Journal of Analytical & Bioanalytical Techniques
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It?s quite often that there are small unknown peaks showing up between the polymer peak and the solvent peaks in a GPC
or SEC chromatogram. Those small peaks could be polymer oligomers, or polymer additives, or even the residues of the
catalyst system. But the common GPC/SEC detectors like RI, Lighter Scattering and Viscometer lack the capability for chemical
identification. In many cases, those small peaks are just ignored in molecular weight (MW) and molecular weight distribution
(MWD) measurement. The research effort and instrumentation advance to identify those small peaks are far behind those for
volatile analysis by GC-MS and polymer additive analysis by LC-MS.
But those small peaks are part of the polymers. If their chemical identification can be determined, it will be sure to help
to understand more of the polymer?s physicochemical properties, and the polymer ?leachables?, ?extractables?, and the ?xylene
This presentation will show how to setup the ?hybrid? instrument of a GPC/SEC system with the triple quadrupole mass
spectrometer from a readily available LC-MS/MS system, and how to modify the post-column mobile phase to make it suitable
to the MS/MS detector.
Our results show the GPC-MS/MS/DAD system is a very powerful tool to identify those small peaks. The MS spectra of
different ionization modes, negative and positive, along with the UV spectra will greatly narrow down the candidate list of the
small unknown peaks. With some MS interpretation experience and/or standard matching, many of those small peaks can be
identified without much difficulty.
Nasser M Al-Harbi is the Chromatography Technical Leader at SABIC Technology Center at Riyadh (STC-R). He completed his Ph.D. research in
the University of Manchester in 2011. He did more research for about two years in the Petrochemical Research Institute at King Abdulaziz City for
Science and Technology before he joined SABIC. He has been doing research on chromatography at STC-R for nine years. He is also serving as a
Board Member of the Saudi Arabia Chemical Society and the Technology Leader of the QAIF-05 Conference.
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