Spray chambers nebulizers and

Flame Sources Atomization and excitation in flame atomic emission is accomplished using the same nebulization and spray chamber assembly used in atomic absorption (see Figure 10.38). The burner head consists of single or multiple slots or a Meker-style burner. Older atomic emission instruments often used a total consumption burner in which the sample is drawn through a capillary tube and injected directly into the flame. 

In addition to conventional aspiration, using a nebulizer and spray chamber, samples may be introduced in to atomic spectrometers in a number of different ways. This may be because a knowledge of speciation (i.e. the organometallic form or oxidation state of an element) is required, to introduce the sample while minimizing interferences, to increase sample transport efficiency to the atom cell or when there is a limited amount of sample available. 

Nebulizers and Spray Chambers The nebulizer converts the sample liquid into an aerosol. Unlike FAAS/FAES, where solution uptake is by free aspiration, the solution to be nebulized in ICP is usually moved by a peristaltic pump. 

The typical ICP-MS instrument (Fig. 3.1) consists of a sample introduction system (a nebulizer and spray chamber), an inductively coupled plasma source, a differ-... 

This may be either a continuous process, used when the sample size is relatively large (1 ml or more), or a discrete process, used with samples of less than 20 /il. Continuous-flow systems are simpler to use and more precise, but they are less sensitive. They employ a nebulizer in association with a flame or gas plasma, and either a rotating electrode (Rotrode) or drip-feed to the electrode with the arc or spark. The pneumatic nebulizer has an efficiency of 5-10% and generates an inhomogeneous aerosol. Efiiciency can be improved by proper design of the nebulizer and spray chamber (N4), by use of heated nebulizer gas (R6) or ultrasonic devices (S23). The maximum improvement is a 5- to 10-fold increase in sensitivity. There is also an increase in the complexity and cost of the instrument which usually offsets these benefits. The effect... 

ICP-MS vith double focusing vas evaluated by Riondato et al. (1997). With this method, serum samples diluted 5-fold in 0.14 M HNO3 are analyzed using flow injection for sample introduction. As the nebulizer and spray-chamber are constructed from borosi-licate glass, this method holds a substantial risk for contamination that may result in a high blank. The concentration is assessed against aqueous standards. 

The major advantage of this method lies in its multi-element capability and high sensitivity (detectivity) (Hill etal. 1993). On-line combinations with separation techniques are easily set up. The excitation source is an inductively coupled plasma or - less commonly - a direct current- (DCP) or microwave- plasma (MIP) plasma temperatures are around 5000-9000°K. Chemical interferences, such as molecular emissions are rarely observed, but background compensation should be applied in any case. Sample introduction is performed via a nebulizer and spray chamber (see earlier in this chapter for details of nebulizer types and related problems and solutions). Sequential... 

Liquids are the most common form of sample to be analyzed by plasma emission. These are usually introduced with a nebulizer and spray chamber combination, similar to that used for A AS. An aerosol is formed and introduced into the plasma by the nebulizer gas stream through the injector tube. Nebulizers and spray chambers come in a variety of designs to handle aqueous solutions, high salt (high total dissolved solids) solutions, HF-containing solutions, and organic solvents. 

The most common samples analyzed by ICP-MS are aqueous solutions. The sample is dissolved in acid, digested or fused in molten salt (all described in Chapter 1), and then diluted to volume with water. All acids, bases, reagents, and water must be of extremely high purity, given the sensitivity of the ICP-MS technique. Ultratrace metals grade acids, solvents, and deionized water systems are all commercially available. The aqueous solution is introduced into the plasma using a peristaltic pump, nebulizer, and spray chamber system identical to those used for ICP-OES (Chapter 7, Section 7.3.1.3). 

Detection limits via either direct aspiration or pumped delivery are similar for the same solvent (toluene-pyridine), since nebulizer and spray chamber are identical. Precision of analysis, however, is considerably improved in the latter case. This observation was most pronounced when pyridine solutions of coal derived material were being examined rather than solutions of elemental standards. The relatively high viscosity of the concentrated coal derived solutions ( 5-7% w/w) no doubt leads to inconsistency in aspirated sample delivery. Relative standard deviations (RSD) were also improved on going from 10 second to 30 second integration times. Table II compares detection limits and RSD s in pyridine employing direct aspiration (10 second integrations) and pumped delivery (30 second integrations). The RSD s for most elements were less than 10% for the pumped delivery. 

Premix air-acetylene flame, pneumatic nebulizer and spray chamber (Lundegardh) ... 

The ICP-MS used for this protocol must have a sapphire (alumina) injector. All glass or quartz parts such as the nebulizer and spray chamber that will contact the acid solution must be replaced with comparable PP or PFA parts. 

Figure 2.17 provides a schematic overview of a quadrupole-based ICP-MS instrument. Typically, the sample solution is pumped to a nebulizer by means of a peristaltic pump. The nebulizer converts the sample solution into an aerosol. This primary aerosol is introduced into a spray chamber that filters out the droplets with diameter > 10 pm. Although this process is highly inefficient - it reduces the analyte introduction efficiency by 1-2 orders of magnitude, depending on the actual type of nebulizer and spray chamber used - it is necessary to obtain a stable plasma... 

Chapter 3 examines one of the most critical areas of the instrument—the sample introduction systan. It discusses the fundamental principles of converting a liquid into a fine-droplet aerosol suitable for ionization in the plasma, and presents an overview of the different types of commercially available nebulizers and spray chambers. Although this chapter briefly touches upon some of the newer sampling components introduced in the past few years, the new breed of desolvating nebulizers and chilled spray chambers are specifically addressed in Chapter 17. 

Let us now look at the most common nebulizers and spray chamber designs used in ICP-MS. We cannot cover every conceivable design, because over the past few years there has been a huge demand for application-specific solutions, which has generated a number of third-party manufacturers that sell sample introduction components directly to ICP-MS users. 

When coupling an HPLC system to an ICP mass spectrometer, it is very important to match the flow of sample being eluted off the column with the ICP-MS nebulization system. With today s choice of sample introduction components, there are specialized nebulizers and spray chambers on the market that can handle sample flows... 

The gaseous sample introduction line is connected directly to the central tube of the plasma torch, eliminating the need for the conventional nebulizer and spray chamber. Additional equipment to handle gas mixing and dilution at controlled flow rates may be required. 

As described previously, vapour introduction approaches are by far the most common application of atomic fluorescence. Despite this, mention of other methods should be made. If a conventional nebulizer and spray chamber assembly (see AAS section) is used, it is possible to introduce liquid samples directly to the atom cell. In circumstances such as these, it is necessary to use more robust air-acetylene or nitrous oxide-acetylene flame, or perhaps an ICP. The use of an ICP as an atom cell for AFS measurements has led to the development of a number of different techniques, e.g. ASIA, an acronym for atomiser, source, inductively coupled plasmas in AFS. This technique uses a high-powered ICP as a source and a low-powered ICP for the atom cell. It has been found that ICP-AFS yields linear calibrations over 4—6 orders of magnitude and is more sensitive than ICP-AES. 

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