Effect of Concentration on Spectra

From the discussion in Section 7.5, it is clear that the absorbance at the wavelength of maximum absorbance increases as the concentration increases and decreases as the concentration decreases. This is true not just at the wavelength of maximum absorbance but at all wavelengths. This means that an entire absorption spectrum is affected by concentration changes. It is important to note, however, that the pattern of the absorption—the characteristic of the spectrum that makes it useful for qualitative 

At Los Alamos National Laboratory, the silicon content of plutonium samples is determined spectrophotometrically using a silica-molybdenum blue complex ion, which has a blue color. The sample is dissolved in a mixture of hydrochloric acid and hydrofluoric acid. After the excess hydrofluoric acid is removed, the absorbance is measured at 825 nm. All operations are carried out in a silica-free apparatus. 

Technician Velma Montoya, of the Actinide Analytical Chemistry Group at Los Alamos, works in a silica-free glove box to determine silicon content in plutonium samples using visible (near infrared) spectrophotometry. 

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