Direct-probe ToFMS

If we consider only a few of the general requirements for the ideal polymer/additive analysis techniques (e.g. no matrix interferences, quantitative), then it is obvious that the choice is much restricted. Elements of the ideal method might include LD and MS, with reference to CRMs. Laser desorption and REMPI-MS are moving closest to direct selective sampling tandem mass spectrometry is supreme in identification. Direct-probe MS may yield accurate masses and concentrations of the components contained in the polymeric material. Selective sample preparation, efficient separation, selective detection, mass spectrometry and chemometric deconvolution techniques are complementary rather than competitive techniques. For elemental analysis, LA-ICP-ToFMS scores high. 

State-of-the-art ToF-MS employs reflection lenses and delayed extraction [176] to improve resolution by minimising small differences in ion energies, and in these cases up to 12000 mass resolution (FWHM, m/z 600) is available. This is sufficient for most modern applications. Solid probe ToF-MS (or direct inlet high-resolution mass spectrometry, DI-HRMS) is a breakthrough. DIP-ToFMS is a thermal separation technique. Advantages of DIP-ToFMS are ... 

In direct insertion techniques, reproducibility is the main obstacle in developing a reliable analytical technique. One of the many variables to take into account is sample shape. A compact sample with minimal surface area is ideal [64]. Direct mass-spectrometric characterisation in the direct insertion probe is not very quantitative, and, even under optimised conditions, mass discrimination in the analysis of polydisperse polymers and specific oligomer discrimination may occur. For nonvolatile additives that do not evaporate up to 350 °C, direct quantitative analysis by thermal desorption is not possible (e.g. Hostanox 03, MW 794). Good quantitation is also prevented by contamination of the ion source by pyrolysis products of the polymeric matrix. For polymer-based calibration standards, the homogeneity of the samples is of great importance. Hyphenated techniques such as LC-ESI-ToFMS and LC-MALDI-ToFMS have been developed for polymer analyses in which the reliable quantitative features of LC are combined with the identification power and structure analysis of MS. 

DIP-ToFMS is theoretically another option for the separation of additives from polymer in dissolutions using a probe temperature ramp. However, the technique also allows direct handling of solid substrate material, which is even more convenient. The technique has profitably been used for the analysis of non-UV cured ink, revealing diluent, photo-initiator and polymer [54]. 

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