Laser desorption - Fourier transform techniques

These relatively new techniques viz laser desorption/ionization Fourier transform mass spectrometry and fast atom bombardment and laser desorption Fourier transform ion cyclotron resonance mass spectrometry have been applied to the determination of non volatile polymer additives (thioester, phosphite, phosphonate and hindered amine antioxidant types) and antioxidants, ultraviolet absorbers and amide waxes. 

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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. 

A relatively unknown technique (laser desorption fourier transform ion cyclotron resonance mass spectroscopy) has been used (397) to identify dyes in plastics such as polymethylmethacrylate. A detection limit of 0.1% was obtained, which compared with a limit of 1-2% using an ATR infrared spectroscopy technique. 

Laser desorption Fourier transform ion cyclotron resonance spectrometry. Laser desorption FTICR-MS looks very promising for the analysis of high ethoxylates, but this technique is still the province of research universities. It has been demonstrated for determination of oligomer distribution of OPE of average degree of ethoxylation of 59 (74). 

Another exciting possibility for high sensitivity molecular surface mass spectrometry is the use of laser-excited ion desorption in a pulsed ion cyclotron resonance experiment using Fourier transform techniques. In an ideal situation, this scheme could include all those attributes which are desirable for solid-surface molecular characterization ... 

After focusing the accelerating potential (V) is applied for a much shorter period than that used for ion production ca 100 nsec) so that all the ions in the source are accelerated almost simultaneously. The ions then pass through the third electrode into the drift zone and are then collected by the sensor electrode. The velocity of the ions after acceleration will be inversely proportional to the square root of the ion mass. With modern ion optics and Fourier transform techniques Erickson et al. (6) could sum twenty spectra per second for subsequent Fourier transform analysis. The advantage of the time of flight mass spectrometer lies in the fact that it is directly and simply compatible with direct desorption from a surface, and thus can be employed with laser desorption and plasma desorption techniques. 

Using a matrix-assisted laser desorption/ionisation (MALDI) technique with an ion-source Fourier transform (FT) mass spectrometer, van Rooji and co-workers [25] carried out high-resolution end-group analysis of polyethylene glycols (PEG). 

The laser desorption experiments which we describe here utilize pulsed laser radiation, which is partially absorbed by the metal substrate, to generate a temperature jump in the surface region of the sample. The neutral species desorbed are ionized and detected by Fourier transform mass spectrometry (FTMS). This technique has... 

Alternative approaches consist in heat extraction by means of thermal analysis, thermal volatilisation and (laser) desorption techniques, or pyrolysis. In most cases mass spectrometric detection modes are used. Early MS work has focused on thermal desorption of the additives from the bulk polymer, followed by electron impact ionisation (El) [98,100], Cl [100,107] and field ionisation (FI) [100]. These methods are limited in that the polymer additives must be both stable and volatile at the higher temperatures, which is not always the case since many additives are thermally labile. More recently, soft ionisation methods have been applied to the analysis of additives from bulk polymeric material. These ionisation methods include FAB [100] and LD [97,108], which may provide qualitative information with minimal sample pretreatment. A comparison with FAB [97] has shown that LD Fourier transform ion cyclotron resonance (LD-FTTCR) is superior for polymer additive identification by giving less molecular ion fragmentation. While PyGC-MS is a much-used tool for the analysis of rubber compounds (both for the characterisation of the polymer and additives), as shown in Section 2.2, its usefulness for the in situ in-polymer additive analysis is equally acknowledged. 

Laser desorption methods (such as LD-ITMS) are indicated as cost-saving real-time techniques for the near future. In a single laser shot, the LDI technique coupled with Fourier-transform mass spectrometry (FTMS) can provide detailed chemical information on the polymeric molecular structure, and is a tool for direct determination of additives and contaminants in polymers. This offers new analytical capabilities to solve problems in research, development, engineering, production, technical support, competitor product analysis, and defect analysis. Laser desorption techniques are limited to surface analysis and do not allow quantitation, but exhibit superior analyte selectivity. 

In 1974, Comarisov and Marshall60 developed Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). This technique allows mass spectrometric measurements at ultrahigh mass resolution (R = 100000-1000000), which is higher than that of any other type of mass spectrometer and has the highest mass accuracy at attomole detection limits. FTICR-MS is applied today together with soft ionization techniques, such as nano ESI (electrospray ionization) or MALDI (matrix assisted laser/desorption ionization) sources. 

Technological advances of ion-trap mass spectrometers are the ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and the recently released technique, the Orbitrap Fourier transform mass spectrometry (Hu et al., 2005), which enable the determination of molecular formulae with a high mass resolution and mass accuracy in mixtures. Today these ion-trap mass spectrometers are most frequently coupled with atmospheric pressure ionization (API) techniques such as electrospray ionization (ESI) (e.g., Fievre et al., 1997 Qian et al., 2001 Kujawinski et al., 2002 Llewelyn et al., 2002 Stenson et al., 2002,2003 Fard et al., 2003) or matrix-assisted laser desorption/ionization (MALDI) (e.g., Solouki et al.,... 

The technique of laser desorption (LD) has been widely used in mass spectrometry (J, 2) to desorb and to ionize high molecular weight or other nonvolatile samples, most often using time-of-flight (3. 4 ) or Fourier transform ion cyclotron resonance (FTICR) ( 5. 6 ) mass spectrometers for mass analysis. In this technique, highly focussed laser irradiation, most often with a power density of at least 10° W/cm, is used to desorb and ionize a solid sample that has been inserted into the high vacuum system of the mass spectrometer. 

Several ionization methods have been applied for CE-MS couphng. Matrix-assisted laser desorption ionization (MALDI), continuous flow fast atom bombardment (FAB), laser vaporization ionization with UV laser, sonic spray ionization and electrospray ionization (ESI) have all been used for coupling CE to MS. However, ESI is now undoubtedly the most widely used ionization technique, employing numerous analyzers including quadrupoles, magnetic sector, Fourier transform ion cyclotron resonance, time-offlight and trapping devices. However, quad-rupole detectors have predominantly been applied in CE-MS [6-8]. 

The following techniques for the characterization of supported vanadia catalysts and vanadia will briefly reviewed temperature programmed reduction (TPR) [26, 30], oxidation (TPO) [30] and desorption (TPD) [33, 36, 41, 44] laser Raman spectroscopy (LSR) [5, 25, 35, 36, 39, 44] Fourier-transform infrared spectroscopy... 

There are a number of techniques that can be used in the field. These include electrochemical sensors for gases such as O2 and SO2 and diffusive samplers containing immobilized reagents that produce a visible color change with visual detection on exposure to a specific chemical. Passive diffusion tubes can also be used for analyte preconcentration. Subsequent laboratory analysis is usually undertaken by thermal desorption coupled with GC. This approach is particularly useful for trace organic compounds such as polyaromatic hydrocarbons (PAHs) and VOCs. Spec-trometric techniques such as Fourier transform infrared (FTIR) spectrometry, correlation spectrometry, and the laser based LIDAR (light detection... 

In the last decade there has been a fast progress in the field of mass spectrometry employing soft ionization techniques such as electrospray ionization mass spectrometry (ESI-MS), Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), and matrix-assisted laser desorption ionization mass spectrometry (MALDI)-MS. These tools provide molecular level information on humic substances. 

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