Module 4 Flashcards
(22 cards)
What is the purpose of a wavelength scan?
Determines the wavelength that a substance maximally absorbs.
Plotted to an absorbance curve.
What is Max A?
The wavelength that a substance absorbs the most.
What is transmittance?
The proportion of incident light that is transmitted.
How is transmittance calculated?
%T = transmitted (Isol)/transmitted (Iorg) x 100%
How does concentration relate to light?
Increased concentration results in more light absorbed and less is transmitted.
What characteristic of light is measured directly?
Transmittance.
How does absorbance relate to concentration and transmittance?
Directly related to concentration.
Inversely related to absorbance.
How do you calculate absorbance?
A = 2-log%T
Reported to 3 decimal places.
What is Lambert’s Law?
Absorbance is proportional to the distance the light must travel/path length.
How does path length affect absorbance?
As path length increases the light absorbed also increases.
What represents path length?
Cuvette diameter
What is Beer’s Law?
The greater the concentration of absorbing molecules the more light will be absorbed.
What wavelength produces the best linearity between concentration and absorption?
Max A
What is the Beer-Lambert/Beer’s Law?
Absorbance is proportional to the product of concentration, depth of solution and a constant.
How is absorbance calculated using Beer’s Law?
A = a x b x c
a = absorptivity
A = E x b x c
E = molar absorptivity
How is Beer’s Law plotted?
Concentration x-axis
Absorption y-axis
What deviations in absorbance readings are due to method/operator?
Incorrect wavelength
High analyze concentration
Unmatched cuvettes
Failure to set 0%T/100%T properly
Failure to maintain pH and temp
Impurities or turbidity
Interfering substances that absorb the same wavelengths
What deviations in absorbance readings are due to instrument error?
Stray light
Inability to select a narrow band of wavelengths
Line voltage fluctuations
Unstable light source
Nonlinear detector response
How can Beer’s law be used for quantitative analysis?
Calculate the unknown concentration by comparing its absorbance to a standard.
Making a calibration curve of known standards that can be used to determine the unknown concentration.
When can a concentration be calculated by comparing absorbances?
If:
Beer’s law is obeyed
Using A
Setting the blank at 0A
The standard is close in concentration to the unknown
The standard and unknown are analyzed at the same time
How are the unknown and standard concentrations related?
Au/As = Cu/Cs
How does wavelength relate to substance characteristics?
The wavelengths transmitted and absorbed result in unique colour properties.
Allows for detection and quantification of substances.
Transmitted and absorbed colours are complimentary.