Chemistry Reference
In-Depth Information
Exhaust flow
Drift flow
Ion shutter
Faraday plate
detector
Sample carrier flow
Ionization region
Drift rings
Figure 6.4
Basic scheme of an ion mobility spectrometer.
Several applications of IMS can be highlighted such as fast screening of explosives in security checkpoints
[51], meat freshness through the analysis of biogenic amines [52] and air quality monitoring in industrial or
laboratory areas [53]. Although IMS has been conceived for monitoring volatile analytes, the on-line coupling
of efficient sample introduction systems allows the fast monitoring of solid and liquid samples [54].
6.1.3.3
Other spectroscopy based portable analyzers
Colorimetric and UV/Vis spectrophotometric monitors for gases and vapors are widely used in the industry.
Colorimetric analyzers use a reaction between a selective reagent and the target analyte in order to form a
colored complex which is measured in the visible range. Those analyzers provide limits of detection of the
order of parts per million (ppm), offering a continuous monitoring capability. They are available as portable,
battery-powered devices for personal monitoring and equipped with external power sources for static
monitoring of a predetermined area. There are also chemiluminescent detectors for measuring ozone and
nitrogen oxides, based on the excitation of O
3
molecules via chemical reaction and the subsequent detection
of photon emission from the excited state species. Luminol and ethylene have been used as reactants in the
determination of NO
2
and ozone. Photometric analyzers for the determination of sulfur or phosphorus
compounds are commonly used for real time monitoring with detection limits in the parts per billion range.
Moreover, fluorescence analyzers are commercially available for monitoring CO and SO
2
providing detection
limits in the part per billion (ppb) range.
It should be also mentioned the usefulness of IR hand held analyzers. Their lightweight and compact size
is perfect for applications that require repetitive analyses on large surfaces or in locations that are physically
restricted. An example of this type of IR analyzers is the Flexscan and Exoscan from Agilent Technologies [55].
At the same line, Axsun has developed the AnavoTM Analyzer which is a hand held portable NIR analyzer
designed specifically for industrial applications [56].
6.2
Process monitoring: in-line, on-line and at-line measurements
Measurement of safety and quality in industrial processes requires an on-line detection technique with the
following properties: (1) it should be compact and robust to be mounted in or close to the production line and
take place under realistic environment, (2) provide real time, (3) non-destructive measurements, (4) relatively
low cost and (5) permanent monitoring. Raman and FTIR, in the mid (MIR) and near (NIR) range,
spectroscopies are considered as privileged methods for in- or on-line process monitoring applications due to
