Thermal pretreatment-atomization curves

Double curves (thermal pretreatment/atomization curves) are used to determine the limits for both thermal pretreatment and atomization temperatures for the elements and matrices involved. These curves can also be applied to drawing conclusions about the atomization mechanism. In the first curve the absorbance signal at the optimum atomization temperature is plotted versus the pretreatment temperature as the variable. In the second curve the absorbance at the optimum pretreatment temperature is plotted versus the atomization temperature as the variable (Figure 65). The pretreatment curve (ash curve) shows the temperature to which the sample can be heated without loss of the analyte. From this curve it is also possible to derive the lowest temperature at which the element is quantitatively volatilized. From the atomization curve can be derived the temperature at which the atomization is first evident, the appearance temperature, and the optimum atomization temperature at which the maximum atom cloud density is attained. 

It is possible to draw conclusions about the atomization mechanism from the thermal pretreatment/atomization curves, when melting point, boiling point, and decomposition point for the analyte and its compounds are entered on these plots. Figure 66 shows the thermal pretreatment/atomization curves for cadmium and aluminium. The initial pre-atomization losses and the appearance temperature are below the melting point of cadmium. This... 

Figure 65 Thermal pretreatment/atomization curve. A The absorbance measured at the optimum atomization temperature B The absorbance plotted versus the atomization temperature 1 The maximum thermal pretreatment temperature 2 The lowest temperature at which the analyte is quantitatively volatilized 3 The appearance temperature of the analyte 4 The optimum atomization temperature...

Figure 66 Thermal pretreatment/atomization curve for cadmium and aluminium...

The analyte may be lost during the thermal pretreatment phase for two reasons (i) The analyte may be present in the sample as a compound which is appreciably volatile at the thermal pretreatment temperature used (ii) The analyte may be converted into a volatile form by a matrix component or solvent. From the thermal pretreatment/atomization curves (described in section 4.5) it can immediately be seen, whether or not the thermal pretreatment temperature is too high. These plots also show the best thermal pretreatment and atomization temperatures for a given matrix. 

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