Mass spectrometry Ionisation

A. G. Harrison, Chemical Ionisation Mass Spectrometry, CRC Press, Boca Raton, Fla., 1983. 

For off-bead analysis, coupling between chromatographic separation and mass spectrometric detection has proven especially powerful. The combination between high performance liquid chromatography (HPLC) and electrospray ionisation mass spectrometry has the advantage that purity of product mixtures can be coupled on-line with the product identification. 

FI-MS, FIMS Field ionisation mass spectrometry spectrometry... 

The technique is referred to by several acronyms including LAMMA (Laser Microprobe Mass Analysis), LIMA (Laser Ionisation Mass Analysis), and LIMS (Laser Ionisation Mass Spectrometry). It provides a sensitive elemental and/or molecular detection capability which can be used for materials such as semiconductor devices, integrated optical components, alloys, ceramic composites as well as biological materials. The unique microanalytical capabilities that the technique provides in comparison with SIMS, AES and EPMA are that it provides a rapid, sensitive, elemental survey microanalysis, that it is able to analyse electrically insulating materials and that it has the potential for providing molecular or chemical bonding information from the analytical volume. 

Crawford, E., Dyson, P., Forest, O., Kwok, S. Mclndoe, J. S. Energy-dependent Electrospray Ionisation Mass Spectrometry of Carbonyl Clusters. 

Experimental considerations Sample preparation and data evaluation are similar to membrane osmometry. Since there is no lower cut-off as in membrane osmometry, the method is very sensitive to low molar mass impurities like residual solvent and monomers. As a consequence, the method is more suitable for oligomers and short polymers with molar masses up to (M)n 50kg/mol. Today, vapour pressure osmometry faces strong competition from mass spectrometry techniques such as matrix-assisted laser desorption ionisation mass spectrometry (MALDI-MS) [20,21]. Nevertheless, vapour pressure osmometry still has advantages in cases where fragmentation issues or molar mass-dependent desorption and ionization probabilities come into play. 

Olah, T. V., McLoughlin, D. A., Gilbert, J. D., The simultaneous determination of mixtures of drug candidates by liquid chromatography/ atmospheric pressure chemical ionisation mass spectrometry as an in-vivo drug screening procedure, Rapid Commun. Mass Spec. 1997, 11, 17—23. 

Stintzing F C, Schieber A and Carle R (2002), Identification of betalains from yellow beet (Beta vulgaris L.) and cactus pear (Opuntia ficus-indica (L.) Mill.) by high-performance liquid chromatography - electrospray ionisation mass spectrometry , J Agric Food Chem, 50, 2302-2307. 

M.P. Colombini, F. Modugno, E. Ribechini, Chemical study of triterpenoid resinous materials in archaeological findings by means of direct exposure electron ionisation mass spectrometry and gas chromatography/mass spectrometry, Rapid Communications in Mass Spectrometry, 20, 1787 1800 (2006). 

E. Rihechini, F. Modugno and M. P. Colomhini, Direct Exposure (chemical ionisation) Mass Spectrometry for a rapid characterization of raw and archaeological diterpenoid resinous materials, Microchim. Acta, 162, 405 413 (2008). 

Mass spectrometry is used to identify unknown compounds by means of their fragmentation pattern after electron impact. This pattern provides structural information. Mixtures of compounds must be separated by chromatography beforehand, e.g. gas chromatography/mass spectrometry (GC-MS) because fragments of different compounds may be superposed, thus making spectral interpretation complicated or impossible. To obtain complementary information about complex mixtures as a whole, it may be advantageous to have only one peak for each compound that corresponds to its molecular mass ([M]+). Even for thermally labile, nonvolatile compounds, this can be achieved by so-called soft desorption/ionisation techniques that evaporate and ionise the analytes without fragmentation, e.g. matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS). 

Besides the well-established chromatographic/mass spectrometric or spectroscopic methods there is always a need for complementary methods for the study of organic materials from art objects. The application of laser desorption/ionisation mass spectrometry (LDI-MS) methods to such materials has been reported only sporadically [12, 45 48] however, it is apparently increasing in importance. After GALDI-MS had been applied to triterpenoid resins, as described in Section 5.2, this relatively simple method was evaluated for a wider range of binders and other organic substances used for the production or conservation of artwork. Reference substances as well as original samples from works of art were analysed. 

J.J. Boon, and T. Learner, Analytical Mass Spectrometry of Artists Acrylic Emulsion Paints by Direct Temperature Resolved Mass Spectrometry and Laser Desorption Ionisation Mass Spectrometry, J. Anal. Appl. Pyrol., 64, 327 344 (2002). 

Microprobe laser desorption laser ionisation mass spectrometry (/xL2MS) is used to provide spatial resolution and identification of organic molecules across a meteorite sample. Tracking the chemical composition across the surface of the meteorite requires a full mass spectrum to be measured every 10 p,m across the surface. The molecules must be desorbed from the surface with minimal disruption to their chemical structure to prevent fragmentation so that the mass spectrum consists principally of parent ions. Ideally, the conventional electron bombardment ionisation technique can be replaced with an ionisation that is selective to the carbonaceous species of interest to simplify the mass spectrum. Most information will be obtained if small samples are used so that sensitivity levels should be lower than attomolar (10—18 M) fewer than 1000 molecules can be detected and above all it must be certain that the molecules came from the sample and are not introduced by the instrument itself. 

Vallejo F, Tomas-Barberan FA and Ferreres F. 2004. Characterisation of flavonols in broccoli (Brassica oleracea L. var. italica) by liquid chromatography-UV diode-array detection-electrospray ionisation mass spectrometry. J Chromatogr A 1054(1—2) 181—193. 

Amao MB, Cano A, Alcolea JF and Acosta M. 2001b. Identification of hydrolysable tannins in the reaction zone of Eucalyptus nitens wood by high performance liquid chromatography-electrospray ionisation mass spectrometry. Phytochem Anal 12(2) 120—127. 

Flegal and Stokes [59] have described a sample processing technique necessary for avoiding lead contamination of seawater samples prior to lead stable isotope measurements by thermal ionisation mass spectrometry. Levels down to 0.02 ng/kg were determined. 

Flegal and Stukas [406] described the special sampling and processing techniques necessary for the prevention of lead contamination of seawater samples, prior to stable lead isotopic ratio measurements by thermal ionisation mass spectrometry. Techniques are also required to compensate for the absence of an internal standard and the presence of refractory organic compounds. The precision of the analyses is 0.1 -0.4% and a detection limit of 0.02 ng/kg allows the tracing of lead inputs and biogeochemical cycles. 

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