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 (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. report that described the results of an international interlaboratory comparison involving 21 laboratories. MALDI-MS MALDI-MS Matrix assisted Laser Desorption Ionisation Mass Spectrometry , a form of mass spectrometry mass spectrometry or mass spectroscopy Analytic technique by which chemical substances are identified by sorting gaseous ions by mass using electric and magnetic fields. in which laser ablation Laser ablation is the process of removing material from a solid (or occasionally liquid) surface by irradiating it with a laser beam. At low laser flux, the material is heated by the absorbed laser energy and evaporates or sublimes. 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 Gel permeation chromatography (GPC) is a separation technique based on hydrodynamic volume (size in solution). Molecules are separated from one another based on differences in molecular size. This technique is often used for polymer molecular weight determination. 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 spec·tro·scope n. An instrument for producing and observing spectra. spec  tro·scop 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 In statistics, the average amount a number varies from the average number in a series of numbers. (statistics) standard deviation - (SD) A measure of the range of values in a set of numbers. 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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