54
5 Calibration
and the filled flask should be weighed again. The weight of water in the flask is the
difference between those two values. Considering the density of water and including
correction for temperature, the volume of given volumetric flask may be calculated.
The calibration of balances or volumetric flasks may be ordered as a metrological
service from the producers or calibrating laboratories. In both cases, a document
confirming their metrological status is the calibration certificate, in which the values
are given for the magnitude and uncertainty of measurement.
Calibration and Measurement Capability (CMC) is considered to be a feature
of mutual recognition of national standards.
The best measurement capability (always referring to a particular measured quantity) means the smallest uncertainty that a given calibration laboratory can achieve in
practice determining the values of the measured quantity. In the case of measurements
of chemical quantities, the calibration correlation is established for specified chemical references. Primary methods of measurement
* are considered to be of importance
in the chain of traceability as they provide the direct correlation between the abstract
definition of a unit of the SI to its practical use in measurement. In the field of
chemical measurements, a definition of a primary method of measurement has been
developed by the Consultative Committee for Amount of Substance (CCQM), which
distinguishes between those methods that measure a quantity directly and those that
measure the ratio of two quantities. In several cases, for the methods recognized as
primary, where unequivocally described the chemical reaction of known stoichiometry can be used, it is possible to perform calibration by measuring, for example, the
mass of precipitate, the volume of the standard solution, the amount of electricity
used for the transfer of matter (in coulometry) or the isotopic ratio of stable isotopes.
* The primary method of measurement is one in which the measured quantity
is obtained by direct measurement of the base quantity (mass, volume, electrical
current, time). Absolute methods include, for example, gravimetry (weight), titration
(volume), coulometry (electric charge), isotopic ratio (current counts). In the case
of trace analysis, absolute methods include neutron activation analysis (NAA) and
isotopic dilution mass spectrometry (ID MS). A primary method of measurement
is a method for which: (a) a measurement model is completely understood; (b) no
empirical factor has to be included in a mathematical equation; and (c) it is possible
to realize in a way that achieves a very small combined uncertainty for the given
measurand.
In analytical practice, calibration means to determine the relationship between
the value of the detector respond relates to the scale on Y (analytical signal) and
the value of the content of analyte in a standard relate to the scale on X, generating
respective respond. The values of the recorded signals and the known quantity of the
given chemical substance in the chemical standard allows for the designation of the
calibration relationship in a range of concentrations. In order to draw the calibration
curve, the value of the analytical signal is attributed on the vertical axis (Y) and the
5 Calibration
and the filled flask should be weighed again. The weight of water in the flask is the
difference between those two values. Considering the density of water and including
correction for temperature, the volume of given volumetric flask may be calculated.
The calibration of balances or volumetric flasks may be ordered as a metrological
service from the producers or calibrating laboratories. In both cases, a document
confirming their metrological status is the calibration certificate, in which the values
are given for the magnitude and uncertainty of measurement.
Calibration and Measurement Capability (CMC) is considered to be a feature
of mutual recognition of national standards.
The best measurement capability (always referring to a particular measured quantity) means the smallest uncertainty that a given calibration laboratory can achieve in
practice determining the values of the measured quantity. In the case of measurements
of chemical quantities, the calibration correlation is established for specified chemical references. Primary methods of measurement
* are considered to be of importance
in the chain of traceability as they provide the direct correlation between the abstract
definition of a unit of the SI to its practical use in measurement. In the field of
chemical measurements, a definition of a primary method of measurement has been
developed by the Consultative Committee for Amount of Substance (CCQM), which
distinguishes between those methods that measure a quantity directly and those that
measure the ratio of two quantities. In several cases, for the methods recognized as
primary, where unequivocally described the chemical reaction of known stoichiometry can be used, it is possible to perform calibration by measuring, for example, the
mass of precipitate, the volume of the standard solution, the amount of electricity
used for the transfer of matter (in coulometry) or the isotopic ratio of stable isotopes.
* The primary method of measurement is one in which the measured quantity
is obtained by direct measurement of the base quantity (mass, volume, electrical
current, time). Absolute methods include, for example, gravimetry (weight), titration
(volume), coulometry (electric charge), isotopic ratio (current counts). In the case
of trace analysis, absolute methods include neutron activation analysis (NAA) and
isotopic dilution mass spectrometry (ID MS). A primary method of measurement
is a method for which: (a) a measurement model is completely understood; (b) no
empirical factor has to be included in a mathematical equation; and (c) it is possible
to realize in a way that achieves a very small combined uncertainty for the given
measurand.
In analytical practice, calibration means to determine the relationship between
the value of the detector respond relates to the scale on Y (analytical signal) and
the value of the content of analyte in a standard relate to the scale on X, generating
respective respond. The values of the recorded signals and the known quantity of the
given chemical substance in the chemical standard allows for the designation of the
calibration relationship in a range of concentrations. In order to draw the calibration
curve, the value of the analytical signal is attributed on the vertical axis (Y) and the