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BU Forensic Chemistry
Forensic Chemistry Lecture 5
Which type of chromatography is an analytical technique for separating compounds based primarily on their voltalities?
T/F: In the sample injection process for GC, the process is reproducible, highly efficient, and provides a representative sample for chromatographic separation.
What are 3 of the reasons you would derivatize your sample in GC?
increase volatility and polarity
decrease thermal stability
What is the difference between split and splitless injections?
T/F: As column length increases, resolution also increases.
As the _____ of the mixture increases, the elution speed decreases.
What are the 3 types of detectors in GC?
Flame Ionization Detector (FID)
Electron Capture Detector (ECP)
Flame Photometric Detector (FPD)
Which detector is the most common in GC?
flame ionization dectector
Describe the FID.
-provides universal ionization by burning
-immediate, stable, predictable response
-sensitive with large dynamic range
-column effluent passes through the flame
Describe the ECD.
-as sensitive as FIDs but with limited dynamic range
-uses radioactive beta-emitter to ionize carrier gas to produce current between electrodes
Flame Photometric Detector
-detection of sulfur and phosphorus specifically
-chemiluminescent reactions occur in a hydrogen/air flame
adjusted retention time
the time a compound spends in the stationary phase
time for unretained peak
-the time a compound spends in the mobile phase
the total time that a compound spends in both the mobile and the stationary phase
relates the column diameter and film thickness of the stationary phase
concentration of solute in stationary phase
concentration of solute in mobile phase
T/F: A large distribution constant means there was good separation with an increase in solute retention.
What are the 3 parameters affecting K
capacity factor (or partition factor)
the ration of the mass of a compound in the stationary phase relative to the mass of the compound in the mobile phase
- a measure of the columns retention of a compound