ARS | Publication request: GC-MS QUANTIFICATION OF THE METHANOL AND ACETIC ACID CONTENT OF PECTIN USING HEADSPACE SOLID-PHASE MICROEXTRACTION

Submitted to: Journal of Chromatography A
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 16, 2003
Publication Date: July 16, 2003
Citation: Savary, B.J. and Nunez, A. 2003. Gas chromatography-mass spectrometry quantification of the methanol and acetic acid contents of pectin using headspace microextraction with stable isotope dilution. Journal of Chromatography A. 1017: p.151-159.

Interpretive Summary: Pectin is a complex plant cell wall polysaccharide that is used as a food gum and in pharmaceutical and nutraceutical applications. Pectin's functional properties and bioactivity are influenced by structural decorations known as methyl- and acetyl-esters. There is a critical need for specific and sensitive analytical methods capable of determining the content of these decorations, especially for research on new uses for U.S. agricultural processing residues such as sugar beet pulp. Current standard methodologies for these determinations are obsolete, particularly since they are labor-intensive time-consuming and require large sample sizes. What we have accomplished is to exploit advances in analytical instrumentation to develop a new method that can simultaneously determine the methanol and acetic acid contents of pectin in a simple, fast, and direct manner. Research scientists and industrial technicians will benefit by this greatly improved method for chemical characterization of pectin.

Technical Abstract: A simple, fast, and direct procedure was developed for the simultaneous determination of the methanol and acetic acid present as esters in the plant cell wall polysaccharide pectin. After base-hydrolysis of esters and acidification of pectin samples, headspace solid-phase microextraction was performed using a Carboxen-PDMS fiber assembly. Methanol and acetic acid were separated by gas chromatography with a Chrompak PoraPlot Q capillary column and detected using electron impact mass spectrometry with selected ion monitoring. Stable deuterated isotopomers (d3-methanol and d3-acetic acid) were used as internal standards and for constructing calibration curves, providing accurate and absolute quantification of analytes. The methanol and acetic acid content in 1 mg quantities of citrus and sugar beet pectins were readily quantified by this procedure. The procedure was also applicable to demonstrating enzymatic hydrolysis of pectin methyl and acetyl esters.