External standard absorption correction

M HNO3. The concentration of Cu and Zn in the diluted supernatant is determined by atomic absorption spectroscopy using an air-acetylene flame and external standards. Copper is analyzed at a wavelength of 324.8 nm with a slit width of 0.5 nm, and zinc is analyzed at 213.9 nm with a slit width of 1.0 nm. Background correction is used for zinc. Results are reported as micrograms of Cu or Zn per gram of FFDT. 

Finally, although temperature had a large effect on both the position (wavelength) and the intensity of the water absorption bands in the emulsion NIR spectra, careful experimentation demonstrated that the 1618 nm vinyl C—H band used in the calibration model did not shift in either position or intensity with temperature, in the temperature range used in these studies (25-75° C). Therefore, it was not necessary to correct the calibration model for temperature effects, either by the use of internal or external standards, or by including temperature variations in the calibration set. 

By measuring absorbance changes as a function of time, the cumulative undersize particle distribution can be obtained by mathematical manipulation. However, in converting Equation 34-18 to the size distribution, it is necessary to know how the absorption coefficient K varies with d,. Alternatively, an external standard can be used for calibration. If correction is not made for variations in K. results are valid only for comparison purposes. 

The instrument is calibrated for a given element for each series of samples. Direct calibration requires detailed knowledge of the milieu to be analysed. Precise results depend on the composition of the calibration solutions being as close as possible to that of the solutions to be analysed. The standard addition method can be u.sed in cases where it is not possible to produce external reference solutions similar to the solutions to be analysed. This method should be used with considerable caution because it assumes that the absorption is due solely to the element under analysis and, in particular, that the non specific absorption is fully corrected for. If this is not the case, any interfering absorption leads to an overestimate of the values observed. On the other hand, this method does have the advantage of eliminating the matrix effect. 

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