172
4 The Measurement Process in Chemistry
Thus, there are experimental data (signals) provided by the measuring instrument (second step) for the samples or measurement standards used. In
addition, a laboratory can use tabulated or stated data not experimentally
produced in the CMP concerned; such is the case with values assigned to chemical standards (e.g. atomic weights, the Faraday), physico-chemical constants
(e.g. ionic equilibrium constants, partition coefficients in separation techniques), conversion factors (which are dimensionless numbers such as that used
to convert protein nitrogen contents when determined in various types of matrix)
by which some experimental data must be multiplied to be made consistent with
the known constraints of a CMP. This type of datum also includes statistical
values such as Student's t (see Box 2.2) that allow one to express the specific uncertainty of the results when a number of aliquots are individually subjected to
the CMP in question (see Fig. 2.10). This step can also be conducted by hand
(with or without a pocket calculator, for example) or automatically (with a computer). The way experimental data are to be treated is also strongly dependent on
the type of analytical method (primary, relative) used in the CMP, as well as on
the static or dynamic nature of the primary data it produces.
The growing availability and power of computers has brought about dramatic
changes in the third step of the CMP. Computers playa central role in this context
and will foreseeably continue to do so. The relationship between an instrument
and a computer is schematically depicted in Fig. 4.18. When coupled on-line, the
computer can govern the instrument's operation via an active electronic interface; in addition, the computer can acquire data via a passive interface and, with
simple, commercially available, software, also process them. In the off-line mode,
the human interface acquires the data, which are manually input into the
computer for processing. Current instruments are increasingly being equipped
with dedicated microcomputers for this purpose.
Off-line
t
- -+
INSTRUMENT
Printer
• : : ~e~u}t~ : ;
On-line
Operation
Fig. 4.18. Most common types of relationship between an instrument and a computer in the
third step of the analytical process: off-line and on-line. Control of the instrument operation
by the computer is also considered. For details, see text
4 The Measurement Process in Chemistry
Thus, there are experimental data (signals) provided by the measuring instrument (second step) for the samples or measurement standards used. In
addition, a laboratory can use tabulated or stated data not experimentally
produced in the CMP concerned; such is the case with values assigned to chemical standards (e.g. atomic weights, the Faraday), physico-chemical constants
(e.g. ionic equilibrium constants, partition coefficients in separation techniques), conversion factors (which are dimensionless numbers such as that used
to convert protein nitrogen contents when determined in various types of matrix)
by which some experimental data must be multiplied to be made consistent with
the known constraints of a CMP. This type of datum also includes statistical
values such as Student's t (see Box 2.2) that allow one to express the specific uncertainty of the results when a number of aliquots are individually subjected to
the CMP in question (see Fig. 2.10). This step can also be conducted by hand
(with or without a pocket calculator, for example) or automatically (with a computer). The way experimental data are to be treated is also strongly dependent on
the type of analytical method (primary, relative) used in the CMP, as well as on
the static or dynamic nature of the primary data it produces.
The growing availability and power of computers has brought about dramatic
changes in the third step of the CMP. Computers playa central role in this context
and will foreseeably continue to do so. The relationship between an instrument
and a computer is schematically depicted in Fig. 4.18. When coupled on-line, the
computer can govern the instrument's operation via an active electronic interface; in addition, the computer can acquire data via a passive interface and, with
simple, commercially available, software, also process them. In the off-line mode,
the human interface acquires the data, which are manually input into the
computer for processing. Current instruments are increasingly being equipped
with dedicated microcomputers for this purpose.
Off-line
t
- -+
INSTRUMENT
Printer
• : : ~e~u}t~ : ;
On-line
Operation
Fig. 4.18. Most common types of relationship between an instrument and a computer in the
third step of the analytical process: off-line and on-line. Control of the instrument operation
by the computer is also considered. For details, see text