Metal sample plate

FIGURE 20-7 Diagram o( the MALDi process. The analyte is uniformly dispersed in a matrix and placed on a metal sample plate. A pulsed laser beam strikes the sample causing desorption ol a plume of matrix, analyte, and other ions. The analyte can be protonated. be deproto-nated, or form adducts before entering the TOF analyzer. 

The extraction procedure parameters (such as extraction solvent and volume) will vary depending upon the tissue and compound being investigated. An example of a simple tissue extraction method we use for compounds is spike uncoated tissue sections with 5 p,L drops of extraction solvent (50 50 (v/v) ACN H20) and transfer 3x1 p,L extracts onto a blank metal sample plate using a pipette. Add 1 xL of the matrices for assessment onto each extract, allow to dry, and acquire a spectrum using MALDTMS. This method allows for direct comparison of three different matrices. 

In IMS, supportive materials, whose surfaces are coated with conductive materials, are used in principal. In the simplest way, the tissue slices can be placed on a metal MALDI plate directly.9 In this case, however, the target plate must be cleaned carefully after the measurement is over. Currently, the method commonly used is that samples are prepared on a disposable plastic sheet or a glass slide coated with series of conductive materials. In particular, a plastic sheet (ITO sheet) or glass slide (ITO glass slide available from Bruker Daltonics K.K., Billerica, MA, or Sigma, St. Louis, MO) coated with ITO (indium-tin oxide) is useful because it has superior optical transparency... 

Solutions of the analyte and the matrix (from nanolitre to microlitre amounts) are deposited or spotted on a flat metal target plate. Owing to evaporation of the solvent, matrix and analyte co-crystallize. Short laser pulses (1 20 ns) bombard the solid and cause the sample and matrix to be volatilized. The formation of ions occurs by acid base reaction between the ionized matrix molecules and the analyte molecules (Figure 2.5). 

FIGURE 8.18 Left, a demountable cell with spacer. Right, a demountable cell without spacer. Note that there are no drilled holes for the sample and no inlet or outlet ports. Both metal frame plates (front and back) have holes for light to pass. 

Cavelier C, Foussereau J, Gille P, et al. 1988. Nickel allergy Tolerance to metallic surface-plated samples in nickel-sensitive humans and guinea pigs. Contact Dermatitis 19 358-361. 

Finely divided metal samples can also be prepared in the form of evaporated films in high vacuum, usually deposited on IR-transparent alkali halide plates (76-78). Such spectra are of interest in themselves, but tend to be much weaker than those obtained from the metal-particles-in-depth, oxide-supported catalysts. The rough surfaces of films of Cu, Ag, and Au, prepared by deposition on cold surfaces, can lead to very high-quality surface-enhanced Raman spectra (27, 28, 79, 80). The results from such experiments will be discussed in the later sections devoted to particular adsorbed hydrocarbons and metals, alongside the majority of spectra that are obtained on oxide-supported samples. 

X-ray diffractometry was performed, by methods described in a companion paper (8), between 80 and 600 K at ambient pressure on thin solid wafers cut from the prepared samples. Mounted with high temperature cement on relatively massive metal backing plates, these wafers could be maintained at temperatures constant to within 3 K, as measured by either a platinum thermometer or a copper-constantan thermocouple. The... 

Digestion of solid samples with acid or solvent may be performed in small crucibles heated on a metal hot plate, or in an air bath (Fig. 11.38), or in the glass apparatus illustrated in Fig. 11.46. The last-named is heated over a micro burner, and then rotated so that supernatant liquid or solution may be poured off drop-wise without danger or loss. 

The method may be used in a semi-quantitative manner by visually comparing the sample plate against plates prepared with known concentrations ofmetals. The identity of any metal found in abnormal amounts should be confirmed by specific methods described later. 

To run a spectrum of a neat liquid (free of water) remove a demountable cell (Fig. 3) from the desiccator and place a drop of the liquid between the salt plates, press the plates together to remove any air bubbles, and add the top rubber gasket and metal top plate. Next, put on all four of the nuts and gently tighten them to apply an even pressure to the top plate. Place the cell in the sample compartment (nearest the front of the spectrometer) and run the spectrum. 

The sample is immobilized on a metallic sample puck (see arrow) on the sample holder plate (Fig. 2.18a). This plate is finally attached from below as shown by several screws. Care has to be taken not to touch the probe tip as a result of inadequate screw positions. 

Derive the sampled-current voltammogram for the reduction of a simple metal ion to a metal that plates out on the electrode. The electrode reaction is... 

Fig. 9.9 Cuvette for the preparation of EP-metal samples consisting of a PTFE plate, covered with a polypropylene film to assure optical quality, a PTFE spacer ring (d = l mm), and a polished metal plate (Al or Cu) as the substrate for the epoxy.

For a number of years the following desiccator method of corrosive tests was used at MPRI NASH [49-51,98]. Metallic samples in the form of plates 50 X 50 X 2 in size are wrapped in an inhibited film and placed into the desiccator inside which 98 2% relative air humidity is maintained by aqua solution of glycerin, and are subjected to cyclic heating-cooling. One cycle consists of the endurance of the samples in the same humidity at a temperature of 55 2°C for 8h and at a similar humidity and a temperature of 20 2°C for 16 h. The protective ability of the films is estimated by the corrosion resistance of metallic samples after 21 test cycles (Table 1.11). 

The ionisation principle is based on the soft desorption of the solid sample molecules into the vacuum and subsequent ionisation. First, the sample is cocrystallised with a 1,000-10,000 excess of a suitable matrix on a metallic plate. Small, organic, UV-absorbing molecules like sinapinic acid are used as matrix materials (Table 4.1). An electric field is applied between the sample plate and the entrance to the time-of-flight analyser (Fig. 4.2). A pulsed laser beam is then... 

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