Plasma desorption mass spectrometry PDMS

Thus as a starting point for understanding the bombardment process we have developed a classical dynamics procedure to model the motion of atomic nuclei. The predictions of the classical model for the observables can be compared to the data from sputtering, spectrometry (SIMS), fast atom bombardment mass spectrometry (FABMS), and plasma desorption mass spectrometry (PDMS) experiments. In the circumstances where there is favorable agreement between the results from the classical model and experimental data It can be concluded that collision cascades are Important. The classical model then can be used to look at the microscopic processes which are not accessible from experiments In order to give us further insight into the ejection mechanisms. 

Plasma-desorption mass spectrometry (PDMS) also allowed location of the acyl functions. Thus, 252Cf-PDMS of LOS V in M. kansasii gave27 molecular-weight-associated ions at mlz 2499. The major acylating function of the intact LOS was determined to be a 2,4-dimethyltetradecanoate. Addition of three of these fatty acyl residues to the oligosaccharide portion gave a mass of 2476 daltons. Thus, the ion at mlz 2499 must be equivalent to [M + Na]+, and therefore LOS V must be a tri-O-acyl-undecasaccharide. However, exact location of the acyl functions was not obtained in this way. 

Plasma desorption mass spectrometry (PDMS) has been used for the characterization of macrocycles and their complexes. PDMS seems to be able to produce molecular ions reliably giving a semiquantitative picture of the compounds with very minimal fragmentation. PDMS has been used to compare the binding of various metal ions to individual hosts <92JOC6403,92TL3035>,... 

Another early desorption technique is that of plasma desorption mass spectrometry (PDMS). The sample is deposited onto a thin aluminum or aluminized polyester foil (0.5-1 pm in thickness) and placed just in front of a californium-252 emitter which is located in a time-of-flight (TOF) mass spectrometer (Figure 7). Californium is an a-emitter that decays into two highly energetic a-particles that are expelled in diametrically opposite directions. One of these particles collides with and ionizes the sample while the other hits a collection plate and triggers the timing circuit for the TOF mass spectrometer. 

One of the major problems in analytical chemistry is the detection and identification of non-volatile compounds at low concentration levels. Mass spectrometry is widely used in the analysis of such compounds, providing an exact mass, and hence species identification. However, successful and unequivocal identification, and quantitative detection, relies on volatilization of the compound into the gas phase prior to injection into the analyser. This constimtes a major problem for thermally labile samples, as they rapidly decompose upon heating. In order to circumvent this difficulty, a wide range of techniques have been developed and applied to the analysis of nonvolatile species, including fast atom bombardment (FAB), field desorption (FD), laser desorption (LD), plasma desorption mass spectrometry (PDMS) and secondary-ion mass spectrometry (SIMS). Separating the steps of desorption and ionization can provide an important advantage, as it allows both processes to be... 

Field desorption (ED) Multiphoton ionization (MPI) Fast atom bombardment (FAB) Plasma desorption mass spectrometry (PDMS)... 

Much of the current interest in time-of-flight mass spectrometers is driven by instruments which desorb nonvolatile molecules (particularly peptides and other biological molecules) from surfaces. These methods include plasma desorption mass spectrometry (PDMS), laser desorption (LD), and matrix-assisted laser desorp-tion/ionization (MALDI), and they greatly simplify the design of time-of-flight mass spectrometers, since they effectively eliminate both the time- and spatial-distribution problems. 

We reported earlier (Ddmemann and Senger, 1982) a molecular mass increase of 51-55 units for Chl/RC I ccnpared to Chi a. By repeated experiments it could be shown that Chi RC I did not contain water, but that only Chi a under the conditions of plasma desorption mass spectrometry (PDMS) undergoes the addition of a 15 mass unit breakdown product with an M -ion of 909 units. 

Several mass spectrometric techniques including fast atom bombardment (FAB), plasma desorption (PD), matrix-assisted laser desorption/ionization (MALDI), and electrospray (ES) mass spectrometry (MS) are presently available for the analysis of peptides and proteins (Roepstorff and Richter, 1992). Of these techniques, mainly PDMS has gained footing in protein laboratories because the instrumentation is relatively cheap and simple to operate and because, taking advantage of a nitrocellulose matrix, it is compatible with most procedures in protein chemistry (Cotter, 1988 Roepstorff, 1989). Provided that the proper care is taken in the sample preparation procedure most peptides and small proteins (up to 10 kDa) are on a routine basis amenable to analysis by PDMS. Molecular mass information can be obtained with an accuracy of 0.1% or better. Structural information can be gained by application of successive biochemical or chemical procedures to the sample. 

---