skip to main content

Title: Rapid and simple determination of average molecular weight and composition of synthetic polymers via electrospray ionization‐mass spectrometry and a Bayesian universal charge deconvolution

Simple, affordable, and rapid methods for identifying the molecular weight (MW) distribution and macromolecular composition of polymeric materials are limited. Current tools require extensive solvent consumption, linear calibrations, and expensive consumables. A simple method for the determination of average MW (Mn,Mw) and chain end groups is demonstrated for synthetic homopolymer standards using direct injection electrospray ionization‐mass spectrometry (ESI‐MS) and an open‐sourced charge deconvolution (CDC) algorithm.


Five homopolymer standards in the 1–7 kDa MW range were analyzed using direct‐injection ESI‐MS on a quadrupole/time‐of‐flight mass spectrometer. The samples investigated, viz. two poly(ethylene oxide) (PEO) and two poly(styrene sulfonic acid) (PSS) standards with narrow polydispersity and one poly(d,l‐alanine) (pAla) standard with undefined polydispersity, were chosen to illustrate challenges with ESI‐MS quantitation. Using the UniDec program, weight average MWs (Mw) obtained from the charge‐deconvoluted spectra were compared to the reportedMwdata of the standards from size exclusion chromatography (SEC) measurements.


The MW data derived for the PSS, PEO, and pAla standards agreed well with the corresponding reportedMwor MW range values. The method was able to provide MW, degree of polymerization (DP), and polydispersity index (PDI) information for polymers with narrow (PSS, PEO) as well as broader (pAla) molecular weight distribution; this feature provides an advantage over MW analysis via matrix‐assisted laser desorption/ionization (MALDI) for ESI‐compatible materials. PSS standards differing in average MW by only a few repeat units could be confidently distinguished. Additionally, the oligomeric resolution observed for all samples studied unveiled chain‐end information not available through chromatographic analysis.


Overall, the free and easy‐to‐use UniDec CDC algorithm provides a simple, alternative method to measuring MW and DP for polymeric materials without high solvent consumption, expensive ionization sources, or calibration curves. Information about the masses of individual oligomers and the possibility to further characterize these oligomers using tandem mass spectrometry and/or ion mobility techniques constitutes additional benefits of this approach vis‐à‐vis traditional MW and PDI elucidation through SEC.

more » « less
Author(s) / Creator(s):
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Rapid Communications in Mass Spectrometry
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Rationale

    Examining surface protein conformations, and especially achieving this with spatial resolution, is an important goal. The recently discovered ionization processes offer spatial‐resolution measurements similar to matrix‐assisted laser desorption/ionization (MALDI) and produce charge states similar to electrospray ionization (ESI) extending higher‐mass protein applications directly from surfaces on high‐performance mass spectrometers. Studying a well‐interrogated protein by ion mobility spectrometry‐mass spectrometry (IMS‐MS) to access effects on structures using a solidvs.solvent matrix may provide insights.


    Ubiquitin was studied by IMS‐MS using new ionization processes with commercial and homebuilt ion sources and instruments (Waters SYNAPT G2(S)) and homebuilt 2 m drift‐tube instrument; MS™ sources). Mass‐to‐charge and drift‐time (td)‐measurements are compared for ubiquitin ions obtained byinletandvacuumionization using laserspray ionization (LSI), matrix‐ (MAI) and solvent‐assisted ionization (SAI), respectively, and compared with those from ESI under conditions that are most comparable.


    Using the same solution conditions with SYNAPT G2(S) instruments, td‐distributions of various ubiquitin charge states from MAI, LSI, and SAI are similar to those from ESI using a variety of solvents, matrices, extraction voltages, a laser, and temperature only, showing subtle differences in more compact features within the elongated distribution of structures. However, on a homebuilt drift‐tube instrument, within the elongated distribution of structures, both similar and different td‐distributions are observed for ubiquitin ions obtained by MAI and ESI. MAI‐generated ions are frequently narrower in their td‐distributions.


    Direct comparisons between ESI and the new ionization methods operational directly from surfaces suggest that the protein in its solution structure prior to exposure to the ionization event is either captured (frozen out) at the time of crystallization, or that the protein in the solid matrix is associated with sufficient solvent to maintain the solution structure, or, alternatively, that the observed structures are those related to what occurs in the gas phase with ESI‐ or MAI‐generated ions and not with the solution structures.

    more » « less
  2. null (Ed.)
    Ion mobility spectrometry (IMS) mass spectrometry (MS) centers on the ability to separate gaseous structures by size, charge, shape, and followed by mass-to-charge (m/z). For oligomeric structures, improved separation is hypothesized to be related to the ability to extend structures through repulsive forces between cations electrostatically bonded to the oligomers. Here we show the ability to separate differently branched multiply charged ions of star-branched poly(ethylene glycol) oligomers (up to 2000 Da) regardless of whether formed by electrospray ionization (ESI) charged solution droplets or from charged solid particles produced directly from a surface by matrix-assisted ionization. Detailed structural characterization of isomers of the star-branched compositions was first established using a home-built high-resolution ESI IMS-MS instrument. The doubly charged ions have well-resolved drift times, achieving separation of isomers and also allowing differentiation of star-branched versus linear oligomers. An IMS-MS “snapshot” approach allows visualization of architectural dispersity and (im)purity of samples in a straightforward manner. Analyses capabilities are shown for different cations and ionization methods using commercially available traveling wave IMS-MS instruments. Analyses directly from surfaces using the new ionization processes are, because of the multiply charging, not only associated with the benefits of improved gas-phase separations, relative to that of ions produced by matrix-assisted laser desorption/ionization, but also provide the potential for spatially resolved measurements relative to ESI and other ionization methods. 
    more » « less
  3. Rationale

    Successful coupling of a multi‐ionization automated platform with commercially available mass spectrometers provides improved coverage of compounds in complex mixtures through implementation of new and traditional ionization methods. The versatility of the automated platform is demonstrated through coupling with mass spectrometers from two different vendors. Standards and complex biological samples were acquired using electrospray ionization (ESI), solvent‐assisted ionization (SAI) and matrix‐assisted ionization (MAI).


    The MS™ prototype automated platform samples from 96‐ or 384‐well plates as well as surfaces. The platform interfaces with Thermo Fisher Scientific mass spectrometers by replacement of the IonMax source, and on Waters mass spectrometers with additional minor source inlet modifications. The sample is transferred to the ionization region using a fused‐silica or metal capillary which is cleaned between acquisitions using solvents. For ESI and SAI, typically 1 μL of sample solution is drawn into the capillary tube and for ESI slowly dispensed near the inlet of the mass spectrometer with voltage placed on the delivering syringe barrel to which the tubing is attached, while for SAI the sample delivery tubing inserts into the inlet without the need for high voltage. For MAI, typically, 0.2 μL of matrix solution is drawn into the syringe before drawing 0.1 μL of the sample solution and dispensing to dry before insertion into the inlet.


    A comparison study of a mixture of angiotensin I, verapamil, crystal violet, and atrazine representative of peptides, drugs, dyes, and herbicides using SAI, MAI, and ESI shows large differences in ionization efficiency of the various components. Solutions of a mixture of erythromycin and azithromycin in wells of a 384‐microtiter well plate were mass analyzed at the rate ofca1 min per sample using MAI and ESI. In addition, we report the analysis of bacterial extracts using automated MAI and ESI methods. Finally, the ability to perform surface analysis with the automated platform is also demonstrated by directly analyzing dyes separated on a thin‐layer chromatography (TLC) plate and compounds extracted from the surface of a beef liver tissue section.


    The prototype multi‐ionization automated platform offers solid matrix introduction used with MAI, as well as solution introduction using either ESI or SAI. The combination of ionization methods extends the types of compounds which are efficiently ionized and is especially valuable with complex mixtures as demonstrated for bacterial extracts. While coupling of the automated multi‐ionization platform to Thermo and Waters mass spectrometers is demonstrated, it should be possible to interface it with most commercial mass spectrometers.

    more » « less

    Neodymium‐based catalysts coordinated with phosphate ligands (NdCl3·3L), where L = triethyl phosphate (TEP) or tris(2‐ethylhexyl) phosphate (TEHP), were synthesized. The ring‐opening polymerizations (ROP) of ɛ‐caprolactone (ɛ‐CL) with these catalysts in the presence of benzyl alcohol initiator were performed, yielding polymers with well‐defined molecular weights and relatively narrow polydispersity index (PDI = 1.22–1.65).In situNMR analysis of the reaction between NdCl3·3TEP and benzyl alcohol indicated that ROP proceeds through a coordination‐insertion mechanism. The end groups of the resultant polymers were determined using MALDI‐ToF mass spectrometry and NMR spectroscopy. Thequasi‐livingnature of this catalytic system was demonstrated by kinetic studies and the successful synthesis of the block copolymer poly(ɛ‐caprolactone)‐block‐poly(l‐lactide) by sequential monomer addition. Kinetic studies revealed that the catalyst with the bulkier TEHP ligand increased the rate of ROP of ɛ‐CL as compared to the TEP ligand. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2018,56, 1289–1296

    more » « less

    This article reports a chain‐growth coupling polymerization of AB difunctional monomer via copper‐catalyzed azide–alkyne cycloaddition (CuAAC) reaction for synthesis of star polymers. Unlike our previously reported CuAAC polymerization of ABn(n ≥ 2) monomers that spontaneously demonstrated a chain‐growth mechanism in synthesis of hyperbranched polymer, the homopolymerization of AB monomer showed a common but less desired step‐growth mechanism as the triazole groups aligned in a linear chain could not effectively confine the Cu catalyst in the polymer species. In contrast, the use of polytriazole‐based core molecules that contained multiple azido groups successfully switched the polymerization of AB monomers into chain‐growth mechanism and produced 3‐arm star polymers and multi‐arm hyperstar polymers with linear increase of polymer molecular weight with conversion and narrow molecular weight distribution, for example,Mw/Mn ~ 1.05. When acid‐degradable hyperbranched polymeric core was used, the obtained hyperstar polymers could be easily degraded under acidic environment, producing linear degraded arms with defined polydispersity. © 2019 Wiley Periodicals, Inc. J. Polym. Sci.2020,58, 84–90

    more » « less