On the Kendrick Mass Defect Plots of Multiply Charged Polymer Ions: Splits, Misalignments, and How to Correct Them

Abstract

The Kendrick mass defect (KMD) analysis of multiply charged polymeric distributions has recently revealed a surprising isotopic split in their KMD plots-namely a 1/z difference between KMDs of isotopes of an oligomer at charge state z. Relying on the KMD analysis of actual and simulated distributions of poly(ethylene oxide) (PEO), the isotopic split is mathematically accounted for and found to go with an isotopic misalignment in certain cases. It is demonstrated that the divisibility (resp. indivisibility) of the nominal mass of the repeating unit (R) by z is the condition for homolog ions to line up horizontally (resp. misaligned obliquely) in a KMD plot. Computing KMDs using a fractional base unit R/z eventually corrects the misalignments for the associated charge state while using the least common multiple of all the charge states as the divisor realigns all the points at once. The isotopic split itself can be removed by using either a new charge-dependent KMD plot compatible with any fractional base unit or the remainders of KM (RKM) recently developed for low-resolution data all found to be linked in a unified theory. These original applications of the fractional base units and the RKM plots are of importance theoretically to satisfy the basics of a mass defect analysis and practically for a correct data handling of single stage and tandem mass spectra of multiply charged homo- and copolymers. Graphical Abstract ᅟ.

Thermal desorption and pyrolysis direct analysis in real time mass spectrometry for qualitative characterization of polymers and polymer additives

“…Peak series differing by the monomer mass may be easily recognized, as in the case of nylon polymers. Mass defect analysis, in particular Kendrick mass analysis may be used to identify characteristic peak series for cases in which the monomer series is not readily evident by inspection, and/or when multiple polymer types are present. …”

MSPolyCalc: A web‐based App for polymer mass spectrometry data interpretation. The case study of a pharmaceutical excipient

“…Interestingly, the dot size directly expresses the relative intensities of the signals, making shifts of maxima between distributions more emphasized. The interest in deconvoluted KMD plots as a reporting tool is further underlined in the frame of multiply charged species, where splits and misalignment may occur (Figure S5, supporting information). Ultimately, the Kendrick Tab represents a practical tool to support reporting needs and well complements the other tab menus.…”

An arsenal of tools based on Kendrick mass defects to process congested electrospray ionization high‐resolution mass spectra of polymers with multiple charging

“…A charge-dependent KMD plot has been implemented in Kendo and MZmine 2 but it would also be computed using an empty spreadsheet with manual coding of formulas (supporting information). 39 Using Z = 2 as implemented in Kendo, the doubly charged series are clustered in one cloud only for each KMD plot computed from the two mass spectra, similarly to the regular KMD analysis of a singly charged series ( Figure 3A). The isotopic split can be cancelled for all the charge states at once using the least common multiple (LCM) of the charge-state distribution (e.g.…”

“…A regular KMD plot computed with PO as the base unit for the new mass scale displays a so-called isotopic split which reveals the charge-state distribution at a glance with no need for deisotoping and deconvolution. 39 Using a multiplication factor set at one of the charge states z removes the isotopic split, and clusters the associated ion series into a single cloud in a so-called chargedependent KMD plot for a simpler filtering. 39 Combined with the recently introduced enhancement of resolution relying on the use of a base unit PO/x with x being a integer or non-integer "divisor", 40,41 the different ion series at a given charge state are finely separated in a charge-dependent resolution-enhanced KMD plot.…”

“…39 Using a multiplication factor set at one of the charge states z removes the isotopic split, and clusters the associated ion series into a single cloud in a so-called chargedependent KMD plot for a simpler filtering. 39 Combined with the recently introduced enhancement of resolution relying on the use of a base unit PO/x with x being a integer or non-integer "divisor", 40,41 the different ion series at a given charge state are finely separated in a charge-dependent resolution-enhanced KMD plot. The KM "remainders" plot (noted KMR plot) developed for the profiling of end-groups of singly charged homopolymers analyzed by MALDI-MS 28 is also extended to the case of multiply charged series for the first time.…”