Determination of methionine-enkephalin and leucine-enkephalin by LC-MS in human plasma: Study of pre-analytical stability

The method with a limit of quantitation of 10 pg/mL showed good reproducibility with excellent accuracy and precision, and was linear up to 2000 pg/mL. An extensive evaluation of the pre-analytical stability of these peptides in human blood was carried out to ensure an adequate sample collection procedure to obtain reliable results in the analysis of clinical samples.