Skip to main content
Q: "What is background?"
A: In a photoabsorption measurement, an analytical line may be darkened due to causes other than absorption by a target metallic element. This darkening is called background.
For example, in the case of sodium chloride (NaCl) in sea water, the wavelengths absorbed by Na, cadmium (Cd), and nickel (Ni) are overlapped.
For a specimen containing a large quantity (several percent) of NaCl, like sea water, a trace amount of (ppm) Cd or Ni cannot be measured accurately. If the background absorption is not corrected accurately, the measurement result will be ruined.
Let's see how BKG is corrected, in principle.
However, before that... "How to measure only the background absorption" is the point.
A hollow cathode lamp and a D2 lamp are used as light sources (The following diagram shows the optical system). Please imagine that there are two photometers, one using an HCL as its light source, and one using a D2 lamp as its light source. The signals from the two photometers are electric signals which are processed and distinguished.
From (1) - (2), true atomic absorption can be measured.
A lighting method for a hollow cathode lamp (HCL) is devised.
Excess current discharge causes a self absorption phenomenon, leading to a spectrum like this.
The self-absorption correction method uses the spectrum obtained by lighting with an excessive current instead of the D2 lamp light source spectrum of the previous section.