Polymers MALDI

On the other hand, for broad-MMD polymer, MALDI underestimates both Mn and Mw [4-6]. This problem is usually called mass discrimination [4-6]. Many... 

Next to electrospray ionization (Ch. 6.3), MALDI is the most important ionization technique in the MS analysis of biomacromolecnles. MALDI was introduced by Tanaka et al. [12] and Karas and Hillenkamp in 1988 [13], Today, MALDI plays an important role in the characterization of proteins, oligonncleotides, sugars, and synthetic polymers. MALDI-time-of-flight MS is an essential tool in the current proteomics research (Ch. 18.2). 

An outstanding quaHty of polymer MALDI is that it offers the possibiUty of measuring molar masses. Very accurate values can be obtained for oligomers with molar masses up to several thousand gmoh, but the determination of much higher molar masses is difficult. Nevertheless, the successful analysis of a polystyrene sample of molar mass 1.5x 10 g moT has been claimed [78]. Typical MALDI mass spectra of high molar mass polystyrene samples are shown in Fig. 9.9. 

Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry of Polymers (MALDI-MS)... 

Recent studies have shown that MALDl-MS is a useful method to analyze pyrolysis products from polar polymers. MALDI has been used to examine pyrolyzates from poly(bisphenol-A carbonate), segmented polyurethane, PEG, poly(tetrahydrofuran) (PTHF), and poly(propylene glycol). MALDI-MS was foxmd to have advantage because, with respect to traditional mass spectral techniques such as GC/MS (Chapter 4) and DPMS (Chapter 5), pyrolyzates with much higher MM can be studied. Further development has recently resulted from comparing DPMS and MALDI-TOF in the study of the thermal degradation processes of polymers. ... 

Hanton, S.D. and Owens, K.G. (2005) Using M ESIMS to analyze polymer MALDI matrix solubility./. Am. Soc. Mass Spectrom., 16,1172-1180. 

Matrix assisted laser desorption ionization (MALDI) is a frequently used ionization technique, but it is rarely used as an online detector. The sample stream is appUed to a target plate, and it is allowed to cocrystallize with the matrix, which is subsequently desorbed, ionized with a lasCT, and analyzed in the MS. MALDI/TOF has been successfully used to determine molecular weight distributions of fractions collected after thermal FFF separation of polydis-pCTse polymers. MALDI is a good ion source, due to the soft ionization with high effrciency and simple mass spectra, even for heavier molecules, since the m ority carry only a single charge. 

Hilker, B., Clifford, K.J., Sauter, A.D. Jr., Sauter, A.D. Ill, Gauthier, T, Harmon, J.P. (2009) Electric field enhanced sample preparation for synthetic polymer MALDI-TOF mass spectrometry via induction based fluidics (IBF). Polymer, 50,1015-1024. 

Two relatively new techniques, matrix assisted laser desorption ionization-lime of flight mass spectrometry (MALDI-TOF) and electrospray ionization (FS1), offer new possibilities for analysis of polymers with molecular weights in the tens of thousands. PS molecular weights as high as 1.5 million have been determined by MALDI-TOF. Recent reviews on the application of these techniques to synthetic polymers include those by Ilantoif54 and Nielen.555 The methods have been much used to provide evidence for initiation and termination mechanisms in various forms of living and controlled radical polymerization.550 Some examples of the application of MALDI-TOF and ESI in end group determination are provided in Table 3.12. The table is not intended to be a comprehensive survey. 

Table 3.12 Application of MALDI-TOF or ESI Mass Spectrometry to Polymers Prepared by Radical Polymerization...

The effects of the feed ratio in the lipase CA-catalyzed polymerization of adipic acid and 1,6-hexanediol were examined by using NMR and MALDI-TOF mass spectroscopies. NMR analysis showed that the hydroxyl terminated product was preferentially formed at the early stage of the polymerization in the stoichiometric substrates. As the reaction proceeded, the carboxyl-terminated product was mainly formed. Even in the use of an excess of the dicarboxylic acid monomer, the hydroxy-terminated polymer was predominantly formed at the early reaction stage, which is a specific polymerization behavior due to the unique enzyme catalysis. 

The mass spectrometer is a mass-flow sensitive device, which means that the signal is proportional to the mass flow dm/dl of the analyte, i.e. the concentration times the flow-rate. It is only now possible to realise the high (theoretically unlimited) mass range and the high-sensitivity multichannel recording capabilities that were anticipated many years ago. Of considerable interest to the problem of polymer/additive deformulation are some of the latest developments in mass spectrometry, namely atmospheric pressure ionisation (API), and the revival of time-of-flight spectrometers (allowing GC-ToFMS, MALDI-ToFMS, etc.). 

Matrix-assisted laser desorption ionisation (MALDI) MH+ (M - H) ToF, IT, FTMS Polar and some nonpolar biopolymers, synthetic polymers >250000... 

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. 

Direct solid-state polymer/additive mass analysis has involved various ionisation modes El (Section 6.2.1), Cl (Section 6.2.2), DCI (Section 6.2.2.1), FAB (Section 6.2.4), FI (Section 6.2.5), FD (Section 6.2.6) and LD. Survey mass spectra obtained with soft ionisation methods (FI-MS, CI-MS) provide diagnostic overviews of chemical composition. The supplemental tandem (MS/MS) and atomic composition (AC-MS) techniques are used to make specific identifications of various organic ingredients. Direct analysis of polymer systems for more than a few thousand daltons has only just begun. Ionisation methods employed are FD, ESI and MALDI. Solid-probe ToF-MS (or DI-HRMS) is a breakthrough [188]. 

---