Norm temperature

From Eqs. (63) and (64), which give the intensity of a line, and from the Saha equation [Eq. (68)], it can be understood that for each spectral line emitted by a plasma source there is a temperature where its emission intensity is maximum. This is the so-called norm temperature. In a first approximation [18], it can be written as ... 

In the case where we have to consider the norm temperature for a line of an element which is only present as an impurity in a plasma, e.g., one formed in a noble gas, the dilution in the plasma (a) also has to be considered. For a system with more components P is given by ... 

At a dilution of 0.1 the change in norm temperature will thus be —7.2%. In a source such as the inductively coupled plasma the analyte dilution can be very high [of the order of 108 (1 mL/min of a 1-10 pg/mL solution for an element with a mass of 40, which is nebulized with an efficiency of 1% into an argon flow of... 

From what is known about the norm temperatures, it becomes clear which types of lines will be optimally excited in a plasma of a given temperature, electron pressure and gas composition, and the norm temperatures thus give important indications for line selection in a source of a given temperature. Atom lines often have their norm temperatures below 4000 K, especially when the analyte dilution in the plasma is high, whereas ion lines often reach 10000 K. Both types of lines are often denoted as soft and hard lines, respectively. 

Sources for atomic spectrometry include flames, arcs, sparks, low-pressure discharges, lasers as well as dc, high-frequency and microwave plasma discharges at reduced and atmospheric pressure (Fig. 5) [28], They can be characterized as listed in Table 2. Flames are in thermal equilibrium. Their temperatures, however, at the highest are 2800 K. As this is far below the norm temperature of most elemental lines, flames only have limited importance for atomic emission spectrometry, but they are excellent atom reservoirs for atomic absorption and atomic fluorescence spectrometry as well as for laser enhanced ionization work. Arcs and sparks are... 

These can be performed successfully with AES. Indeed, the unambiguous detection and identification of a single non-interfered atomic spectral line of an element is sufficient to testify to its presence in the radiation source and in the sample. The most intensive line under a set of given working conditions is known as the most sensitive line. These elemental lines are situated for the various elements in widely different spectral ranges and may differ from one radiation source to another, as a result of the excitation and ionization processes. Here the temperatures of the radiation sources are relevant, as the atom and ion lines of which the norm temperatures (see Section 1.4) are closest to the plasma temperatures will be the predominant ones. However, not only will the plasma temperatures but also the analyte dilutions will be important, so as to identify the most intensive spectral lines for a radiation source. Also the freedom from spectral interferences is important. 

The plasma temperature in the carbon arc is of the order of 6000 K and it can be assumed to be in local thermal equilibrium. According to the temperatures obtained, it could be expected that in arc emission spectrometry mainly the atom lines will be the most sensitive lines, when considering their norm temperatures. Arcs are usually used for survey trace analysis but also for the analysis of pure substances when the highest power of detection is required. However, they may be hampered by poor precision (RSDs of 30% and higher). 

The only binary halide known is the fluoride MnF4 and, although ternary compounds are well established for both F and Cl, the latter are particularly unstable at norm temperatures and all are, to varying degrees, sensitive to water. ° ... 

From what is known about the norm temperatures, it becomes dear which types of lines will be optimally excited in a plasma of a given temperature, electron pres-... 

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