Chromatography Part A Obj 3 Flashcards
The carrier gas is the ________________ phase that carries the sample through the column
to the detector.
mobile
Why is Helium the most common carrier gas?
1) Chemically inert
2) Has high thermal conductivity
3) Available in high purity
Why is hydrogen not normally chosen as a carrier gas even though it is superior to helium in
thermal conductivity?
Can explode if it leaks and mixes with Oxygen
What design allows for better control of carrier flow rates and why is this important in
chromatography?
Cylinder pressure regulator to better suit the instrument and achieve a more constant flow rate
How are high pressure (2000 psi) cylinders switched for carrier gases without interrupting
flow to the analyzer?
A second cylinder and a manifold is always used to switch between cylinders
What is used to prevent contamination from moisture & O2 when changing gas cylinders?
Moisture and Oxygen absorbers
What are 3 types of chromatography valves?
1) Rotary
2) Sliding Plate
3) Diaphragm
How many positions do chromatographic valves have?
Fill or inject
What factors can affect peak resolution?
1) Type of column used
2) Temperature
3) Flow rate of the carrier gas through the column
What is column efficiency? Which of the two GLC column types is typically more efficient?
Column’s ability to separate mixtures and generate a chromatograms with narrow peak widths. Capillary column are more efficient.
What is “N” used for?
“N” is used to compare efficiencies of many different columns and can be used to find an optimal flow rate for a certain column.
In many applications sample components may not separate completely, column can clog or
elution times may be too long …. these issues may be resolved with 4 basic configurations.
What are they?
Using 4 types of different column configurations:
1) Backflushing
2) Heart-cut
3) Trap and Hold
4) Parallel
What is the most common method used to reduce cycle time?
Backflushing
What is the function of a “heart cut” configuration?
To quantify one component when that component’s elution time is the same as another component. The component of interest gets separated in the heart cut column while all other components are vented.
The trap & hold column typically uses a different
___________ material than the main analytical column to allow separation of components
that would otherwise stay clumped together in the main column
Stationary phase
What are parallel systems?
When 2 different column configurations are used in parallel to optimize separation.
Compared to a basic column configuration, what hardware is required to add a backflush step to the system?
1) Tubing
2) Chromatographic valve
3) Carrier gas connections
What effects will temperature change in the oven have on the system?
1) Retention times due to a different sample vaporization time
2) Retention times due to changes in carrier gas flow rate
3) Peak areas due to a change in the output of the detectors
What are the functions of the programmer-controller?
1) Sample injection
2) Column switching
3) Detector signal processing
4) Determining peak area and concentration
5) Calibration to determine response factors
6) Data communication
_________________ column configuration allows the most efficient (time-wise) separation of a trace component of interest from another, more abundant component that is not of interest.
Heart cut
