Hexanoyl-L-carnitine may be used as an analytical reference standard for the quantification of the analyte in dried blood spots using high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS). Hexanoyl-L-carnitine may also be used as an analytical standard for the separation and identification of underivatized hexanoyl-L-carnitine in human plasma samples using HPLC-MS/MS.