Jeremi D. Johnson

The University of Tennessee Medical Center at Knoxville, Knoxville, Tennessee, United States

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Publications (2)3.59 Total impact

  • Benjamin S. Prebyl, Jeremi D. Johnson, Kelsey D. Cook
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    ABSTRACT: Monomer ions appear in electrospray mass spectra of poly(styrene sulfonate-co-maleic acid) as the cone voltage (CV) is changed from −20 to −100V. For a 1:1 styrene sulfonate (SS): maleic acid (MA) copolymer at CV=−100V, the SS:MA monomer ion intensity ratio r1:1(im/z183/im/z115)1:1 is 18.50±0.64, reflecting the relatively high acidity of SS (pKa 0.7, versus 1.92 for MA). When sampling a 3:1 SS:MA copolymer, r3:1 is 84.64±1.83. The ratio of these ratios (r3:1/r1:1)polymer is 4.57±0.18, significantly higher than the value expected [(3:1)/(1:1)=3] based on the relative (nominal) monomer ratios in the copolymers. This compromises the use of one polymer sample as a standard for assessing the monomer ratio in the other at this CV. Use of monomer mixtures as standards is also precluded at CV=−100V due to extensive fragmentation when sampling free MA monomers. Use of a lower CV and consideration of fragments as well as the monomer ions leads to better performance. At CV=−40V, total polymer ion intensity ratios (Σim/z⁡183+im/z⁡119+im/z⁡80im/z⁡115+im/z⁡71) are 42.60±2.01 and 13.11±0.87 for the 3:1 and 1:1 copolymers, respectively. The ratio of these ratios (Σ3:1/Σ1:1)polymer is 3.25±0.29, in good agreement with the nominal composition ratio. Similar results were obtained at CV −40 to −90V. Using monomer mixtures as calibrants at CV=−40V also provides accurate quantitation of the copolymer monomer ratios, provided that the total intensity ratios are used. Comparison of monomer and polymer breakdown diagrams provides the insight needed to determine the appropriate CV for quantitation with either polymer or monomer standards. Similar results are obtained for a second ionic copolymer system (2-acrylamido-2-methylpropane sulfonic acid-co-acrylic acid). Once optimum conditions are achieved, monomer ratio determination can proceed very quickly, suggesting potential utility for routine quality monitoring.
    International Journal of Mass Spectrometry - INT J MASS SPECTROM. 01/2004; 238(3):207-214.
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    ABSTRACT: Collision-induced dissociation in the source of an electrospray (ES) mass spectrometer was employed to characterize putative samples of the ionic terpolymer poly(styrene sulfonate-co-acrylic acid-co-2-acrylamido-2-methyl-1-propanesulfonic acid). Qualitative and semi-quantitative information about the monomer content was quickly obtainable from ES spectra, and indicated that some samples contained little or none of one or two expected comonomers. For two representative samples, confirmatory nuclear magnetic resonance (NMR) data were acquired. The NMR experiments required sample clean-up (to remove additives) and long acquisition times (up to 720 min) for 13C NMR. Cleanup also improved the ES results, providing better agreement with the NMR data. However, qualitative and semi-quantitative information was obtainable by ES (but not by NMR) without the cleanup step. Full quantitation of monomer ratios would require suitable standards, but even without such standards the ES measurements provide a rapid (<1 min) means for differentiating these samples (e.g., for process or quality control).
    Journal of the American Society for Mass Spectrometry 09/2002; 13(8):921-7. · 3.59 Impact Factor