Chemistry Reference
In-Depth Information
requirements, low power consumption is the most crucial. Smaller analytical instruments consume much less
energy and produce faster analyses for higher sample throughput.
The current trend in analysers, especially for on-line use, is toward sensors that are amenable to
miniaturization. The new generation of sensors offers tremendous potential for obtaining the desired analytical
information in a manner that is faster, simpler and cheaper than that of traditional laboratory-based instruments.
A chemical sensor can be defined as a device that, as a result of a process of chemical interaction, transforms
chemical or biochemical information into a signal (usually electrical or optical), in a way that responds to
changes in sample concentration in the chemical environment. A sensor contains three parts: a recognition
element, a transducer, and a signal processor capable of continuously and reversibly reporting a chemical
concentration [53, 54]. The transducer transforms a signal obtained by the sensor element into an electrical
signal. In addition to rapidly transforming information about the concentration of a specific compound into a
signal, and maintaining its activity over a long period of time, a sensor is usually small and inexpensive.
Because of its size, the energy requirements of sensors are rather low.
The following groups of sensors have been developed:
Optical sensors based on absorbance, reflectance, fluorescence, refractive index, optothermal effects and
light scattering;
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Electrochemical sensors based on voltammetry and potentiometry;
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Electrical sensors based on metal oxides, organic semiconductors and electrolytic conductivity;
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Mass sensitive detectors based on piezoelectric devices and surface acoustic waves;
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Paramagnetic sensors for oxygen; and
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Thermometric sensors based on the heat effects of chemical reactions.
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Biosensors, which offer prospects for combining the recognition of biological events with electronic signal
transduction and for designing a new generation of bio-electronic devices that can perform novel functions,
are especially promising. From an energy perspective, their operating temperature is close to room temperature,
so the requirement for heating or cooling is minimal; the temperature merely needs to be stabilized.
Progress in electronics and instrumentation has made it possible to measure extremely low electrical
signals. Wireless technology enables, responses from individual sensors to be received automatically, the
signals transformed into analytical information and changes over time assessed from a remote location. This
is far more economical than conventional process control and environmental monitoring, in which samples
are collected and transported to a central laboratory to determine their chemical composition. A high degree
of integration, efficiency, speed, and disposability makes these systems attractive for on-site environmental
or industrial applications.
Periodic calibration or completely removing the need for calibration is a particular challenge. If it can be
guaranteed that all the sensors within a batch are exactly equal within stipulated limits of uncertainty, then
only one of them needs to be calibrated. Another challenge is producing a real-time response without kinetic
effects, an impediment to the use of flow systems. By providing timely, safe and effective analytical
information such devices offer direct and reliable assessment of the production process or of the effects and
gradient of contaminants on site, greatly reducing analytical costs. Recent developments in wireless
communication technology and miniaturizing electronics have created the possibility to easily form sensor
networks that will greatly enhance monitoring the natural environment (which might be a home or hospital)
and, in some cases, lead to new measurement techniques or the deployment of sensors that was previously
impossible. As mentioned previously, the quality assurance of the data from instrumentation deployed
remotely and for long periods of time is a major issue that must be addressed. However, according to
Lieberzeit and Dickert [55], despite the great potential of sensors, studies have mainly been confined to
research laboratories and have often not yet reached the stage of technical development.
