Page 8 - Illustrated Pocket Dictionary of Chromatography

P. 8

absorbance The mathematical representation for the loss of inci-
dent radiant energy intensity (e.g., ultraviolet, visible, infrared) as it
passes through the sample is the absorbance, A:
A = log P P),
(
o
where P o is the power of the incident beam and P is the attenuated
beam that leaves the sample and impinges the detector. Because
absorbance is the logarithm of the ratio of radiant energies, it is unit-
less. Absorbance is also related to the solution concentration of an
analyte through Beer’s law: A =ebC, where e is the absorptivity of the
analyte, b is the cell path, and C is the concentration of the analyte.

absorption (1) The partitioning process for an analyte between the
mobile phase and a liquid or liquidlike stationary phase. (2) The
process by which incident radiation on a sample is attenuated by inter-
action with the sample.

absorptivity A proportionality constant used in the relationship
between absorbance and analyte concentration (i.e., Beer’s law).
Absorptivity is a function of analyte identity, wavelength, solvent com-
position, and temperature. The units of measure for absorptivity are
determined by the units of measure used to express the analyte con-
centration: When concentration is expressed as moles/liter (molarity)
and the path length in centimeters then the molar absorptivity, e, has
units of L/cm◊mole.
accuracy The accuracy of a result is deﬁned as how closely the
experimentally derived result comes to the “true” or “accepted” value.
In the method development process the accuracy of a method is often
determined by spiking a matrix blank [a sample containing every
component except the analyte(s) of interest] to the desired level and
calculating the percent recovery, 100% being expected.

acetic acid (glacial) Molecular weight: 60.1; boiling point:
117.9°C; refractive index (20°C): 1.3716; density (20°C): 1.049g/mL;

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