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6 Reference Materials in Chemical Measurements
the respective ISO GUM Guides. Additionally, they are otherwise subject to control
within the framework of interlaboratory comparisons (i.e. the key comparisons).
Lower in the metrological hierarchy are secondary RMs, which are prepared by
accredited calibration laboratories or accredited RMPs. On the lower levels of the
metrological hierarchy are materials prepared in the laboratory and used in the daily
processes of quality control.
Commonly used terms for the RMs prepared in the laboratory:
– Laboratory materials;
– Secondary reference materials;
– Control laboratory materials;
– Materials for quality control;
– Control samples.
For users of RMs, their position in the metrological hierarchy is important, but
so is the utility aspect—what materials we have and what purposes they can be
used for. Itemized are the non-matrix materials, meaning pure chemicals of specified
high purity and matrix materials that may be synthetic (prepared by blending the
ingredients in defined proportions) or natural (with the natural content of substance)
or natural with added substance to be determined. A special group of materials
is dedicated to a particular technique (analytical method) or to a specific sample
preparation (e.g., extraction of metals from soil using aqua regia).
It is worth noting that sometimes the metrological quality (the positioning in the
metrological hierarchy) of RM and its usefulness in a given measurement situation
do not always match. In many textbooks, the metrological hierarchy of standards
is given: the primary measuring standard is a pure substance, such as cholesterol;
the secondary measuring standard would be cholesterol in the blood. In chemical
measurements, the matrix material (secondary standard) can be more useful than
standard of pure substance.
Below examples of RMs are listed, according to their use:
– Pure chemical substances of known purity (or known content of impurity) or their
solutions commonly used as standards for calibration of measuring instruments
(e.g., stock solution of cadmium nitrate used to prepare the series standards of
cadmium for atomic absorption spectrometry), or to identify the presence of the
substance (e.g., a solution containing nitrate (III) and nitrate (V) ions to confirm
their presence in the water by ion chromatography).
– Pure chemical substances of known purity, used for reconstitution of the matrix
(e.g., high purity copper of 99.99% Cu, used to prepare a series of standard solutions of zinc in the presence of copper for ICP-OES). Such materials should not
contain the analyte determined in an analysis (e.g., copper with a purity of 99.99%
does not contains zinc).
– Matrix RMs with the certified content of the substance (e.g., blood serum with
certified cholesterol content).
– Matrix RMs used for the defined analytical procedure, reproducing the certified
value provided the described procedures are used (e.g., fractionation of metals in
soil with specified extraction media).
6 Reference Materials in Chemical Measurements
the respective ISO GUM Guides. Additionally, they are otherwise subject to control
within the framework of interlaboratory comparisons (i.e. the key comparisons).
Lower in the metrological hierarchy are secondary RMs, which are prepared by
accredited calibration laboratories or accredited RMPs. On the lower levels of the
metrological hierarchy are materials prepared in the laboratory and used in the daily
processes of quality control.
Commonly used terms for the RMs prepared in the laboratory:
– Laboratory materials;
– Secondary reference materials;
– Control laboratory materials;
– Materials for quality control;
– Control samples.
For users of RMs, their position in the metrological hierarchy is important, but
so is the utility aspect—what materials we have and what purposes they can be
used for. Itemized are the non-matrix materials, meaning pure chemicals of specified
high purity and matrix materials that may be synthetic (prepared by blending the
ingredients in defined proportions) or natural (with the natural content of substance)
or natural with added substance to be determined. A special group of materials
is dedicated to a particular technique (analytical method) or to a specific sample
preparation (e.g., extraction of metals from soil using aqua regia).
It is worth noting that sometimes the metrological quality (the positioning in the
metrological hierarchy) of RM and its usefulness in a given measurement situation
do not always match. In many textbooks, the metrological hierarchy of standards
is given: the primary measuring standard is a pure substance, such as cholesterol;
the secondary measuring standard would be cholesterol in the blood. In chemical
measurements, the matrix material (secondary standard) can be more useful than
standard of pure substance.
Below examples of RMs are listed, according to their use:
– Pure chemical substances of known purity (or known content of impurity) or their
solutions commonly used as standards for calibration of measuring instruments
(e.g., stock solution of cadmium nitrate used to prepare the series standards of
cadmium for atomic absorption spectrometry), or to identify the presence of the
substance (e.g., a solution containing nitrate (III) and nitrate (V) ions to confirm
their presence in the water by ion chromatography).
– Pure chemical substances of known purity, used for reconstitution of the matrix
(e.g., high purity copper of 99.99% Cu, used to prepare a series of standard solutions of zinc in the presence of copper for ICP-OES). Such materials should not
contain the analyte determined in an analysis (e.g., copper with a purity of 99.99%
does not contains zinc).
– Matrix RMs with the certified content of the substance (e.g., blood serum with
certified cholesterol content).
– Matrix RMs used for the defined analytical procedure, reproducing the certified
value provided the described procedures are used (e.g., fractionation of metals in
soil with specified extraction media).