Instant Notes: Analytical Chemistry

Section B – Assessment of data

B4 CALIBRATION AND LINEAR

REGRESSION

Many quantitative analytical procedures rely on instrumental measurements

where a property of the analyte(s) is monitored by a suitable detection system.

The detector generates an electrical signal, the magnitude of which is deter-

mined by the mass or concentration of the analyte. Before using a particular

analytical procedure to analyze samples, it is first necessary to establish the

detector responsesto known amounts of the analyte (calibration standards)

over a selected mass or concentration range, a process known as calibration.

The relation between the two variables is often linear(directly proportional),

but there is generally an upper limit to the range of values beyond which a

curved or curvilinearrelation is observed. In some instances, there may be no

direct linear relation at all, or a logarithmic or more complex mathematical

correlation may be found.

Calibration

Key Notes

Calibration is the process of establishing a relation between a detection or

measurement system and known amounts or concentrations of an analyte

under specified conditions.

The coefficient is used to assess the degree of linearity between two

variables, e.g. an instrument response and an analyte mass or

concentration.

Calculations to define the best straight line through a series of calibration

points represented graphically are described as linear regression.

The smallest mass or concentration of an analyte that can be measured

quantitatively at a defined level of probability defines a limit of detection.

This is a calibration procedure that avoids matrix interference by

measuring instrument response for an analyte in both the sample and a

sample to which known amounts of an analyte standard have been

added.

This is a calibration procedure where the ratio of the instrument response

for an analyte to that of an added standard is measured for a series of

analyte standards and samples.

Internally normalized results give the relative composition of a mixture

by expressing the instrument response for each analyte as a fraction or

percentage of the sum of the responses for all of the analytes.

Related topic Calibration and standards (A5)

Calibration

Correlation

coefficient

Linear regression

Limit of detection

Standard addition

Internal

standardization

Internal

normalization