Analog mass spectrometry

A somewhat related technique is that of laser ionization mass spectrometry (LIMS), also known as LIMA and LAMMA, where a single pulsed laser beam ablates material and simultaneously causes some ionization, analogous to samples beyond the outer surface and therefore is more of a bulk analysis technique it also has severe quantiBaction problems, often even more extreme than for SIMS. 

Wingerath, T. et al. (1999). Analysis of cyclic and acyclic analogs of retinol, retinoic acid, and retinal by laser desorption ionization-, matrix-assisted laser desorption ionization-mass spectrometry, and UV/Vis. spectroscopy. Anal. Biochem. 272(2) 232-242. 

Continuous distribution functions Some experiments, such as liquid chromatography or mass spectrometry, allow for the determination of continuous or quasi-continuous distribution functions, which are readily obtained by a transition from the discrete property variable X to the continuous variable X and the replacement of the discrete statistical weights g, by the continuous probability density g(X). For simplicity, we assume g(X) as being normalized J ° g(X)dX = 1. Averages and moments of a quantity Y(X) are defined by analogy to the discrete case as... 

In this section the technique of PMM, using MALDI-TOF mass spectrometry, is described in detail. This method has been used both for model samples as well as for mortars and painting fragments (Section 6.4). It should be emphasised that the samples could be treated analogically if a different mass spectrometric technique was used. 

The investigations directed at the synthesis of thymine-substituted polymers demonstrate that the type of functional groups displayed by nucleic acid bases are compatible with ROMP. Moreover, the application of MALDI-TOF mass spectrometry to the analysis of these polymers adds to the battery of tools available for the characterization of ROMP and its products. The utility of this approach for the creation of molecules with the desired biological properties, however, is still undetermined. It is unknown whether these thymine-substituted polymers can hybridize with nucleic acids. Moreover, ROMP does not provide a simple solution to the controlled synthesis of materials that display specific sequences composed of all five common nucleic acid bases. Nevertheless, the demonstration that metathesis reactions can be conducted with such substrates suggests that perhaps neobiopolymers that function as nucleic acid analogs can be synthesized by such processes. 

Tandem mass spectrometry has been used to demonstrate that M+ as well as MH+ of substituted A-(ort/zo-cyclopropylphenyl)benzamides isomerizes before the fragmentation, with formation of 3-aryl-1-ethyl-lH-benzoxazines and 5-ethyl-2-oxodi-benzoazepines (Scheme 5.14). The methyl group in /V-[ortho-( 1 -methylcvclopropyl )-phenyl]benzamides quenches the latter process, leaving the formation of benzoxazines as the only cyclization reaction. A subsequent chemical experiment in solution confirmed the mass spectral predictions [24]. A similar study confirmed the analogy of cyclization of substituted A-(ort/zo-cyclopropylphenyl)-A -aryl ureas and N- ortho-cyclopropylphenyl)-A -aiyl thioureas in the ion source of mass a spectrometer and in solution [25]. 

Perhaps the most mechanically complex solution ever developed for uniting HPLC with mass spectrometry was the moving belt interface [54]. The heart of this system was a mechanically driven continuous belt (analogous to an escalator or moving walkway) to which the HPLC eluent was applied. The majority of the mobile phase was evaporated by a heat source (ideally hot enough to vaporize the solvents but not to... 

On studying the KDO content of LPS from Xanthomonas sinensis, Volk and coworkers64 found that only one KDO residue per LPS chain is present in this organism. Moreover, the authors observed the formation of 4,7- and 4,8-anhydro derivatives (39 and 40) of KDO (see Scheme 14) under the conditions used for mild hydrolysis of the LPS with acetic acid. Free KDO was also shown to yield the anhydro derivatives under analogous conditions. The structures of these unusual side-products were identified by mass spectrometry, as follows. Reduction of 39 and 40 with sodium borohydride gave the two epimeric mixtu.es, 41 and 42. These were subjected to periodate treatment followed by borohydride reduction, the products separated by paper electrophoresis, and their trimethylsilyl ether derivatives analyzed by... 

---