Page 111 - Illustrated Pocket Dictionary of Chromatography

108 INTERNAL STANDARD

peaks have very shallow rises or declines (such as extreme fronting
or tailing). Because the integrated area of a peak is often used in
analyte quantitation, reproducible integration is critical to generating
acceptable results.

internal standard An internal standard method is used when
the reproducibility of the analytical instrument is not as precise
as needed. An internal standard is a compound that is similar in chem-
ical/physical properties to the analyte of interest, does not coelute
with any other component in the sample, is stable and obtainable in
a high-purity form, and has an acceptable linear range. An internal
standard is added to a sample before analysis and is then quantitated
against its standard curve to determine its overall recovery. If
the recovery is not 100% of that expected, then it is assumed that
the recovery of the analyte is the same and the result is corrected
accordingly.
internal surface reversed phase (ISRP) An internal surface
reversed-phase support is a porous packing material that is deriva-
tized on the surfaces external to the pores with a nonadsorptive
hydrophilic bonded phase and derivatized on the pore interior with a
hydrophobic bonded phase. This type of column is also called a
Pinkerton column. It is used in the analysis of complex samples con-
taining protein and smaller analytes (such as drug compounds). The
protein is excluded from the pores and does not adsorb to the packing
surface, whereas the smaller compounds enter the pores and are
retained in the reversed-phase mode.
interpolation The process used to determine an unknown result
from its response/output as compared against a series of standards
whose responses/outputs bracket the result. See extrapolation.

e Represents the volume contained within
interstitial porosity, e o
the column but outside the packing material, V e, with respect to the
total column volume, V c:

e o = e VV c
The velocity of the mobile phase moving
interstitial velocity, u e
outside the packing material particles represents the elution volume
of an analyte that is totally excluded from the pore volume:

u e = F A o e