Lab 1 Colorimetry Flashcards
What is a spectrophotometer?
An instrument that passes a selected wavelength of electromagnetic radiation through a solution and measures the amount absorbed or transmitted.
What are the three types of spectrophotometers mentioned?
- Ultraviolet (UV) spectrophotometers
- Infrared (IR) spectrophotometers
- Visible wavelength spectrophotometers (colorimeters)
What is colorimetry?
A procedure in which a colorimeter is used to analyze the composition of solutions.
Define absorbance (A).
The relative amount of light of a given wavelength that is absorbed by a solution.
Define percent transmittance (%T).
The fraction of light entering the solution that passes through unimpeded.
What happens when different types of dye molecules are dissolved in water?
They absorb different wavelengths of light, resulting in different colors being transmitted to the eye.
What is the relationship between absorbance and percent transmittance?
They are reciprocally related; as one rises, the other falls.
What is an absorption spectrum?
A graph of light absorption as a function of wavelength.
How does one calibrate a colorimeter?
By using a blank solution to correct for light absorption by the glass and solvent.
What is the purpose of the blank in colorimetry?
To calibrate/standardize the instrument and ignore light absorption by everything except the molecule of interest.
What is riboflavin?
A water-soluble vitamin that can be measured using colorimetry.
What is the significance of 565 nm for phycoerythrin?
It is the wavelength location of the highest peak in the absorption spectrum of phycoerythrin.
Fill in the blank: The scales for absorbance and %T run in _______ directions.
opposite
What is the equation that relates absorbance (A) to percent transmittance (T)?
A = log (1 / T)
What steps are taken to collect data for riboflavin’s absorption spectrum?
- Fill a cuvette with riboflavin solution
- Insert cuvette into spectrometer
- Click Collect and then Stop after a few seconds.
True or False: %T has a linear scale while absorbance has a logarithmic scale.
True
What should be done before using the colorimeter to measure samples?
Calibrate/standardize the instrument with a blank.
What is the main function of a colorimeter in biological studies?
To quantify the concentration of specific solutes in solutions based on light absorption.
