA, and has three Critical Ratios.  The [MH]+/ S[DAG]+ ratio is the first Critical Ratio, the [AC]+/([AB]++[BC]+) ratio is the second Critical Ratio, and the [BC]+/[AB]+ ratio is the third Critical Ratio.  The second critical ratio for a Type III TAG can be compared to regioisomeric standards, to provide an estimate of the percentage composition of the regioisomers.  The three Critical Ratios for a Type III TAG can be processed through the Bottom Up Solution to calculate the four ion abundances that made up the APCI-MS mass spectrum.  The Critical Ratios constitute a ‘reduced data set’ that provides more information in fewer values than the raw abundances.



The manuscript given by the link below is the original text submitted to the journal. The final form of the journal article is not available here due to copyright restrictions. Only my own version of the manuscript is presented here. For the published journal article see the link below.

The unofficial manuscript may be accessed by clicking


This version of the manuscript is in 8 1/2 x 11 inch single column format, and has larger, easier to read graphics and figures.


The final version that appeared in the journal (Lipids, 40:383-417 (2005)) is available from AOCS Press by clicking



A note about the manuscripts:  There are passages that are more verbose and redundant than I would have preferred.  Some statements were reiterated in response to comments made by the reviewers, or to emphasize some points so they would be fully understood.

© 2005-2009

The names “The Bottom Up Solution” and “The Unit Simulacrum” and all equations, figures and schemes are copyrighted in 2005-2009 by William Craig Byrdwell.  No portion of the equations, figures or schemes may be used without prior written permission from the copyright holder, William Craig Byrdwell.