Page 32 - Illustrated Pocket Dictionary of Chromatography

CARRYOVER 27

solubility parameter (d): 8.6; solubility in water (20°C): 0.08%; water
solubility in carbon tetrachloride (20°C): 0.008%. Volatile, carbon
tetrachloride is a solvent used in GC, TLC, and normal-phase HPLC.

CCl 4
Carbon tetrachloride

carrier The support to which an affinity ligand is bonded.

carrier ampholyte Used in capillary isoelectric focusing to
produce a pH gradient across the column, thereby forcing the analyte
to its point of isoelectric pH.

carrier electrolyte Typically a buffered solution that is used to
control the pH and ionic strength of a solution. In capillary elec-
trophoresis carrier electrolyte solution concentrations are generally
between 10 and 100mM. The upper limit results from the generation
of too much conductivity, whereas the lower limit defines the injec-
tion amount of the sample.
carrier gas The mobile phase used in GC work. An ideal carrier
gas is inert to the analyte, column, and detector, is available in a high-
purity form, and is safe and economical. The choice of carrier gas has
direct implications for the overall efficiency of the GC system. Hydro-
gen and helium produce the highest efficiency, but for reasons of
safety (hydrogen is combustible) and cost (helium is relatively expen-
sive) nitrogen is frequently used, with concomitant loss of efficiency.
For capillary columns optimal flow rates range from 10 to 40cm/s,
whereas for packed bed columns flows range from 20 to 60mL/min.
carryover Refers to the presence of a peak from a previous sample
appearing in the current chromatogram. A strong indication of carry-
over is that the peak reappears in subsequent injections but at lower
and lower intensities (as the contamination is swept out of the
system). An obvious source of carryover is the incomplete injection
of the sample. Less obvious is when an elution time for a run is not
long enough to elute all components in the previous sample and they
appear in the subsequent injection. Finally, carryover can also be the
direct result of components in the chromatographic system that are