Definition:
internal standard
An Internal
Standard is a compound purposely added to both samples and
standards at a known concentration in order to provide a basis for
comparison in quantitation. Computationally, the only difference
between "internal standardization" and "external standardization" is
that the former works with area ratios and concentration ratios rather
than areas and concentrations. Internal standardization can improve
precision when the dominant sources of error are related to sample
preparation or injection; because such errors affect both the internal
standard and the analyte peak in the same way, they will tend to cancel
out when the ratio of areas is calculated. Internal standardization can
degrade precision when the dominant sources of error are related to
separation, peak shape, or integration; because such errors affect the
internal standard peak and the analyte peak differently, they will tend
to combine when the ratio of areas is calculated.