MALDI, analytical method

Matrix-assisted laser desorption ionization (MALDI) A method used for the ionization of high-molecular-weight compounds. In this approach, the analyte is crystallized with a solid matrix and then bombarded with a laser of a frequency which is absorbed by the matrix material. 

The extraordinary complexity of human genes and their products has encouraged the development of extremely high-resolution analytical methods.75 Capillary electrophoresis is competitive with slab gel methods, with resolution up to the order of about 1,000 base pairs for sequencing, sizing, and detection of mutation. Reversed phase HPLC is useful for restriction digest mapping and MALDI-MS up to about 1000 base pairs. 

An analytical method based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) was applied to provide information on the structure of copolymer 29, for example, repeat units and end groups <2002ANC6252>. 

This unit describes procedures for extraction, purification, and identification by MALDI-MS of fiavonol glycosides from a plant source. The extraction and purification protocols are not meant to be comprehensive, but rather to offer guidelines for sample preparation prior to a MALDI-MS analysis. The MALDI-MS technique is suggested as a complement to other analytical methods such as HPLC or NMR. Its strength lies in the ability to rapidly screen a number of samples for the presence of fiavonol glycosides, which can be identified on the basis of their molecular weights. 

Our ongoing target is the development of fully automated glycan analysis and structural profiling systems, by combining SweetBlot and such versatile mass spectrometers as MALDI-TOFMS and other analytical methods used in general... 

Fifty-three peptide samples were submitted by 48 laboratories. Previous studies by this committee have demonstrated the need for multiple analytical methods for the assessment of purity. Therefore the peptides in this study were analyzed by AAA, HPLC, ESI-MS and MALDI-MS to determine purity (Table I). Only two peptide samples had less than 50% of the desired product, and three other samples had less than 70% of the desired product, as judged by their mass spectra, amino acid composition and HPLC retention time. Overall, the peptides were of excellent quality. 

In assessing peptide purity, there were occasional discrepancies noted among the different analytical methods. MALDI-MS analysis of the peptide samples often revealed impurities not readily observed by ESI-MS and HPLC. In most of these cases, greater dilution of the sample prior to MALDI-MS yielded data more consistent with ESI-MS and HPLC assessment. This is illustrated by sample 1354 in Figure 3A-C and in Table I. These results underscore the importance of using more than one analytical method to evaluate peptide purity, and of testing samples under several different conditions. 

There was generally agreement between the results from determination of racemization by AAA following reaction with Marfey s reagent, by HPLC, with somewhat less agreement by CPA/MALDI-MS. However, in some cases the three analytical methods yielded divergent results. Therefore, the possible sources of discrepancy among the methods were also evaluated as part of this... 

To date, the MALDI-TOF spectrometer provides the most specific separation spectrograms. Based on numerous test series with a known reference material, an extensive data base of spectrograms has been acquired. For goose, duck, eider duck, chicken, pheasant and turkey, the accuracy of bird species identification is almost 100%. Accuracy of the visual quantitative method is 5%. For most quality control purposes, this is sufficient (see also Section 2.4, Visual analytical methods). 

Mass spectrometry is an analytical method of choice for identification of volatile compounds and has been employed in investigation of thermolysis and acidolysis mechanisms of chemical amplification resists [96, 121, 122]. This technique has been also utilized in screening of resists systems, especially Si-containing 193 nm bilayer resists,for outgassing [438,439]. MALDI-TOF mass spectroscopy has been applied to characterization of dendritic resist polymers. 

A second important focus of our work is the development of suitable analytical methods for the solid state and in solution. The physical characterization of metallo-supramolecular systems has mainly relied on crystal structure determination. Studies have also been performed on surface layers 40-42). The classical analytical methods (like FAB mass spectrometry) or most polymer methods (like light scattering, vapor pressure osmometry or membrane osmometry) can not be used. In solution, ESI mass spectrometry (43-45) and NMR (27,46) have been succesfully applied. We have explored whether MALDI-TOF mass spectrometry in the solid state (Schubert, U. S. Lehn, J.-M. Weidl, C. H. Spickermann, J. Goix, L. Rader, J. Mullen, K., unpublished data.) and sedimentation equilibrium analysis in the analytical ultracentrifuge for solutions may be employed. Grid-like cobalt coordination arrays ([2 X 2] Co(n)-Grid) were used as model systems in the analytical ultracentrifuge (47). 

Elucidation of degradation pathways and identification of transformation products (TPs) is of crucial importance in understanding their fate in the environment and requires the employment of advanced instrumental techniques. Analytical methods that can be used for this purpose include Uquid chromatography with diode array or fluorescence detector (LC-DAD/FL), nuclear magnetic resonance (NMR), infrared spectroscopy (IR), matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS), gas... 

In summary, MALDI-MS is an important tool for polymer characterization, with many attributes that complement those of other analytical techniques. Future advances in analytical method development, as well as of our understanding of... 

AU ionization techniques used for quantitative analysis present the possibility of ionization suppression (and sometimes enhancement) of the analyte(s) by co-eluting compounds arising from the sample matrix or elsewhere this phenomenon is a form of matrix effect. This problem is much more serious for API techniques than the others presented in this chapter, with ESI presenting the highest occurrence of matrix effects. Matrix effects are also of concern in MALDI analyses, especially in the quantitation of small molecules. It is always advisable to be aware of the importance of matrix effects in any proposed analytical method and to minimize them as far as possible. Use of an appropriate isotope-labeled standard in conjunction with matrix matched calibrant standards should give reliable results if all other appropriate precautions are taken, but it is important to investigate the possibility of relative matrix effects if one suspects that the matrix in the analytical sample might differ appreciably from that used to make the matrix matched cahbrants. 

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