exam 2 Flashcards
What is wavelength
it is the linear distance between successive maxima or minima
what is frequency
it is the number of oscillations of the field that occur per second
what is the product of frequency and wavelength
the speed of light
What happens to the energy of a molecule when light is absorbed
it increases
What is the irradiance
it is P it is the energy per second per unit area of the light beam
what happens to the irradiance when light is absorbed by the analyte
P decreases
What is P0 and it’s relationship to P
P0 is the irradiance before it passes through the sample, it is greater than P which is the irradiance after it passes through the sample
What is transmittance
it is T (P/P0) it is the quantity of light that passes through the sample
what is absorbance and how is it connected to concentration?
the absorbance is how much of the light is absorbed, it can be used to tell us how much concentration is there
In a spectroscopic experiment with beers law, what is the y-axis and what is the x-axis? What is the slope?
the y-axis is the absorption, it is dependent on the concentration
the x-axis is the concentration, it is independent
the slope is the molar absorptivity x the wavelength
what is b in beers law
the pathlength
what is QA and QC
it is a sample that we can analyze to represent the precision and accuracy of our method
what are calibration checks
they are repeated analyses of a calibration standard that checks the precision
what are blanks
they are samples containing no analyte, they check for contamination which could affect accuracy and precision
what are lab, method spikes
they are samples with a known amount of analyte and analyzed as a sample
when are lab method spikes analyzing accuracy
when it is a single analysis
when are lab method spikes analyzing precision
when it has multiple analyses
what is a detection limit
it is the lowest amount of analyte in a sample that gives a signal that we can say is significantly different from the blank signal
what is the signal detection limit
=y blank + 3s
where y blank is the signal in blank and s is the standard deviation in the replicates
what is the relationship between y blank + 3s = mx+b
y blank is equal to b (the y-intercept)
the concentration detection limit is x= (3s)/m
what is the purpose of signal detection limits
they allow us to differentiate between error, lab contamination, and the presence of analyte in a sample
does the best method have a high or low limit of detection?
the method is better with a low LOD
if the detection is less than the limit how do we describe it?
it is not zero. we say it is between 0- and the line of detection(ex. 0.1 ug/L)
is absorption constant with respect to the wavelength
no, it varies. We need to make our standards the same wavelength
what is molar absorbtivity
he molar absorptivity is a measure of how well the species absorbs the particular wavelength of radiation that is being shined on it.
what type of transition gives a high molar absorbtivity
ones that are more efficient
if you have a higher molar absorbtivity, what is true of the absorbance
it is higher, the absorptivity is directly proportional to the absorbance
what is the absorbance directly proportional to
tha absorbance is propportional to the concentration of the absorbing material, the constant pathlength, and the molar absorptivity
does wavelength factor in absorbance
yes but in a different way, the absorbance is a constant that various depending on the wavelength of the light
is absorption directly proportional to the wavelength
no, the absorbance is not directly proportional to the wavelength.
Each substance absorbs light at different wavelengths
whats the difference between molecular and atomic spectroscopy
in molecular spec, we can see various bond vibrations and molecular transitions
in an atomic spec, we only see the single transition from the ground state so there is only one absorption frequency
what is internal screening
when the concentration is too high and a shadow effect occurs that causes the calibration curve to flatten out
what happens if our concentrations are too low
the P0 and P are basically the same and we can’t see a significant difference between the two
what is a chemical deviation in beers law
when an analyte changes in the presence of the solvent to form compounds that have a different light absorptivity than the parent species, this can be controlled with a buffer which resists a PH change
what is an instrumental deviation
occurs from the instrument being ass
if there are two absorbing species in a mxture
the absorbance at a given wavelength will be the result of the absorbance of both species
why do we want a low detection limit
it gives us more room to capture our concentration
what is the purpose of recovery% it tells us how accurate a method is
what is chromatography
it allows us to separate, identify, and purify the components of a mixture for qualitative and quantitative analysis
what is an LLE
it is a liquid liquid extraction which is a classical form of separation
it allows us to transfer the analyte of interest from one phase into another
what are the two phases of an LLE
the aqueous phase (S1) and the Organic phase (S1)
what is the organic phase usually?
the second phase, it is usually on top since it is less dense
does the K change with the concentration of S
no, it is constant at equilibrium
When talking about LLE’s, what does it mean when K>1
it means we have more organic concentration in phase 2
when talking about LLEs, what does it mean when K<1
it means we have less organic concentration in phase 2
What type of material would we see in the organic layer of an LLE?
molecules with a lack of polar character, not charged
what type of material would we see in the aqueous layer of an LLE
molecules that have polar character and are charged
what is the mobile phase
the phase of an LLE that is moving; solvent is moving through a column
what is the stationary phase
the phase of an LLE that is solid; solvent is fixed in a column
molecules that like the mobile phase move through the system in what fashion?
they move through it quickly
molecules that like the stationary phase move through the system in what fashion?
they move through it slowly
