Several kits for measuring small peptides are supplied with an Extraction Solution (X123) that can be used to purify samples that would otherwise be unusable in those assays. This acidic, organic solvent solution will precipitate proteins and other interfering substances, but leave the analyte of interest in solution. Any sample that might contain contaminants can be treated, but serum, plasma, and saliva must be extracted in order to get usable results from the Oxytocin (K048-H), Arginine-Vasopressin (K049-H, K049-C), or ET-1 (K045-H1) assays. To prepare samples, 1 volume of sample is mixed with 1.5 volumes of Extraction Reagent, vortexed, and then mixed for 90 minutes. After centrifuging the mixture for 20 minutes at 1660 g, the supernatant is removed to a separate tube and dried down in a SpeedVac. At this point, the sample can be reconstituted in the Assay Buffer (supplied with the kit) and measured in the assay. Please note samples can also be extracted with C18 solid phase columns if preferred; a protocol for that can be found under “protocols” in the resources section of our website at: