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4 Metrological Traceability
The mole (SI base unit for the amount of substance) is the amount of substance
of a system that contains as many elementary entities as there are atoms in
0.012 kg of carbon-12. When the mole is used, the elementary entities must
be specified and may be atoms, molecules, ions, electrons, other particles, or
specified groups of such particles.
IUPAC. Compendium of Chemical Terminology, (2014) 2nd ed. (the ‘Gold
Book’).
Metrological traceability can be defined not only by comparison with the standard
unit of measurement of SI but also in relation to the generally accepted scale of values;
for example, pH, hardness or octane scale. However, regardless of the way in which
we determine the consistency of the measurement result obtained and the structure
of the chain of comparisons, it is important to agree on the highest measurement
standard of the hierarchy. The lack of a hierarchical system of comparisons leads to
possible multiplication of systematic error (e.g., bias).
One particular anecdote illustrates this problem well:
In a small town, with a charming market place, citizens respect the local radio station as well
as the local watchmaker. One day, the young, inquiring journalist of the newspaper went to
the radio station, asking how they knew the exact time. The radio station employee replied
that it was because of the watchmaker in the market place. So, the journalist went to the
watchmaker with the same question. The answer was: “But that’s obvious: from our local
radio station!”
I wonder how the journalists from the radio—who I listen to while driving in the
morning—would have answered my question: how do they know when to give the
message ‘it is now 7 o’clock’?
Prior to an in-depth discussion on the traceability of chemical measurements, let
us devote a moment to the typical measurements of physical quantities; for example,
time. For thousands of years, humans have been dealing with time by preparing
calendars, creating patterns of time, and using external machines measuring the
passing of time in order to plan each day. The measurement of time is essential
both in everyday life and in all fields of science and technology, including chemical
measurements. From the very beginning, man has tried to determine the time of day
and season of the year, since this was connected with the need to organize life in a
society. Initially, these were the observations of the position of the sun and moon, as
well as the surrounding nature.
As mentioned earlier, each measurement consists in comparing the unknown
quantity to the reference. This must be of the same character as the measured quantity:
for example, the length standard must be a section of a certain length; mass standard—
a mass of an object; and here is a critical question referring chemical measurements:
how we can establish a standard of iron content in human serum?
The creation of an artefact for a standard of time as was done initially (e.g., to
measure the length and mass) is not possible. Passing time is, in fact, independent of
the will of the individual, and may be passively monitored and in an indirect way—by
4 Metrological Traceability
The mole (SI base unit for the amount of substance) is the amount of substance
of a system that contains as many elementary entities as there are atoms in
0.012 kg of carbon-12. When the mole is used, the elementary entities must
be specified and may be atoms, molecules, ions, electrons, other particles, or
specified groups of such particles.
IUPAC. Compendium of Chemical Terminology, (2014) 2nd ed. (the ‘Gold
Book’).
Metrological traceability can be defined not only by comparison with the standard
unit of measurement of SI but also in relation to the generally accepted scale of values;
for example, pH, hardness or octane scale. However, regardless of the way in which
we determine the consistency of the measurement result obtained and the structure
of the chain of comparisons, it is important to agree on the highest measurement
standard of the hierarchy. The lack of a hierarchical system of comparisons leads to
possible multiplication of systematic error (e.g., bias).
One particular anecdote illustrates this problem well:
In a small town, with a charming market place, citizens respect the local radio station as well
as the local watchmaker. One day, the young, inquiring journalist of the newspaper went to
the radio station, asking how they knew the exact time. The radio station employee replied
that it was because of the watchmaker in the market place. So, the journalist went to the
watchmaker with the same question. The answer was: “But that’s obvious: from our local
radio station!”
I wonder how the journalists from the radio—who I listen to while driving in the
morning—would have answered my question: how do they know when to give the
message ‘it is now 7 o’clock’?
Prior to an in-depth discussion on the traceability of chemical measurements, let
us devote a moment to the typical measurements of physical quantities; for example,
time. For thousands of years, humans have been dealing with time by preparing
calendars, creating patterns of time, and using external machines measuring the
passing of time in order to plan each day. The measurement of time is essential
both in everyday life and in all fields of science and technology, including chemical
measurements. From the very beginning, man has tried to determine the time of day
and season of the year, since this was connected with the need to organize life in a
society. Initially, these were the observations of the position of the sun and moon, as
well as the surrounding nature.
As mentioned earlier, each measurement consists in comparing the unknown
quantity to the reference. This must be of the same character as the measured quantity:
for example, the length standard must be a section of a certain length; mass standard—
a mass of an object; and here is a critical question referring chemical measurements:
how we can establish a standard of iron content in human serum?
The creation of an artefact for a standard of time as was done initially (e.g., to
measure the length and mass) is not possible. Passing time is, in fact, independent of
the will of the individual, and may be passively monitored and in an indirect way—by