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Analytical Science - Research Highlights |
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Analytical Science@LoughboroughResearch HighlightsClick here to download this file in pdf format Back to Centre for Analytical Science home page Advanced Systems: Design and Development of Next Generation Measurements
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Preparing complicated materials for analysis is expensive, time consuming and often introduces errors and problems into a measurement. We developed an advanced system that generates a bean of ions that cuts into the surface of a sample and release the ions directly into the chemical separation stage. In this we used an ion mobility spectrometer-linked to a mass spectrometer, in fact we were on of the first team in the world to do this. We were able to analyse in a few seconds what would normally have taken much longer perhaps hours to accomplish. This work showed how combining these new generation ionisation and separation technologies could revolutionise the custom and practice of many chemical measurements. |
Anal. Chem. 2005, 77, 7572-7580
A novel approach to the rapid analysis of pharmaceutical drug formulations using hyphenated ion mobility spectrometry (IMS) and time-of-flight mass spectrometry (ToFMS) that requires no sample pretreatment or chromatographic separation is described. A modified quadrupole time-of-flight mass spectrometer containing an ion mobility drift cell was used for gas-phase electrophoretic separation of ions prior to ToF-MS detection. The generation of sample ions directly from tablets and cream formulations was effected by desorption electrospray ionization (DESI) using a modified electrospray ion source. The analysis of a range of over-the-counter and prescription tablet formulations is described, including histamine H2 receptor antagonist (ranitidine), analgesic (paracetamol), opiate (codeine), and aromatase inhibitor anticancer (anastrozole) drugs. The successful determination of active drugs from soft formulations, such as an antiseptic cream (chlorhexidine) and a nicotine-containing skin patch, is also presented. Limits of detection for the active drugs using the DESI/IMS/ToF-MS method fell within the high-picomole to nanomole range. In all cases, the use of ion mobility drift tube separation showed increased selectivity for active drug responses (present as low as 0.14% w/w) over excipient responses such as poly-(ethylene glycol). Tandem mass spectrometric analysis of precursor ions separated by IMS allowed positive confirmation of active drugs with little loss of ion mobility efficiency. The ability to analyze hard or soft pharmaceutical formulations directly by DESI combined with ion mobility spectrometry/mass spectrometry in < 2 min demonstrates the potential applicability of this novel method to pharmaceutical screening of low-molecularweight drug formulations with high selectivity over the formulation vehicle.
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Here we explored how to couple laser excited ionic fluorescence, operated in coincidence detection mode, to an inductively coupled plasma (ICP) mass spectrometer (MS). Our motivation was to deliver ultimate detection sensitivity for rare isotopes in complex matrices. We have discovered that the spread of ion energies produced by the ICP potentially reduces the optical pumping efficiency of the laser. So now we are striving to understand the origin of the energy broadening phenomenon to invent methods to reduce it. We are excited by this research because we are on the threshold of of delivering a paradigm shift in the performance of the ICP-MS technique, which will transform the research environment for elemental detection. |
J. Anal. At. Spectrom., 2007, 22, 1447-1470.
This paper reports a theoretical study of the feasibility of using laser-excited ionic fluorescence in time correlation with ion counting, termed coincidence laser spectroscopy (CLS), for improved specificity in the detection of ions in ICP-MS. The technique is here named ICP-MS-CLS. A number of factors are considered including: the preferred instrumental configuration, simulation of the performance of the optical detector and correlation step in reducing background, the spectroscopy of the selected of isotopes, 10Be+, 55Fe+, 63Ni+, 90Sr+, 99Tc+, 147Pm+, 238U+, 238Pu+ and 241Am+, which might be appropriate candidates for ICP-MS-CLS detection, the laser power required to attain saturation, the effects of ion energy and energy spread on pumping efficiency, the optical abundance sensitivity for adjacent isotopes of the same element, and the detection limits obtainable under a variety of scenarios. The ICP is established as an ideal ion source for elemental mass spectrometry, but as shown here, the ion energy spread produced is too large for optimum optical pumping because the ions are Doppler shifted to an extent that not all of them would be excited efficiently by a narrow-line laser source. This necessitates the inclusion of an ion cooler into the instrumental configuration so that ions maybe brought into resonance with the laser with 100% efficiency. The calculations show that for ions with simple spectra, such as 90Sr+ which can be repetitively pumped by the laser to produce a photon burst, ICP-MS-CLS can reduce the effect of very high backgrounds, 106 cps on mass and 1010 cps at adjacent mass, to low levels and improve detection limits by 2–3 orders of magnitude compared with the normal technique. Optical abundances of 10_5–10-9 are achievable which, combined with the mass abundance sensitivity of 10-5, yields overall abundance sensitivities of 10-10–10-14. This is of the same order as techniques such as accelerator mass spectrometry (AMS) or resonance ionisation mass spectrometry (RIMS). The technique is much less efficient for ions that undergo optical trapping and emit only one photon when pumped and/or exhibit hyperfine structure which distributes the oscillator strength over several hyperfine components. These factors significantly degrade performance and indicate a requirement for further refinement in terms of using two colour excitation, or quenching of meta-stable levels, to enable the recycling of ions for further pumping.
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Smiths Detection have invented a remarkable alternative to 63Ni as an ion source for ion mobility spectrometers. This study funded by DSTL characterised the ion species produced in this source, developed a new instrument to enable single point ionisation events to be studied by ion mobility-mass spectrometry and provided data confirming that the ion chemistry generated was the same as that produced by 63Ni. Pulsed corona discharge sources are now used in modern instruments and the development and validation of this system paves the way for IMS to be adopted in many more situations where the presence of a radioactive source would be problematic. |
Analyst, 2003, 128, 55–60; DOI: 10.1039/b207558j
A pulsed corona discharge ionisation source, a candidate replacement for 63Ni ionisation sources for ion mobility spectrometry, is described along with a new design of ion mobility spectrometer-mass spectrometer. Preliminary research on the characterisation of the reactant ion peaks associated with the use of this ionisation source was undertaken by assembling a pulsed corona discharge ionisation switchable high-resolution ion mobility spectrometer-mass spectrometer to enable the mobility spectra, atmospheric chemical ionisation mass spectra and selected-mass mobility spectra to be obtained. With ammonia doping at 2.39 mg m-3 in air and a water content of approximately 80 mg m-3 in the positive mode the observed response was attributable to the formation of [(H2O)nNH4]+ and [(H2O)n(NH3)NH4]+ in the reaction region. The observed responses in the negative mode were more complex with evidence for the formation [(H2O)nO2]-, [(H2O)nCO3]-, [(H2O)nHCO3]-, [(H2O)nCO4]- and [(H2O)nNO3]-. The responses due to these species were clearly discernible in the resultant mobility spectra, with enough oxygen-based species formed to support analytically useful responses.
We use collision and/or reaction cells in inductively coupled plasma (ICP) –mass spectrometry (MS) to remove the artefacts and problems that are sometimes produced by chemical reactions between our analyte and the analytical system. The ICP generates ions with a range of energies and this range of energy affects the reactivity of the ions. So this work examined the effects of ion energy on the efficiency of these ion reactions and the amount of reaction product ions that were detected. To this we had define a reactivity indicator ratio to provide a generic measurement of the collision and/or reaction cell performance. This approach has been really helpful for us because now we are able to optimise the sensitivity of our analytical systems for the detection of bio-molecules, and we can do this by using the exquisite sensitivity of ICP-MS towards the presence of phosphorus.
J. Anal. At. Spectrom., 2002, 17, 676-681.
This paper describes experiments aimed at discriminating the different effects of ion energy in collision/reaction cell ICP-MS. It is demonstrated that the input ion energy, as determined by the plasma offset potential and ion energy distribution, is a key determinant of cell reactivity and this is termed the ion kinetic energy effect (IKEE). The ion kinetic energy is varied by alteration of the potential difference between the plasma and the hexapole cell. The plasma offset potential and ion energy distribution are not accurately known but are inferred from ‘‘stopping curves’’ produced by varying the pole bias of the quadrupole analyser. Kinetic energy discrimination (KED), where the difference in bias potentials between the quadrupole mass analyser and the hexapole cell is exploited to reject slow cell-formed ions, is shown to be a different effect. It can be used to change the relative levels of polyatomic ions arriving at the detector. The influence of IKEE and KED on the levels of plasma and analyte oxide (MO+) ions and on the 21(H3O)+/36Ar+ reactivity indicator ratio are considered. It is shown that IKEE can be used to influence the reactive attenuation of argide ions and the production of MO+ in the cell. KED is shown to preferentially reject cell-formed MO+ from the mass analyser.
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These beautiful gas chromatography positive mode differential mobility spectrometry responses were produced at The University of Manchester and show how synchronising the temperature programme of the gas chromatography to dispersion field strength programming opens up the analytical space. This was a new methodology and has enabled a volatile marker for chronic obstructive pulmonary disease to be isolated by GC-DMS. |
Journal of Chromatography A, 1173 (2007) 129-138; DOI: 10.1016/j.chroma.2007.09.082
Enhancing the analytical space of differential mobility spectrometry with dispersion field amplitude programming was proposed. Six volatile organic compound candidate breath markers, 1,3-butanediol, butanone, ethylbenzene, heptan-2-one, nonanal, and o-xylene were used to characterise the effect of programming the amplitude of the dispersion field on the sensitivity, and resolution of the responses observed. Sensitivity followed two patterns of behaviour. Sensitivity to heptan-2-one and 1,3-butanediol increased to a maximum at approximately 20 kV cm-1, attributed to dissociative ionisation effects. The remaining four compounds responses were dominated by wall-loss phenomena resulting in a constant reduction in sensitivity as dispersion field amplitude was increased. The effect of the dispersion field on analytical space was pronounced. At a field strength of 18 kV cm-1 protonated monomers and proton-bound dimers could be observed within the chromatographic responses for the carbonyl compounds. Dissociative ionisation products were also discerned for 1,3-butanediol and butanone. The ion chemistry of the two hydrocarbons was not affected by the dispersion field amplitude. Resolution of the product ions and their separation from the reactant ion peaks increased significantly with increasing dispersion field amplitude. With a range of behaviours observed. Peak resolutions increased from the range 0 to 1.2 to 1.2 to 7, while resolving power increased from 0 (at low dispersion field amplitudes) to the range 0.2 to 6 at 20 to 24 kV cm-1. The effect of programming the dispersion field amplitude on a “real-life” application was demonstrated with replicate breath samples obtained from a subject with chronic obstructive pulmonary disease.
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Laser ablation–ICP-MS is an exciting and interesting technique for the direct analysis of solid samples in forensic, environmental and clinical applications. However, in these cases it is difficult to prepare calibration standards so that scientist can demonstrate the accuracy and reliability of their measurements, and until this can be done the power of this approach will not be unleashed. We studied this problem and then invented an integrated device to constantly deliver a calibration solution to the laser ablated products, and we have discovered that this approach works well for a different types of solid sample. We needed to use a “wet” plasma to do this and another unforeseen benefit was that we also enhanced the stability of the plasma and improved the heat flow to the ablated material. |
J. Anal. At. Spectrom., 2006, 21, 556-565.
This paper describes the theory of on-line additions of aqueous standards for calibration of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Establishment of a calibration curve enabled investigation of: fractionation, matrix effects, mass flow ratios, and the relative merits of wet and dry plasma conditions for laser ablation sampling. It was found that a wet plasma was much more tolerant of increased sample loading without reducing plasma robustness, leading to less severe and more constant mutual matrix effects. These findings indicate that the on-line addition of water is the preferred mode of operation for quantification by LAICP-MS. The analytical performance of the method was validated by the analysis of three certified reference materials: National Institute of Standards and Technology (NIST) 612 Trace Elements in Glass, European Reference Material (ERM) 681 Trace Elements in Polyethylene and British Chemical Standards (BCS) No. 387 Nimonic 901 Alloy. Analysis of NIST 612 was performed under both wet and dry plasma conditions, and the correlation with certified elemental concentrations was much better when a wet plasma was employed. Analyses of ERM 681 and BCS No. 387 were performed under wet plasma conditions, due to that method’s proven advantages. The differences between the found and certified elemental concentrations varied between 1–10% for the majority of elements, for all three certified reference materials.
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Fast quantitative characterisation of differential mobility responses. Would you like to be able to calibrate an instrument across its dynamic range in under 6s? You would? Then this is the paper for you. Exponential concentration dependences have been used for a long time in analytical science. This methodology extends this approach to exploit the exponential relationships inherent in the elution profiles from gas chromatography columns.
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The Analyst, 129 (2004) 198-204; DOI: 10.1039/b310760d
A chromatography-based method for producing mass flux-response surfaces for differential mobility spectrometers is described as a replacement for exponential dilution and mixing approaches. An exponential dilution or mixing experiment typically takes 150 min; while the exponential function in the Gaussian elution profile obtained from linear chromatography may be exploited in approximately 10 s. The approach was demonstrated with a gas chromatograph-mass spectrometer and the correlation of the calibration results to nominal on-column masses was within experimental error for 19 separate analyses. The method was then applied to a gas chromatographic (10.6 eV UV) differential mobility spectrometer. Mass fluxes in the range 10 pg s–1 to 250 ng s–1 were generated over the 5 s to 10 s associated with the elution of a chromatographic peak. The characterisations were repeated for a range of electrical field strengths from 10 kV cm–1 to 30 kV cm–1. Triplicate runs indicated that the approach was reproducible and that response surfaces could be generated rapidly from chromatographic data. The effects of trace impurities associated with the chromatographic eluent on the relationship between compensation voltage and electrical field strength was observed. This emphasised the importance of managing this aspect of the operation if reliable estimates of alpha functions for the compounds under study were to be obtained. Application of this approach to other detection systems with an 85% reduction in the analytical operations required to produce a reliable calibration function was also noted.
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Connecting advanced sensitive and delicate instruments to industrial processs or environmental systems is one of the most challenging and difficult taks in analytical science. Get it wrong and we could end up with a very expensive instrument full of “goop”. We invented a sampler for extracting polar materials, alcohols in this instance, from a non-polar solvent. This type of technology is known as process analysis and is very important for many industrial and environmental monitoring proplems. |
Anal. Chem. 2002, 74, 300-304
Reversed-phase membrane inlet mass spectrometry incorporating a hollow-fiber Nafion membrane has been evaluated for the determination of low molecular weight alcohols in chloroform. The hydrophilic Nafion membrane preferentially transports methanol and ethanol, allowing percentage concentrations of the alcohols to be determined in a chloroform matrix. A linear response was observed for ethanol over the working range 0.5-2.5%, with a limit of detection of 0.1%. The application of reversed-phase membrane inlet mass spectrometry using a Nafion membrane to the monitoring of a chloroform recovery process has been investigated using a residual gas analyzer. Evolving methanol and ethanol concentrations were determined in real time and compared favourably with off-line determinations by gas chromatography.
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ICP-MS is exquisitely sensitive, resilient to chemical interferences and delivers accurate and reliable quantitation of trace elements over a wide concentration range. It uses solar temperatures to annihilate chemical complexes and molecules to reduce the constituent elements to a plasma; which it then analyses isotope by isotope. It does the chemical equivalent of finding the needle in the haystack in the middle of the night when the haystack is covered with mud, snow and ice. It used to be the case that many very biologically important molecules could not be measured with this powerful technique because they did not contain a metal atom. No-longer though, for we describe an elegant technique where we label a bio-molecule with a gold nano-particle. The result? A new, exquisitely sensitive, resilient and versatile technique for bio-molecular assays. |
Chem. Comm., 2007, 43, 4537-4539
Oligonucleotides containing a biotin functionality were successfully labelled with a streptavidin nanogold conjugate and subsequently separated and analysed by high performance liquid chromatography–inductively coupled plasma–mass spectrometry (HPLC-ICP-MS)
Our aim is a reliable method of determining 129I at 10 pg g-1 in milk, in working towards this goal we have come across interesting observations on iodine chemistry and the behaviour of Mo in the collision and/or reaction cell in inductively coupled plasma (ICP) mass spectrometry (MS). We have developed a new column preconcentration technique that enables iodine and molybdenum concentrations in milk to be determined. In aqueous samples the detection levels are even lower still.
Talanta (2007), DOI: 10.1016/j.talanta.2007.10.051
A reliable method for the determination of iodine and molybdenum in milk samples, using alkaline digestion with tetramethylammonium hydroxide and hydrogen peroxide, followed by quadrupole ICP-MS analysis, has been developed and tested using certified reference materials. The use of He + O2 (1.0 ml min-1 + 0.6 ml min-1) in the collision-reaction cell of the mass spectrometer to remove 129Xe+ - initially to enable the determination of low levels of 129I - also resulted in the quantitative conversion of Mo+ to MoO2+ which enabled the molybdenum in the milk to be determined at similar mass to the iodine with the use of Sb as a common internal standard. In order to separate and pre-concentrate iodine at sub µg l-1 concentrations, a novel method was developed using a cation-exchange column loaded with Pd2+ and Ca2+ ions to selectively retain iodide followed by elution with a small volume of ammonium thiosulfate. This method showed excellent results for aqueous iodide solutions, although the complex milk digest matrix made the method unsuitable for such samples. An investigation of the iodine species formed during oxidation and extraction of milk sample digests was carried out with a view to controlling the iodine chemistry during preparation of these samples for analysis.
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Science and technology is a global endeavour. Data and measurements are continuously transferred between laboratories and researchers in all parts of the world. It is absolutely vital then that the results obtained in one institute can be properly reproduced by fellow scientists, wherever they may be. We set up two international panels to enable us to identify possible problems in the transfer of scientific information in the area of chemical separations. We worked with 23 other labotatories and found that a major source of difficulty in sharing chemical separation information was the differences in the temperature control of the systems that different laboratories use. This knowledge is going to be invaluable in the future development of interlaboaratory and international collaborations involving data and analytical method transfers. |
Chromatographia Supplement Vol. 57, 2003
The reproducible transferability of HPLC methods between laboratories requires careful specification of the method, especially the temperature control of the column. The methods were examined in two international collaborative studies for a series of column characterisation tests for ODS-bonded phase columns. The results from 16 laboratories in the first study and 7 laboratories in the second study are analysed. Differences in the type of column oven can cause significant differences in the effective column temperature and hence in the relative retention times used to calculate hydrophobicity and shape selectivity. Water bath or water jackets gave markedly different results to air ovens at the same nominal temperature and were recommended as providing more transferable results. However, although the incoming eluent was controlled to be at the column temperature the efficiency of the separations were lower than in an air bath oven but were more repeatable.
Rapid Communications in Mass Spectrometry, 2002, 16, 176-184; DOI: 10.1002/rcm.563
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When we studied the reproducibility of data transferred between laboratories we discovered that different instruments control the temperature of the column used to separate chemicals in complicated mixtures in different ways. The result of these different approaches was that the true, that is the effective temperature at the heart of the chromatography columns varied, and was not accurately measured by the different instruments involved. We decided to develop a new approach to measuring temperature that used the properties of molecules rather than an external measurement. We were successful and now it is possible for scientists across the world to standardise their temperatures and separations. An additional discovery in this research was trhe dioscovery that running the mobile phase at a lower temperature to the column caused the quality of the chemical separations to increase. |
Monitoring effective column temperature by using shape selectivity and hydrophobicity and the effects of mobile phase temperature
Relative changes in the hydrophobicity and shape selectivity of standard analytes are shown to be a valuable method to monitor the reproducibility of the effective temperature experienced by the analytes in a chromatographic column in different ovens. Significant differences were observed between ovens with the same nominal temperature and could be a major cause of problems encountered in transferring methods between instruments or laboratories. By using two parameters, changes due to the column temperature can be distinguished from those caused by mobile phase composition differences. In addition marked increases in column efficiency were noted as the mobile phase temperature was reduced below the column temperature in contrast to claims that thermal equilibration is essential.
Uncontrolled levels of water in the gases used in in inductively coupled plasma (ICP) mass spectrometry (MS) results in variable performance of the instrument. We investigated the effects of water on the collision and/or reaction cell chemistry in ICP-MS. We found that for reactive mixtures of gases such as He–H2 mixture there was no real effect. However when an unreactive gas, He for example is used alone water contamination significantly alters the chemistry in the collision and/or reaction. So we developed protocols for controlling the levels of water in such experiments with stainless steel tubing and equilibration volumes, and through this control exploit the reactivity of water.
J. Anal. At. Spectrom., 2002, 17, 183-188; DOI: 10.1039/b110281h
This paper considers several aspects of the role of water in collision cell inductively coupled plasma mass spectrometry. Studies with water and deuterium oxide, employed both as samples and as impurities in the cell gas, were used to investigate the origins of the polyatomic ions. It was found that no new species were formed in the cell as water from the plasma provides the basic reactive components; however, some were greatly enhanced when the cell gas was deliberately wetted. The reactivity of the water/deuterium oxide dominated the cell chemistry when an unreactive gas such as He was used, indicating a need for careful control of water content, but the effects were greatly reduced when a reactive gas such as hydrogen was also employed. It is concluded that water could be a useful reagent molecule, if its partial pressure can be adequately controlled. Seeking complete removal of water from the reagent gas is unnecessary as there is a baseline contribution from the plasma and, in any case, when reactive reagent gases are used its effect is minimal.
Correlation patterns observed between species produced in the hexapole collision and /or reaction cell of a quadrupole ICP-MS under varying gas conditions enabled the identification of key ion ratios - in particular 21H3O+/36Ar+ - which could be used as a sensitive monitor to optimise cell conditions for multi-element analysis. The figure shows correlation plots of these two species measured over a wide range of gas flows, showing their contrasting profiles.
J. Anal. At. Spectrom., 2001, 16, 1076-1084; DOI:10.1039/b103025f
Holistic analysis of ICP-MS spectra modified by the use of H2, He and mixtures thereof in a hexapole collision cell has enabled the identification of the major chemistries affecting cell performance. Correlation analysis has shown that groups of ions exist that have similar behaviours across a wide range of gas conditions. Examination of these groups indicates that the dominant reactions are related to species derived from argon and water, in particular 17OH+, 19H3O+, 21H3O+, 36Ar+, 38Ar+ and 80Ar2+. The ion signals at these m/z values reflect the concentrations of such species and are ratioed to produce indicators that are highly discriminant of the cell conditions. The objective variable used for optimisation was the S/N, calculated from an equation incorporating terms for the Poisson and flicker noise for both the signal and the background intensities. Detection limits for isotopes such as 28Si, 56Fe and 80Se are greatly improved at the expense of a general increase in oxide levels and some loss of sensitivity due to ion scattering for isotopes up to approximately m/z 70. It is further demonstrated that, in this largely charge-conservative system, the terminal fate of the charge occurs in parts of the spectrum that are not detrimental to elemental analysis.
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Not everyone, (the frail, the very young the sleeping or unconscious subject for example) is able to provide a forced exhalation breath sample. Further, very few are able to provide reproducible and traceable breath samples free from environmental contamination; in other words a “scientific” sample. We designed built and tested a breath sampling system that addressed these problems. Using tyhis technology we were able to characteris, for the first time, how individuals’ breathing profiles change. We are pleased and proud that this methodology is now being applied in clinical based studies in chronic obstructive pulmonary disease, lung cancer and in the future with community acquired infections. |
The Analyst, 132 (2007) 153-163; DOI: 10.1039/b608608j
An adaptive sampler for collecting 2.5 dm3 samples of exhaled air from human subjects with an impaired respiratory function is described. Pressure in the upper respiratory tract is continuously monitored and the data used to control an automated system to collect select portions of the expired breathing cycle onto a mixed bed Tenax
and Carbotrap
adsorbent trap for analysis by GC-MS. The sampling approach is intended for use in metabolomic profiling of volatiles in human breath at concentrations greater than µg m–3. The importance of experimental reproducibility in metabolomic data is emphasised and consequently a high purity air supply is used to maintain a stable exogenous volatile organic compound profile at concentrations in the range 5 to 30 µg m–3. The results of a 90 day stability study showed that exogenous VOCs were maintained at significantly lower levels (40 times lower for isopropyl alcohol) and with significantly higher reproducibility (80 times lower standard deviation for isopropyl alcohol) than would have been be the case if ambient air had been used. The sampling system was evaluated with healthy controls alongside subjects with chronic obstructive pulmonary disease. Subjects were able to breathe normally with control subjects observed to breathe at a rate of 9 to 17 breaths per minute, compared to 16 to 30 breaths per minute for subjects with COPD. This study presents, for the first time, observations and estimates of intra-subject breath sample reproducibility from human subjects. These reproducibility studies indicated that VOCs in exhaled breath exhibit a variety of dynamic behaviours, with some species recovered with a RSD <30%, while other species were observed to have significantly more variable concentrations, 30 to 130% RSD. The approach was also demonstrated to reliably differentiate the differences in the VOC profiles between alveolar and dead space air.
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Silicone is a polymer used a lot in medical devices and Nottingham University have invented a new form of silicone that has anti-microbial properties. They are able to impregnate the silicone with silver nano-particles using supercritical carbon dioxide. We tested the performance of this material by monitoring the release of silver ions when the new anti-microbial silicone was immersed in water. Our tests lasted up to 5 days and were conducted with inductively coupled plasma (ICP) – mass spectrometry (MS). The ICP-MS analysis showed that very little Ag ion was released into the water. However when a similar test was run with blood-plasma the levels of silver release were significantly higher. On closer examination of the plasma we discovered that a precipitate had developed, which when we analysed it was found to contain very high concentrations of silver. This appears to be due to proteins in the plasma reacting with the silver and extracting them from the silicone. |
Journal of Antimicrobial Chemotherapy, 2004, 54(6), 1019-1024; DOI: 10.1093/jac/dkh478
Objectives: Implantable devices are major risk factors for hospital-acquired infection. Biomaterials coated with silver oxide or silver alloy have all been used in attempts to reduce infection, in most cases with controversial or disappointing clinical results. We have developed a completely new approach using supercritical carbon dioxide to impregnate silicone with nanoparticulate silver metal. This study aimed to evaluate the impregnated polymer for antimicrobial activity.
Methods: After impregnation the nature of the impregnation was determined by transmission electron microscopy. Two series of polymer discs were then tested, one washed in deionized water and the other unwashed. In each series, half of the discs were coated with a plasma protein conditioning film. The serial plate transfer test was used as a screen for persisting activity. Bacterial adherence to the polymers and the rate of kill, and effect on planktonic bacteria were measured by chemiluminescence and viable counts. Release rates of silver ions from the polymers in the presence and absence of plasma was measured using inductively coupled plasma mass spectrometry (ICP-MS).
Results: Tests for antimicrobial activity under various conditions showed mixed results, explained by the modes and rates of release of silver ions. While washing removed much of the initial activity there was continued release of silver ions. Unexpectedly, this was not blocked by conditioning film.
Conclusions: The methodology allows for the first time silver impregnation (as opposed to coating) of medical polymers and promises to lead to an antimicrobial biomaterial whose activity is not restricted by increasing antibiotic resistance.
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We are excited at the prospect of developing new separation science based around water and in so doing reduce or eliminate the need for expensive, toxic, flammable and environmentally harmful organic solvents in chemical separations. As well as the practical advantages associated with just using water in our experiments there are also analytical benefits. In this research our superheated water chromatography was interfaced to several detectors including mass spectrometry and nuclear magnetic resonance spectrometry. You can not do this when using organic solvents as the signals they generate swamp the analytical information from the analytes. A range of water soluble vitamins were used to test this concept successfully. |
Journal of Pharmaceutical and Biomedical Analysis 36 (2004) 477–482; doi: 10.1016/j.jpba.2004.07.023
The water-soluble vitamins, pyridoxine, riboflavin, and thiamine, were separated by reversed-phase liquid chromatography using hot or superheated water as the mobile phase and were detected using a range of detectors, including ultraviolet and fluorescence spectroscopy and mass spectrometry. By using deuterium oxide as the eluent, direct on-line nuclear magnetic resonance spectra could be obtained with minimal spectral interference from the mobile phase. Some of the compounds showed deuterium exchange of alkyl-protons when separated at high temperatures.
Not all chemistry takes place in reaction flasks and vessels. Often in analytical science we need to devise new chemistries that occur between our analytes and chemicals at very low concentratiosn inside instrument. Doing this enables us to model how molecules interact under highly controlled and monitored conditions and provides us with useful information about their size and shape. It also often enables us to fine tune the performance of the separation and detection processes we are using . Here we developed gas phase chemical reactions that enable us to study how the building blocks of life, amino acids and peptides interact and bind with other species. All of this takes place in the gas phase in time scales of a few milliseconds.
International Journal of Mass Spectrometry 229, 2003, 209-216; doi:10.1016/S1387-3806(03)00339-7
The non-covalent complexes formed between cyclic (e.g., 12-crown-4 (12C4), 15-crown-5 (15C5), and 18-crown-6 (18C6)) and acyclic (e.g., triglyme and tetraglyme) polyethers with amino acids (histidine and arginine) and peptides (MRFA, MFAR, gp70 and bradykinin) have been analysed by atmospheric pressure nano-electrospray ionisation (nano-ESI) ion mobility spectrometry and ion trap mass spectrometry. The reduced mobilities for these complexes are reported and correlate well with the mass and size of the polyether. The ability of IMS to distinguish between cyclic and acyclic polyethers and their complexes with biomolecules, based on differences in their reduced mobilities, is demonstrated. These differences are attributed to variations in the collision cross-section arising from subtle changes in conformation in these ligand–receptor complexes.
Much of the research into how heavy metals and radioactive isoptopes behave in the environment assume that the pollutants are in chemical equilibrium with the environment. In other words the research concentrates on the thermodynamic factors of the system. We have assessed this assumption and shown that it isn’t necessarily valid in that chemical equilibrium is not the whole picture and that the rate of chemical reactions, that is reaction kinetics, is also a factor. Our research therefore highlights paper that the kinetics of interactions between heavy metal pollutants and their environment is very important in determining how such pollutants move in groundwater systems.
Journal of Environmental Monitoring 2007, 9, 329–347 DOI: 10.1039/b701891f
Metal ions form strong complexes with humic substances. When the metal ion is first complexed by humic material, it is bound in an ‘exchangeable’ mode. The metal ion in this fraction is strongly bound, however, if the metal–humic complex encounters a stronger binding site on a surface, then the metal ion may dissociate from the humic substance and be immobilised.
However, over time, exchangeably-bound metal may transfer to a ‘non-exchangeable’ mode. Transfer into this mode and dissociation from it are slow, regardless of the strength of the competing sink, and so immobilisation may be hindered. A series of coupled chemical transport calculations has been performed to investigate the likely effects of non-exchangeable binding upon the transport of metal ions in the environment. The calculations show that metal in the nonexchangeable mode will have a significantly higher mobility than that in the exchangeable mode.
The critical factor is the ratio of the non-exchangeable first-order dissociation rate constant and the residence time in the groundwater column, metal ion mobility increasing with decreasing rate constant. A second series of calculations has investigated the effect of the sorption to surfaces of humic/metal complexes on the transport of the non-exchangeably bound metal. It was found that such sorption may reduce mobility, depending upon the humic fraction to which the metal ion is bound. For the more weakly sorbing humic fractions, under ambient conditions (humic concentration etc.) the non-exchangeable fraction may still transport significantly. However, for the more strongly sorbed fractions, the non-exchangeable fraction has little effect upon mobility. In addition to direct retardation, sorption also increases the residence time of the nonexchangeable fraction, giving more time for dissociation and immobilisation. The nonexchangeable dissociation reaction, and the sorption reaction have been classified in terms of two Damkohler numbers, which can be used to determine the importance of chemical kinetics during transport calculations. These numbers have been used to develop a set of rules that determine when full chemical kinetic calculations are required for a reliable prediction, and when equilibrium may be assumed, or when the reactions are sufficiently slow that they may be ignored completely.
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Triazine herbicides are used widely throughout the world. They are persistent and build up in soils and groundwaters. During spring and summer levels of these chemicals is streams and rivers also increase as they are washed from cropland. The recovery and analysis of these compounds from soils and sediments is therefore of interest. In this research we extended our work with super-heated to water to include the extraction of analytes, triazines from compost. A single step extraction and analysis all based on super-heated water was accomplished. |
Journal of Chromatography A, 1084 (2005) 194–200
An on-line method, with a purely aqueous mobile phase, has employed linked super-heatedwater extraction and super-heated water separation for the analysis of triazine herbicides in spiked compost samples. After the superheated water extraction, a X-Terra solid-phase trap was used to collect and focus the extracted analytes. The trapped analytes were then released by thermal desorption and passed directly to a superheated water chromatographic separation using a PGC column. Two clean-up steps (prior to extraction and separation) were included to remove most of the interfering matrix components. The effects of the sample matrix and the extraction temperatures on the recovery of the triazines were investigated. Despite some thermal degradation of the chloro-triazines during the SWE, the on-line SWE–SWC method was sensitive and rapid. The coupled method could potentially reduce costs and labour and by using only water in every stage is compatible with the concepts of green chemistry.
Intermediate level nuclear waste (ILW) generated in the UK is often mixed with other laboratory waste materials, so much so that there is a lot of cellulose. The chemical conditions under which ILW are to be stored in the UK are anaerobic with a high pH. So how will the cellulose degrade under these condions and what will be the effect on the radionuclides contained within the decomposing cellulose matrix? Well, cellulose degrades to form α-isosaccharinic acid a reactive molecule that will form complexes with radionuclides. Therefore, we studied the chemistry between ISA and three important radionuclides, Cd2+, Co2+ and UO22+. to measure the changes in solubility, and hence mobility, that might occur during ILW storage.
Radiochimica Acta, 94(6-7), 2006, pp 363-369
The presence of organic complexants, such as α-isosaccharinic acid (ISA) in an intermediate-level radioactive-waste (ILW) repository may have a detrimental effect on the sorption of radionuclides by forming organic complexes in solution. To assess this, stability constants are required for the complexes formed. Constants have been determined for the divalent metal ions, Cd2+, Co2+ and UO22+ with α-isosaccharinic acid (ISA) in near-neutral and alkaline conditions. The effect of these complexes on radionuclide solubility in the near-field and alkaline-disturbed zone is shown. The constants were measured by the ion-exchange (Schubert) method [1] with the exception of U(VI) at pH 13.3, for which the solubility product method [2] was used. At pH 7 each complex was of the form M1ISA1, with log β values suggestive of salt formation. At high pH, log β values were between 13 and 20. The number of hydroxide ions involved in the complexation reactions was determined using Bjerrum plots, conductometric titrations and spectrophotometric methods [1]. The constants have enabled speciation calculations to be performed showing the effect of ISA on the metal’s solubility. Solubility is predicted to increase in the presence of ISA from pH 9 to 13.5, suggesting that it may have an impact on radionuclide behaviour. The largest solubility increases are for Cd and Co, the smallest for U(VI)
The proposed Intermediate level nuclear waste (ILW) repository in the UK will be anaerobic in nature Under these conditions uranium will be in its +4 oxidation state (U(IV)), and this species is difficult to obtain and perform experiments on. We were the first to publish data on the effect of complexing ligands on U(IV).
Radiochimica Acta, 92, 2004, 897-902
Conditional and pH independent stability constants have been determined for U(IV) α-isosaccharinic acid (ISA) and gluconic acid (Gl) complexes, under anaerobic and carbonate-free conditions, from pH 3 to 14. The constants are needed for nuclear waste repository performance assessment purposes. The constants were obtained by developing an approach based on the solubility product of amorphous UO2.2H2O. The derived pH independent log β values for U(OH)4ISA and U(OH)4Gl were 49 ± 2 and 50 ± 1 respectively.
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Tetraphenylphosphonium bromide (TPPB) is used to stabilise radionuclides though a chemical process known as sequestering. But before nuclear waste is buried in an underground repository it is vital to make sure that we know how chemicals which have been used to condition the radioactive waste are likely to react. We examined the role of TPPB, used as a sequestrating agent for technetium. |
Chemosphere, 66(4), 2007, 672-676
Recently, tetraphenylphosphonium bromide (TPPB) has been used to remove technetium from some radioactive waste streams. However, before TPPB could be approved for use it was necessary to show that TPPB and its degradation products would not have a significant detrimental effect on post-closure performance of a radioactive waste repository. TPPB is known to be stable at neutral pH, however, under alkaline conditions it degrades by an alkaline hydrolysis mechanism to triphenylphosphonium oxide (TPPO). Degradation can also occur by radiolysis to produce triphenylphosphine (TPP). The kinetics of the alkaline hydrolysis degradation of TPPB is described and the solubility of europium, iodine, nickel, technetium(VII) and uranium(VI) in aqueous solutions of TPPB and its degradation products is reported. These results were used to support the use of TPPB in removing technetium from some waste streams.
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