IMS in LAEC
Investigations in the field of Ion Mobility Spectrometry (IMS)
have been carried out in the Laboratory of Applied Environmental Chemistry
since 2005. Researchers are committed in different projects based on theoretical
and practical aspects of this analytical method. Chromatographic and
spectrometric techniques with particular emphasis on IMS have been exploited in
the projects.
The group organise IMS seminars concerning related topics such as phenomena
taking place in ionised gases, theory of ion transport and applications of IMS
in environmental analysis. In last years the annual IMS Workshop for Finnish IMS
researchers is organised in Mikkeli.
Currently IMS group in LAEC consists of following researchers:
Sanna
Holopainen (M.Sc.), Marko Mäkinen (Ph.D.) and
Marjaana Nousiainen
(Ph.D.). Former members include Jarosław Puton (Ph.D.), Riikka-Marjaana
Räsänen (M.Sc.), Alexander Tolstoguzov (Ph.D.) and Yonsuang
Arnanthigo (M.Sc).
Basics of Ion Mobility Spectrometry
Ion mobility spectrometry (IMS) is a technology for qualitative and
quantitative analysis of organic and inorganic compounds present in the
gas-phase. Numerous compounds can be analyzed; however IMS is mainly used for
monitoring hazardous compounds. The detection of explosives, chemical warfare
agents as well as toxic industrial chemicals including environmental pollutants
are examples of different applications.
The technique is based on ionisation of analyte molecules and mobility
measurement of created ions. The conventional time-of-flight IMS detector
consists of two main parts. The first one is ion reactor (reactant section), in
which ionisation occurs. Ions are introduced into the second part of the
detector, i.e. drift section, in which ions are separated in constant electric
field. Ions reaching the collector generate time dependent current inducing
signal, which is typically presented as drift time spectrum.
Peaks in drift time spectra represent ions created in reactant section.
Position of peak, i.e., drift time of particular ions, corresponds to
characteristic mobility coefficient that depends on ion’s mass, size and
electric properties. The intensity and area of peaks correlate with the
concentration of the analyte in carrier gas.
In practice, quantitative analysis with IMS may be complicated. Several kinds
of ionic species can be observed for a given analyte because of both
fragmentation and clusterisation processes. Also cross-sensitivity effects,
caused by the presence of interfering agents, can change both position and
intensity of the analyte peak.
In addition to classic time-of-flight instruments also other kinds of IMS
devices are used: the most known are aspiration ion mobility spectrometer (AIMS).
In AIMS ions are moved both in electric field and in stream of gas; detector
with high electric field utilizes non-linear dependency between field value and
ion velocity.
Important part of instrumentation is the vapour generator.
It is used for producing gaseous mixtures of organic and inorganic compounds
in concentrations ranging from 0.1 ppb up to 1000 ppm. Independent, precise
and repeatable concentration adjustments can be made simultaneously to two
compounds.
Results of such measurements can be used in fundamental studies of
detectors properties and testing and calibration of particular instruments.
Signal of different concentrations of analyte (1-pentanol) is presented as
an example.<return>
Utilisation, development and validation of analytical methods for detecting
environmentally hazardous industrial chemicals have been one of the key research
areas in LAEC. The ongoing research is focused on investigating the potential of
IMS as an early warning system for monitoring volatile toxic chemicals in
municipal waters and waste waters. The results will contribute to the
development of novel strategies in water quality control and strengthening of
environmental management in terms of water monitoring.
IMS has been successfully applied for the detection of gasoline additives
like MTBE. The recent studies have concentrated to detect MTBE in water
solutions using the combination of solid phase microextraction (SPME) and IMS.<return>
Traditionally, radioactive ion sources are most commonly used in ion mobility
spectrometers. However, due to strict regulations of radioactive materials new
ionisation methods are required. Such methods are e.g. corona dischargers, photo
ionisation, surface ionisation and electrospray. <return>
In general, humidity is seen in IMS-spectra as protonated water clusters
producing the reaction ion peak (RIP). These cluster ions are also abundantly
present in measurements having low sample concentrations. The influence of
humidity to the detection limits and sensitivity of IMS instrument are
investigated and stated by measuring different concentrations of selected sample
compounds with excess of water vapour. <return>
The theoretical studies include modelling of ions behaviour in reactant
region of IMS detector. The goal is both to optimise detectors construction and
to explain experimental results. The results can be used to predict calibration
relationships and to obtain assumed sensitivity of detection.
Mathematical models of reactant region are based on time independent balance
equations that take into account movement of ions in electric field and flow of
gas, recombination, ion-molecule reactions and diffusion. <return>
Partners
- Environics Oy, Mikkeli
- University of Helsinki
- Tampere University of Technology
- Military University of Technology, Warsaw, Poland
Funding
- The Academy of Finland
- Tekes, The Finnish Funding Agency for Technology and Innovation
- The Regional Council of South Savo
- City of Mikkeli
- European Community
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