Nebulizer capillary

The nebulizer capillary position may be adjustable on a screw thread to permit optimization of sample uptake and drop size. Alternatively or additionally, an impact bead may be placed in the path of the initial aerosol to provide a secondary fragmentation and so improve the efficiency of nebulization. Such a device is illustrated in Fig. 2.9. 

Pneumatically assisted electrospray,24 also called ion spray, is illustrated in Figure 22-17a. Liquid from the chromatography column enters the steel nebulizer capillary at the upper left, along with a coaxial flow of N2 gas. For positive ion mass spectrometry, the nebulizer is held at 0 V and the spray chamber is held at —3 500 V. For negative ion mass spectrometry, all voltages would be reversed. The strong electric field at the nebulizer outlet, combined with the coaxial flow of N2 gas, creates a fine aerosol of charged particles. 

Figure 22-17b provides more detail on ionization. Voltage imposed between the steel nebulizer capillary and the inlet to the mass spectrometer creates excess charge in the liquid by redox reactions. If the nebulizer is positively biased, oxidation enriches the liquid in positive ions by reactions such as... 

Figure 17 Block diagram of a direct injection nebulizer capillary electrophoresis inductively coupled plasma mass spectrometry (DIN CE-ICP-MS) interface. (From Ref. 101.)...

As in all flame spectrometric techniques, care should be taken to make sure that the nebulizer performance, if the nebulizer is adjustable, is optimized. This may involve direct adjustment of the nebulizer capillary position or minor adjustments to the position of the impactor, if fitted. 

In the early days of flame spectrometry, some very elaborate accessories were designed to give reproducible discrete sample nebulization.16,17 However, as the technique became more widely employed, the devices used became progressively simpler, often taking the form of small funnels with a capillary bore outlet connected directly to the nebulizer capillary.17 Even this is not really necessary, because all that is required is a small (1-2 ml capacity) beaker with a conical depression in the bottom. Conventional Auto Analyser sample cups work very well. The end of the flexible nebulizer aspiration tube is simply dipped into the droplet of solution in the cone. This is especially useful if, for example, such sample cups have been used for evaporative pre-concentration of water samples in a vacuum desiccator.19... 

Manning (1975) was the first to exploit the observations that small sample volumes (100 nL) could be used for peak absorption measurements by FAAS with negligible loss in sensitivity. He applied this to the determination of copper in serum by injecting 100 sample volumes into PTFE cone coupled directly to the capillary of a nebulizer burner and obtained an RSD of 3% at 15.7 [Pg.365]

The nebulizer described is a self-aspirating, pneumatic nebulizer and is the one shown schematically on the lower left of Fig. 6.8(b). The nebulizer capillary is usually made of stainless steel but other materials such as Pt, Ta, and polymers may be used for corrosive solvents when contamination from the elements in steel must be avoided. A variety of other nebulizer designs have been developed for specific applications but are not commonly used in AAS. These other nebulizers are often used in atomic emission spectrometry and will be described in Chapter 7. 

Geometric parameters of the source were as follows the distauce betweeu capillaries was set to 5 mm the nebubzation capillary height over the sample was 2 mm nebulization capillary angle was 58° MS inlet height over the sample was 1 mm and nebulizing gas pressure (nitrogen) was 11 atm. 

Choosing an optimal solvent for TLC plate analysis is also very important. Solvent in the DESI source is delivered to the analyzed surface via nebulizing capillary, as a... 

Capillary protrusion Gas pressure Solvent flow Capillary voltage Nebulization capillary angle Nebulization capillary height Capillary distance MS inlet height... 

The chromatogram presented in Figure 11.3 supports the choice of solvent. Here, we may see how rapidly methanol is able to extract the substance (PMMA in this case) from the surface of the TLC plate. The arrows in Figure 11.3 indicate the time when the nebulizing capillary was placed exactly above the new PMMA spot. Intensity of the signal drops down quite rapidly, which demonstrates that the substance is quickly eluted from the spot. 

Since the sample solution must pass through one of the nebulizer capillaries, partial clogging or blockage can result from suspended particulate matter in the sample or to a lesser extent high dissolved solids concentrations in the samples that precipitate at the tip as a result of solvent evaporation. This can be a particularly insidious problem because partial blockage... 

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