Instant Notes: Analytical Chemistry

Section A – The nature and scope of analytical chemistry

A5 CALIBRATION AND

STANDARDS

Calibration With the exception of absolute methods of analysis that involve chemical reac-
tions of known stoichiometry (e.g., gravimetric and titrimetric determinations), a
calibration orstandardization procedureis required to establish the relation
between a measured physico-chemical response to an analyte and the amount or
concentration of the analyte producing the response. Techniques and methods
where calibration is necessary are frequently instrumental, and the detector
response is in the form of an electrical signal. An important consideration is the
effect of matrix components on the analyte detector signal, which may be
supressed or enhanced, this being known as the matrix effect. When this is
known to occur, matrix matchingof the calibration standards to simulate the
gross composition expected in the samples is essential (i.e. matrix components
are added to all the analyte standards in the same amounts as are expected in the
samples).
There are several methods of calibration, the choice of the most suitable
depending on the characteristics of the analytical technique to be employed, the
nature of the sample and the level of analyte(s) expected. These include:

● External standardization. A series of at least four calibration standards

containing known amounts or concentrations of the analyte and matrix

components, if required, is either prepared from laboratory chemicals of guar-

anteed purity (AnalaR or an equivalent grade) or purchased as a concentrated

standard ready to use. The response of the detection system is recorded for

each standard under specified and stable conditions and additionally for a

blank, sometimes called a reagent blank(a standard prepared in an identical

Key Notes

Calibration or standardization is the process of establishing the response

of a detection or measurement system to known amounts or

concentrations of an analyte under specified conditions, or the

comparison of a measured quantity with a reference value.

A chemical standard is a material or substance of very high purity

and/or known composition that is used to standardize a reagent or

calibrate an instrument.

A reference material is a material or substance, one or more properties of

which are sufficiently homogeneous and well established for it to be used

for the calibration of apparatus, the assessment of a measurement method

or for assigning values to materials.

Related topic Calibration and linear regression (B4)

Calibration

Chemical standard

Reference material