6.3 Relative Quantitation Methods
275
I 6.3.2 Comparative Methods
These quantitation methods are essentially similar to relative methods but have
some special connotations that have led ISO to deal with them separately. They
are also based on comparisons of the signals yielded by the sample and a standard. However, they differ from relative methods in the following respects:
(a) They are used when the response of the instrumental technique of choice is
highly sensitive to changes in sample matrix.
(b) As a rule, they are employed when available equipment is amenable to direct
insertion of untreated solid samples.
(c) The standards used are certified reference materials (CRMs) the matrices of
which are as similar as possible to that of the sample.
In the ideal situation, CRMs spanning a range of analyte concentrations would
be available. In such a case, the above-described interpolation method is used. In
daily practice, however, only a single CRM is usually available, so the analyte
concentration has to be determined by comparing the sample signal with that
provided by the CRM, which will contain a certified concentration (or amount)
of analyte.
This approach is frequently associated to such techniques as arc or spark
atomic emission spectroscopy and X-ray fluorescence.
275
I 6.3.2 Comparative Methods
These quantitation methods are essentially similar to relative methods but have
some special connotations that have led ISO to deal with them separately. They
are also based on comparisons of the signals yielded by the sample and a standard. However, they differ from relative methods in the following respects:
(a) They are used when the response of the instrumental technique of choice is
highly sensitive to changes in sample matrix.
(b) As a rule, they are employed when available equipment is amenable to direct
insertion of untreated solid samples.
(c) The standards used are certified reference materials (CRMs) the matrices of
which are as similar as possible to that of the sample.
In the ideal situation, CRMs spanning a range of analyte concentrations would
be available. In such a case, the above-described interpolation method is used. In
daily practice, however, only a single CRM is usually available, so the analyte
concentration has to be determined by comparing the sample signal with that
provided by the CRM, which will contain a certified concentration (or amount)
of analyte.
This approach is frequently associated to such techniques as arc or spark
atomic emission spectroscopy and X-ray fluorescence.