The Nebulizer

The sample to be analyzed can be dissolved in an organic solvent, xylene or methylisobutyl ketone. Generally, for reasons of reproducibility and because of matrix effects (the surroundings affect the droplet size and therefore the effectiveness of the nebulization process), it is preferable to mineralize the sample in H2SO4, evaporate it and conduct the test in an aqueous environment. 

Flame atomization assembly equipped with spray chamber and slot burner. The inset shows the nebulizer assembly. 

Additional ionization is effected by including radioactive substances or plasma or glow discharges in the evaporation chamber or by electrical charging of the nebulizer. Such techniques are also discussed in Chapters 8 and 11. 

A typical arrangement for producing a particle beam from a stream of liquid, showing (1) the nebulizer, (2) the desolvation chamber, (3) the wall heater, (4) the exit nozzle, (5, 6) skimmers 1, 2, (7) the end of the ion source, (8) the ion source, and (9) the mass analyzer. An optional GC inlet into the ion source is shown. 

The nebulization and evaporation processes used for the particle-beam interface have closely similar parallels with atmospheric-pressure ionization (API), thermospray (TS), plasmaspray (PS), and electrospray (ES) combined inlet/ionization systems (see Chapters 8, 9, and 11). In all of these systems, a stream of liquid, usually but not necessarily from an HPLC column, is first nebulized... 

Suitable inlets commonly used for liquids or solutions can be separated into three major classes, two of which are discussed in Parts A and C (Chapters 15 and 17). The most common method of introducing the solutions uses the nebulizer/desolvation inlet discussed here. For greater detail on types and operation of nebulizers, refer to Chapter 19. Note that, for all samples that have been previously dissolved in a liquid (dissolution of sample in acid, alkali, or solvent), it is important that high-purity liquids be used if cross-contamination of sample is to be avoided. Once the liquid has been vaporized prior to introduction of residual sample into the plasma flame, any nonvolatile impurities in the liquid will have been mixed with the sample itself, and these impurities will appear in the results of analysis. The problem can be partially circumvented by use of blanks, viz., the separate examination of levels of residues left by solvents in the absence of any sample. 

The nebulization concept has been known for many years and is commonly used in hair and paint spays and similar devices. Greater control is needed to introduce a sample to an ICP instrument. For example, if the highest sensitivities of detection are to be maintained, most of the sample solution should enter the flame and not be lost beforehand. The range of droplet sizes should be as small as possible, preferably on the order of a few micrometers in diameter. Large droplets contain a lot of solvent that, if evaporated inside the plasma itself, leads to instability in the flame, with concomitant variations in instrument sensitivity. Sometimes the flame can even be snuffed out by the amount of solvent present because of interference with the basic mechanism of flame propagation. For these reasons, nebulizers for use in ICP mass spectrometry usually combine a means of desolvating the initial spray of droplets so that they shrink to a smaller, more uniform size or sometimes even into small particles of solid matter (particulates). 

These factors make it necessary to reduce the amount of solvent vapor entering the flame to as low a level as possible and to make any droplets or particulates entering the flame as small and of as uniform a droplet size as possible. Desolvation chambers are designed to optimize these factors so as to maintain a near-constant efficiency of ionization and to flatten out fluctuations in droplet size from the nebulizer. Droplets of less than 10 pm in diameter are preferred. For flow rates of less than about 10 pl/min issuing from micro- or nanobore liquid chromatography columns, a desolvation chamber is unlikely to be needed. 

Solutions can be examined by ICP/MS by (a) removing the solvent (direct and electrothermal methods) and then vaporizing residual sample solute or (b) nebulizing the sample solution into a spray of droplets that is swept into the plasma flame after passing through a desolvation chamber, where excess solvent is removed. The direct and electrothermal methods are not as convenient as the nebulization inlets for multiple samples, but the former are generally much more efficient in transferring samples into the flame for analysis. 

The solution to be nebulized can be a one-off sample, pumped or drawn into the nebulizer at a rate varying from a few microliters per minute to several milliliters per minute. Alternatively, the supply of solution can be continuous, as when the nebulizer is placed on the end of a liquid chromatographic column. 

The sample solution is pumped along a narrow capillary tube, the end of which becomes the nozzle of the nebulizer. On the outside of the capillary near its nozzle end, an electrical heater rapidly... 

The first form of aerosol modifier is a spray chamber. It is designed to produce turbulent flow in the argon carrier gas and to give time for the larger droplets to coalesce by collision. The result of coalescence, gravity, and turbulence is to deposit the larger droplets onto the walls of the spray chamber, from where the deposited liquid drains away. Since this liquid is all analyte solution, clearly some sample is wasted. Thus when sensitivity of analysis is an issue, it may be necessary to recycle this drained-off liquid back through the nebulizer. 

The aerosol is swept to the torch in a stream of argon gas. During passage from the nebulizer to the plasma flame, the droplets rapidly become smaller, as solvent evaporates, and evenmally become very small. In many cases, almost all of the solvent evaporates to leave dry particulate matter of residual analyte. 

To assist in the deposition of these larger droplets, nebulizer inlet systems frequently incorporate a spray chamber sited immediately after the nebulizer and before the desolvation chamber. Any liquid deposited in the spray chamber is wasted analyte solution, which can be run off to waste or recycled. A nebulizer inlet may consist of (a) only a nebulizer, (b) a nebulizer and a spray chamber, or (c) a nebulizer, a spray chamber, and a desolvation chamber. Whichever arrangement is used, the object is to transfer analyte to the plasma flame in as fine a particulate consistency as possible, with as high an efficiency as possible. 

The transfer efficiencies of analyte solution from the nebulizer to the plasma flame depend on nebulizer design and vary widely from about 5-20% up to nearly 100%. 

The role of the nebulizer in ICPMS is to transform the liquid sample into an aerosol. This is carried into the plasma by an ai on flow after passing through a... 

Kennedy describes a method using an ultrasonic nebulizer to generate a fog of water droplets w hich is used in the same way as smoke to visualize airflows. Several types of nebulizers are available but they require an electrical connection and are not hand-held. Food dye can be added to the water to produce colored fog. The nebulizers are expensive (about 1500 ECU) but have negligible operating costs. Although the amount of smoke produced is small, it is nontoxic and nonirritating. 

Race the mouthpiece in your mouth and turn on the nebulizer. 

When pentamidine is prescribed for aerosol use at home, the nurse reviews the use of the special nebulizer, as well as directions for cleaning and maintaining the nebulizer equipment (see Home Care Checklist Administering Pentamidine at Home). 

If the nurse is responsible for administering the medication by nebulization, it is important to place the patient in a location where he can sit comfortably for 10 to 15 minutes. The compressor is plugged in and the medication mixed as directed, or the prepared unit dose vial is emptied into the nebulizer. Different types of medication are not mixed without checking with the physician or the pharmacist. The mask or mouthpiece is assembled and the tubing connected to the compressor. The patient is placed in a comfortable, upright position with the mask over the nose and mouth. The mask must fit properly so that the mist does not flow up into the eyes. If using a mouthpiece instead of a mask, have the patient place the mouthpiece into the mouth. The compressor is turned on and the patient instructed to take slow, deep breaths. If possible, the patient should hold his breath for 10 seconds before slowly exhaling. The treatment is continued until the medication chamber is empty. After treatment, the mask is washed with hot, soapy water, rinsed well, and allowed to air dry. 

The patient demonstrates an understanding of the drug regimen and use of the nebulizer or aerosol inhalator. 

Repetitive routine analysis of a specific sample (e.g., for Quality Control) will usually require a dedicated instrument. Therefore, the chromatograph and, in particular, the detector will be chosen for that specific analysis. Consequently, only one detector will be necessary and the purchase of an armory of detectors on the basis that they might be needed in the nebulous future is not advised. An alternative detector can always be obtained if and when the demand arises. The same argument applies to multi-solvent reservoirs and multi-solvent gradient programmers and other accessories that are not immediately required for the specific analysis in mind. 

Flgure 9.6 Schematic diagram of a heated pnewaatic nebulizer LC/MS interface combined with an APCI ion source and cross-sectional view of the nebulizer probe. 

Ipratropium is the most commonly used anticholinergic for treating bronchoconstriction in asthma. It is available as an MDI and solution for nebulization. Ipratropium has an onset of action of approximately 30 minutes and a duration of action of 4 to 8 hours. Care should be taken not to spray the metered-dose inhaler into or allow the nebulized solution to get in the patient s eyes, as it can cause mydriasis and blurred vision. 

Albuterol is the preferred bronchodilator for treatment of acute exacerbations because of its rapid onset of action. Ipratropium can be added to allow for lower doses of albuterol, thus reducing dose-dependent adverse effects such as tachycardia and tremor. Delivery can be through metered-dose inhaler (MDI) and spacer or nebulizer. The nebulizer route is preferred in patients with severe dyspnea and/or cough that would limit delivery of medication through an MDI with spacer. If response is inadequate, theophylline can be considered however, clinical evidence supporting its use is lacking. 

But what about the elements How many were there Could the elements then known to man not be further expanded. Could they only be found on Earth Did God create them in the beginning or were they the result of some process of evolution Even the existence of atoms was doubted. The nebulous concepts and the countless deadends led to the eminent French chemist Jean B. A. Dumas writing in 1837 to state that "If I had the power, I would strike the word "atom" from science". 

Coupling of CE with MS is a difficult task, because of the incompatibility of the EOF (100 500 nl min ) and optimal ESI ionization conditions. Moreover, a stable current for reproducible electrophoretic separations must be ensured. Fortunately, both these problems can be solved by adding make-up solution (10 100 g min ), which also ensures an electric connection between the nebulizer and the tip of a capillary. 

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