Exam 2 Flashcards
Spectral Transmittance curve
A plot of all the wavelengths used vs the observed transmittance of the solution - or the amount of light allowed to pass through the solution at each wavelength
Spectral Absorbance curve
A plot of all the wavelengths used vs the observed absorbance of the solution - or the amount of light absorbed by the solution at each wavelength
Absorbance Max (Max A)
Wavelength that is absorbed the most
Highest point on a Spectral Absorbance curve, lowest point on a Spectral Transmittance curve
Best wavelength of light to use in order to identify and quantitate a substance
Why is the concept of transmittance important?
Only the amount of light transmitted (through a solution) can be measurable directly - absorbance cannot be measured directly
Lambert’s law
Absorbance is directly proportional to the distance the light must travel through. Thus, the greater the path length the light must travel through, the greater the amount of light absorbed
In a photometer, what represents the path length?
the diameter of the cuvette
Beer’s law
The amount of radiant energy of a particular wavelength absorbed varies directly with the concentration of the absorbing molecules. The greater the number (concentration) of the absorbing molecules, the more light will be absorbed.
Combined Beer-Lambert law (Beer’s law)
The absorbance (A) of a solution is directly proportional to the product of the concentration (c) times the depth of the solution that the light must travel (b) times a constant (a) A = a x b x c
Molar absorptivity
The absorbance of a solute in a concentration of one mole/L of solution measured in a 1cm light path at a specified wavelength, temp, pH, and solvent
Can be used in place of absorptivity (a)
Represented by epsilon
What is the minimum amount of standards you need to make a cal curve?
3
How are sensitivity and minimum detection limit related?
Good sensitivity produces a higher minimum detection limit
Used to construct a standard graph (calibration curve) to determine unknown concentrations
Standards (Calibrators)
Other terms for linear range
Analytical range
Reportable range
Internal standard
Used to account for variations within the system
Structurally similar compound of known concentration added to all samples
Not used to determine unknowns, only to detect changes in the system that may have affected the samples
What piece of glassware would be most appropriate for preparing a stock standard?
Volumetric flask
