Quantitative LC−MS of Polymers: Determining Accurate Molecular Weight Distributions by Combined Size Exclusion Chromatography and Electrospray Mass Spectrometry with Maximum Entropy Data Processing

Abstract

We report on the successful application of size exclusion chromatography (SEC) combined with electrospray ionization mass spectrometry (ESI-MS) and refractive index (RI) detection for the determination of accurate molecular weight distributions of synthetic polymers, corrected for chromatographic band broadening. The presented method makes use of the ability of ESI-MS to accurately depict the peak profiles and retention volumes of individual oligomers eluting from the SEC column, whereas quantitative information on the absolute concentration of oligomers is obtained from the RI-detector only. A sophisticated computational algorithm based on the maximum entropy principle is used to process the data gained by both detectors, yielding an accurate molecular weight distribution, corrected for chromatographic band broadening. Poly(methyl methacrylate) standards with molecular weights up to 10 kDa serve as model compounds. Molecular weight distributions (MWDs) obtained by the maximum entropy procedure are compared to MWDs, which were calculated by a conventional calibration of the SEC-retention time axis with peak retention data obtained from the mass spectrometer. Comparison showed that for the employed chromatographic system, distributions below 7 kDa were only weakly influenced by chromatographic band broadening. However, the maximum entropy algorithm could successfully correct the MWD of a 10 kDa standard for band broadening effects. Molecular weight averages were between 5 and 14% lower than the manufacturer stated data obtained by classical means of calibration. The presented method demonstrates a consistent approach for analyzing data obtained by coupling mass spectrometric detectors and concentration sensitive detectors to polymer liquid chromatography.

The role of mid‐chain radicals in acrylate free radical polymerization: Branching and scission

“…74 From a chemical point of view, the latter option seems advantageous, because no addition of a controlling or regulating agent is required to artificially suppress the molecular weights. However, the interpretation and reproducible generation of ESI-MS spectra of high charge states is complex and does not lend itself to the throughput of large amounts of samples.…”

Design of Experiment (DoE) as a Tool for the Optimization of Source Conditions in SEC‐ESI‐MS of Functional Synthetic Polymers Synthesized via ATRP

“…The mass spectrometer was coupled to the column in parallel to an RIdetector (G1362A with SS420x A/D) in a setup described previously. [19] Eluent (0.27 mL Á min À1) was directed through the RI-detector and 30 mL Á min À1 infused into the electrospray source after post-column addition of a 100 mM solution of sodium trifluoroacetate in methanol at 20 mL Á min À1 by a micro-flow HPLC syringe pump (Teledyne ISCO, Model 100DM). A polymer solution (10 mL) with a concentration of 2 mg Á mL À1 was injected onto the HPLC system.…”

“…[18] Therefore, the analysis is usually limited to samples with molecular weights below 2-3 kDa. Despite of this, Gruendling et al [19] and Aaserud et al [20] have shown that this problem can be alleviated by coupling ESI-MS to size exclusion chromatography (SEC), effectively broadening the analyzable mass range of polymers exhibiting multiple charging. In offline LC-MS, optimization is performed easily, as the prefractionated sample can be introduced into the mass spectrometer almost indefinitely in a repetitive fashion.…”

Reversible Diels‐Alder Chemistry as a Modular Polymeric Color Switch

“…[ 41 ] A 0.27 mL·min −1 aliquot of the eluent was directed through the RI detector and 30 μL·min −1 infused into the electrospray source after postcolumn addition of a 0.1mM solution of sodium iodide in methanol at 20 μL·min −1 by a micro fl ow HPLC syringe pump (Teledyne ISCO, Model 100DM). The polymer solutions (20 μL) with a concentration of ∼ 2 mg·mL −1 were injected into the HPLC system.…”