Thesis-2012-Moll.pdf (3.71 MB)
Control and calibration of atmospheric pressure chemical ionisation processes in ion mobility spectrometry using piezoelectric dispensers
thesis
posted on 2011-11-25, 12:37 authored by Victor MollIf the analyses of trace components in complex organic samples are to be optimised,
then these compounds must be isolated either physically or chemically from
surrounding matrices. Ion mobility spectrometry (IMS) is an analytical technique used
worldwide for the detection of on-site trace compounds. The technique can be
optimised to isolate the target species from complex matrices through both physical
separation, based on the mobility of the analyte ions at ambient pressure, and
chemical discrimination through preferential ionisation of the target. Optimisation of
the latter is commonly achieved through doping the spectrometer with a selective
reagent gas, termed a dopant. The chemical processes required to optimise the
responses of target analytes are dependent on the identity and concentration of the
dopant. As such, a variety of dopants have been successfully implemented in ion
mobility spectrometers. The technology for the deliverance of dopants in IMS is
commonly through permeation sources, which provide a stable chemical environment
in the ion mobility cell. Althoughrelatively inexpensive and durable, these devices are
difficult to change and generally deliver a single dopant concentration. As a result,
only one type of chemistry is possible and the responses cannot be optimised for a
range of analytical applications. Such limitationsbecome increasingly significant when
IMS is hyphenated to a chromatograph where a range of different dopant conditions
may be sought over the course of a chromatographic run.
This thesis sought to overcome these limitations through the development and
implementation of piezoelectric dispensers, interfaced directly to the transport gas
regions of IMS cells. The study demonstrates for the first time the ability to use
piezoelectric dispensing as a dopant introduction methodology in IMS for controlling
and calibrating a range of dopant chemistries. 2-butanol, acetone, dichloromethane,
1-chlorohexane, 4-heptanone and 1-bromohexane were the candidate dopants
chosen for the studies, covering a wide range of physical and chemical properties.
The novel technology was used to dispense the target dopants into IMS cells at
concentration ranges over three orders of magnitude. Dopant chemistries were
achieved within three seconds from the point of dispensing, administered in drop-ondemand
formats, and could be delivered either transiently or at steady-state
concentrations. The concept was validated through integrated spectral dopant
responses. In transient control, dynamic linear relationships of R2 = 0.991 – 0.998
were achieved between dispensed dopant mass and peak area. Under continuous
operation, the RSD of the dopant level was < 18% for all dopants. Clear out times for
dopant responses were in the order of 3-5 seconds, indicating negligible hysteresis
effects.
The study also proved the concept of controlling monomer and dimer ion chemistries
from 2-butanol actuations when interfaced to a differential mobility spectrometer at
mass fluxes between 21 – 1230 ng m-3
, and the simultaneous control of dopants in
negative and positive ionisation modes to RSDs <10%. This thesis describes the
techniques used to optimise the piezoelectric dispensing of the full dopant range, as
well as the full design protocols required to interface to mobility spectrometers. The
outcomes from these studies provide a realisation for piezoelectric dispensers as a
future mainstream dopant introduction technique for the analysis of complex
samples
History
School
- Science
Department
- Chemistry
Publisher
© Victor MollPublication date
2011Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en