SFC&E Flashcards
What is supercritical fluild chromatography (SFC)?
Supercritical fluid chromatography (SFC) is a hybrid of gas and liquid chromatography that combines some of the best features of each. Supercritical fluid chromatography is of importance because it permits the separation and determination of a group of compounds that are not conveniently handled by either gas liquid or liquid chromatography.
Describe the apparatus for SPC?
The soluble compound is placed inside the thimble and the fluid is then dispensed throughout the apparatus. The extraction of the compound is done at the collection trap area through a restrictor nozzle. The supercritical fluid is aspirated in the collection trap which enables the solvent to either escape or be recompressing for other experimental purposes.
What are the properties of supercritical fluids?
Supercritical fluid is a state of matter that is intermediate between a gas and liquid in its properties. This state formed when a gas or liquid solvent is subjected to temperature and pressure condition exceeding a particular critical point. The temperature and pressure at which this point Occurs are known as the Critical temperature and Critical pressure and are Characteristic of the solvent. Beyond this point, the solvent Will be neither a gas or liquid, but will possess properties of both phases . Whether this supercritical fluid acts more like a gas or liquid will depend on the pressure and temperature
label the components of SFC apparatus in the purple boxes
How does pressure affect SFC?
Pressure changes in supercritical chromatography have a pronounced effect on the capacity factor k’. This effect is a consequence of the increase in density of mobile phase with increase in density of the mobile phase with increases in pressure.
What are the stationary phases used for SPC?
Both open-tubular and packed columns are used for SFC although currently the former are favored. Open-tubular columns are similar to the fused-silica columns with internal coatings of bonded and crossed-linked siloxanes of various types
What are the mobile phases used for SPC?
The most widely used mobile phase for SPC is carbon dioxide. It is an excellent solvent for a variety of organic molecules. In addition, it transmits in the ultraviolet and is odorless, nontoxic, readily available, and remarkably inexpensive when compared with other chromatographic mobile phases.
What types of detectors can used for SPC?
A major advantage of SFC over HPLC is that the flame ionization detector of gas chromatography can be employed. Mass spectrometers are also more easily adapted as detectors for SFC than HPLC.
One major advantage of SFC is its ability to use detector available for either GC or LC, such as FID, UV-Vis, and Fluorescence detectors. This gives it a wide range of both universal and selective detections for use in either analytical or preparative-scale work.
label the supercritical fluid extraction apparatus. explain each components in detail.
Instrument components include a fluid source, commonly a tank of carbon dioxide followed by a syringe pump having a pressure rating of at least 400 atm a valve to control the flow of the critical fluid into a heated extraction cell having a capacity of a few ml, and lastly an exit valve leading to a flow restrictor that depressurizes the fluid and transfers it into a collection device.
What are the advantage of SFE (supercritical fluid extraction)?
There are several advantages of supercritical fluid extraction (SFE):
a. SFE is generally fast. The rate of mass transfer between a sample matrix and an extraction fluid is determined by the rate of diffusion of a species in the fluid and the viscosity of the fluid—the greater the diffusion rate and the lower the viscosity, the greater will be the rate of mass transfer.
b. The solvent strength of a supercritical fluid can be varied by changes in the pressure and to a less extent in the temperature.
c. Many supercritical fluids are gases at ambient condition.
d. Some supercritical fluid are cheap, inert, and nontoxic.
d. Depending on which supercritical fluid is used, it is also possible to use SFC at lower T than GC. This makes it more useful in the separation of thermally unstable compounds.
e. The stationary phases used in SFC can be similar to those in LC as well as GC. Either packed or open-tubular columns may be used.
f. Because of these advantages, SFC is commonly viewed as a technique which is complementary to both LC and GC.
What is the theory of SFC?
Since supercritical fluids have properties between those of gases and liquid, their use as a mobile phase offers several advantages.
a. One of advantages is that supercritical fluid have lower densities and viscosities than liquids. This results in larger diffusion coefficients for solutes is SFC than LC. This results in Better efficiencies and higher optimum linear Velocities in SFC than LC. The plate height of a SFC system is given by the van Deemter equation.
H = A + B/u + Cu
b. SFs have higher densities than gas, so that mobile phase has a greater chance of interacting with the solute than that in GC (i.e., carrier gas). This makes the mobile phase important in determining the retention of solutes on the system and give more flexibility in optimizing the separation. For example, retention of solutes in SFC can be changed by using a different column (i.e. different stationary phases) as in GC, or by changing the mobile phase strength as in LC.
What is the main difference of a SFC than LC or GC system?
The main difference of a SFC than a LC or GC system is the need to control bother temperature and pressure of mobile phase. This must be done to keep the mobile phase as a Supercritical fluid. Control of the pressure (density) of the supercritical fluid can also used to vary strength of mobile phase during the gradient elution in SFC .
