Increasing the reliability of compound identification in biological samples using 16 O/ 18 O-exchange mass spectrometry

The task of multipurpose analysis of biological samples and identification of individual compounds in them is actual for many organizations in various fields; the results of such analyses can affect lives. The most frequently used, most accurate, and highly sensitive method used for this kind of analysis is the combination of gas/liquid chromatography and high-resolution mass spectrometry. However, in some areas, it is necessary to increase the reliability of compound identification. In this paper, we present a method that combines the reaction of oxygen isotope exchange with mass spectrometry; the method allows to increase the reliability of identification of individual compounds. Oxygen isotope exchange reaction is a “selective” one, which means that not all oxygen present in the molecule can exchange, but only in certain functional groups. Thus, by the number of isotope exchanges that have occurred in this molecule, the right structural formula might be more accurately chosen. The method was tested both on pure pharmaceutical substances and on real human urine samples. In both cases, the effectiveness of the method was shown: the number of expected exchanges in known substances coincided with the experimental one, and from several possible structures of unknown substances, the correct one was chosen based on the number of isotope exchanges. Graphical abstract