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7 Validation of the Measurement Procedure
Validation is confirmation by examination and the provision of objective evidence that the particular requirements for a specific intended use have been
fulfilled.
Clause 5.4.5.1.ISO/IEC 17025:2005
7.7 Measurement Techniques
Before the introduction of analytical instrumental techniques, analytical methods
using chemical reactions were commonly used. The course of the reaction was
observed visually or determined based on direct measurements of characteristics
such as mass, volume or current. For example, determination of the amount of sulphate present was performed by weighting the precipitate of low soluble barium
sulphate; the more sulphates there were in the solution, the greater the mass of the
precipitate. For the determination of chloride by the coulometric method: the more
chloride ions there were in the solution, the greater the measured electric charge.
The dependence of the response of the measuring instrument (such as balance or
voltameter) from the amount of substance (e.g., sulphate, chloride ions) was directly
proportional only for the model systems containing the only determined substance.
A more complex situation occurs in the case of real samples with a complex composition. In this case, it is important to evaluate the selectivity of the applied method
in respect to a given property. The measurement of the mass of the substance is nonselective, which means that if the conditions of the precipitation of barium sulphate
cause precipitation of the other compounds, the weighted mass includes all of the
precipitated substance—meaning that it is not possible to distinguished individual
components. Similarly, in the coulometric measurements, if other compounds that
are carriers of charge are present, the coulometer will record the electrical signal (the
number of coulombs) that corresponds to the content of all compounds undergoing
an electrochemical reaction. These two simple examples indicate clearly that in some
cases the chemical measurements do not only depend on the amount of substance
of interest but may also depend on the composition of the object. These effects are
the reason that in the case of real samples, attention should be paid to the proper
selection of the conditions in which the test is conducted.
The rapid development of measurement techniques has meant that contemporary
analytical chemistry uses various physical and chemical processes, the effects of
which can cause various phenomena, which in turn can be measured—as long as a
suitable measuring system is available. In spectral methods, various effects of the
electromagnetic radiation within a wide wavelength range can be measured. There
are also phenomena occurring during the exposure of the sample with a stream of
electrons, ions, or uncharged particles. The electrochemical methods use electric
quantities for measuring electroactive substances. In addition, immunological and
7 Validation of the Measurement Procedure
Validation is confirmation by examination and the provision of objective evidence that the particular requirements for a specific intended use have been
fulfilled.
Clause 5.4.5.1.ISO/IEC 17025:2005
7.7 Measurement Techniques
Before the introduction of analytical instrumental techniques, analytical methods
using chemical reactions were commonly used. The course of the reaction was
observed visually or determined based on direct measurements of characteristics
such as mass, volume or current. For example, determination of the amount of sulphate present was performed by weighting the precipitate of low soluble barium
sulphate; the more sulphates there were in the solution, the greater the mass of the
precipitate. For the determination of chloride by the coulometric method: the more
chloride ions there were in the solution, the greater the measured electric charge.
The dependence of the response of the measuring instrument (such as balance or
voltameter) from the amount of substance (e.g., sulphate, chloride ions) was directly
proportional only for the model systems containing the only determined substance.
A more complex situation occurs in the case of real samples with a complex composition. In this case, it is important to evaluate the selectivity of the applied method
in respect to a given property. The measurement of the mass of the substance is nonselective, which means that if the conditions of the precipitation of barium sulphate
cause precipitation of the other compounds, the weighted mass includes all of the
precipitated substance—meaning that it is not possible to distinguished individual
components. Similarly, in the coulometric measurements, if other compounds that
are carriers of charge are present, the coulometer will record the electrical signal (the
number of coulombs) that corresponds to the content of all compounds undergoing
an electrochemical reaction. These two simple examples indicate clearly that in some
cases the chemical measurements do not only depend on the amount of substance
of interest but may also depend on the composition of the object. These effects are
the reason that in the case of real samples, attention should be paid to the proper
selection of the conditions in which the test is conducted.
The rapid development of measurement techniques has meant that contemporary
analytical chemistry uses various physical and chemical processes, the effects of
which can cause various phenomena, which in turn can be measured—as long as a
suitable measuring system is available. In spectral methods, various effects of the
electromagnetic radiation within a wide wavelength range can be measured. There
are also phenomena occurring during the exposure of the sample with a stream of
electrons, ions, or uncharged particles. The electrochemical methods use electric
quantities for measuring electroactive substances. In addition, immunological and