SELECTIVE IN-SITU DETECTION OF POLYMER ADDITIVES USING LASER MASS-SPECTROMETRY

A series of polymer additives, including phenolic antioxidants and UV (Tinuvin) stabilizers, have been analyzed using two-step laser desorpt ion/laser photoionization time-of-flight mass spectrometry (L2MS). A p ulsed CO2 laser was used to desorb the additives as neutral species in to the gas phase, where they were postionized using a second UV laser operating at either 266 or 193 mn, For all the antioxidants studied, t he 266 nm photoionization mass spectra are dominated by the molecular ion peak; very-little fragmentation is observed, In contrast, at 193 m n, the molecular ion peak is usually absent from the photoionization m ass spectra, Similar behavior is exhibited by the UV (Tinuvin) stabili zers in their photoionization mass spectra, This wavelength-dependent fragmentation can be exploited for unambiguous identification of many polymer additives, For example, it is shown that the isomeric UV stabi lizers Tinuvin 320, Tinuvin 343, and Tinuvin 329 can be differentiated on the basis of the extent or nature of the observed fragmentation in their photoionization mass spectra, Several commercial polymer formul ations containing these types of additives have also been analyzed usi ng this experimental approach: the samples were interrogated directly without any pretreatment or extraction, It is shown that UV laser post ionization enables selective defection of the additives in preference to the polymer, providing unambiguous in situ identification. The pote ntial of this technique for surface analysis and depth profiling is al so discussed,