SEC / MALDI-TOF

The earliest SEC/MALDl studies on MM determination were prompted from the finding ° that MM estimates derived from MALDI-TOF measurements are accurate only in the case of monodisperse polymers. The SEC fractionation of polydisperse polymers provided nearly monodisperse fractions, and MM measurements by MALDl on the samples collected could be used to calibrate the molar mass vs. retention volume in SEC plots. Thus, average MM of polydisperse polymers could be determined. At the same time, it was realized that the MALDl analysis of the frachons obtained in the SEC procedure allowed the idenhficahon of polymer end-groups as a funchon of the Both off-line and on-line SEC/MALDI-TOF... 

Gallet, G., Carroccio, S., Rizzarelli, P., Karlsson, S. (2002). Thermal degradation of poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer comparative study by SEC/NMR, SEC/MALDI-TOF-MS and SPME/GC-MS. Polymer, 43(4), 1081-1094. 

Combined SEC-MALDI. Mark-Houwinkr-Sakurada (MHS) Parameters As mentioned earlier, combination of the quantitatively reliable LC techniques with the identification power of MS was used to overcome the limitations inherent in the use of either LC or MS alone. In addition to ESI-MS/SEC, combined applications already mentioned, several approaches to SEC/ MALDI time-of-flight (TOF) MS coupling have also been reported [78-83]. In the case of polydisperse polymers, determination of molecular mass by SEC/MALDI-TOF involves the fractionation of the samples through an analytical SEC. Selected fractions are then analyzed by MALDI-TOF and the mass spectra of these nearly monodisperse samples allow the determination of the MWD moments. Montaudo et al. [81] have tested the reliability of the method for different polydisperse samples, such as poly(methylmethacrylate) (PMMA), poly(dimethylsiloxane) (PDMS), and copolyesters. 

Improvements in consistency of sample preparation have been achieved with a recent innovation involving the use of a robotic interface for polymer analysis using microscale SEC/MALDI-ToF MS [33, 71]. The MALDI matrix solution is coaxially added to the column effluent and spotted onto MALDI targets in a robotic interface. Each spot corresponded to a 10 second elution window from the SEC. 

MALDI-ToF-MS (Figure 5.15). The SEC based number and average molar masses and and the mass at peak maximum (M ) of a 1 1 polymer calculated from the conventional calibration are strongly overestimated with respect to those obtained by the SEC-MALDI-ToF-MS coupling technique. 

Determined by absolute calibration curve obtained by SEC/MALDI-ToF-MS Determined by SEC, calibration obtained with PEG standards Reproduced with permission from G. Gallet, B. Erlandsson, A-G. Albertsson and S. Karlsson, Polymer Degradation and Stability, 2002, 77, 55. 2002, Elsevier [46]... 

During the past decade, MALDI-TOF MS has proven to be an effective tool for the analysis of oligo- and polymeric mannoglucans (for extensive reviews see [222,223]). SEC/MALDI mass spectrometry was employed in the analysis of hemicelluloses isolated by microwave heat-fractionation from spruce and aspen wood [94]. These methods allowed the separation and characterization of the oligo- and polysaccharide fractions derived from the xylan and mannan components of both woods [224]. 

GPC/SEC, MALDI-MS, membrane osmometry, vapour pressure osmometry, viscometry, light scattering, TDFRS, SAXS, SANS, SEC-HPLC, SEC-MS, SEC-IR, FFF, ultracentrifugation, MALDI-TOF-MS, NMR, capillary electrophoresis... 

Figure 31 MALDI-ToF mass spectrum of a SEC fraction (fraction 43, see Figure 30) from a PC sample oxidised at 300°C. Reprinted from Montaudo et al. [84]. Copyright 2002, with permission from Elsevier.

Liquid chromatography (LC) encompasses several techniques, which includes HPLC and SEC (sometimes referred to as GPC). Many variants of and developments from these techniques exist, and are used in the study and analysis of polymer degradation/oxidation. As discussed earlier, SEC is often coupled with MALDI-ToF-MS to facilitate the identification of the products of polymer degradation. SEC has also been coupled with mid-infrared detection and similarly used for studies of polymer degradation. SEC/GPC is discussed further below. 

Furthermore, size-exclusion chromatography (SEC) analyses generally reveal a bimodal distribution of molecular weights of the copolymers. Concomitantly, MALDI-ToF mass spectral measurements exhibit two sets of peaks corresponding to copolymer end groups of -OH and -X. For example, utilizing a (salen)CrCl/bis (triphenylphosphme)iminium chloride ([PPNjCl) catalyst for the copolymerization of cyclohexene oxide and carbon dioxide, the two copolymers illustrated in Fig. 6 were observed [26]. 

Figure 6 MALDI-Tof mass spectrum. A protein spot separated from rat serum by SP chromatography (indicated by arrow in Fig. 5, fraction II) was digested with trypsin as described in Sec. Ill and analyzed by MALDI-Tof mass spectrometry (TofSpec-E, Micromass). Ions generated as a result of autocatalytic cleavage of trypsin and two internal standards, angiotensin I and adrenocorticotrophic hormone, are indicated.

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