Micronebulizers

M. P. Field, J. T. Cullen, and R. M. Sherrell. Direct Determination of 10 Trace Metals in 50 xL Samples of Coastal Seawater Using Desolvating Micronebulization Sector Field ICP-MS. J. Anal. Atom. Spectrom., 14(1999) 1425-1431. 

From the sample solution to be analyzed, small droplets are formed by the nebulization of the solution using an appropriate concentric or cross-flow pneumatic nebulizer/spray chamber system. Quite different solution introduction systems have been created for the appropriate generation of an aerosol from a liquid sample and for separation of large size droplets. Such an arrangement provides an efficiency of the analyte introduction in the plasma of 1-3 % only.6 The rest (97 % to 99%) goes down in the drain.7 Beside the conventional Meinhard nebulizer, together with cooled or non-cooled Scott spray chamber or conical spray chamber, several types of micronebulizers together with cyclonic spray chambers are employed for routine measurements in ICP-MS laboratories. The solvent evaporated from each droplet forms a particle which is vaporized into atoms and molecules... 

The use of a desolvating system improves the sensitivity and can extend the matrix effect with respect to conventional sample introduction apparatus.85 The current trend is towards total consumption systems. Fundamental studies concerning the analysis of microsamples with common micronebulizer based systems have been reviewed by Todoli and Mermet.85... 

A frequently used micronebulizer with heated spray chamber and membrane desolvator is the Aridus from CETAC Technologies, Ohama, NE. The experimental setup of the Aridus II microconcentric nebulizer is shown in Figure 5.16. 

Figure 6.23 Experimental arrangement of solution based calibration using a micronebulizer (DS-5, CETAC) inserted in a cooled laser ablation chamber for imaging of thin sections of brain tissue. (/. S. Becker et ai, Anal. Chem. 77, 3208 (2005). Reproduced by permission of American Chemical Society.)...

Maestre, S.E., J.L. Todolf, and J.M. Mermet. 2004. Evaluation of several pneumatic micronebulizers with different designs for use in ICP-AES and ICP-MS. Future directions for further improvements. Anal. Bioanal. Chem. 379 888-899. 

Almagro, B., A.M. Ganan-Calvo, M. Hidalgo, and A. Canals. 2006. Flow focusing pneumatic nebulizers in comparison with several micronebulizers in inductively coupled plasma atomic emission spectrometry. J. Anal. At. Spectrom. 21 770-777. 

Figure 5 Micronebulizers (a) Meinhard high-efficiency nebulizer (HEN), (b) Cetac microconcentric nebulizer (MCN).

As can be seen from the results in Table 3.1, the analyte transport efficiency is similar for both conventional and micro- or high-efficiency nebulizers when compared under identical flow rates. The increase in analyte transport efficiency with decrease in the sample uptake rate (sometimes called starving the nebulizer because uptake rates less than the natural aspiration rate are used) was reported long ago [21,22]. So the main advantage of the newer micronebulizers is that their internal volume is small, a feature that becomes more important as the uptake rate is reduced. A capillary can also be inserted into a conventional concentric, pneumatic nebulizer to decrease its internal dead volume [23,24]. 

Vapor phase dissolution (VPD) is commonly used for surface and contamination analysis of semiconductor wafers [374-379]. HF vapor is used to remove a silicon oxide or native silicon layer. A drop of hydrofluoric acid or deionized water (with a volume of 50 to 200 jxL) is placed on the surface and rolled around the surface to dissolve the metals. The small drop is then analyzed by ICP-MS by using either a direct injection nebulizer, a micronebulizer, or ETV. The ability of ICP-MS to measure several elements rapidly in a small volume of solution is essential. 

The key to a successful HPLC-ICP-MS coupling is the interface. In the simplest case the outlet of an HPLC column (4.6 D10 mm) is connected to a conventional pneumatic or crossBow nebulizer. The use of capillary or megabore (0.32D1.0mm) HPLC systems that are becoming popular, especially for RPC, requires the use of micronebulizers, either direct injection nebulizers (DIN) or micronebulizers (e.g., Micromist, DS-5) bttcd with a small-volume nebulization chamber. 

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