Rapid Measurement of Cyclosporine and Sirolimus in Whole Blood by Paper Spray-Tandem Mass Spectrometry.

To the Editor: Paper spray (PS)1 is a recently described method for the direct mass spectrometry (MS) analysis of blood and other biological samples (1–3). Paper spray is performed by depositing a sample such as whole blood onto a paper substrate contained within a disposable cartridge; extraction and ionization occur directly from the disposable cartridge with an automated MS attachment (Fig. 1). No punching or offline extraction is required. Total analysis time, including sample extraction, is several minutes. Fig. 1. Paper spray for direct analysis of blood spots by MS. Ion chronograms from the lowest calibrator in whole blood, overlaid with representative chronograms from blank blood, are shown for cyclosporine and sirolimus. Quantification was performed with the entire area under the curve for each analyte, normalized by SIL-IS, to obtain calibration curves as shown. Because of its simplicity, paper spray could lower the barrier for implementation of MS-based assays in clinical laboratories. We previously used PS-MS/MS to monitor tacrolimus in clinical samples and showed good correlation with 2 immunoassays and an external HPLC-MS/MS method (4). Here we extend this approach by demonstrating the simultaneous quantification of cyclosporine and sirolimus by PS-MS/MS. Therapeutic drug monitoring of these drugs is important for organ transplant patient care. The method used was similar to our …