Dried-droplet method

The solid-sample preparation is usually achieved by the deposition on a metallic surface of the solution of matrix and analyte with a concentration suitable to obtain the desired analyte/matrix ratio. The solution is left to dry under different conditions (simply at atmospheric pressure, reduced pressure, or under a nitrogen stream). This method is usually called the Dried Droplet Method. In all cases, what is observed is the formation of an inhomogeneous solid sample, due to the different crystallization rate of the matrix and analyte. Consequently, the 10 molar ratio is only a theoretical datum In the solid sample, different ratios will be found in different positions and the only way to overcome this is to average a high number of spectra corresponding to laser irradiation of different points. 

Digital ion trap 64,85 Digital waveform 65 Double-focusing mass analyzers 47 Double-focusing mass spectrometers 50 Dried droplet method 39 Droplet radius 18... 

Helocovoptera zea the pheromone biosynthesis activating neru opeptide gene in neru onal clusters from the sub esophageal ganglion. MS and immuno- cytochemistry results. using dried droplet method. ... 

List for concentration tolerances of buffers components for MALDI analysis using dried droplet method (http //w3.ouhsc.edu/biochem/sampleprep.htm). 

The dried droplet method is the method originally introduced by Hillenkamp and Karas (Fig. 4.7). A saturated matrix solution, 5-10 g depending on the solubility of the matrix, is prepared in water, water-acetonitrile, or water-alcohol mixtures. In a second vessel, the sample is diluted to about 100 mg L Mn a solvent that is miscible with the matrix solution. The matrix and sample solutions are then mixed such that the final molar ratio is 10,000 1 with a final volume of a few tiL. 

The oldest procedure is the so-called dried droplet method. In this method the three soluHons are mixed, and 0.5-1 /rl of the mixture is applied to the target and air-dried at room temperature. Under these conditions crystallization is relatively slow, thereby increasing the risk of segregation between sample and matrix and cationization salt. 

A simple air spray deposition method was used with some PEG samples. This metirod gave excellent spot-spot reproducibility, compared with the classical dry droplet method, and increased the usefulness of MALDI-TOF for end-group analysis of PEGs. ... 

If the dried-droplet method does not produce good results, then various other sample deposition techniques should be attempted, including various sandwich methods [2,18] and the fast evaporation method, also referred to as the thin-layer method [19]. 

Electrospray sample deposition (ESDEP) is a sample preparation method where matrix and analyte solutions are sprayed on the target surface under the influence of a high-voltage electric field [44,45]. ESDEP is reported to yield much better shot-to-shot and spot-to-spot reproducibility than the dried-droplet method. The improved results are ascribed to the small and evenly sized crystals that are formed, and as a consequence, improved homogeneity of the MALDI sample surface. Hanton et al. [45] analyzed PEG1450, a narrowly distributed poly(ethylene oxide) sample, using an uncommon... 

Figure 1.25 shows MALDI mass spectra of the HALS occluded in the PP composite (a) obtained by the dried droplet method after conventional solvent extraction from the PP... 

In principle, this increase in reproducibihty would allow for the detection of small features and/or differences between the mass spectra of closely related microorganisms. Assnming the direct transfer method has a variance similar to that of the dried-droplet method used in this study (Fig. 2.6), it can be inferred that a significant rednction in the variance can be realized by simply premixing the intact bacteria with the matrix solution prior to its deposition onto the MALDl plate, rather than performing sequential depositions of bacteria followed by matrix. This improvement in the reproducibility would also be expected to be observed in the protein extraction protocols, adding only a single dilution step in the overall procedure (1 1 sample/matrix). However, to date, all standard protocols (Freiwald and Sauer 2009) used in profile-based MALDI-MS analyses implement a dried-droplet approach to deposit the sample onto the MALDl plate. 

It is clear that matrix application by the dried-droplet method is not the preferred method for (neuro)peptide imaging... 

This does not mean that dried-droplet preparations cannot be imaged. Indeed, clearly dependent on the chemical structure, certain compounds do remain in the tissue (e.g., the (prenol) lipid ion at 610.444). For specific analyte molecules such as these latter compounds, the dried-droplet method can thus be used as a specific sample preparation method to wash away unwanted compounds. In this respect, it is interesting to note that the corpora cardiaca are the main synthesis sites of the insect juvenile hormone (JH), also a prenol lipid of the class of terpenoids. JH as such is not secreted in the adult stage of the insect imaged here, but the presence of other terpenoids in this tissue is expected. 

FIGURE 9.9 Water solutions of P-amyloid (42-1), bovine insulin, and amixture of the two small proteins were prepared and 50 pmol applied to the glass slide using the dried droplet method and 2,5-DHB as matrix. Heat (ca. 225 °C) was applied to the copper transfer tube with the ion source set at 150 °C. Mass spectra of (A.l) P-amyloid (42-1), (B.l) hovine insulin, and (C.l) of the mixture. The DriftScope tj v,s. miz representations are displayed in (A.2) to (C.2) showing clean separation of the two peptides in (C.2). 

---