HPLC and GC Flashcards
how can we determine the content of compound in a sample?
we integrate the area under the peak
how do we integrate the area under the peak?
beer lambert law/ must be fully resolved
how can purity be assigned?
as a % of the total peak area- all peaks are integrated ,add all up and put one of interest/ total
when assigning a purity what does it wrongfully assume?
that all the constituents can be detected by UV light
and purity does NOT assign concentration
how do you externally calibrate?
known conc of standards and samples are injected
Linear range should include expected sample concentration
–The peak area is plotted against the concentration and used as a calibration graph
what are the drawbacks of an external calbirated graph?
time consuming method –Requires analytical standard – Available? Cost? –Matched matrix –Injection reproducibility
what is the comparative method?
injection of a standard at a known concentration
–Identify the retention time and record peak area : Area(Std)
–Injection of unknown sample
–Record area of peak with the same tR as above: Area(Sample)
what is the equation for the comparative method?
Area(Std) / Conc(Std) = Area(Sample) / Conc(Sample)
what does the IS account for?
Accounts for injection / some sample prep variation
what are the IS requirements?
Chemically + physically similar to the analyte, but not co-elute
•Not be present in the sample
•Not be reactive with the analyte / matrix
•Be chemically pure (analytical grade)
what compounds is gas chroatography for?
volatile compounds ( liquids)
is GC high or low efficiency? and why?
very high efficiency
Low flow resistance = long columns
–No eddy diffusion
–Rapid mass transfer (thin internal film)
what is GC readily coupled to?
Readily coupled to EI-MS systems
what is separation dependent on in GC?
dependant on distribution ratio between stationary phase (internal film coated silica capillary).
What is the distribution in GC dependent on?
distribution ration dependant on volatility (and hence boiling point)
