Figure 6.

The effect of mobile phase modifiers on the long-term stability (200 injections) of retention times in ESI(−). Examples shown for (a) PI 34:3 (PI 16:0_18:3) detected as [M − H]⁻ and (b) PC 34:3 (PC 16:0_18:3) detected as [M + CH₃COO]⁻ or [M + HCOO]⁻. The initial retention time was assigned to 1, and the follow-up retention times were proportionally calculated to provide the normalized retention times. Legend: AA, 0.02% acetic acid; AmAc and AA, 10 mM ammonium acetate and 0.1% acetic acid; AmF and FA, 10 mM ammonium formate and 0.1% formic acid; AmAc, 10 mM ammonium acetate; AmF, 10 mM ammonium formate.