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
is the process by which a sample is carried through the stationary phase by a mobile phase. It is analogous to elution in liquid chromatography
Plate development
is a separation method based on the differential rates of migration
of charged species in an applied dc electric field. This separation technique for macrosize samples was first developed by the Swedish chemist Arne Tiselius in the 1930s for the study of serum proteins; he was awarded the 1948 Nobel Prize for his work
Electrophoresis
has been applied to a variety of difficult analytical separation problems: inorganic anions and cations, amino acids, catecholamines, drugs, vitamins, carbohydrates, peptides, proteins, nucleic acids, nucleotides, polynucleotides, and numerous other species, which has a unique ability to separate charged macromolecules of interest to biochemists, biologists, and clinical chemists.
eletcrophoresis
powerhouse method for separating proteins and nucleic acids for which it offers unparalleled resolution
electrophoresis
A unique feature of capillary electrophoresis is called _________________, which the solvent migrates toward the electrode
electroosmotic flow.
is usually sufficient to sweep all positive,
neutral, and even negative species toward the same end of the capillary so that all
can be detected as they pass by a common point
electroosmotic flow
looks like a chromatogram but with narrower peaks
electropherogram
is the ratio of the migration rate of an ion
to the applied electric field.
electrophoretic mobility
is proportional to the charge on the ion and inversely proportional to the frictional
retarding force on the ion.
electrophoretic mobility
TRUE or FALSE
The frictional retarding force on an ion is determined by the size and shape of the ion and the viscosity of the medium
TRUE
Capillary electrophoretic separations are performed in several ways called modes, such as
isoelectric focusing
isotachophoresis
capillary zone electrophoresis
is a hybrid of HPLC and capillary
electrophoresis (CE) that offers some of the best features of the two methods. Like
HPLC, it applies to the separation of neutral species. Like CE, however, it
provides highly efficient separations on microvolumes of sample solution without the need for the high-pressure pumping system required for HPLC
capillary electrochromatography
