Evaluation of the spectral accuracy of mass spectrometers using compounds containing Cl or Br atoms

Abstract

Current procedures for the evaluation of spectral accuracy of mass spectrometers are limited by the lack of certified isotopic reference materials and the high uncertainty in the isotopic composition of natural abundance molecules. The calculated uncertainties in the ratio M + 1/M for natural abundance molecules containing any number of C, H, N and/or O atoms are close to 5% relative because of the natural variability of the isotopic composition of carbon. So, we have developed two alternative measurement procedures with much lower theoretical uncertainties for a better evaluation of spectral accuracy in both single and triple quadrupole analysers. The first method is based on the measurement of the M + 2/M, M + 4/M + 2, etc. ratios for halogenated organic compounds containing either Cl or Br. The theoretical uncertainties for these ratios because of natural variability are in the order of 0.3 to 1.0% making them suitable for the evaluation of spectral accuracy with the additional advantage that there is no need to take into account other limitations such as cluster purity or poor mass resolution. This procedure was applied to the evaluation of a single quadrupole GC-MS instruments using natural abundance PCB and PBDE standards with satisfactory results. The second method can be applied to tandem instruments and takes advantage of the loss of two halogen atoms when PCB and PBDE standards are fragmented by Collision Induced Dissociation. Theoretical SRM transition ratios can be calculated as a pure combinatorial probability with theoretical uncertainties lower than 0.1%. By combining PCBs and PBDEs with different number of halogen atoms, a mass range from 100 to 700 u and abundance ratios from 0.1 to 10 can be evaluated. The use of penta-chlorinated PCBs and/or penta-brominated PBDEs is finally recommended for the evaluation of spectral accuracy of mass spectrometers with the EI source. Copyright © 2016 John Wiley & Sons, Ltd.

HILIC-Enabled 13C Metabolomics Strategies: Comparing Quantitative Precision and Spectral Accuracy of QTOF High- and QQQ Low-Resolution Mass Spectrometry

“…Defined non-labeled metabolite mixtures of reference standards were analyzed with both LC-MS systems to investigate spectral accuracy. To evaluate experimental data, theoretical abundances of naturally occurring isotopologues and related uncertainties were calculated following the approach of Somoano-Blanco et al, 2016 [29]. As a measure of spectral accuracy experimental metabolite-specific m+1 -to- m+0 isotope ratios (ISR 1:0 ) were calculated and compared with theoretical values (Figure 3).…”

“…The reliable identification of intermediates and isotope labeling patterns in complex biological matrices within metabolic tracer studies (e.g., 13 C) requires comparatively high or at least sufficient mass accuracy of time-resolved data. The straightforward evaluation of spectral accuracy was based on the comparison of the m+1 -to- m+0 isotopologue abundance ratios (ISR 1:0 ) [44,45,46] of obtained experimental MS datasets and theoretical, natural isotope distributions [29]. Experimental ISR 1:0 mean standard deviations of measured metabolite standard mixtures were in the range of the recommended 5% isotope abundance error [22] and previously published datasets for QTOF [47] and QQQ platforms [48].…”

“…Theoretical m+1 -to- m+0 ratios were calculated according to Somoano-Blanco et al, 2016 [29] to evaluate experimental m+1 -to- m+0 ratios. With these values, relative error calculations were performed.…”

Restricted spectral accuracy analysis to identify the single correct organic compound elemental‐composition from Orbitrap accurate mass data lists obtained at very high resolution

“…Determining the elemental composition (EC) of an organic compound is often performed by using combined GC, high‐performance liquid chromatography (HPLC), or supercritical fluid chromatography with accurate mass spectrometry (ie, a determination of a single m / z data point , the position of the monoisotopic line, to 4 or 5 decimal places beyond the nominal m / z value of an ionized, intact molecule). The determination of EC is done at resolutions typically from 20 000 to 240 000 by using various mass analyzers or combinations thereof, but many examples at lower and higher resolutions appear in the literature as well (and references therein).…”

“…Spectral accuracy of 100% is a “perfect” overlay, and it is not unusual for “real” samples to attain SA over 95% to 99% for the correct EC. As many SA‐based publications have shown, it is not always true that the correct EC answer shows the highest SA, and it is often the case that candidate EC scores are closely bunched (eg, with several candidates in the 97‐100% range). Last, confusing results have been reported (ie, better scores at lower resolutions), which can potentially be explained by excessive ion populations causing line shape distortions under higher resolutions.…”