## 2 Materials and Methods
The solid-phase microextraction (SPME) device was prepared using a dip-coating method optimized at the Schroeder Arthritis Institute--Centre for Arthritis Diagnostic and Therapeutic Innovation: Metabolomics Core Facility. First, the stainless steel blades were prepared using a previously established protocol [35]. Briefly, the blades were etched in concentrated hydrochloric acid for one hour, rinsed with tap water, and dried overnight in an oven. A 7% w/v polyacrylonitrile (PAN) solution was then prepared in N,N-dimethylformamide (DMF). A specialized software-operated dip-coating machine coated the stainless steel support with a slurry mixture consisting of 7% w/v 1:1 HLB and PS-DVB-WAX particles in PAN solution. The coating was cured in an oven at 150 \({}^{\circ}\)C for 1 min after each layer of slurry. The solution was used to coat a total of 32 combs, each of which had 12 blades. Every 8 combs were assembled to create a SPME brush for sample preparation. Each brush was cleaned with 50:25:12.5:12.5 (v/v) water:methanol:acetonitrile:isopropanol and then measured for reproducibility. The final coating on each blade was 2 cm long with an average thickness of 2 mm. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **Healthy Controls** & **Psoriasis** & **Psoriatic Arthritis** \\ \hline Number of patients & 25 & 27 & 26 \\ \hline Number of females (\%) & 40 & 51 & 46 \\ \hline Mean age (years) & 48 & 43 & 47 \\ \hline BMI & 29 & 27 & 26 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Patient demographics. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Compound** & **Lipid Category** & _m/z Positive Mode_ & _m/z Negative Mode_ \\ \hline
150-18:1(d7) PC & Glycerophospholipids & 753,6134 & N/A \\ \hline
18:1(d7) Lyso PC & Glycerophospholipids & 529,3994 & N/A \\ \hline
150-18:1(d7) PE & Glycerophospholipids & 711,5664 & 709,5519 \\ \hline
18:1(d7) Lyso PE & Glycerophospholipids & 487,3524 & 485,3379 \\ \hline
150-18:1(d7) PG & Glycerophospholipids & 759,5875 & 740,5464 \\ \hline
150-18:1(d7) PI & Glycerophospholipids & 847,6036 & 828,5625 \\ \hline
150-18:1(d7) PS & Glycerophospholipids & 755,5562 & 753,5417 \\ \hline
150-18:1(d7)-15:0 TAG & Glycerolipids & 829,7985 & N/A \\ \hline
150-18:1(d7) DAG & Glycerolipids & 605,5844 & N/A \\ \hline
18:1(d7) MAG & Glycerolipids & 364,3429 & N/A \\ \hline
18:1(d7) Chol Ester & Sterol Lipids & 675,6779 & N/A \\ \hline d18:1-18:1(d9) SM & Sphingolipids & 738,647 & N/A \\ \hline
150-18:1(d7) PA & Glycerophospholipids & N/A & 666,5097 \\ \hline Cholesterol-d7 & Sterol Lipids & 411,4326 & N/A \\ \hline Dodecanediolic acid & Fatty Acyls & 231,1591 & 229,1445 \\ \hline Isobutyryl-L-carnitine & Fatty Acyls & 232,1544 & 230,1398 \\ \hline
12-Aminolauric acid & Fatty Acyls & 216,1958 & 214,1812 \\ \hline
1,11- & & & \\ Undecanedicarboxylic acid & Fatty Acyls & N/A & 243,1602 \\ \hline
10-Hydroxy-2-decenoic acid & Fatty Acyls & N/A & 185,1183 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Standards analyzed in positive and negative modes. Serum samples were then processed using SPME. Each well of a 96-well plate was filled with 200 \(\mu\)L of serum and 400 \(\mu\)L of phosphate buffered saline (PBS) containing deuterated nordiazepam. The serum samples were then agitated for 30 min at 500 rpm prior to extraction. During this time, the SPME device was placed onto the Concept-96 manual kit and was conditioned in a mixture of 1:1 methanol:water (v/v) for 30 min at 1500 rpm. Subsequent to conditioning, the device underwent a 15 min rinse with water at 1500 rpm, followed by exposure to the serum samples for 1 h at 1500 rpm for extraction. The device underwent another 10 s rinse with water at 500 rpm, and the extracted metabolites were then desorbed for 1 h at 1500 rpm in 600 \(\mu\)L of 4:3:3 methanol:acetonitrile:water (v/v/v) + 0.1% ascorbic acid containing the following deuterated compounds: amphetamine-d5, MDMA-d5, ketamine-d4, diazepam-d5, oxazepam-d5, codeine-d3, fentanyl-d5, heroin-d9, buprenorphine-d4, and SPLASH LIPIDOMIX Mass Spec Standard.