Chapter 32: Miscellaneous Separation Methods Flashcards
are an important class of solvents that have unique solvating properties. Such fluids have proven quite useful in chromatography and solvent extraction.
supercritical fluid
In what chromatographic technique does the supercritical fluid act as the mobile phase?
supercritical fluid chromatography
was considered as a hybrid of gas and liquid
chromatography, but now it is thought of as being more similar to HPLC in its operation and instrumentation
SFC
is formed whenever a substance is heated above its critical temperature
supercritical fluid
is the temperature above which a substance
cannot be liquified.
critical temperature
Above the _____________, a substance can no longer be condensed to a liquid by simply applying pressure
critical temperature
are capable of dissolving large nonvolatile
molecules.
supercritical fluids
has been called a green alternative to HPLC.
SFC
TRUE or FALSE
Instruments for supercritical fluid chromatography are similar in design to high-performance liquid chromatographs except that in SFC the pumping system must
include a chilled pump head to keep the fluid in the liquid state and that there
must be provision for controlling and measuring the column pressure
TRUE
TRUE or FALSE
The density of a supercritical fluid increases rapidly and nonlinearly with pressure increases
TRUE
TRUE or FALSE
Density increases also change retention factors (k) and thus elution times
TRUE
TRUE or FALSE
The most uncommon pressure profiles
used in SFC are often constant (isobaric) for a given length of time followed by a linear
or asymptotic approach to a final pressure
FALSE
it is most common
difference between packed columns and open tubular columns
packed columns can provide more theoretical plates and handle larger sample volumes that open tubular columns
TRUE or FALSE
Because of the low viscosity of supercritical
media, columns can be much longer than those used in liquid chromatography, and
column lengths of 10 to 20 m and inside diameters of 50 or 100 μm are common
TRUE
The most widely used mobile phase for supercritical fluid chromatography is
CO2
It is an excellent solvent for a variety of nonpolar organic molecules. In addition, it transmits in the ultraviolet and is odorless, nontoxic, widely available, and remarkably inexpensive relative to other chromatographic solvents.
CO2
other substances that have served as mobile phases in SFC
ethane,
pentane,
dichlorodifluoromethane,
diethyl ether,
tetrahydrofuran
TRUE or FALSE
Thus, like gas chromatography, supercritical fluid chromatography is inherently faster than liquid chromatography because of the lower viscosity and higher diffusion rates in the mobile phase
TRUE
TRUE or FALSE
Supercritical fluid chromatography appears to have a niche in the spectrum of column
chromatographic methods because it can be applied to compounds that are not
readily separated by gas or liquid chromatography
TRUE
TRUE or FALSE
Supercritical fluid chromatography is today not one of the primary separation methods for chiral compounds, such as those encountered in drug discovery. It has the potential to replace some of the reversed-phase HPLC separations of these compounds.
FALSE
Supercritical fluid chromatography is today one of the primary separation
methods for chiral compounds, such as those encountered in drug discovery. It
has the potential to replace some of the reversed-phase HPLC separations of these
compounds.
methods include thin-layer chromatography (TLC), paper chromatography (PC), and electrochromatography. Each makes use of a flat, relatively thin layer of material that is either self-supporting or is coated on a
glass, plastic, or metal surface
Planar chromatographic methods
was once called two-dimensional chromatography
Planar Chromatography
can be considered a form of liquid-solid chromatography in which the stationary phase is a thin layer on the surface of an appropriate plate.
TLC
common plate dimensions in centimeters of TLC plates are
5x20
10x20
20x20