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INTERNATIONAL INTERLABORATORY TESTING ADVANCES MASS DISTRIBUTION MEASUREMENT METHOD FOR SYNTHETIC POLYMERS.

The quality of mass spectrometric measurements of mass distribution in synthetic polymers was assessed in a recent NIST report that described the results of an international interlaboratory comparison involving 21 laboratories. MALDI-MS, a form of mass spectrometry in which laser ablation is used to produce volatile charged molecules, is being explored as an absolute method for molecular mass distribution of synthetic polymers. Most current methods yield only moments of the mass distribution. For instance, gel permeation chromatography yields the mass distribution but requires calibration with hard-to-find standards of known mass. Published results of mass distribution by mass spectrometry yield conflicting findings; hence the interlaboratory comparison was undertaken to determine the current status of measurements on a single, well-characterized polymer and to identify measurement issues that require attention. The polymer, polystyrene, evaluated in the round robin was custom synthesized to NIST specif ications with molecular characteristics such that it could be investigated not only by mass spectrometry but also by traditional spectroscopic methods and light scattering.

Participants of the interlaboratory comparison reported the mass spectrum of the polystyrene and moments of the distribution calculated from mass spectrometric data. NIST staff calculated the moments from the submitted data as well. In some cases, the moments calculated by NIST using the participants data differed significantly from moments reported by the participants. The distribution in values of moments calculated by NIST was very narrow, with a standard deviation of one polystyrene repeat unit, approximately. Furthermore, analysis of these data yielded moments of the mass distribution lower than those obtained from current methods but within the measurement uncertainty. Nonetheless, it was found that calibration of mass spectrometers was not performed correctly by several participants and that methods of data analysis differed widely with some participants reporting moments of the distribution that differed significantly from the mean. The findings of the report will be used to improve the quantifica tion of the new mass spectrometric method for the determination of synthetic polymer mass distributions.
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Publication:Journal of Research of the National Institute of Standards and Technology
Article Type:Brief Article
Geographic Code:1USA
Date:Nov 1, 2000
Words:328
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