LD-FTMS

Sterically hindered phenols and other additives containing thioesters, phosphites, phosphonites and hindered amine moieties were analysed by FAB-MS and LD-FTMS. The laser desorption technique was preferred for analysis of polymer additives because of undesirable fragmentation from FAB experiments [93]. 

Kenion et al. [225] used LD FTMS for direct analysis of a discoloured adhesive. MALDI-FTICR-MS is a direct way of examining molecular weight distributions. FTMS is not yet widely being used for industrial problem solving, despite long-lasting expectations. Instead, FTICR-MS is the method of... 

Laser Desorption/FTMS. Laser desorption (LD)/FTMS [20] has been applied to a variety of chemical problems, ranging from fundamental studies of ion-molecule reactions [21,22], to the analysis of pharmaceuticals [4,23-29], to polymers [7,30-35], to organometallics [6-39], and to surface analysis [4,40], The large number of papers being generated from the few laboratories working... 

A simple example of the use of LD/FTMS for surface analysis may be found in the analysis of blue stain on the surface of a copper part. In order to determine the nature of the stain, we obtained LD/FTMS spectra for samples of both stained and unstained copper. Both samples were mounted on the automatically rotated sample insertion probe on the FTMS-2000. The samples were rotated after each laser shot to expose a fresh surface at the laser focus. Approximately twenty-five laser shots were signal averaged for each spectrum, in order to increase signal-to-noise, and to provide a spectrum which would represent the averaged composition of the surface. 

Laser desorption Fourier transform mass spectrometry (LD-FTMS) results from a series of peptides and polymers are presented. Successful production of molecular ions of peptides with masses up to 2000 amu is demonstrated. The amount of structurally useful fragmentation diminishes rapidly with increasing mass. Preliminary results of laser photodissociation experiments in an attempt to increase the available structural information are also presented. The synthetic biopolymer poly(phenylalanine) is used as a model for higher molecular weight peptides and produces ions approaching m/z 4000. Current instrument resolution limits are demonstrated utilizing a polyethylene-glycol) polymer, with unit mass resolution obtainable to almost 4000 amu. 

FAB-MS, due to their insolubility in the liquid matrix. Thus, LD-FTMS should be considered complementary to FAB-MS. 

Due to the relatively small number of laboratories equipped with LD-FTMS, the method is not as well known or as highly developed as FAB ionization which is now available for most commercial magnetic sector and quadrupole instruments. The pulsed nature of the lasers typically employed are ideally matched with mass spectrometers capable of simultaneous detection or rapid analysis. Thus FTMS or time of flight (TOF) instruments are best suited for LD applications. However, the latter possesses limited mass resolution. This chapter will attempt to present the current capabilities and limitations of LD-FTMS and to address its future potential. 

Peptides. One of the applications that has benefited most from the development of soft ionization methods for mass spectrometry has been the analysis of polar biological materials. Peptides, in particular, have been extensively studied by a variety of soft ionization methods, primarily FAB, with excellent results being obtained for peptides in the 1000-10000 dalton range. LD-FTMS also has proved to be very successful for analysis of simple peptides and an examination of these results should help delineate the analytical potential of LD-FTMS in this important area. 

Table I. Representative Peptides Successfully Examined by LD-FTMS...

The analytical applications of LD-FTMS have just begun to be developed. As more work is done, LD-FTMS will continue to be applied to analysis of difficult samples. It is a promising technique for stable samples such as polymers, organometallics and... 

For infrared laser desorption Fourier transform mass spectrometry (LD-FTMS), all den-drimer samples were prepared by dissolving ca. 1 mg of sample in CH2CI2, followed by deposition upon stainless steel probe tips by the aerosol spray technique described previously [37]. Dendrimer samples 4 and 5 were deposited directly onto a stainless steel probe tip. The sample 6 was prepared by first spraying 50 mL of a saturated silver nitrate/ethanol solution (containing ca. 3 mg of silver nitrate) onto the rotating probe tip, prior to dendrimer deposition. Samples were introduced into the vacuum system and the source cell pressure reduced to 2.2 X 10 Torr and the analyzer cell pressure to 2.0 x 10 Torr, before analysis. 

Laser-Desorption Fourier-Transform Mass Spectrometr (LD FTMS) was used by Rice and Weil... 

LD-FTMS Laser Desorption Fourier Transform Mass Spectrometry... 

Campana and co-workers wrote a general tutorial on polymer analysis providing an excellent introduction to LD-FTMS. 

It would be remiss not to discuss polymer additive analysis. Such materials are used as antioxidants, UV absorbers, and stabilizers, and dyes. An early paper dealt with LD-FTMS analysis of poly(methyl methacrylate) dyes such as 12-H-phthaloperine-12-one (orange dye), l-(methylamino)antiiraquinone (red dye), and l,8-bis(phenylthio)an raquinone. Hsu and Marshall ... 

It is clear that laser desorption Fourier transform mass spectrometry has significant potential as a polymer analysis tool. It works especially well for polar polymers and additives witii molecular weights lower than 10000 Da. AAftth proper attention to analytical details, it is a highly accurate and quite specific way to characterize tiiese substances and can provide unrivaled mass resolution. As is obvious from this chapter, the application of LD-FTMS to polymer analytical problems is an active area of investigation in many laboratories. AAftth the continuing proliferation of commercial FTMS instruments, LD-FTMS applications of polymer analysis should be expected to expand for the foreseeable future. There is no question tiiat tiiis method provides a versatile alternative to tire numerous less specific analytical methods employed to date. 

Determinations of MM in relatively low MM polymer samples (up to a mass limit of about 10,000 Da) have appeared in the last decades, by a number of soft ionization MS techniques as static SIMS-TOF, LD-FTMS, DCC FD, FAB, ESI. The ESl-TOF technique, which for proteins is capable of providing high MM measurements, in the case of synthetic polymers yields spectra only below 5000 Da, due to chain entanglement. ... 

Figure 1.13 Comparison of positive ion spectra of DLTDP acquired by (a) FAB, (b) CO2 LD-FTMS and (c) Nd YAG LD-FTMS Reproduced from Johlman and co-workers, American Chemical Society [63]...

Fig. 3.8. LD-FTMS spectmm of Oxypmf-20 (MW 1313.3). After Campana et al [183]. Reproduced by permission of...

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