Quantitative determination of four immunosuppressants by high resolution mass spectrometry (HRMS)

Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) utilizing triple-quadrupole instruments has been widely used for quantification of endogenous compounds, drugs or metabolites in clinical laboratories. In contrast, high-resolution mass spectrometry (HRMS) is typically used for compound identification due to its limited dynamic range. Recently HRMS instruments with enhanced linear dynamic range have become available. The aim of this study was to evaluate HRMS for fast quantitative applications in a clinical laboratory.

A high throughput UPLC-TOF-MS assay for simultaneous quantification of cyclosporin A, tacrolimus, sirolimus and everolimus was developed. All immunosuppressants were analyzed as sodium adducts in TOF-only mode using an Agilent 6540 Q-TOF system. Extracted ion chromatograms of analytes and internal standards were created from full-scan data. The assay was evaluated and compared to an established LC-MS/MS assay according to CLSI recommendations.

The novel HRMS assay has a total run time of 3 min. The assay is linear in a clinical relevant concentration range for all four immunosupressants. Method correlations vs. established LC-MS/MS assay were between R2=0.99 and R2=0.97. Total coefficients of variation (CVT) ranges were 4.5%-6.4% (tacrolimus), 7.4%-8.0% (sirolimus), 8.0%-8.8% (everolimus) and 6.1%-7.4% (cyclosporine A) for three relevant concentration levels each.

High resolution TOF-MS and LC-MS/MS show equivalent quantitative performance for monitoring of cyclosporin A, tacrolimus, sirolimus and everolimus. HRMS has the potential to replace conventional LC-MS/MS in clinical laboratories because it simplifies assay development (no optimization of fragmentations and product ions necessary) and its full-scan data can provide additional information.