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Abstract
Chromatography is often used as a method for reducing sample complexity prior to analysis by mass spectrometry, the use of retention time (RT) is becoming increasingly popular to add valuable supporting information in lipid identification.
The RT of lipids with the same headgroup in reverse-phase separation can be predicted using the effective carbon number (ECN) model. This model describes the effect of acyl chain length and degree of saturation on lipid RT, which increases predictably with acyl chain length and degree of saturation. Furthermore, we have found a robust correlation in the chromatographic separation of lipids with different headgroups that share the same fatty acid motive. By measuring a small number of lipids from each subclass it is possible to build a model that allows for the prediction of the RT of one lipid subclass based on another.
Here, we utilise ECN modelling and inter-class retention time conversion (IC-RTC) to build a glycerophospholipid RT library with 481 entries based on 136 MS/MS characterised lipid RTs from NIST SRM-1950 plasma and lipid standards.
The library was tested on a patient cohort undergoing coronary artery bypass grafting surgery (n=37). A total of 129 unique circulating glycerophospholipids were identified, of which, 57 (4 PC, 24 PE, 4 PG, 15 PI, 10 PS) were detected with IC-RTC, thereby demonstrating the utility of this technique for the identification of lipid species not found in commercial standards.
Supplementary materials
Title
Supplementary Figures and Tables
Description
Supplementary Table 1: Identified lipids in MSE acquisition of 37 clinical samples + 1 injection of NIST SRM-1950 plasma. Detection rate indicates the number of samples in which a specific lipid was detected.
Supplementary Table 2: Imputation of missing lipid values. Number of times values were imputed into the targeted data analysis for each listed lipid.
Supplementary Figure 1: Range of peak areas detected for deuterated internal standards.
Supplementary Figure 2: Double bond distribution of total identified lipid signal. Proportional peak area was significantly higher in stable coronary artery disease and myocardial infarction groups vs NIST SRM-1950 plasma for species with a total of 5 (p = 0.05), 6 (p = 0.01) and 7 (p = 0.01) double bonds (one-way ANOVA). No significant changes in double bond distribution were identified between stable coronary artery disease and myocardial infarction groups.
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