Flow Nebulizers

In the cross-flow arrangement, the argon gas flows at high linear velocity across the face of an orthogonal capillary tube containing sample solution. The partial vacuum causes liquid to lift above the end of the capillary. Here, it meets the argon and is nebulized. 

In this cross-flow arrangement, a thin film of sample solution is obtained as it flows around the edge of a small opening, through which there is a fast linear flow of argon. The liquid film is rapidly nebulized along the rim of the orifice. 

A sample solution is drawn or pumped into a V-shaped groove cut into the end of a capillary tube. The crossed gas and liquid streams form an aerosol. An impactor bead can be used to provide an even smaller droplet size. 

Finally, in yet another variant, the sample liquid stream and the gas flow are brought together at a shaped nozzle into which the liquid flows (parallel-path nebulizer). Again, the intersection of liquid film and gas flow leads to the formation of an aerosol. Obstruction of the sample flow by formation of deposits is not a problem, and the devices are easily constructed from plastics, making them robust and cheap. 

There are problems in use of the frit nebulizer. Memory effects tend to be severe, and each sample needs to be followed by several wash-outs with clean solvent before the pores of the frit become free of residual sample. Biological samples frequently contain detergent-like materials, and 

In the so-called V-groove device, sample solution flows as a thin stream along a V-shaped groove cut into a metal block. A gas flow is arranged almost coincident with and in the direction 

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The drop in pressure when a stream of gas or liquid flows over a surface can be estimated from the given approximate formula if viscosity effects are ignored. The example calculation reveals that, with the sorts of gas flows common in a concentric-tube nebulizer, the liquid (the sample solution) at the end of the innermost tube is subjected to a partial vacuum of about 0.3 atm. This vacuum causes the liquid to lift out of the capillary, where it meets the flowing gas stream and is broken into an aerosol. For cross-flow nebulizers, the vacuum created depends critically on the alignment of the gas and liquid flows but, as a maximum, it can be estimated from the given formula. 

Using Poiseuille s formula, the calculation shows that for concentric-tube nebulizers, with dimension.s similar to those in use for ICP/MS, the reduced pressure arising from the relative linear velocity of gas and liquid causes the sample solution to be pulled from the end of the inner capillary tube. It can be estimated that the rate at which a sample passes through the inner capillary will be about 0.7 ml/min. For cross-flow nebulizers, the flows are similar once the gas and liquid stream intersection has been optimized. 

The flows of gas and liquid need not be concentric for aerosol formation and, indeed, the two flows could meet at any angle. In the cross-flow nebulizers, the flows of gas and sample solution are approximately at right angles to each other. In the simplest arrangement (Figure 19.11), a vertical capillary tube carries the sample solution. A stream of gas from a second capillary is blown across this vertical tube and creates a partial vacuum, so some sample solution lifts above the top of the capillary. There, the fast-flowing gas stream breaks down the thin film of sample... 

Nebulizers — Nebulizers of existing systems have been the object of extensive controversy. An ICP nebulizer can be the source of serious problems, if either the nebulizer or sample solutions are not treated properly, since most ICP nebulizers are fragile and easily clogged by excessive amounts of undissolved matter. However, the failure rate of the cross flow nebulizer is no greater than that of most FAA nebulizers. (This is... 

The application of the cross flow nebulizer to ICP-AES was first described by... 

Doses Continuous flow nebulization Intermittent flow nebulization ... 

Do not exceed the maximum daily dose of 8 mg with an intermittent flow nebulization system or 14 mg with a continuous flow nebulization system. 

The commonest form of sample introduction is by means of an aerosol generated using a pneumatic nebulizer. Several types of nebulizer can be used. All-glass concentric nebulizers (Fig. 4.7a) operate in a similar manner to those used for FAAS. Cross-flow nebulizers (Fig. 4.7b) operate by directing a high-velocity stream of gas across the mouth of a capillary... 

Cairns, W. R. L Barbante, C Capodaglio, G Cescon, P Gambaro, A. and Eastgate, A. (2004). Performance characteristics of a low volume spray chamber with a micro-flow nebulizer for ICP-MS. Technical note, http //www.rsc.org/jaas. 

The principal methods of interfacing SFC with ICP-MS have been discussed by Carey and Caruso [94]. Where packed SFC columns are used, the SFC restrictor is connected to a heated cross flow nebulizer and the nebulizer gas flow carries the sample to the plasma. For the more commonly used capillary columns, the SFC restrictor is passed through a heated transfer line that is connected directly to the torch of the ICP-MS. For optimal resolution of peaks, the restrictor should be positioned so that it is level with the injector of the ICP torch. This position may be varied slightly (Fig. 10.15). Heat is applied where the transfer line and torch connect to prevent freezing of the mobile phase when it decompresses after exiting the restrictor. To transport the analyte to the plasma efficiently, a gas flow of approximately 0.8-1.0 mL/min is used. This gas flow may also be heated to improve peak resolution. 

The potential of CE-ICP-MS for use in speciation studies offers the analyst a useful alternative for the separation of compounds of environmental and clinical importance. Detection limits for CE-ICP-MS are often superior to those achieved with traditional detection methods such as refractive index and uv spectroscopy. The use of low-flow nebulizers, such as the direct injection nebulizer and the high-efficiency nebulizer, which can accommodate the low electroosmotic flow of CE, offers significant advantages in terms of improved sensitivity. 

CE-ICP-MS fg Low detection limits are possible, but low-flow nebulizers are required 20, 102... 

The elements Al, Mn, and Sr were determined by means of a Perkin-Elmer Optima 4300DV inductively coupled plasma emission spectrometry (ICP-AES) instrument (axial mode), equipped with an AS-90 Plus autosampler, a cross-flow nebulizer, and a Scott-type spray chamber in Ryton. The instrumental operating parameters are listed in Table 10.1. 

To quantify the trace elements of interest plasma-based techniques were used, namely (i) ICP-AES using an Optima 3100 instrument (Perkin-Elmer, Norwalk, CT, USA) equipped with a cross-flow nebulizer and a Ryton Scott spray chamber (ii) Dynamic Reaction Cell (DRC) Q-ICP-MS using an Elan 6100 spectrometer (PerkinElmer, Norwalk, CT, USA) equipped with a quartz cross-flow Meinhard nebulizer and a cyclonic spray chamber (iii) SF-ICP-MS using an Elementl (ThermoElectron, Bremen, Germany) with a pneumatic nebulizer and a Ryton Scott spray chamber. 

Unlike some published studies [47], the authors of this chapter have found that the different As species give similar mass counts when analyzed by ICP-MS using a cross-flow nebulizer. 

B. Gammelgaard, O. Jons, Comparison of an ultrasonic nebulizer with cross-flow nebulizer for selenium speciation by ion-chromatography and inductively coupled plasma mass spectrometry, J. Anal. Atom. Spectrom., 15 (2000), 499-505. 

For many years pneumatic nebulizers of the V-groove, Meinhard and cross-flow type have been the most widely used sample insertion devices for aerosol generation. The interaction geometry between the gas and liquid sample streams allows pneumatic nebulizers to be classified into two major groups, namely (a) pneumatic concentric nebulizers, which involve concentric interaction and (b) cross-flow nebulizers, which involve perpendicular interaction between the liquid and gas streams. Pneumatic nebulizers are well established and widely used on account of their simplicity, robustness, ease of use and low cost however, they provide low transport efficiency and tend to be clogged by high salt-content solutions [4]. 

Fig. 2 (A) The concentric nebulizer (B) The cross-flow nebulizer (C) The ultrasonic nebulizer (USN) (D) The microconcentric...

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