LAUSR

To the Editor: With the continuing expansion of mass spectrometry into the clinical laboratory for the quantification of proteins and small molecules, laboratories are being equipped with different instrument platforms from different manufacturers. This requires specific training for laboratory personnel on each data analysis software package that is unique to each instrument, which can increase method deployment time and potentially increase errors in data analysis. Skyline is a freely available, vendor-neutral software package that facilitates quantitative analysis of both protein and small-molecule mass spectrometry data (1). We implemented calibration features in Skyline and used 2 methods to demonstrate the new features and compare these results with those obtained from vendor software for small-molecule and protein quantification. Because the chromatographic characteristics are slightly different for peptides and small molecules, we quantitatively analyzed serum concentrations of 25-hydroxy vitamin D [25(OH)D]1 and vitamin D binding globulin (VDBG), as previously described (2, 3). Briefly, 25(OH)D was immunoaffinity enriched from 154 single-donor human serum samples, and the derivatized extracted analytes and stable isotope-labeled analogs were chromatographically separated using Waters Acquity UPLC coupled online via an electrospray ionization source operating in positive ion detection mode for analysis by multiple reaction monitoring …