Biomedical Engineering Reference
In-Depth Information
2.3.2 Development of NIR Spectroscopy
The development of NIR spectroscopy as a quality and process control tool is
largely due to the availability of efficient chemometric techniques and varying
spectrometer configurations [
107
].
Process environments vary considerably, and selecting the most appropriate
sampling interface is of paramount importance. A large degree of process
understanding is vital prior to choosing the sampling interface. The physical,
chemical and optical nature of the process stream should be known in order to
determine if the results will be significantly impacted by light scattering. This is
particularly important where NIR is concerned, as the strong light source and the
weak absorbance allow infrared radiation to penetrate further into the sample,
allowing particulates present in a suspension or slurry to cause light scattering.
Other aspects such as the potential of the process fluid to foul the probe or sample
system should also be evaluated [
107
]. Typically NIR sampling systems for in situ
process monitoring are in the form of one of the following two types: extractive
sampling systems, or immersion probe sampling. A number of variations of each
of the above two types exist. Invariably, it is the process conditions which dictate
the system of choice.
2.3.3 Development of Raman Spectroscopy
During the 1920s, scattering effect theory was investigated by a number of
researchers, including the physicist C. V. Raman, who in 1928 was the first to
experimentally demonstrate the Raman effect in liquids [
108
]. A modified FT-IR
instrument was also used to collect Raman spectra, and the use of such instruments
is now known as FT-Raman spectroscopy. Dispersive Raman spectroscopy and
FT-Raman spectroscopy each have their own specific advantages, and both con-
tinue to be used for different applications [
109
-
111
].
The basic components of any Raman spectrometer are the excitation source, the
spectrometer and the detector. Significant advances in all three areas have led to
the possibility of using Raman spectroscopy as a PAT tool.
2.3.4 Interpretation of Spectral Data Using Chemometrics
It is almost impossible to discuss the use of spectral data without a brief discussion
on the concept of chemometrics, as the various chemometric techniques maximise
the information available from spectroscopic instruments. Chemometrics can be
defined as the chemical discipline that uses mathematical, statistical and other
methods employing formal logic (a) to design or select optimal measurement
procedures and experiments, and (b) to provide maximum relevant chemical
information by analysing chemical data [
112
] (see also Chap. 7). When applied to
spectra collected online during a bioprocess by MIR, NIR or Raman spectrometers,
Search WWH ::
Custom Search