Extraction of oxytocin and arginine–vasopressin from serum and plasma for radioimmunoassay and surface-enhanced laser desorption–ionization time-of-flight mass spectrometry

Oxytocin and arginine–vasopressin (AVP) are secreted into the blood in low concentrations. To analyze these peptides, we investigated two common extraction procedures, acetone–ether precipitation and C18-SepPak columns. Recovery from both procedures approached 70–80% of the spiked amount, though the SepPak columns were more efficient. C18-SepPak columns were used to sequentially separate oxytocin from AVP by eluting oxytocin first with 98% acetone followed by elution of AVP with 80% acetonitrile. Surface-enhanced laser desorption–ionization time-of-flight mass spectrometry (SELDI-TOF MS) was used to analyze oxytocin and AVP extracted with C18-SepPak columns from an autistic patient’s plasma sample. We conclude that C18-SepPaks provide more consistent and efficient peptide extraction from serum or plasma that augments both quantitative and qualitative analysis by radioimmunoassay and SELDI-TOF MS.