## 4 Materials and Methods
### Quality Assurance and Quality Control  
For quality assurance and quality control, the samples and desorption solution were injected with isotopically labeled compounds as internal standards. The purpose of internal standards within the desorption solution is to monitor the instrument stability during data acquisition. The internal standards within the samples allow the monitoring of extraction efficiency and technical variability during the sample preparation process in addition to the instrument stability during data acquisition.  
Briefly, 200 \(\mu\)L of each sample was diluted with 400 \(\mu\)L of phosphate-buffered saline (PBS), which contained the following deuterated standards: docosquentaenoic acid-d5, eicosapentaenoic acid-d5, itraconazole-d5, alpha-linolenic acid-d5, oxazepam-d5, palmitoleic acid-d13, taurocholic acid-d4, and nordiazepam-d5. The resulting concentration of each internal standard prior to extraction was 250 ng/mL. The desorption solution contained the following deuterated standards at a concentration of 250 ng/mL: dihomo-gamma-linolenic acid-d6, ketoconazole-d3, diazepam-d5, progesterone-d9, lignoercic acid-d3, docosahexaenoicenoic acid-d3, and arachidonic acid-d8.  
Internal standards oxazepam-d5, itraconazole-d5, taurocholic acid-d4, and nordiazepam-d5 were recovered in the samples, while ketoconazole-d3, diazepam-d5, progesterone-d9, docosahexaenoic acid-d5, and dihomo-gamma-linolenic acid-d6 were recovered in desorption solution in positive mode, with a maximum variation of 34%. In negative mode, internal standards oxazepam-d5, docosquentaenoic acid-d5, taurocholic acid-d4, and eicosapentaenoic acid-d5 were recovered in the sample, while docosahexaenoic acid-d5, dihomo-gamma-linolenic acid-d3, arachidonic acid-d8, and lignoercic acid-d3 were recovered in desorption solution in negative mode, with a maximum variation of 35%.  
Instrument stability during data acquisition was monitored via periodic injection of instrumental quality controls (InstQCs) after every ten samples.  
In positive mode, the following compounds were monitored: stearidonic acid, alpha-linolenic acid, eicosapentaenoic acid, arachidonic acid, dihomo-gamma-linoleic acid, docosahexaenoic acid, docosapentaenoic acid, adrenic acid, 18:1(d7) Monoacylglycerollyceride, 18:1(d7) Lyso PE, 18:1(d7) Lyso PC, 15:0-18:1(d7) diacylglycerollyceride, 18:1(d7) chol ester, 15:0-18:1(d7) PE, d18:1-18:1(d9) SM, 15:0-18:1(d7) PC, trans-m-Coumaric acid, 18:1 monoacylglycerol, 18:1 Lyso PE, C15 ceramide, 15:0-18:1 diacylglycerolle, 15:0-18:1 PE, d18:1-18:1 SM, and 15:0-18:1 PC. The compounds were recovered with variations between 7-25%.  
In negative mode, the following compounds were monitored: Hexanoic acid, Octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, lauric acid, myristic acid, palmitoleic acid, palmitic acid, stearidonic acid, alpha-linolenic acid, gamma-linolenic acid, linoleic acid, stearic acid, eicosapentaenoic acid, arachidonic acid, dihomo-gamma-linolenic acid, arachidonic acid, docosahexaenoic acid, docosapentaenoic acid, adrenic acid, nervonic acid, lignoercic acid, 15:0-18:1(d7) PE, 18:1(d7) Lyso PE, dodecanediolic acid, 1,11-undecanedicarboxylic acid, 15:0-18:1 PE, 18:1 Lyso PE, and C15 ceramide. The compounds were recovered with variations between 2-22%.