Is your sample pure?
SDC-CID: Stage-discriminated correlation collision-induced dissociation
What are you going to do when the sample you are analyzing by using mass spectrometry contains impurity with same m/z value? Fears about the potential problems associated to the contaminated structural isomers such as diastereomers and sequential isomers in your sample always exist. The presence of these isomeric structures cannot be identified by the method based on mass spectrometry. But, this is no longer true. Based on the new method called “stage-discriminated correlation” tells you whether a sample is “pure” or not. (Carbohydr. Res., 2009)
If you own a mass spectrometer capable of carrying out the low-energy collision-induced dissociation (CID) that often called MS/MS, you can obtain a very useful spectrum of energy-resolved mass spectrometry (ERMS). (Anal. Chem., 2006) With the ERMS, you will be able to distinguish structurally related ions having same m/z value. The method allows distinguishing ions of structural isomers such as diastereomers in general.
When QIT-MS (quadrupole ion trap mass spectrometry) is used for obtaining ERMS spectra, important information is obtained. That is ratio of product ions are constant regardless of the applied CID energy. (Rapid Commun. Mass Spectrom. 2010) The reason of this is the fact that the activated species during the CID conditions is the precursor ion only. Although all the ions should be “activated” in order for those to be trapped, the energy of these ions are in the equilibrium between collision activation and cooling, thus these ions except for the precursor do not fragment.
Using QIT-MS, it is possible to examine the pureness (not purity) of the sample being analyzed. Let us consider a case that your sample is pure. First, you carry out the ERMS experiments and obtain a spectrum. Having this spectrum in hand, you carry out second experiments by applying certain CID energy where ca 20 to 30 % of the precursor ion is consumed and the remaining precursor ion is “isolated” for the next ERMS experiment. (Note) What you see is the exactly same ERMS spectrum with one obtained beforehand. (Proc. Jpn Acad. Ser. B, 2009, Carbohydr. Res., 2009) The comparison is made by correlation plot. When two spectra is identical, the correlation curve obtained thus is y = x. An experimental error results in some deviation.
We now consider a case that your sample is not pure contaminated by a molecule with same molecular weight. Individual ions associated with such molecules require specific activation energies. For this reason, the spectra obtained at separate stages become different, which can be judged by the large deviation in a correlation plot.
Note: MS/MS (MS2) is the method of obtaining fragment ions generated from a precursor ion. And, MS3 is to obtain fragments of a fragment generated at a previous stage by definition. Our experiment therefore is not considered as MS3! This is funny, but this was a reason that our manuscript was once rejected.
Significance
The pureness of your sample is obtained just by doing ERMS twice
References
Ion-trap mass spectrometry unveils the presence of isomeric oligosaccharides in an analyte: Stage-discriminated correlation of energy-resolved mass spectrometry. Daikoku, S. Kurimoto, A. Mutuga, S. Ako, T. Kanemitsu, T. Shioiri, Y. Ohtake, A. Kato, R. Saotome, C. Ohtsuka, I. Koroghi, S. Sarkar, S. K. Tobe, A. Adachi, S. Suzuki, K. Kanie, O. Carbohydr. Res., 2009, 344, 384-394.
Analysis of energy-resolved mass spectra at MSn in a pursuit to characterize structural isomers of oligosaccharides. Kurimoto, A. Daikoku, S. Mutsuga, S. Kanie, O. Anal. Chem., 2006, 78, 3461-3466.
Analysis of behavior of sodiated sugar hemiacetals under low-energy collision-induced dissociation conditions and application to investigating mutarotation and mechanism of a glycosidase. Kanie, O, Kurimoto, A. Daikoku, S. Mutsuga, S. Kanie, Y. Suzuki, K. Proc. Jpn Acad. Ser. B, 2009, 85, 204-215.
Multi-stage mass spectrometric information obtained by deconvolution of energy-resolved spectra acquired by triple-quadrupole mass spectrometry. Kanie, O. Kanie, Y. Daikoku, S. Shioiri, Y. Kurimoto, A. Mutsuga,S. Goto, S. Ito, Y. Suzuki, K. Rapid Commun. Mass Spectrom. 2010, 25, 1617-1624.
