4.4 Measurement and Transducing of the Analytical Signal
169
Box 4.11
The following scheme places some analytical instruments typically used in (MPs in the different categories of Fig. 4.16.
Instrument
Category of Fig. 4.16
1
2
3
4
5
6
Balance
Mass
Instrument Passive Off-line
Primary Quantitative
proper
Manual
Mass
Instrument Passive Off-line
Primary Quantitative
burette
volume proper
Human
senses
Autoburette Mass
Instrument Active
Off-line
Primary Quantitative
volume proper
UV-Visible
Optical Instrument Active
Off-line
Relative Quantitative
photometer
proper
On-line
(ch romatograph)
Atomic em is- Optical Instrument Active
Off-line
Relative Qualitative
sion spectroproper
and
meter
quantitative
PotentioElectro- Instrument Passive Off-line
Relative Quantitative
meter (pH,
anaproper
(special)
pM measure- Iytica l
ments)
Note: Only the most usual options are considered.
The measured signal can be a response to a chemical (reactivity) or physicochemical property of the analytes or their reaction products. As such, signals can
be of various types (optical, electrochemical, mass, thermal, magnetic) and
require instruments of widely variable design for measurement. The primary
signal is transduced (and amplified) into another - usually electrical - signal
which is that usually measured in practice (in volts or millivolts). The output can
be in analog, digital or printed form, but is normally given in units related to
those of the initial signal (e. g. absorbance in photometry, fluorescence intensity
in luminescence techniques). Computers are being increasingly used to acquire
and process signals, and also to deliver the ensuing analytical data or results.