Biomedical subjects

C L Paul Thomas

Publications and source records attributed to C L Paul Thomas.

5 recordsLinked to original sources

PubMed2007

Photochemistry of refractive index structures in poly(methyl methacrylate) by femtosecond laser irradiation.

Femtosecond, subablation threshold photomodification of poly(methyl methacrylate) (PMMA) at 387 nm is explored to enable fabrication of optical components. Volatile fragment analysis (thermal desorption gas chromatography-mass spectrometry) and molecular weight distribution monitoring (size exclusion chromatography) suggest photochemical modification, involving direct cleavage of the polymer backbone and propagation via chain unzipping under formation of monomers, similar to the pyrolytic degradation of PMMA. Waveguides were produced in undoped, clinical-grade PMMA, showing an increased refractive index in the laser focal region (Dnmax=4x10(-3)).

Journal Article↗

PubMed2006

Free flow isotachophoresis in an injection moulded miniaturised separation chamber with integrated electrodes.

An injection moulded free flow isotachophoresis (FFITP) microdevice with integrated carbon fibre loaded electrodes with a separation chamber of 36.4mm wide, 28.7 mm long and 100 microm deep is presented. The microdevice was completely fabricated by injection moulding in carbon fibre loaded polystyrene for the electrodes and crystal polystyrene for the remainder of the chip and was bonded together using ultrasonic welding. Two injection moulded electrode designs were compared, one with the electrode surface level with the separation chamber and one with a recessed electrode. Separations of two anionic dyes, 0.2mM each of amaranth and acid green and separations of 0.2mM each of amaranth, bromophenol blue and glutamate were performed on the microdevice. Flow rates of 1.25 ml min(-1) for the leading and terminating electrolytes were used and a flow rate of 0.63 ml min(-1) for the sample. Electric fields of up to 370 V cm(-1) were applied across the separation chamber. Joule heating was not found to be significant although out-gassing was observed at drive currents greater than 3 mA.

Electrodes↗

PubMed2006

The presumptive detection of benzene in water in the presence of phenol with an active membrane-UV photo-ionisation differential mobility spectrometer.

Studies with a new technique, active membrane-differential mobility spectrometry, with aqueous standards of benzene and phenol are described. The atmospheric pressure photo-ionisation chemistries of benzene and phenol in the presence of oxygen are similar in that benzene forms phenol radicals that subsequently react to yield diphenylether and 4-phenoxyphenol products. Further phenol sequesters charge from benzene ions leading to a significant loss of sensitivity. This is an important consideration in the development of screening techniques for the presence of benzene in environmental water samples. This challenge was addressed by including a pre-separation stage prior to photo-ionisation, and a 10 cm long polydimethylsiloxane active membrane inlet using nitrogen as a carrier gas was used to sample, concentrate and deliver low resolution separations to the 10.6 eV UV-ionisation region of a differential mobility spectrometer. Acetone was also proposed as a charge carrier for the UV photo-ionisation source; to promote phenol protonation and inhibit charge sequestration from benzene. The responses of the system to aqueous standards of benzene and phenol with and without acetone doping at 10.2 mg m(-3) were evaluated and four to five-fold increases in sensitivity were obtained with acetone doping. With a sampling time of 60 s and a total measurement cycle of 180 s it was possible to obtain quantitative responses to single standards over the concentration range 6 to 177 microg cm(-3) with linear correlations with R(2) values ranging from 0.97 to 0.99. The effects of the heating rate of the membrane and the dispersion field strength of the differential mobility spectrometer on sensitivity and the differentiation of benzene from phenol responses were optimised, leading to a configuration where a voltage heating programme of 4.75 V s(-1) was applied to a 124 microm stainless steel wire heating element within the active membrane, and a dispersion field strength of 22 kV cm(-1) was used to test a mixture of benzene (14 microg cm(-3)) and phenol (6 microg cm(-3)) in water. The presence of benzene was identified through the presence of a peak corresponding to a benzene response, V(C) = -9 V FWHM = 1 V, that followed the thermal desorption profile of benzene.

Journal Article↗

PubMed2005

Programmable gate delayed ion mobility spectrometry-mass spectrometry: a study with low concentrations of dipropylene-glycol-monomethyl-ether in air.

The concept of using a short ionisation event, in this case a pulsed corona discharge, in conjunction with programmed gate delay is described. This technique is proposed for the selective study of different ionisation processes within the reaction region of an ion mobility spectrometer. The utility of such an approach was tested in a study of the ionisation of dipropylene-glycol-monomethyl-ether (DPM); a compound commonly used to test the operation of ion mobility spectrometers. Dipropylene-glycol-monomethyl-ether at a concentration of 113 microg m(-3) in air, with a water level of 75 mg m(-3) in air, was analysed using a switchable, high resolution ion mobility spectrometer, operating in the positive mode at 40 degrees C at ambient pressure. The ion mobility spectrometer was fitted with a pulsed corona discharge ionisation source, doped with ammonia at a concentration of 1.3 mg m(-3) in the reaction region, and interfaced to a mass spectrometer. Synchronisation of the ionisation event to the operation of the shutter grids for the drift region enabled different parts of the product ion population to be injected into the drift tube, and programming the gate delays produced a map of the gate delay verses drift time response surface. Ammonium bound dipropylene-glycol-monomethyl-ether was observed, [(DPM)NH4]+ (m/z 166) as well as the ammonium bound dimer [(DPM)2NH4]+ (m/z 314), the same as those observed with a 63Ni source. Two other species were also observed, but their molecular identity was not elucidated. One of them m/z 146, also observed with 63Ni, formed ammonium bound ions [(m/z 146)NH4]+ (K0= 1.49 cm2 V(-1) s(-1)), ammonium bound dimer ions [(m/z 146)2NH4]+(K0= 1.18 cm2 V(-1) s(-1)) and a mixed cluster ion with DPM [(m/z 146)(DPM)NH4]+(K0= 1.18 cm2 V(-1) s(-1)); while the other, m/z 88 a decomposition product, formed ammonium bound monomer [(m/z 88)NH4]+(K0= 1.68 cm2 V(-1) s(-1)), dimer ions [(m/z 88)2NH4]+(K0= 1.40 cm2 V(-1) s(-1)) and a mixed cluster ion containing DPM and ammonium, [(DPM)(m/z 88)2NH4]+(K0= 1.40 cm2 V(-1) s(-1)). The assignment of responses to these ions required the additional dimensionality in the data provided from the gate delay studies. The relationships evident in the programmable gate delay data enabled these ions to be differentiated from alternative assignments of possible nitrogen clusters, formed at the interface of the mass spectrometer.

Air↗

PubMed2002

Characterisation of the phosgene response of a membrane inlet 63Ni ion mobility spectrometer.

A membrane inlet 63Ni ion mobility spectrometer interfaced to a quadrupole mass spectrometer with permeation, exponential dilution approaches and syringe-based systems were used to characterise the ion mobility spectrometry (IMS) response to phosgene in dry air (water concentration less than 16.5 mg m(-3)). Phosgene produced a principle product ion in the negative mode with a reduced mobility of 2.16 cm2 V(-1) s(-1), with an unresolved artefact at higher concentrations having a reduced mobility of 2.32 cm2 V(-1) s(-1). The limit of detection of the system with a membrane inlet fitted was estimated to be less than 1 mg m(-3), with an upper limit to the dynamic range of 32 mg m(-3). Mass spectrometric data indicated the existence of [(H2O)nCl]-, [(H2O)nCl2]-; [(H2O)n(O2)Cl]-; [(H2O)n(O)Cl]-; and, [(H2O)n(CO2)Cl]-. The existence of two possible mechanisms for product ion formation is proposed: dissociative electron capture, as well as hydrolysis followed by electron capture. The effect of water contamination of the drying media within the ion mobility spectrometer was also investigated, and the effects were similar to those observed previously with studies on chlorine. Reduced mobility of the product ions was observed to decrease with increasing water contamination of the drying media used within the instrument, while limits of detection increased slightly to less than 2.4 mg m(-3), with no significant effect on dynamic ranges of response or resolution. Preliminary results also indicated a positive mode response for phosgene, albeit at significantly higher concentrations to those observed in the negative mode.

Chemical Warfare Agents↗