Absorption Spectroscopy Technique

Laboratory

Absorbance Spectroscopy Background

We saw previously how to use a

titration to quantitatively determine

the amount of a compound of interest

in a sample. Here we will learn about

absorbance spectroscopy, which is

another widely used technique for

quantitative analysis. One example of

an application where absorbance

spectroscopy can be used is in

determining the nitrate concentration

in water. Large amounts of nitrate can

enter waterways via run-off from

fertilizer application in farming. High

concentrations of nitrate in drinking

water can lead to deleterious health

impacts. Excessive nitrate in water has

also contributed to harmful algae

blooms in lakes. The western basin of

Lake Erie is one example where algae

blooms have contributed to drinking

water problems.

Absorbance spectroscopy uses the

quantity of light that passes through a

sample to determine how much of a

particular substance is in a mixture.

The use of light to quantify the amount

of chemical is beneficial because it

allows for remote sensing where we

can determine quantities of different

species even if they are in other solar

systems. The basic idea is that atoms

and molecules can absorb light when

the energy of the photon of light is

60

Figure 8.1: "Harmful algae bloom. Kelley's Island,

Ohio. Lake Erie" by NOAA Great Lakes

Environmental Research Laboratory is marked

with Public Domain Mark 1.0.

Figure 8.2: Energy level diagram that shows how

different wavelengths of light interact with a

molecule.