Chromotography Flashcards
chromotograohy
a technique used to seperate the different substances present in a mixture
all chromotograohy methods have a
- a stationary phase, a medium which the sample can adsorb to 2. a mobile phase, where a solvent carries the sample over the stationary phase (deadsorbtion)
what are the three different types of chromotography
papa\er chromotography, thin layer chromotography and HPLC (high pressure liquid chromotography)
paper chromotograhy
uses high quality absorbent paper as the stationary phase, a small sample of the specific mixture is placed on the stationary phase and placed in a solvent
thin-layer chromotograohyy
uses a thin layer of absorbent materials such as aluminium oxide, silica or cellulose, a small sample of the specific mixture is placed on the stationary phase and placed in a solvent
the place where the sample is put is called the
origin
the spread of colours on the stationary phase is called
chromatogram
standards
used to determine the components in a mixture by containing a sample of known cehmicals on the same chromotogram as the inks own sample
retention factor (Rf)
the distance each component has travelled compared to the solvent front, can then be compared to checmicals of lnown values under the same conditions
equation to calculate rf
distance travelled by compound/distance travelled by solvent front
variables that affect Rf
temperature, type of solvent and stationary phase
HPLC
a chromotographyy technique that consists of a solid stationary phase which is tightly packed into a column (usually glass) annd a solvent acting as a mobile phase,
which ideas dooes HPLC rely on
how well the stationary phase adsrobs to yje sample through a force of attraction and how well the mobile phase can dissolve the sample through desorption
desorption
previously adsorbed substance is realesed from a surface into the mobile pahse
the more strongly a compound bonds to a stationary phase
the slower the rate of movement of that compound over the stationary phase
the more soluble a component is in the mobile phase
the faster it will move
HPLC rf
the time that a component of the sample spends in the HPLC column, time taken to pass through stationary phase
factors that influence Rf in HPLC
identitity and composition of the stationary and mobile phase, length and temp of column, S:A of stationary phase
increased S:A of stationary phase effect
increased Rf as there arre more interactions between the component and stationary phase and therefore it will take longer to elute
The area under a peak of a chromatogram shows
the concentration of the componenet when comparing to a standard
steps in determining oncentration of components in HPLC
standard solutions are prepared and a fixed volume of each is injected into the instrument, the area under the peak of each solution is measured, a calibration graph is plotted using the results obtained from the standard solutions, tthe sample is injected and its peak area is measured, the samples concentration is determined using the calibration graph
adsorption
adhering onto the solid stationary phase
desorption
following adsorption, dissolving into the mobile phase
qualitive analysis chromotography
the determination of the chemical composition of a sample
