## 2 Materials and Methods
Patients with PsC (n = 27) and PsA (n = 26) as well as healthy controls (n = 25) were included (see Table 4 for patient demographics). Sample collection took place from 2009 to 2019. Blood was collected in red-top serum separator tubes without additives and allowed to clot at room temperature before centrifugation at 2000\(\times\)\(g\) for 15 min. Serum was aliquoted in 0.5 mL vials and frozen at \(-\)80 \({}^{\circ}\)C until analysis. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{1}{c}{**Method Study**} & \multicolumn{1}{c}{**Mobile Phase A**} & \multicolumn{1}{c}{**Mobile Phase B**} & \multicolumn{1}{c}{**Gradient Length (min)**} & \multicolumn{1}{c}{**Flow Rate**} & \multicolumn{1}{c}{**Column**} \\  & & & & & & \\ \hline \multirow{2}{*}{1} & [21, 22] & 60\% ACN 40\% H\({}_{2}\)O + 10 mM & 90\% IPA 10\% ACN + 10 mM & \multirow{2}{*}{31} & \multirow{2}{*}{0.3} & \multirow{2}{*}{50} \\  & ammonium formate + 0.1\% & & ammonium formate + 0.1\% & & & \\  & formic acid & formic acid & & & & \\ \hline \multirow{2}{*}{2} & N/A & 60\% ACN 40\% H\({}_{2}\)O + 10 mM & 90\% IPA 10\% ACN + 10 mM & \multirow{2}{*}{31} & \multirow{2}{*}{0.3} & \multirow{2}{*}{50} \\  & ammonium formate & & ammonium formate & & & \\ \hline \multirow{2}{*}{3} & [23] & 60\% H\({}_{2}\)O 40\% MeOH + 0.02\% & 90\% IPA 10\% MeOH + 0.02\% & \multirow{2}{*}{50} & \multirow{2}{*}{0.2} & \multirow{2}{*}{55} \\  & acetic acid & & acetic acid & & & \\ \hline \multirow{2}{*}{4} & [24] & 50\% ACN 50\% H\({}_{2}\)O + 5 mM & 85\% IPA 10\% ACN 5\% H\({}_{2}\)O & \multirow{2}{*}{32} & \multirow{2}{*}{0.325} & \multirow{2}{*}{50} \\  & ammonium formate & & + 5 mM ammonium formate & & & \\ \hline \multirow{2}{*}{5} & [27] & H\({}_{2}\)O + 0.1\% formic acid & \multirow{2}{*}{ACN + 0.1\% formic acid} & \multirow{2}{*}{22} & \multirow{2}{*}{0.4} & \multirow{2}{*}{40} \\  & & & & & \\ \hline \multirow{2}{*}{6} & [28] & H\({}_{2}\)O + 0.1\% formic acid & \multirow{2}{*}{ACN + 0.1\% formic acid} & \multirow{2}{*}{25} & \multirow{2}{*}{0.4} & \multirow{2}{*}{60} \\  & & & & & \\ \hline \multirow{2}{*}{7} & [29] & H\({}_{2}\)O + 0.1\% formic acid & \multirow{2}{*}{MeOH + 0.1\% formic acid} & \multirow{2}{*}{25} & \multirow{2}{*}{0.4} & \multirow{2}{*}{60} \\  & & & & & \\ \hline \multirow{2}{*}{8} & [32] & H\({}_{2}\)O + 0.1\% formic acid & \multirow{2}{*}{MeOH} & \multirow{2}{*}{15} & \multirow{2}{*}{0.4} & \multirow{2}{*}{50} \\  & & & & & \\ \hline \multirow{2}{*}{9} & [30] & H\({}_{2}\)O + 12 mM ammonium & \multirow{2}{*}{12 mM ammonium acetate + 0.02\% acetic acid} & \multirow{2}{*}{35} & \multirow{2}{*}{0.5} & \multirow{2}{*}{30} \\  & acetate + 0.02\% & & & & \\  & & & & & \\  & & & & & \\ \hline \multirow{2}{*}{10} & [31] & H\({}_{2}\)O + 20 mM ammonium & \multirow{2}{*}{60\% IPA 36\% ACN 4\% H\({}_{2}\)O + 10% formic acid} & \multirow{2}{*}{25} & \multirow{2}{*}{0.4} & \multirow{2}{*}{60} \\  & formate & & + 0.1\% formic acid & & & \\ \hline \multirow{2}{*}{11} & [33] & 60\% ACN 40\% H\({}_{2}\)O + 10 mM & \multirow{2}{*}{50\% ACN 50\% IPA + 10 mM} & \multirow{2}{*}{23} & \multirow{2}{*}{0.450} & \multirow{2}{*}{55} \\  & ammonium acetate & & ammonium & & & \\ \hline \multirow{2}{*}{12} & [34] & 90\% H\({}_{2}\)O 10\% MeOH & \multirow{2}{*}{80\% MeOH 20\% ACN} & \multirow{2}{*}{8} & \multirow{2}{*}{0.3} & \multirow{2}{*}{50} \\  & & & & & \\ \hline \multirow{2}{*}{13} & [21, 22] & 60\% ACN 40\% H\({}_{2}\)O + 10 mM & \multirow{2}{*}{90\% IPA 10\% ACN 10 mM} & \multirow{2}{*}{31} & \multirow{2}{*}{0.3} & \multirow{2}{*}{50} \\  & ammonium formate + 0.1\% & & ammonium formate + 0.1\% & & & \\ \hline \multicolumn{6}{c}{Abbreviations: ACN—acetonitrile; H\({}_{2}\)O—water; IPA—isopropanol; MeOH—methanol; Temp.—temperature.} \\ \end{tabular}
\end{table} 
Table 2: Liquid chromatographic gradients used for separation in negative mode.