1. The Use of Smart Materials with
Infrared Spectrometry for
Determination of hydrocarbons
Fiona Regan
National Centre for Sensor Research (NCSR)
School of Chemical Sciences
Dublin City University
2. Outline
Sensors and their applications
Principles of ATR-FTIR spectroscopy
Examples of materials for sensing
Analytes determined using polymer-based
sensors
4. ATR spectroscopy
Infrared light propagating in a crystal of high
refractive index is internally reflected.
Some of the light penetrates into the sample region
outside the crystal in the form of an evanescent wave.
Analyte absorption spectra can therefore be recorded
Principle:
6. Background
Mid-infrared spectroscopy is a well established and
powerful technique for off-line analysis.
It relies on the IR absorption characteristics of many
chemicals in the “finger print” region of the
electromagnetic spectrum.
IR analysis is limited in aqueous systems due to
strong water absorption.
ATR spectroscopy can overcome many of the limits
of MIR spectroscopy in aqueous solution.
7. Evanescent field sensing
(EFS)
EFS with optical fibres is an extension of the
established spectroscopic measurement ATR.
Routinely applied to the measurement of aqueous
systems / analytes.
IR radiation is coupled to an ATR element (fibre/
crystal) which is non-absorbing and has a higher
refractive index than the surrounding medium.
The medium is a thin film or the absorbing analyte.
8. Polymer-ATR spectroscopy
Why use a polymer?
Removal of background water absorption
To enable the detection of weaker signals at very low
concentrations of analyte.
Overcome by coating the internal reflection element
(crystal or fibre) with a hydrophobic polymer.
The polymer also serves to enrich the analytes within
the penetration depth.
9. Role of the polymer
PIB film
ZnSe crystal
From IR source
To detector
CHC
Evanescent
wave
Aqueous phase
Penetration depth
11. Polymer selection criteria
No, or only weak, intrinsic polymeric IR bands in the region
of interest;
Substances to be analysed must be reversibly absorbed in the
film;
The time constant for the enrichment process should be low;
The polymer should be easily prepared and be chemically
inert with respect to the analyte components;
The polymer material must be resistant against water and
organic compounds;
Must adhere well to the internal reflection element.
20. Plasticiser types
A. Adipic acid derivatives
B. Azelaic acid derivatives
C. Epoxy derivatives
D. Lauric acid derivatives
E. Mellitates
F. Palmitic acid derivatives
G. Phthalic acid derivatives
H. Sebaic acid derivatives
I. Stearic acid derivatives
J.Oleic acid derivatives
K. Linoleic acid derivatives
L. Isophthalic acid derivatives
M. Isobutyrate derivative
25. Investigation of reproducibility
using a 2% PIB film
0
0.05
0.1
0.15
0.2
0.25
0 20 40 60 80 100 120 140 160
Time (seconds)
Absorbance(AU)
MCB
CF
TeCE
Sparging @ 50oC, 0.02 L/min. 50 ppm each.
26. Analysis of solvent residues in pharmaceuticals
using sparging
Chloroform
Tablet sample batch analysis for chloroform residues
Tablets crushed, dissolved in water, sparged
Sparging @ 18oC, 1 L/min
27. Outcomes & Potential
Basic research project è applied
technologies
Novel materials for enrichment of
hydrocarbon species present in industrial
samples
Laboratory-based infrared ATR technology and
this will lead to development of a laboratory-
based fibre-optic or a planar waveguide
approach to developing è novel sensing
device.
28. Materials may also find uses for application to
other parameters.
The area of materials development for
sensors is under exploited and is an area of
great potential.
Materials can be designed for particular analytes
e.g. using sol-gels or molecular imprinting
where even greater potential of selectivity
can be realized.
29. Develop a modular system for monitoring water quality,
The materials è probes for monitoring solvent
residues
They may also find uses in occupational monitoring
The cost of the materials will be small.
The complexity of the devices to which they are
applied will influence the cost of the final sensor.
The sensor design in the longer term will be determined
by the need of the user.
Alarm level devices may be desirable è thus complex
instruments may not be necessary.
