Determination of immunosuppressive drugs in human urine and serum by surface-assisted laser desorption/ionization mass spectrometry with dispersive liquid-liquid microextraction

A rapid and sensitive method for the determination of immunosuppressive drugs through surface-assisted laser desorption/ionization mass spectrometric detection (SALDI/MS) was developed. Colloidal Pd and α-cyano-4-hydroxycinnamic acid (CHCA) were used as the SALDI co-matrix. To eliminate interference and enhance the sensitivity, dispersive liquid-liquid microextraction (DLLME) was employed to extract the immunosuppressive drugs from the aqueous solutions. Under optimal extraction and detection conditions, calibration curves for cyclosporine and everolimus in aqueous solutions were linear over a concentration range from 0.01 to 1.20 μM. For sirolimus, the linear concentration range of the calibration curve was from 0.05 to 2.00 μM. The limits of detection (LODs) were calculated to be 3, 3, and 14 nM for cyclosporine, everolimus, and sirolimus, respectively. The enrichment factors of DLLME were calculated to be 108, 122, and 101 for cyclosporine, everolimus, and sirolimus, respectively. This novel method was successfully applied for the determination of immunosuppressive drugs in human urine and serum samples.