Differentiation between the metabolic processes involving methylation is more demanding, however. Speciation analysis-discerning the difference between an aldehyde and a sulphide, for example-becomes possible with an increase in mass accuracy above the quadrupole limits to 30 ppm, where the two masses differ by 0.035 Da. With their broad reach of specificity and utility, quadrupole time-of-flight (QTOF) instruments, offered by a number of manufacturers today, are replacing other LCMS technologies.Įven though higher order instruments exist, a QTOF instrument’s high mass accuracy falls within a few parts per million of the true, calculated, monoisotopic value, and its high resolution-as much as 10 times higher than a quadrupole instrument’s-permits us to determine empirical formulas according to mass defect (where the critical mass value of hydrogen and other atoms present serve as a differentiator).
Increased, measured mass accuracy and resolution is now a dominant tool for structural characterization in various applications beyond early drug discovery.
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