Lighting matrix

In addition to absorption problems, measurements will be affected by secondary fluorescence and scattered radiations which will enter the detector and increase the general background. Detection limits under optimum conditions (a heavy element in a light matrix) may be as low as 10 ppm. Quantitative analysis is however difficult below the 20-100 ppm region if a reasonable precision (5% or better) is to be obtained. 

Some spectrometers are equipped with delayed extraction. Ions are accelerated from the target only 200 to 300 nsec after the laser beam hits the target. During the short delay, light matrix ions dissipate. This helps to avoid massive collisions during the acceleration between the large molecules and the matrix ions. 

Thus, the measurements made by the sensor can be viewed as a linear transformation of the reflectances. Let us consider only the three wavelengths Xj with i e r, g, b], then the lighting matrix would be given by... 

The opposite limit is represented by a dilute mixture. For this example, let us take 1 cation % of Zn in kaolinite (used as an example of a light matrix). The empirical formula of this sample is AUSi ioCOH Zn.og. Now, the Zn resonant absorption is < 5% of the total, so one is free to use any thickness. Further, non-uniformities in concentration over the beam spot would have no effect, provided that the Zn environment is uniform. 

Use of Matrix-Matched Standards. The use of matrix-matched standards, would, in theory, be the more straightforward solution for light matrix effects. An example illustrating this approach is presented in Aramendia et al. [31], where some novel strategies for rapid Al, Mn, and Si determination in polyamide samples is presented. In this work, a fast digestion of the polyamide sample in concentrated formic acid is proposed. Self-evidently, obtaining matrix-matched standards is very straightforward as formic acid can be used as... 

Figure 8.21a (left) shows the visual image of the PHB/PLA (50 50wt%) blend with dark, circular-shaped islands embedded in a light matrix. For the preparation... 

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