Is orbitrap quantitative? Critical aspects of its potential using natural products and synthetic drugs as models

Orbitrap analyzers represent a new exciting technology in the field of mass spectrometry as they offer unsurpassed mass accuracy (often in the sub-ppm area) along with high resolving power (up to 150.00). Its use is widespread including structure elucidation of natural products, proteomics, metabolism studies and metabolomics as well fragmentation and H/D exchange studies. Nevertheless quantitation studies using such instrumentation are rather scarce and are usually performed using the XIC mode of full scan mass spectra. This study involves a detailed study on the quantitative abilities of the instrument investigating critical factors pertaining its operation, such as the scan range, the resolution, the acquisition mode (centroid or profile) as well as the MS/MS capabilities of the instrument. Five substances (four natural products – oleuropein, hydroxytyrosol, acrovestone and hermanioside B, one semisynthetic –6-bromoindirubin-3-oxime and one synthetic drug – clopidogrel) have been used as model compounds. The evaluation of the results has been based on the statistical comparison of calibration curves constructed under the aforementioned conditions using either the extra sum-of-squares F test or the Akaike's information criterion methodologies.