access, such as in underground pipe systems, brings a number of requirements.
Amongst the most important technical preconditions are robustness of performance,
autonomous operation and low maintenance requirements. The latter means the
instruments themselves are stable, e.g. free from drift and other effects that necessitate recalibrations, do not need (replacement of) consumables and are selfmaintaining, e.g. that keep themselves clean and compensate for deviations. For a
full discussion on the considerations concerning sensor selection and operations,
please refer to van den Broeke et al. [4].
2 Spectroscopy
One type of instrument that is particularly suited for such demanding applications is
the spectrometer. This chapter will describe the principles and applications of a
number of optical methodologies that are in use as water quality sensors. This
chapter is not intended as an exhaustive review, but provides a brief introduction
in the application of various spectroscopic methods in water monitoring and includes
references to more exhaustive texts.
The technologies described in this chapter have been selected because they are
purely optical; they analyse the primary interaction of light with a sample matrix and
its constituents. No additional aids are used to achieve selectivity or to enhance the
signal, apart from sensitive photo detectors to collect the light after its interaction
with the sample and subsequent data processing. Although other optical techniques
are widely used, e.g. reagent-based photometric methods, the discussion herein
focuses on techniques that meet, or have the potential to meet, the requirements
set out above for sensors suitable for integration in smart water solutions. Most
importantly, these technologies make use of solid-state, long-term stable components, do not require chemicals and are compatible with effective auto-cleaning
techniques. Furthermore, with the development of ever smaller electric and optical
components, they lend themselves to further miniaturisation and reduced power
consumption that will be required for large-scale, autonomous deployment in distributed (water) networks.
The analysis of the interaction of light with matter, incidentally, is the oldest
methodology for studying the chemical composition of samples. The history of
spectroscopy begins with the publication of the studies on refraction of light by a
prism by Isaac Newton in 1672. In this work, Newton proved that white light is
composed of light of various colours. Subsequently it became clear that different
chemicals absorb light of various colours and that this was a property that could be
used to study their concentrations in a matrix. The step towards analysis of water
samples was made in 1856 with the development of Nessler’s method, in which
ammonia in water reacts with mercuric iodide and potassium, forming a reddishbrown colloid. The colour intensity of the reaction product depends on the initial
concentration of ammonia in the sample.
Spectroscopic Methods for Online Water Quality Monitoring
285
Amongst the most important technical preconditions are robustness of performance,
autonomous operation and low maintenance requirements. The latter means the
instruments themselves are stable, e.g. free from drift and other effects that necessitate recalibrations, do not need (replacement of) consumables and are selfmaintaining, e.g. that keep themselves clean and compensate for deviations. For a
full discussion on the considerations concerning sensor selection and operations,
please refer to van den Broeke et al. [4].
2 Spectroscopy
One type of instrument that is particularly suited for such demanding applications is
the spectrometer. This chapter will describe the principles and applications of a
number of optical methodologies that are in use as water quality sensors. This
chapter is not intended as an exhaustive review, but provides a brief introduction
in the application of various spectroscopic methods in water monitoring and includes
references to more exhaustive texts.
The technologies described in this chapter have been selected because they are
purely optical; they analyse the primary interaction of light with a sample matrix and
its constituents. No additional aids are used to achieve selectivity or to enhance the
signal, apart from sensitive photo detectors to collect the light after its interaction
with the sample and subsequent data processing. Although other optical techniques
are widely used, e.g. reagent-based photometric methods, the discussion herein
focuses on techniques that meet, or have the potential to meet, the requirements
set out above for sensors suitable for integration in smart water solutions. Most
importantly, these technologies make use of solid-state, long-term stable components, do not require chemicals and are compatible with effective auto-cleaning
techniques. Furthermore, with the development of ever smaller electric and optical
components, they lend themselves to further miniaturisation and reduced power
consumption that will be required for large-scale, autonomous deployment in distributed (water) networks.
The analysis of the interaction of light with matter, incidentally, is the oldest
methodology for studying the chemical composition of samples. The history of
spectroscopy begins with the publication of the studies on refraction of light by a
prism by Isaac Newton in 1672. In this work, Newton proved that white light is
composed of light of various colours. Subsequently it became clear that different
chemicals absorb light of various colours and that this was a property that could be
used to study their concentrations in a matrix. The step towards analysis of water
samples was made in 1856 with the development of Nessler’s method, in which
ammonia in water reacts with mercuric iodide and potassium, forming a reddishbrown colloid. The colour intensity of the reaction product depends on the initial
concentration of ammonia in the sample.
Spectroscopic Methods for Online Water Quality Monitoring
285