Absorbance

Definition

Absorbance is a measure of the amount of light absorbed by a sample as it passes through a solution. It is commonly used in microbiology to quantify the concentration of bacteria or other microorganisms.

5 Must Know Facts For Your Next Test

1. Absorbance is measured using a spectrophotometer, which detects how much light at a specific wavelength is absorbed by the sample.
2. The Beer-Lambert Law relates absorbance to the concentration of the absorbing substance; higher concentrations result in higher absorbance.
3. In microbiology, absorbance can be used to estimate bacterial growth by measuring optical density (OD) at 600 nm (OD600).
4. Absorbance values are dimensionless and typically range from 0 (no absorption) to around 2 (high absorption), though values can be higher depending on the sample and instrument settings.
5. Calibration curves are often used in conjunction with absorbance measurements to determine the exact concentration of a substance in an unknown sample.

Review Questions

• What instrument is commonly used to measure absorbance?
• How does the Beer-Lambert Law relate absorbance to concentration?
• Why is OD600 commonly used in microbiology for measuring bacterial growth?

Related terms

Spectrophotometer: An instrument that measures the amount of light absorbed by a sample at various wavelengths.

Optical Density (OD): A measure of how much a chemical species absorbs light by measuring its attenuation.

Beer-Lambert Law: A linear relationship between absorbance and concentration of an absorbing species.