Theory Of Spectrophotometry Flashcards
Definition of spectrophotometry
A quantitative way of measuring the amount of light that travels through a solution ( amount that is transmitted/ absorbed)
What are the wavelengths of visible light?
400-700nm
What does lamda max mean?
It’s the optimal wavelength for analysis
What does higher absorbance mean about concentration?
Higher absorbance= higher concentrations
What is transmittance?
Light out/ light in
How is transmittance often denoted?
As a percentage
What is absorption
Opposite of transmittance so light in/ light out
What factors affect absorbance?
Concentration of solution (directly proportional)
Path length (proportional to conc x length)
Tendency of a solution to absorb a certain wavelength (path length x conc x tendency)
How wide are most cuvettes
1cm
What is the beer- lambert law?
Relationship between the absorbance of a solution and it’s concentration
What does epsilon mean in the beer-lambert law?
Molar extinction coefficient (depends on substance and wavelength)
Under what conditions can you calculate the conc directly from The absorbance?
If we have a pure substance and know it’s molar correlation coefficient
What are the limitations of the beer-lambert law?
- might not know the molar extinction coefficient
- can’t be used for a mixture as it only applies to a single substance
What happens if the substance isn’t coloured?
- bind it with a dye
- undergo a chem reaction with a coloured result which can then be measured
- possibly could be absorbing infra-red or UV light
