Radiant energy – Ionic separation or analysis – With sample supply means
Patent
1992-02-20
1993-11-09
Dzierzynski, Paul M.
Radiant energy
Ionic separation or analysis
With sample supply means
250282, H01J 4404
Patent
active
052605710
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method of preparing a sample for analysis, and particularly a sample for analysis by Laser Desorption Mass Spectrometry (LDMS) in which ions are sputtered from a condensed phase sample surface by photon bombardment and are then subjected to mass analysis.
BACKGROUND OF THE INVENTION
Many methods of LDMS are known, and a feature common to many is the use of a matrix material in which the analyte (the sample material to be analysed) is dispersed. The matrix material can serve one or more of a plurality of functions. For example it may act as a mediator in transferring energy from the photon bombardment to the sample material molecules; it may provide a physical and chemical environment which enhances the probability of desorption in the desired state of charge and aggregation; and it may remove excess energy from the desorbed species through evaporation of matrix material molecules from a desorbed cluster of sample material and matrix material ions.
Four techniques for using a matrix material to enhance LDMS have been described as set out below.
The first is to dissolve the sample material together with a 10:1 excess of an inorganic salt in a solvent, place a drop of the solution on the target surface, and evaporate to dryness as described by D. V. Davis et. al. in Analytical Chemistry, 55 1302 (1983). The sample material deposit is then irradiated with infra-red photons from a pulsed Neodymium YAG laser.
The second is to mix equimolar amounts of sample material and an inorganic salt in a droplet of glycerol placed on the target surface as described by L. G. Wright et. al. in Biomedical Mass Spectrometry, 12, 159 (1985). The sample mixture is then irradiated with infra-red photons from a continuous wave carbon dioxide laser.
Thirdly, Japanese Patent Specification JP62-43562 discloses a sample preparation technique in which a solution of the sample material is mixed with a slurry of glycerol and fine cobalt powder. A droplet of the mixture is then irradiated with ultraviolet photons from a pulsed nitrogen laser.
Fourthly, M. Karas et. al. (Int. J. Mass Spectrom. Ion Processes, 78, 53 (1987)) describe using a large molar excess of a matrix material which has a strong absorption at the wavelength of the incident radiation. For example, the sample material is dissolved in a solution containing a thousand-fold molar excess of Nicotinic Acid. A drop of the solution is placed on the target surface, evaporated to dryness, and irradiated with 266 nm ultraviolet photons from a frequency quadrupled pulsed Neodymium YAG laser. The use of a matrix material which has a strong absorption for the incident photons represents an important distinction between this approach and the first three described because it allows the use of low power densities which increases the probability of desorbing intact molecular ions.
SUMMARY OF THE INVENTION
According to this invention there is provided a method of preparing a sample for analysis by laser desorption mass spectrometry, comprising applying a substrate material to a target for the mass spectrometer to be used; dissolving the sample material in a solvent and applying the solution to the substrate material on the target to be absorbed thereby; dissolving a matrix material in a solvent; and applying the matrix material solution to the substrate material on the target, the solvent used to dissolve the matrix material being such as to release the sample material from the substrate material thereby to provide on the substrate material on the target, after evaporation of the matrix material solvent, an intimately mixed deposit of sample material and matrix material.
Preferably the matrix material has a strong absorption for the photon bombardment used for mass spectrometry.
Preferably the substrate material is applied to the target by a technique such as electrospraying which provides a deposit with a large surface area .
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described by way of example with reference to
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Davis et al.., "Identification of Naturally Occurring Quaternary Compounds by Combined Laser Desorption and Tandem Mass Spectrometry", Analytical Chemistry, vol. 55 No. 8, (Jul. 1983), pp. 1302-1305.
Karas et al., "Matrix Assisted Ultrviolet Laser Desorption of Non-volatile Compounds," International Journal of Mass Spectrometry and Ion Processes, vol. 78 (1987), pp. 53-68.
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Cottrell John S.
Mock Kuldip K.
Dzierzynski Paul M.
Finnigan Mat Limited
Nguyen Kiet T.
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