exam 2 official woo Flashcards
when is there not an assumed linear relationship in a calibration curve
when we get data points that are outside of our highest and lowest made standards, where can cannot assume linearity
what are the assumptions for LLs Analysis
1.) we assume a linear relationship between the response (y-axis) and the concentration (x-axis)
- all uncertainty is in the y-axis
- the uncertainty in the y-axis is constant
what is the minimum number of points to make a good calibration curve
3 but 4 is the best for a good and accurate linear equation
if we have less than 3 points on a calibration curve what happens?
we have lower accuracy and undefined precision
what should we do if our concentration is too high to plot on a calibration curve?
we can dilute it
what is a calibration check and what does it measure
it is repeated analysis of a calibration standard
this checks precision
what is a blank
it is a sample with no analyte that is ran to check for contamination
this affects accuracy and precision
what is a lab method spike
it is where we run a sample with a known concentration
if we run one analysis, its a measure of accuracy
if we run multiple analysis, it is a measure of precision
what does recovery % tell us?
it allows us to measure the accuracy (or precision if multiple) of our method
we generally want a recovery% close to 100%
what is a detection limit?
it is the lowest amount of analyte in sample that gives a signal that we can say is different from the blank signal
what is the assumption with y blank +3*s= mx+b
that y-blank and b are the same
do we want low or high limits of detection
low limits of detection
what happens to the irradiance (P) as a molecule absorbs light
it decreases
what does the absorption tell us
it is directly proportional to the concentration, so the higher the absorption, the higher the concentration
what is transmittance
it is the fraction of original light that passes through
if we increase the concentration, what happens to the transmittance?
the absorption increases so the transmittance decreases
what is the assumption of Ebc
that the slope is equal to Eb
are the wavelength and absorption proportional
no, a chemical species may be better or worse at absorbing light at different wavelengths (described by molar absorptivity)
when we have too high of a concentration, how is beers law affected and what part of the curve is affected
there is internal screening and the upper end of the curve is affected
if we have too low of a concentration, how is beers law affected and what part of the curve is affected
we have a low absorbance and a high transmittance that makes it hard to tell P0 and P from eachothert
how do chemical deviations affect beers law
if the chemical environment changes (ex. PH in a titration) the absorption might be different
what is true about the phases for liquid chromatography
the mobile phase is liquid and the stationary phase is solid
as analytes spend more time in the column, what happens to the curve?
the concentration may become more diluted and result in a wider and lower peak
where does separation occur in an HPLC
in the column
what is the retention time
the time between the injection and peak
what is the retention factor
stationary/mobile time, it gives us a measure of the analytes retention
what does it mean if we have a larger retention factor
it means there is more time spent in the stationary phase which may lead to better separation or resolution
what does the separation factor describe
it tells us the relative retention of the two solutes and the difference in the partition coefficients
if we have a good separation factor, does that mean the separation is good
no, it just describes the differences in the stationary phases
what does resolution tell us
it tells us how well things are separated
whats the difference between LC and HPLC
in LC, we have lower resolution and larger particles
in HPLC, we have smaller particles in the column that allow for more interactions with the stationary phase, this results in a better resolution but it requires a higher pressure
what elutes first in normal phase separation
nonpolar analytes, the mobile phase is nonpolar while the stationary phase is polar
what elutes first in reverse phase separation
polar analytes, the mobile phase is polar while the stationary phase is nonpolar
what mode of separation do we use to separate nonpolar compounds
reverse phase (np stationary)
what mode of separation do we use to separate polar compounds
normal phase (p stationary)
when we make the stationary phase and mobile phase more similar, what happens to the retention
the retention times are reduced
when we make the stationary phase and mobile phase less similar, what happens to the retention
the retention times are increased
what is the mboile phase in gas chromatography
inert gases carry the molecules through a heated column
how is gas chromatography related to temperature
when heated, the analyte spends more time in the gaseous mobile phase
