General Flashcards
May be hyphenated and linked to MS as a….
Detection method
Five key elements in a chromatography machine….
Stationary phase Mobile phase Mechanism to make components move in MP. A way to add the sample. A detection method.
What is chromatography?
A separation technique for compounds so that they can be quantified and identified. Eg blood.
What is the stationary phase?
A material that interacts with the compound depending on its physical or chemical properties.
What is the mobile phase?
The phase that compounds are dissolved into. This passes over the SP.
Polar compounds…… Water
Love
Non polar…….. Water.
Hate
What is analytical chromatography?
Separation quantitively, to determine how much of a substance there is, and qualitatively, to separate individual compounds for identification.
There is no alteration of……
Compounds.
What is preparative chromatography?
A complex mixture can be separated and purified to give a purer compound with fewer or no contaminants.
What is preparative chromatography used for?
Prep of samples of pure proteins, such as blood.
What is paper chromatography?
Process carried out on a piece of absorbent paper - The SP.
Why is chromatography used?
Most analytical methods are specific for a compound or class of compounds so therefore require the sample to be separated into constituent parts before analysis.
How does the retention time affect the peak shape?
The peak will be broader with an increasing retention time.
The retention time is calculated using the…
Centre of the peak.
The retention time of a compound is….
The time is takes for each compound to move through the column.
A compound that doesn’t interact with the SP will have…
The same retention time as the mobile phase.
The output on a detector is the….
Signal intensity over the time of elution.
The peak resolution (Rs) is the….
Ability of a chromatography process to separate two solutes in a sample.
The equation for peak resolution (Rs) is….
Rs = t R2 - t R1 / 1/2 (Wb1 + Wb2)
Where R1 is first to elute.
Peak resolution values are acceptable around….
1.0
A longer retention time and smaller peak width = a….
Better resolution and high Rs value.
Retention time may vary as…
Some compounds will be retained on the column for longer.
Column efficiency is….
How good a column is at separating solutes.
Theoretical plates (N) can be used in the column, the more plates =
More steps = greater efficiency to separate columns in a reasonable time.
A smaller plate height =
Greater efficiency by having a shorter column length.
The van Deemter equation states that….
Plate height will increase and efficiency will therefore decrease, as the values of the constants A B C increase.
C constant is most dominant in LC because of….
Slow diffusion in liquid MP.
C constant has less impact in….
GC.
