Toward standardizing deuterium content reporting in hydrogen exchange-MS.

We introduce a method to monitor dispensing ratios during labeling reactions in hydrogen exchange (HX)-MS. The method corrects for systematic and random dispensing errors and harmonizes data incorporating variable %D2O in the experiment design. A correction factor for deuterium levels is obtained by quantifying the relative signal intensities arising from nonexchanging heavy caffeine (spiked into labeling buffer) and light caffeine (spiked into sample solutions). Dispensing variability over a wide range of %D2O composition can be detected and corrected to a common value, and although random dispensing error is usually minor, we show it can be the limiting factor in high quality signal measurements. Applying a dispensing control is therefore an effective tool for monitoring measurement precision in HX-MS.