Sample preparation, MALDI

The major distribution, centred at approximately 2000 Da as expected, can be assigned as from di-hydroxyl end-capped oligomers of PPG (18). Addition of lithium salts in the MALDI sample preparation procedure leads to the generation of [18 + Li]+ ions as the major species. A series of low-intensity peaks below... 

Aerni H, Cornett D, Caprioli R. Automated acoustic matrix deposition for MALDI sample preparation. Anal. Chem. 2006 78 827-834. 

S. D. Hanton and D. M. Parees. Extending the Solvent-Free MALDI Sample Preparation Method. J. Am. Soc. Mass Spectrom., 16(2005) 90-93. 

If an analyte is definitely insoluble or only soluble in solvents that are not acceptable for the standard MALDI sample preparation technique, it can alternatively be ground together with the solid matrix, preferably in a vibrating ball mill. The resulting fine powder is then spread onto the target. To avoid contamination, nonadherent material should be gently blown away from the target before insertion into the ion source. [103,108,109]... 

Fig. 10.8. Comparison of spectra of the organic dye pigment red 144 as obtained by (a) LDI, (b) solvent-based and (c) solvent-free MALDI sample preparation. Adapted from Ref. [109] by permission. John WUey Sons, 2001. 

For standard MALDI sample preparation, the analyte should be soluble to about 0.1 mg ml in some solvent. If an analyte is completely insoluble, solvent-free sample preparation may alternatively be applied (Chap. 10.4.3). The analyte may be neutral or ionic. Solutions containing metal salts, e.g., from buffers or excess of non-complexated metals, may cause a confusingly large number of signals due to multiple proton/metal exchange and adduct ion formation even complete suppression of the analyte can occur. The mass range of MALDI is theoretically almost unlimited in practice, limits can be as low as 3000 u, e.g., with polyethylene, or as high as 300,000 u in case of antibodies. 

What is the function of the hydrophobic break in the MALDI sample preparation compact disk (Figure 7.42) (2 marks)... 

Molin L, Cristoni S, Crotti S, Bemardi L, Seraglia R, Traldi P (2008) Sieve-based device for MALDI sample preparation. I. Influence of sample deposition conditions in oligonucleotide... 

Bouschen W, Spengler B (2007) Artifacts of MALDI sample preparation investigated by high-resolution scanning microprobe matrix-assisted laser desorption/ionization (SMALDI) imagine mass spectrometry. Int 1 Mass Spectrom 266 129-137. doi 10.1016/j. ijms.2007.07.017... 

Specimen Sample MALDI Sample preparation Refs... 

The chain aggregates were broken when the SEC fractions, containing a heterogeneous mixture of PC chains of different size, were diluted in the HABA or lAA matrix used for the MALDI sample preparation. These matrices contain the carboxylic acid units, which are able to break the hydrogen bonds responsible for the formation of the chain aggregates. 

Skelton, R., Dubois, R, and Zenobi, R., A MALDI Sample Preparation Method Suitable for Insoluble Poymers, Anal Chem., 72, 1707, 2000. 

Two variations of conventional SIMS have evolved. In one, known as matrix-enhanced SIMS, the MALDI sample preparation protocol is used to coat the sample surface with an organic acid (e.g., 2,5-dihydroxybenzoic acid) or other suitable matrix material to improve ionization efficiency [24,25], This approach has been used to image brain tissue samples from freshwater snails (Lymnaea stagnalis). Another variation employs a coating of a thin layer of gold or other metals to enhance analytical signals [26], This method, known as metal-assisted SIMS, provides images with improved spatial and chemical resolution. 

One limitation of SIMS and LDI is that higher molecular weight compounds (>1000 Da) do not survive the ionization process. The introduction of MALDI (Karas and Hillenkamp, 1988) enabled the analysis of intact higher molecular weight molecules in tissue (Caprioli et al., 1997). Incorporation of a matrix compound during MALDI sample preparation reduces the fragmentation observed in SIMS and LDI. MALDI will be discussed further in Section 14.4.2. 

A practical overview of the various matrices and preparation techniques can be found, for example, on the Internet at http //msr.dom.wustl.edu/Research/ MALDI TOF Mass Spec and Proteomics/MALDI Sample Preparation Methods.htm, as well as on the Internet pages of commercial suppliers of MALDI matrices, for example, http //www.sigrnaaldrich.com/analytical-chromatography/ analytix-newsletter/analytix-2001.htrnl analyttx6. 

The dried droplet standard MALDI sample preparation is very simple. Here, the sample and matrix are dissolved in solvents or solvent systems that are miscible with each other, and mixed either before deposition onto or directly on the MALDI sample support. The matrix-analyte droplet of typically 1 pi volume is then slowly dried in air, or under a forced flow of cold air. This results in a deposit of crystals which, depending on the matrix and preparation conditions (e.g., solvent evaporation rate), vary between submicrometer and several hundred micrometers in size. In cases of solvent systems with a high polarity, surface tension leads to a nonhomogeneous distribution of the individual crystals near the rim of the... 

Skelton, R Dubois, F., and Zenobi, R. (2000) A MALDI sample preparation... 

As Figure 8.6 shows, in MALDI sample preparation, solvent evaporation takes place after the sample solution is deposited onto the probe. If a solvent mixture is... 

Figure 8.6 Effect of solvent composition on MALDI sample preparation, (a) Polymer incorporation into matrix crystals (b) polymer precipitation.

To date, the vast majority of experiments in which liquid separation techniques have been coupled with MALDI have utilized off-line fraction collection. The availability of MALDI sample preparation robots has facilitated the preparation of hundreds of samples as discrete spots on the target plate in a short time frame. If the fraction collection is triggered by detection of a UV signal (or other analytical detector), then MS analysis can be focused only on the chromatographic regions which contain the most abundant analytes. In addition, fraction collection allows... 

Soiid Matrices. Most work on synthetic polymers use the solid matrices developed for the biopol5uner analysis. To use these matrices, solutions of polymer, matrix, and cationizing salt are mixed. The solvent is then allowed to evaporate from these solutions deposited onto a sample surface. The mass proportion ratios of the matrix pol5nner salt in the final solid mixture cover the range of 5 1 2 to 2000 1 1. These proportions are often dependent on molecular mass of the polymer (1). The choice of matrix compounds for synthetic polymers with respect to the polarity of the polymer have been discussed (34). As a general rule, matrix polarity should be matched with the polarity of the polymer so that both are soluble in a common solvent. Since the MALDI sample preparation requires intimate... 

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