Fig. 2.
The correlation between estimated composition and composition determined using [dLPC]− (A, B) and [FA]− (C, D) ions after MS3 fragmentation of the isobaric PC mixture composed of saturated (A, C) and unsaturated (B, D) FAs. The concentration levels express the sum of the concentrations of both isobaric PCs in the particular saturated or unsaturated PC pair. The results for samples at 0.013 μM were identical to those observed for 0.033 nmol/ml and have been omitted for clarity. The dashed line shows where the points should lie in the case of an ideal agreement of the determined values with the actuals. Notice the sigmoidal dependency (C, D) when FA anions are used for composition of isobaric PCs at a concentration of 0.664 nmol/ml. The graph legends displayed in (A) and (B) are also valid for (C) and (D), respectively. The concentrations displayed in the legends exhibit the sum of the concentrations of examined pairs of PCs: PC 14:0_18:0 and PC 16:0_16:0 in (A) and (C) and PC 16:0_20:4 and PC 18:2_18:2 in (B) and (D). PCs were detected as acetate adducts. The analysis was performed using a MP consisting of chloroform:methanol (1:1) with addition of 10 mM of ammonium acetate. Bars represent mean ± SD of three repetitions.