Peptides analysis in blood plasma using on-line system of supported liquid membrane and high-performance liquid chromatography

The potential of using supported liquid membrane (SLM) technique, combined with reversed-phase high-performance liquid chromatography (RP-HPLC) has been investigated for the determination of peptides in human blood plasma. The peptides studied were DLLeuDLPhe, MetLeuPhe, GlyLeuTyr and ValGluProIleProTyr. The carrier (Aliquat 336) was incorporated in membrane phase in order to facilitate the transport of investigated peptides. After extraction, the analyte-enriched acceptor phase was directly injected into an HPLC system for analysis. With SLM, high selectivity and efficiency were achieved for extraction of peptides in aqueous solutions. Lower extraction efficiency was obtained in plasma sample. The limiting factors were the presence of salts and proteins in blood plasma. The necessary of ultrafiltration application before the SLM was required in order to improve its stability. The minimum quantifiable concentration was 90-130 ng/ml of the investigated peptides based on 0.5 ml plasma. The standard curve was linear over the concentration range of 0.05-10 μg/ml.