1.6 Conceptual and Technical Hierarchies
23
The rank of the analytical information produced also increases from the term
"to sense" to the verb "to analyse" as follows (Fig. 1.15):
• To sense involves using a device responsive to the presence (and concentration, if applicable) of a (bio )chemical species in a sample.
• To detect involves the direct use of an instrument to acquire or produce
a signal and transduce it into a readily measured physical (usually electrical) quantity. This function is served by instruments (e.g. photometers,
potentiometers, balances), which produce primary data (e.g. absorbance,
electrical potential or mass units). Indirectly, instruments are the basis for
sensors.
• To characterize entails establishing distinct features of an object or system in
order to define it on the basis of results obtained by mathematical processing
of primary data produced by an instrument.
• To analyse involves interpreting - in addition to characterizing - in qualitative, quantitative and structural terms, which entails converting results into
reports.
Box 1.8
pH paper, the pH electrode and a fibre-optic probe conta ining an immobilized reagent on its
tip for immersion in the sample are typica l examples of sensors. A sensor can only be used if
connected, in a direct or indirect manner, to an instrument for detection. Thus, the
Uinstrument"for pH paper is the human body, which compares the resulting colour with those
on a scale (the "standard"). The pH electrode is a sensor connected to a potentiometer to
measure the potential difference between it and a reference electrode. A fluorimetric fibreoptic sensor must unavoidably be connected to a spectrofluorimeter, which is the actual
instrument that measures the fluorescence intensity.
The two rankings of Fig. 1.15 are significance and scope hierarchies; as a result,
the upper levels rely on the lower ones. Thus, a report cannot be made without
results and a system cannot be characterized without detection. Also, the levels
in the two hierarchies are mutually related (reports ~ to analyse, results ~ to
characterize, primary data ~ to detect).
A different conceptual and technical hierarchy (Fig. 1.16) is needed to clarify
the meaning of words such as "process", "technique", "method" and "procedure",
which are often used indifferently. A technique is a generic principle that is used
to extract information; it uses an instrument and comes into play in the second
step of the analytical process. The analytical process is the body of operations
that separates the uncollected, unmeasured, untreated sample from the results,
expressed as required; Chapter 4 is devoted to it. A method is the specific implementation of an analytical technique to determine one or more analytes in a
given sample; it is thus the materialization of the analytical process. A procedure
is the detailed sequence of actions performed in carrying out an analytical
method. Technique and method should never be confused; techniques (polarography, titrimetry, X-ray spectrometry) are generic in nature whereas methods
are specific to given types of samples and analytes.
23
The rank of the analytical information produced also increases from the term
"to sense" to the verb "to analyse" as follows (Fig. 1.15):
• To sense involves using a device responsive to the presence (and concentration, if applicable) of a (bio )chemical species in a sample.
• To detect involves the direct use of an instrument to acquire or produce
a signal and transduce it into a readily measured physical (usually electrical) quantity. This function is served by instruments (e.g. photometers,
potentiometers, balances), which produce primary data (e.g. absorbance,
electrical potential or mass units). Indirectly, instruments are the basis for
sensors.
• To characterize entails establishing distinct features of an object or system in
order to define it on the basis of results obtained by mathematical processing
of primary data produced by an instrument.
• To analyse involves interpreting - in addition to characterizing - in qualitative, quantitative and structural terms, which entails converting results into
reports.
Box 1.8
pH paper, the pH electrode and a fibre-optic probe conta ining an immobilized reagent on its
tip for immersion in the sample are typica l examples of sensors. A sensor can only be used if
connected, in a direct or indirect manner, to an instrument for detection. Thus, the
Uinstrument"for pH paper is the human body, which compares the resulting colour with those
on a scale (the "standard"). The pH electrode is a sensor connected to a potentiometer to
measure the potential difference between it and a reference electrode. A fluorimetric fibreoptic sensor must unavoidably be connected to a spectrofluorimeter, which is the actual
instrument that measures the fluorescence intensity.
The two rankings of Fig. 1.15 are significance and scope hierarchies; as a result,
the upper levels rely on the lower ones. Thus, a report cannot be made without
results and a system cannot be characterized without detection. Also, the levels
in the two hierarchies are mutually related (reports ~ to analyse, results ~ to
characterize, primary data ~ to detect).
A different conceptual and technical hierarchy (Fig. 1.16) is needed to clarify
the meaning of words such as "process", "technique", "method" and "procedure",
which are often used indifferently. A technique is a generic principle that is used
to extract information; it uses an instrument and comes into play in the second
step of the analytical process. The analytical process is the body of operations
that separates the uncollected, unmeasured, untreated sample from the results,
expressed as required; Chapter 4 is devoted to it. A method is the specific implementation of an analytical technique to determine one or more analytes in a
given sample; it is thus the materialization of the analytical process. A procedure
is the detailed sequence of actions performed in carrying out an analytical
method. Technique and method should never be confused; techniques (polarography, titrimetry, X-ray spectrometry) are generic in nature whereas methods
are specific to given types of samples and analytes.