Sierra Analytics-Software for Mass Spectrometry and Chemistry

Analysis of industrial polymers by mass spectrometry, particularly by MALDI-TOF or other molecular ion mass spectrometry techniques, provides information important to the characterization of these polymers. This information includes the repeating (or monomer) mass, end group mass, and molecular weight distribution, and is described below. Molecular ion mass spectra of hydrocarbons or other materials containing multiple homologous series distributions can be deconvolved to yield information on the distribution among unsaturation states, degree of chemical modification, etc.

Mass spectrometric analysis produces two primary categories of information that are useful to polymer and hydrocarbon chemists. One category includes several forms of molecular weight averages and degree of polymerization values, and the other relates to the characterization and quantification of individual chemical components, or chemical component series, that may be present.

The molecular weight averages and degree of polymerization formulae are shown below. They are calculated from M, the mass in Daltons (Da), N, the number of moles, and R is the mass of the polymer repeat unit. The sums as shown are over all the mass peaks of interest in the spectrum.

Number average molecular weight:
Weight average molecular weight:
Third order molecular weight average:
Polydispersity:
Degrees of polymerization:

Secondly, more detailed characterization of individual chemical component series can be determined. In this case, one or more series, or sets of oligomers, are quantified by molecular ion intensity, and relative amount distributions are calculated. The user interacts with the program to specify the repeating mass, or monomer mass, of interest, and possible adduct masses that may be present. Common adducts in MALDI include sodium, potassium, silver, and other cations. The masses of the two end groups of the polymer or hydrocarbon are also taken into account, either input by the user or calculated by the program. Polymerix then creates a table comprised of the relative responses for each oligomer mass in the series. A more exact determination of the total end group mass is often achieved by computing this remainder mass from each of the oligomer masses seen in the spectrum.

Frequently, industrial polymers are comprised of combinations of different end groups and/or repeat mass, or multi-modal distributions of repeating unit number. Even so, quite often many mass peaks may still be assigned to a particular series to produce useful series distribution tables for these samples, although variances in mass of 1 Dalton would require unit mass resolution. Another complication worth mentioning is that in TOF mass spectra, unit mass resolution may well be achieved at low mass but not at the higher mass end of the spectrum. Sensible quantification of oligomer series also requires that spectra containing isotopic clusters for each component be transformed into its monoisotopic representation, otherwise high mass components that contain wider isotopic cluster distributions than low mass clusters will be improperly reported with too little intensity.

Polymerix takes this knowledge into account, and processes either centroided or continuum spectra. The program is aware of monoisotopic, chemical, and nominal masses. Spectra that contain monoisotopic (i.e. resolved) masses at the lower mass range and chemical masses (i.e. unresolved) at the higher mass range of the spectrum are accommodated. Isotope clusters of resolved or partially resolved spectra are processed by calculating the theoretical distribution of the chemical formula of each oligomer throughout the mass spectrum. The software also predicts the repeat mass and total end group mass of spectra containing a single oligomer series.
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Polymerix Detailed Description