Instrument Flashcards
Three essential components of any mass spectrometer
Ion source, detector, mass separator
Eluate vs eluent
Eluate is the compound that will come out of coloum
eluent is solvent applied at the beginning to the column
equilibrium constant
K=solid phase/mobile phase
Adjusted retention time
Think of tr` as the additional amount of time
after the solvent reaches the detector for the
sample to reach the detector.
Theoritcal plates
N=l/h
Increasing the column length: The number of theoretical plates is directly proportional to the length of the column. Therefore, increasing the column length can increase the number of theoretical plates, which in turn improves separation efficiency.
Rentetnion factor
Using a stationary phase with high selectivity: The choice of stationary phase can significantly affect the separation efficiency. Using a stationary phase with high selectivity for the analytes of interest can increase the number of theoretical plates and improve the separation.
Using a smaller particle size of the stationary phase: Smaller particle sizes of the stationary phase can lead to increased surface area and better equilibration of the analytes with the stationary phase, which can increase the number of theoretical plates.
Using a lower flow rate: Lowering the flow rate of the mobile phase can increase the retention time of the analytes in the column, which can lead to more interactions between the analytes and the stationary phase, and thus improve the number of theoretical plates.
Using a narrower column diameter: Using a narrower column diameter can increase the number of theoretical plates, as the analytes have less space to diffuse in the mobile phase, which leads to better interaction with the stationary phase.
What is a normal stationary phase
immbolize liquid some kind of siloxane
Tempature and pressure programming
n temperature programming the temperature
of the oven (column) is raised during the
separation to increase analyte vapor pressure
and decrease retention times of late-eluting
components.
* In pressure programming, the inlet pressure is
raised during separation. This speeds up the
mobile phase and decreases retention times
43
FID
Flame Ionization Detector
* Eluate is burned in a
mixture of H2 and air.
* Carbon atoms (except
carbonyl and carboxyl
carbons) produce CH
radicals, which produce
CHO+ ions and
electrons in flame.
CH + O → CHO+ + e-
Regardless, ion production is proportional to the
number of susceptible carbon atoms entering the
flame.
* The ions produced are measured by the change
in voltage when the ion hits the collector
(positive electrode).
Flame burns sample,
creating ions
* Current monitored
between burner and
electrode
What kind of calobrations
External calibration:Series of standards containing the analyte in known concentrations
creating a known signal response for a specific analyte concentration
* Response plotted or fitted to mathematical equation
* Predict analyte concentration based on mathematical equation
Internal standards: ubstance added to all
samples, blanks, and calibration standards
* Sometimes a mixture component taken to be constant in
concentration
* Must be present in both sample and standards
* I.S. can compensate for systematic and random
errors
* Matrix effects, instrumental variation
* If the I.S. is major part of samples and standards can
compensate for sample handling
Behave like the analyte in most situations but produce a signal that is easily
distinguishable from the analyte
* If the I.S. is not a major component of the matrix, it must be absent from
matrix
* Elements from the same group can serve as elemental internal
standards
* Structural or isotopic analogs are often used as I.S. for molecular
analytes
Calibration curves are made by plotting ratio of
analyte signal to internal standard signal as function
of analyte concentration
Concentration of Analyte
Analyte Signal/IS Signal
