Suppressor ionization

Remedy The resulting effects of shifts in ionization equilibrium may be eliminated effectively by the addition of an ionization suppressor, that promptly gives a comparatively high concentration of electrons to the flame. This ultimately results in the suppression of ionization by the respective analyte. 

For many elements, the atomization efficiency (the ratio of the number of atoms to the total number of analyte species, atoms, ions and molecules in the flame) is 1, but for others it is less than 1, even for the nitrous oxide-acetylene flame (for example, it is very low for the lanthanides). Even when atoms have been formed they may be lost by compound formation and ionization. The latter is a particular problem for elements on the left of the Periodic Table (e.g. Na Na + e the ion has a noble gas configuration, is difficult to excite and so is lost analytically). Ionization increases exponentially with increase in temperature, such that it must be considered a problem for the alkali, alkaline earth, and rare earth elements and also some others (e g. Al, Ga, In, Sc, Ti, Tl) in the nitrous oxide-acetylene flame. Thus, we observe some self-suppression of ionization at higher concentrations. For trace analysis, an ionization suppressor or buffer consisting of a large excess of an easily ionizable element (e g. caesium or potassium) is added. The excess caesium ionizes in the flame, suppressing ionization (e g. of sodium) by a simple, mass action effect ... 

Also called vapour-phase interferences or cation enhancement. In the air-acetylene flame, the intensity of rubidium absorption can be doubled by the addition of potassium. This is caused by ionization suppression (see Section 2.2.3), but if uncorrected will lead to substantial positive errors when the samples contain easily ionized elements and the standards do not. An example is when river water containing varying levels of sodium is to be analysed for a lithium tracer, and the standards, containing pure lithium chloride solutions, do not contain any ionization suppressor. 

The problem is easily overcome by adding an ionization suppressor (or buffer) in large amount to all samples and standards. 

An ionization suppressor decreases the extent of ionization of analyte. For example, in the analysis of potassium, it is recommended that solutions contain 1 000 ppm of CsCl, because cesium is more easily ionized than potassium. By producing a high concentration of electrons in the flame, ionization of Cs suppresses ionization of K. Ionization suppression is desirable in a low-temperature flame in which we want to observe neutral atoms. 

Aluminum oxide is another stabilizer that is included in glass compositions to improve the resistance to breakage from thermal shock. Because of the refractory nature of the element, the oxidizing N20 + C2H2 flame is used for excitation with the AAS mode. It has been found that a satisfactory ionization suppressor is the 1000pg Caml-1 + 0.07 M HC104 solution. 

Ionization interferences occur most commonly for alkali and alkaline earth metals. The low ionization potential of these metals can lead to their ionization in the relatively hot environment of the flame. If this occurs, no absorption signal is detected, since FAAS is a technique for measuring atoms not ions. This process can be prevented by the addition of an ionization suppressor or buffer , e.g. an alkali metal such as Cs. Addition of excess Cs... 

Only chemical interferences were observed sodium and potassium ionized in the air-acetylene flame, and aluminum ionized in the nitrous oxide-acetylene flame magnesium and calcium exhibited evidence of interference by both phosphorus and aluminum. All the other elements were found to be interference-free. The addition of 1000 ppm of cesium as an ionization suppressor effectively removed the ionization interference in the sodium and potassium solutions. Similarly, 1000 ppm of lanthanum removed the interference due to phosphorus and aluminum in the magnesium and calcium solutions and suppressed the ionization of aluminum. 

Ionization suppressor In atomic spectroscopy, an easily ionized species, such as potassium, that is introduced to suppress the ionization of the analyte. 

Finally, the use of very hot flames can provoke partial ionization of certain elements which decreases the concentration of free atoms in the flame. This phenomenon is corrected by addition of an ionization suppressor in the form of a cation whose ionization potential is lower than that of the analyte. A potassium salt of about 2 g/L is often employed for this purpose. 

The use of branched uptake capillaries, coimected to the nebulizer using a T-piece, may be advantageous when a buffer or ionization suppressor is required. In addition to avoiding time-consuming solution preparation, it is also possible to calibrate organic extracts using aqueous standards in this way. The approach may also be extended to couple more complex flow injection systems employing novel chemistries in the same way. 

Some elements ionize in the flame very easify and such metal ions are not wanted. An ionization suppressor such as lanthanum salt which is preferential ionized can be added. 

Define the following terms (a) releasing agent, lb) protective agent, (c) ionization suppressor, (d) atomization, (el pressure broadenmg- (f I hollow-cathode lamp. 

Ionization interference due to the production of ions is most troublesome with alkali metals because of their low ionization potentials. Occasionally, ionization suppressors such as lithium or lanthanum salts, which are easily ionized, are added. 

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