Electrothermal Atomization ETA

This is also mainly a single-element technique, although multielement instrumentation is now available. It works on the same principle as flame AA, except that the flame is replaced by a small heated tungsten filament or graphite tube. The other major difference is that in ETA, a very small sample (typically, 50 pL) is injected onto the filament or into the tube, and not aspirated via a nebulizer and a spray chamber. Because the ground-state atoms are concentrated in a smaller area than a flame, more absorption takes place. The result is that ETA offers about 100 times lower detection limits than flame AA. 

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We have already seen in Chapter 2 that choice of atomizer system to be used may have a dramatic effect upon sensitivity, and thus upon signal-to-noise ratio. It is necessary to choose not only between flames, electrothermal atomization (ETA), and cold vapour and hydride generation techniques (which are discussed in Chapter 6), but sometimes also between different flames. Those elements which tend to form thermally stable oxides, such as Al, Ti, Si, Zr, may only be determined in a hotter, reducing nitrous oxide-acetylene flame. They cannot be determined with useful sensitivity in the air-acetylene flame. Some elements, Ba and Cr for example, may be determined in air-acetylene, but are more efficiently atomized in nitrous oxide-acetylene. 

Whatever the analytical method and the determinand may be, the greatest care should be devoted to the proper selection and use of internal standards, careful preparation of blanks and adequate calibration to avoid serious mistakes. Today the Antarctic investigator has access to a multitude of analytical techniques, the scope, detection power and robustness of which were simply unthinkable only two decades ago. For chemical elements they encompass Atomic Absorption Spectrometry (AAS) [with Flame (F) and Electrothermal Atomization (ETA) and Hydride or Cold Vapor (HG or CV) generation]. Atomic Emission Spectrometry (AES) [with Inductively Coupled Plasma (ICP), Spark (S), Flame (F) and Glow Discharge/Hollow Cathode (HC/GD) emission sources], Atomic Fluorescence Spectrometry (AFS) [with HC/GD, Electrodeless Discharge (ED) and Laser Excitation (LE) sources and with the possibility of resorting to the important Isotope... 

Electrothermal atomization (ETA) for use with atomic absorption (AA) has proved to be a very sensitive technique for trace element analysis over the last three decades. However, the possibility of using the atomization/heating device for electrothermal vaporization (ETV) sample introduction into an ICP mass spectrometer was identified in the late 1980s. The ETV sampling process relies on the basic principle that a carbon furnace or metal filament can be used to thermally separate the analytes... 

Electrothermal Atomization (ETA) A single analyte by ETA takes about 5-6 min for a duplicate analysis, which is equivalent to approximately 10 analytes per hour or 10,000 analytes per year. For 10 analytes/sample, this represents 1000 samples per year. Based on an annual operating cost of 5960, this equates to 6 per sample. (Note If a multielement GFAA is being used, these costs will be reduced, but the actual cost will depend on how many elements are being determined simultaneously.)... 

Analytical performance can mean different things to different people. The major reason that the trace element community was attracted to ICP-MS almost 20 years ago was its extremely low mnltielement DLs. Other multielement techniques, such as inductively coupled plasma optical anission spectrometry (ICP-OES), offered very high throughput but just could not get down to ultratrace levels. Eveu though electrothermal atomization (ETA) offered much better detection capability than ICP-OES, it did not offer the sample thronghput capability that many applications demanded. In addition, ETA was predominantly a single-element technique and so was impractical for carrying out rapid multielement analysis. These limitations quickly led to the commercialization and acceptance of ICP-MS as a tool for rapid ultratrace element analysis. However, there are certain areas where ICP-MS is known to have weaknesses. For example, dissolved solids for most sample matrices must be kept below 0.2%, otherwise this can lead to serious drift problems and poor precision. 

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