## 2 Materials and Methods
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Method** & **Study** & **Mobile Phase A** & **Mobile Phase B** & **Gradient Length (min)** & **Flow Rate (mL/min)** & **Column Temp. (\({}^{\circ}\)C)** \\ \hline \multirow{2}{*}{1} & [21,22] & 60\% ACN 40\% H\({}_{2}\)O & 90\% IPA 10\% ACN + 10 mM & & & \\  & + 10 mM ammonium & ammonium formate + 0.1\% & 31 & 0.3 & 50 \\  & & formate + 0.1\% formic acid & formic acid & & & \\ \hline \multirow{2}{*}{2} & N/A & 60\% ACN 40\% H\({}_{2}\)O & 90\% IPA 10\% ACN + 10 mM & & & \\  & + 10 mM ammonium formate & ammonium formate & 31 & 0.3 & 50 \\ \hline \multirow{3}{*}{3} & [23] & 60\% H\({}_{2}\)O 40\% MeOH & 90\% IPA 10\% MeOH & & & \\  & & + 10 mM ammonium acetate & + 1 mM acetic acid & 50 & 0.2 & 55 \\  & & + 1 mM acetic acid & + 1 mM acetic acid & & & \\ \hline \multirow{3}{*}{4} & N/A & 60\% H\({}_{2}\)O 40\% MeOH & 90\% IPA 10\% MeOH & & & \\  & & formate + 1 mM ammonium & + 10 mM ammonium & 50 & 0.2 & 55 \\ \hline \multirow{2}{*}{5} & N/A & 60\% H\({}_{2}\)O 40\% MeOH & 90\% IPA 10\% MeOH & & & \\  & & + 10 mM ammonium formate & + 1 mM ammonium formate & 50 & 0.2 & 55 \\ \hline \multirow{2}{*}{6} & [24] & 50\% ACN 50\% H\({}_{2}\)O + 5 mM & 85\% IPA 10\% ACN 5\% H\({}_{2}\)O & & & \\  & & ammonium formate & + 5 mM ammonium formate & & \\ \hline \multirow{2}{*}{7} & [25] & H\({}_{2}\)O + 0.1\% formic acid & ACN & 45 & 0.2 & 30 \\  & & & & & \\ \hline \multirow{2}{*}{8} & [26] & H\({}_{2}\)O + 0.1\% formic acid & ACN + 0.1\% formic acid & 30 & 0.5 & 50 \\ \hline \multirow{2}{*}{9} & [27] & H\({}_{2}\)O + 0.1\% formic acid & ACN + 0.1\% formic acid & 57 & 0.05 & 50 \\  & & & & & \\ \hline \multirow{2}{*}{10} & [28] & H\({}_{2}\)O + 0.1\% formic acid & ACN + 0.1\% formic acid & 22 & 0.4 & 40 \\  & & & & & \\ \hline \multirow{2}{*}{11} & [29] & H\({}_{2}\)O + 0.1\% formic acid & MeOH + 0.1\% formic acid & 25 & 0.4 & 60 \\ \hline \multirow{2}{*}{12} & [30] & H\({}_{2}\)O + 12 mM ammonium & \multirow{2}{*}{90\% ACN 10\% H\({}_{2}\)O + 12 mM ammonium acetate + 0.02\% acetic acid} & & & \\  & & & & 0.02\% acetic acid & & \\ \hline \multirow{2}{*}{13} & [31] & H\({}_{2}\)O + 20 mM ammonium & 60\% IPA 36\% ACN 4\% H\({}_{2}\)O & & & \\  & & formate & + 0.1\% formic acid & 25 & 0.4 & 60 \\ \hline \hline \end{tabular} Abbreviations: ACN—acetonitrile; H\({}_{2}\)O—water; IPA—isopropanol; MeOH—methanol; Temp.—temperature.  
\end{table} 
Table 1: Liquid chromatographic gradients used for separation in positive mode. The Q Exactive Plus Hybrid Quadrupole-Orbitrap Mass Spectrometer included an Ion Max heating source containing a heated electrospray ionization (HESI-II) probe. Mass spectrometer parameters were optimized based on direct infusion with the SPLASH LIPIDOMIX Mass Spec Standard. The mass spectrometer was operated in positive mode at high resolution (70,000), and data was acquired within an \(m/z\) range of 150-1200 with an automatic gain control target of \(1\times 10^{6}\) and an injection time of 100 milliseconds. In negative mode, the mass spectrometer was operated at high resolution (70,000), and data was acquired within an \(m/z\) range of 100-1000 with an automatic gain control target of \(1\times 10^{6}\) and an injection time of 50 milliseconds. The sheath, auxiliary, and sweep gas were set to 48, 11, and 1, respectively, in positive mode and 75, 30, and 1, respectively, in negative mode. The electrospray voltage applied in positive mode was 3.50 kV and \(-\)2.60 kV in negative mode. In each method, several lipid standards (Table 3) were assessed for good peak shape (narrow, symmetrical, and gaussian) and good peak resolution. The relative standard deviation (RSD) of the peak area and the retention time were recorded. An injection volume of 5 uL was used for standards; the autosampler temperature was 5 \({}^{\circ}\)C.  
Serum samples were obtained from the University of Toronto Psoriatic Disease Research Program Biobank. The study received full ethical approval from the University Health Network Research Ethics Board.