High-molecular-mass molecules

This method, introduced by Beckey [79], has been successfully utilized by different groups studying high-molecular-mass molecules which are difficult to volatilize. A number of reviews exists [80-82], including Schulten s most recent one [83]. 

As indicated in the review by Daves [81], there are numerous methods of desorption from surfaces, leading to the vaporization of fragile, high-molecular-mass molecules. 

For polymers and other high molecular mass molecules, T can be very short, in the range 10 to I s. For organic molecules with molecular ma,sses < 1000, values for proton-bonded carbons lie typically in the range 0.1-10 s, and for nonproton-bonded carbons, 10- 300 s. 

For compounds of high molecular mass, however, the formation of derivatives does not help to solve the problem of in volatility. This difficulty may be overcome by breaking the large molecules up into smaller and more volatile fragments which may then be analysed by gas-liquid chromatography, i.e. by using the technique known as pyrolysis gas chromatography (PGC). 

MALDI shares many features with FAB in that it employs a matrix which transfers energy to an analyte molecule to facilitate the ionization of polar and thermally labile, high-molecular-weight molecules. In this case, however, the energy is provided by a pulsed laser at a wavelength which may be absorbed by a matrix material such as nicotinic or sinapinic acids. The ability to obtain mass... 

The corresponding liquid-phase chemistry can be used to promote ion formation by appropriate choice of solvent and pH, salt addition to form M.Na+ or M.NH4+, and postcolumn addition of reagents. The primary applications of ESI-MS are in the biopolymer field. The phenomenon of routine multiple charging is exclusive to electrospray, which makes it a very valuable technique in the fine chemical and biochemical field, because mass spectrometers can analyse high-molecular-mass samples without any need to extend their mass range, and without any loss of sensitivity. However, with ESI, molecules are not always produced with a distribution of charge states [137], Nevertheless, this phenomenon somehow complicates the determination of the true mass of the unknown. With conventional low-resolution mass spectrometers, the true mass of the macromolecule is determined by an indirect and iterative computational method. 

Lasers have advanced the analytical use of mass spectrometers to characterise additives in polymers, and routine application of MALDI is no longer limited to high molecular masses only. MALDI can now clearly produce isotopically resolved mass spectra of small molecules (<800 Da) in an L-ToF instrument, which can be used successfully for the characterisation of molecules of different chemical classes. High mass resolution with an improvement of mass accuracy to... 

Van der Waals forces depend upon the electron density of the atoms. Increasing number of atoms in a molecule increases the van der Waals attractive force. Since the electron number of a neutral atom is equal to its proton number, atoms which have a large proton number have strong van der Waals forces between their molecules. Therefore, van der Waals forces are stronger between molecules with high molecular masses. 

This type of polymerisation generally involves a repetitive condensation reaction between two bt-functtonal monomers. These polycondensatton reacttons may resutt In the toss of some simple molecules as water, alcohol, etc., and lead to the formation of high molecular mass condensation polymers. 

Without doubt, electrospray is the method of choice in the case of CE/ MS hyphenation. The domain of ESI is polar compounds of a wide molecular-weight range, such as the typical CE analytes. Molecules can be transferred directly from the separation capillary to the mass spectrometer via an interface. This allows the detection of multiply chargeable species of high molecular mass. 

In the processing of plastic masses the destruction is traditionally considered as a negative factor deteriorating physical and mechanical properties of products and manufacturers try to avoid it in every possible way. Mechanical destruction of molten polymers takes place, primarily, under the action of shear strains effectuating the tension of macromolecules 65-661 in this case, molecules with a high molecular mass... 

---