mass tolerance February 23, 2020, 05:04:51 PM Hello,Just curious, why are the mass tolerance parameters in Da, rather than ppm?The ppm difference between 100.000 and 100.001 is 10ppm, and between 300.000 and 300.001 it is 3.33ppm.However, Agilent qTofs are only able to reach 10-15ppm mass accuracy when acquiring samples in matrix (eg, plasma/urine). A setting of 0.001 Da would be too narrow for 300m/z. I would need 0.003 Da for 10ppm. But, using 0.003 Da for 100m/z would be 30ppm, which is too large.Perhaps I'm thinking about this incorrectly? For metabolites such as organic acids, a qtof with a resolution of 10,000 at 120m/z, and 10ppm mass accuracy, what tolerances do I use?