Chemical Analysis
Chemical Analysis
Page 48
5940022ChemAnal.fm
9. Adjust the wavelength to 50 nm more than the highest absorbance point on
the initial search (step 8). Re-zero as in step 5.
10. Measure and record the absorbance. Repeat, decreasing the absorbance in 5-nm
steps. Re-zero, then measure and record the absorbance at each increment.
Continue until the entire range of interest is measured (see Tabl e 11 ).
Check to be sure there is enough difference in absorbance between samples with
low and high analyte concentrations by measuring two sample solutions that
contain the expected low and high concentrations of analyte at the optimum
wavelength. The change in absorbance caused by increases/decreases in
concentration depends on the sensitivity of the procedure and the chemistry.
Chemistries with small absorbance changes are less sensitive, but tend to have
larger ranges. Chemistries with large absorbance changes are more sensitive, but
tend to have smaller ranges.
Table 10
Wavelength Absorbance
550 nm 0.477
500 nm 0.762
450 nm 0.355
400 nm 0.134
Table 11
Wavelength Absorbance
520 nm 0.748
515 nm 0.759
510 nm 0.780
505 nm 0.771
500 nm 0.771
495 nm 0.651
490 nm 0.590
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