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Issue 2, 2011
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One-step conversion of dipicolinic acid to its dimethyl ester using monomethyl sulfate salts for GC-MS detection of bacterial endospores

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Abstract

Methyl sulfate (MeSO4) salts were explored as thermochemolysis–methylation (TCM) reagents for gas chromatographic (GC) analysis of dipicolinic acid (DPA) as its dimethyl ester (Me2DPA) from bacterial endospores. The reaction was carried out under non-pyrolytic conditions by inserting a small coiled wire filament coated with the sample and reagents directly inside a GC injection port at 290 °C. Above 10 : 1 methyl donor/DPA ratios, alkali metal salts of MeSO4 effected 80–90% conversion of DPA to Me2DPA, which was 10–20 times more active than the same amount of tetramethylammonium hydroxide (TMA-OH) at this temperature. A quaternary salt mixture consisting of 1 : 3 : 1 : 3 TMA+/Na+/OH/MeSO4 methylated spore DPA with an average conversion of 86% (mean conversion by TMA-OH under the same conditions was 4%). Therefore, the sensitivity for detection of bacterial endospores was increased over 20-fold compared to that observed with the more commonly employed TMA-OH methylating reagent. The limit of detection by this method was 9 × 104 total spores. Mechanisms describing the observed behavior are proposed and discussed. This is the first use of MeSO4 as a TCM reagent for GC.

Graphical abstract: One-step conversion of dipicolinic acid to its dimethyl ester using monomethyl sulfate salts for GC-MS detection of bacterial endospores

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Publication details

The article was received on 27 Apr 2010, accepted on 03 Nov 2010 and first published on 06 Dec 2010


Article type: Paper
DOI: 10.1039/C0AY00270D
Citation: Anal. Methods, 2011,3, 245-258
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    One-step conversion of dipicolinic acid to its dimethyl ester using monomethyl sulfate salts for GC-MS detection of bacterial endospores

    A. N. Nackos, T. V. Truong, T. C. Pulsipher, J. A. Kimball, H. D. Tolley, R. A. Robison, C. H. Bartholomew and M. L. Lee, Anal. Methods, 2011, 3, 245
    DOI: 10.1039/C0AY00270D

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