Absorption within sample, correction

The data and arguments presented indicate that the presence of sea salts alters the atomic absorption signal of these four elements from their response in de-ionized water-acid standards in a consistent manner for each particular element and sea salt concentration. This observation can be used to develop a modified standard addition technique. If a series of curves can be prepared that contain the range of metal and sea salt concentration expected in the samples, correction factors between actual and observed concentrations based on pure water-acid standards can be determined. This modified standard addition technique is illustrated for two of the elements discussed previously. For lead the actual concentration is plotted vs. the calculated concentration for a sea salt range of 1.0-5.0 parts per thousand sodium in Figure 4. This plot was prepared from solutions of known concentrations in a sea water medium. For a sample of unknown lead concentration, within the specified range. 

Make corrections for gamma-ray absorption within the sample and/or between source and detector. 

Sample analysis by thermal ionization mass spectrometry (TIMS) results in measurement of isotopic ratios of minerals. Total mineral content of samples is then determined by one of two methods. One approach is to use flame atomic absorption spectrophotometry (AAS) to determine total mineral content of samples. Since AAS does not have the same level of precision as TIMS a sufficient number of replicates is analyzed for a mineral content determination with a CV of within 1%. Alternatively if a mineral has 3 or more isotopes and fractionation corrections are not made the following procedure may be used. An individual is fed one isotope and another isotope is added to the sample prior to analysis to determine the total mineral content of the sample by dilution of the second isotope. In this way both the amount of the isotope fed which is recovered in the feces and the total mineral content of the sample can be determined simultaneously. If fractionation corrections are to be made a mineral must have at least four isotopes. Details of these procedures will be reported separately. 

Concerning time resolved measurements, special care must be taken of the problem how to monitor the time course of the primary beam intensity during the experiment. Another problem is, how to observe changes in the absorption of X-rays within the sample, when structural changes occur. The measured scattering patterns have to be corrected according to both effects. 

The absorption correction (correcting for the effects arising from variations in irradiated volume as well as in beam path length within the sample) is important, and one way to ensure its accuracy is to obtain a reference sample having the same constitution and shape as the test sample but known to be isotropic and to make sure that the intensity measured with this reference sample is truly constant after the absorption correction is applied. From the intensity /( ) or /( , ) obtained after the absorption correction, the pole distribution r( ) or t( , d>), for a sample of uniaxial or biaxial orientation, respectively, is evaluated according to... 

---