Michael Cooke

A library of atmospheric pressure ionization daughter ion mass spectra based on wideband excitation in an ion trap mass spectrometer

A searchable library of MS/MS spectra obtained using a quadrupole ion trap mass spectrometer and electrospray or atmospheric pressure chemical ionization is presented. The application of wideband excitation (activation) and normalized collision energy leads to highly reproducible mass spectra which are searched using the NIST algorithm. Flow injection and LC/MS/MS applications of this powerful technique in the biomedical (diastereoisomeric steroids, morphine glucuronides, isovalerylcarnitine) and environmental (pirimicarb and desmethyl-pirimicarb) areas are described.

Use of laser ablation inductively coupled plasma mass spectrometry to provide element versus time profiles in teeth

Inductively coupled plasma mass spectrometry has been used to provide multielement profiles of heavy metals in various matrices. The use of laser ablation as a sample presentation step allows the direct determination of elements in solid samples. It also preserves the temporal axis present in the sample which is destroyed by the dissolution approach. Teeth contain such a temporal axis and are, therefore, ideal for study by this technique. They are of interest because they incorporate heavy metals, to which the organism is exposed, into the mineral phase during its formation. That metals are incorporated into the hydroxyapatite lattice during the time of environmental exposure has been confirmed by several studies. As in a previous study we have measured the trends in metal concentration on either side of the neonatal line i.e. in pre- and post-natal human enamel. Such data has value in providing information about exposure of an individual to metals in utero, i.e. via maternal transfer, and during subsequent lifetime via environmental exposure.

Multi-element profiling of human deciduous teeth by laser ablation-inductively coupled plasma-mass spectrometry

Abstract The profiles of deposition of various metals in teeth have been obtained using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). This non-destructive technique, offers spatially resolved measurements of element distribution which can thus be related to a temporal axis via reference to the neo-natal line. Qualitative data affording comparison of elemental profiles between the teeth on a relative basis have been obtained. Owing to the lack of suitable qualified solid reference materials, quantitation has been attempted using a piece of walrus ivory. Average elemental concentration values were obtained by dissolution of a portion of sample followed by determination using ICP-atomic emission spectrometry giving a one point calibration for some 14 elements. These results were then related to the data counts obtained by LA-ICP-MS establishing a semi-quantitative relationship between the MS response and the elemental concentration in the sample. Measurements in different parts of deciduous teeth encompassing pre-and post-natal enamel, neo-natal dentine and circumpupal dentine reveal differences of deposition during the development period of the tooth. Evidence for the consistent incorporation of elements such as zinc and antimony is presented together with data for the occasional inclusion of chromium, iron and mercury. Trends in elemental deposition are also discussed.

Rapid assay for theophylline in clinical samples by reversed-phase high-performance liquid chromatography.

A fast, sensitive and highly specific method for the determination of theophylline in human serum is reported. Using a C18-bonded reversed-phase column with an acetonitrile-acetate buffer mobile phase theophylline is completely resolved not only from other dietary xanthines and their metabolites but also from co-administered drugs such as paracetamol and phenobarbitone. Use of beta-hydroxyethyltheophylline as internal standard allows a within batch precision of 2.0% and a between batch variation of 3.0%. Factors involved in the development of the method and its performance are discussed.

Evidence for selectivity of absorption of volatile organic compounds by a polydimethylsiloxane solid-phase microextraction fibre

Solid-phase microextraction using a 30 microns polydimethylsiloxane fibre has been used to sample the volatile organic compounds from standard mixtures and from mixtures produced by the decomposition of organic compounds. This method of sampling has been compared with the direct injection of an aliquot of headspace gas and shows an enrichment factor of approximately 100 over a 1 ml gas injection for organosulphur gases such as dimethyldisulphide. The performance of the fibre has been evaluated with respect to accuracy and precision at several concentrations in representing the composition of multicomponent mixtures. It was found that the presence of a second component in a gas sample reduced the capacity of the fibre to absorb the primary component. The selectivity of the fibre for various volatile compounds with differing functionality was also studied. It was found that the non-polar polydimethylsiloxane fibre preferentially absorbed the non-polar components of a mixture, e.g. nonane and, correspondingly, under reported the more polar components, e.g. ethanol. Hence, the fibre discriminates in favour of non-polar and against polar components in a mixture in comparison with direct analysis of a headspace sample. Thus, quantitation of a component in a multi-component mixture is liable to error from competitive interference from other components. A major advantage of the technique, however, is that it does not absorb, and therefore introduce, water into the analytical system.

Analysis of Malodorous Sulfur Gases and Volatile Organometalloid Compounds in Landfill Gas Emissions Using Capillary Gas Chromatography with Programmed Temperature Vaporization Injection and Atomic Emission Detection

Volatile compounds containing Group V and Group VI elements in landfill gases are of concern as a source of toxic pollutants and unpleasant odors. Conventional analytical techniques for these compounds e.g. ICP-MS, ICP-AES are complicated, expensive and time consuming. The use of a simple programmed temperature vaporization injection (PTV) technique coupled to gas chromatography with atomic emission detection (GC-AED) has been successfully demonstrated to identify compounds containing arsenic, antimony, and sulfur in landfill gas. With an adapted PTV injection system (using a combination of a ten-port and a six-port Valco valves), problems associated with AED discharge tube damage due to high carrier gas flow rate during sample loading can be overcome. The gas samples generated from both a laboratory biowaste digester and a domestic landfill site were characterized using these techniques. Large sample gas volumes were adsorbed onto a cooled sorbent trap containing Porapak Q, followed by rapid liberation onto a porous layer open tubular column (PLOT) using programmed thermal desorption. Arsenic and antimony were also detected in the landfill leachate collected from the same landfill site using hydride generation-atomic absorption spectrometry (Hy-AAS). The efficiency of different traps has also been compared.

Programmed Temperature Vaporization Injection (PTV) in the Analysis by Gas Chromatography-Mass Spectrometry (GC-MS) of the Constituents of Landfill Gas

Abstract Trace volatile compounds emitted from both domestic and industrial landfills have been identified by programmed temperature vaporization injection (PTV) coupled to gas chromatography with detection by ion-trap mass spectrometry (GC-ITD/MS). The PTV injection system has been developed using a combination of two six-port valves to achieve problems of interference in GC-MS while loading sample. A large volume of landfill gas was re-concentrated onto a sorbent trap, then rapidly liberated into the GC-ITD/MS system by programmed thermal desorption. Using this method, trace volatile compounds in gases from both domestic and industrial landfills such as aromatic hydrocarbons, terpenes, chlorinated hydrocarbons, and sulfur compounds can be identified and quantified.

Adsorption chromatography capillary columns : I. Rubidium chloride

Abstract A new approach to the preparation of adsorption capillary columns for gas chromatography is described. Soda glass capillary tubing is treated with dilute ammonium hydroxide at elevated temperatures to generate a silica layer. Deactivation of this layer of silica is then achieved by coating with rubidium chloride to yield columns of controlled activity and high thermal stability. Separations of polynuclear aromatic hydrocarbons and of n-alkanes have been achieved on these gas-solid columns. The importance of column length and of rubidium chloride concentration is discussed.

Theophylline estimation-a comparative evaluation of a gas chromatographic method and a high-performance liquid chromatographic method.

A comparative evaluation of a gas-liquid chromatographic (GLC) assay and a high-performance liquid chromatographic (HPLC) assay for the determination of plasma theophylline levels has been carried out. Both methods are reliable, accurate, and technically simple and appear to be specific for theophylline. The HPLC system is more sensitive (sample volume 25 μl) than the GLC system (sample volume 500 μl) and is therefore suitable for the estimation of theophylline in microsamples. The HPLC system also has better precision (coefficient of variation: within-batch 2·0%, between-batch 3·0%) than the GLC system (coefficient of variation: within-batch 3·5%, between-batch 5·6%). Good correlation (r = 0·964) was found between plasma theophylline levels (n = 75, observed range 4–186 μmol/l) determined by each procedure. The results of this study indicate that, of the two systems investigated, HPLC is the method of choice.

Detection of low levels of nicotine in air using a portable ion mobility spectrometer

An ion mobility spectrometer has been used to detect nanogram per litre amounts of nicotine vapour in air.