In analytical chemistry, a calibration curve is a general method
for determining the concentration of a substance in an unknown sample by
comparing the unknown to a set of standard samples of known concentration.
A calibration curve is one approach to the problem of instrument
calibration.
The calibration curve is a plot of how the instrumental
response, the so-called analytical
signal, changes with the concentration of the analyte
(the substance to be measured). The operator prepares a series of standards
across a range of concentrations near the expected concentration of analyte in
the unknown. The concentrations of the standards must lie within the working
range of the technique (instrumentation) they are using. Analyzing each of these
standards using the chosen technique will produce a series of measurements. For
most analyses a plot of instrument response vs. analyte concentration will show
a linear relationship. The operator can measure the response of the unknown
and, using the calibration curve, can interpolate to find the
concentration of analyte.
The data - the concentrations of the analyte and the
instrument response for each standard - can be fit to a straight line, using linear
regression analysis. This yields a model described by the equation y
= mx + y0,
where y is the instrument
response, m represents the
sensitivity, and y0
is a constant that describes the background. The analyte concentration (x) of unknown samples may be
calculated from this equation
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