Direct analysis of volatile organic compounds in foods by headspace extraction atmospheric pressure chemical ionisation mass spectrometry.

RATIONALE: The rapid screening of volatile organic compounds (VOCs) by direct analysis has potential applications in the areas of food and flavour science. Currently, the technique of choice for VOC analysis is gas chromatography/mass spectrometry (GC/MS). However, the long chromatographic run times and elaborate sample preparation associated with this technique have led a movement towards direct analysis techniques, such as selected ion flow tube mass spectrometry (SIFT-MS), proton transfer reaction mass spectrometry (PTR-MS) and electronic noses. The work presented here describes the design and construction of a Venturi jet-pump-based modification for a compact mass spectrometer which enables the direct introduction of volatiles for qualitative and quantitative analysis. METHODS: Volatile organic compounds were extracted from the headspace of heated vials into the atmospheric pressure chemical ionization source of a quadrupole mass spectrometer using a Venturi pump. Samples were analysed directly with no prior sample preparation. Principal component analysis (PCA) was used to differentiate between different classes of samples. RESULTS: The interface is shown to be able to routinely detect problem analytes such as fatty acids and biogenic amines without the requirement of a derivatisation step, and is shown to be able to discriminate between four different varieties of cheese with good intra and inter-day reproducibility using an unsupervised PCA model. Quantitative analysis is demonstrated using indole standards with limits of detection and quantification of 0.395 µg/mL and 1.316 µg/mL, respectively. CONCLUSIONS: The described methodology can routinely detect highly reactive analytes such as volatile fatty acids and diamines without the need for a derivatisation step or lengthy chromatographic separations. The capability of the system was demonstrated by discriminating between different varieties of cheese and monitoring the spoilage of meats.

Metabolism of norethisterone in the greyhound.

RATIONALE: Norethisterone has been used as a successful oral contraceptive in humans for many years. It was recently permitted for use as an oestrus suppressant in racing greyhounds. To monitor the use of norethisterone as part of a routine drug surveillance programme, knowledge of its metabolism was required to enable detection. METHODS: Gas chromatography/mass spectrometry and selective derivatisation techniques have been used to identify urinary metabolites of norethisterone following oral administration to the greyhound. Metabolites were extracted using solid-phase and liquid-liquid extraction techniques. RESULTS: Several metabolites were identified, including reduced, mono-, di- and trihydroxylated steroids. The major metabolites observed were 17α-ethynyl-5ß-estrane-3α,17ß-diol, 17α-ethynyl-5α-estrane-3ß,17ß-diol, three 17α-ethynylestranetriol stereoisomers and two 17α-ethynylestranetetrol stereoisomers. The major metabolites were predominantly excreted as glucuronic acid conjugates and detection of the administration of norethisterone was possible for up to 8 days post-dose using the methods described. The nandrolone metabolites, 19-norepiandrosterone, estranediol and 19-noretiocholanolone, were also identified in the post-administration samples collected up to 8 h after dosing the treated animals. CONCLUSIONS: The urinary metabolites identified in this study have further increased the knowledge of steroid metabolism in the greyhound, providing information to support routine drug testing programmes for greyhound racing.

The trapped human experiment.

This experiment observed the evolution of metabolite plumes from a human trapped in a simulation of a collapsed building. Ten participants took it in turns over five days to lie in a simulation of a collapsed building and eight of them completed the 6 h protocol while their breath, sweat and skin metabolites were passed through a simulation of a collapsed glass-clad reinforced-concrete building. Safety, welfare and environmental parameters were monitored continuously, and active adsorbent sampling for thermal desorption GC-MS, on-line and embedded CO, CO(2) and O(2) monitoring, aspirating ion mobility spectrometry with integrated semiconductor gas sensors, direct injection GC-ion mobility spectrometry, active sampling thermal desorption GC-differential mobility spectrometry and a prototype remote early detection system for survivor location were used to monitor the evolution of the metabolite plumes that were generated. Oxygen levels within the void simulator were allowed to fall no lower than 19.1% (v). Concurrent levels of carbon dioxide built up to an average level of 1.6% (v) in the breathing zone of the participants. Temperature, humidity, carbon dioxide levels and the physiological measurements were consistent with a reproducible methodology that enabled the metabolite plumes to be sampled and characterized from the different parts of the experiment. Welfare and safety data were satisfactory with pulse rates, blood pressures and oxygenation, all within levels consistent with healthy adults. Up to 12 in-test welfare assessments per participant and a six-week follow-up Stanford Acute Stress Response Questionnaire indicated that the researchers and participants did not experience any adverse effects from their involvement in the study. Preliminary observations confirmed that CO(2), NH(3) and acetone were effective markers for trapped humans, although interactions with water absorbed in building debris needed further study. An unexpected observation from the NH(3) channel was the suppression of NH(3) during those periods when the participants slept, and this will be the subject of further study, as will be the detailed analysis of the casualty detection data obtained from the seven instruments used.

Miniaturized ultra high field asymmetric waveform ion mobility spectrometry combined with mass spectrometry for peptide analysis.

Miniaturized ultra high field asymmetric waveform ion mobility spectrometry (ultra-FAIMS) combined with mass spectrometry (MS) has been applied to the analysis of standard and tryptic peptides, derived from α-1-acid glycoprotein, using electrospray and nanoelectrospray ion sources. Singly and multiply charged peptide ions were separated in the gas phase using ultra-FAIMS and detected by ion trap and time-of-flight MS. The small compensation voltage (CV) window for the transmission of singly charged ions demonstrates the ability of ultra-FAIMS-MS to generate pseudo-peptide mass fingerprints that may be used to simplify spectra and identify proteins by database searching. Multiply charged ions required a higher CV for transmission, and ions with different amino acid sequences may be separated on the basis of their differential ion mobility. A partial separation of conformers was also observed for the doubly charged ion of bradykinin. Selection on the basis of charge state and differential mobility prior to tandem mass spectrometry facilitates peptide and protein identification by allowing precursor ions to be identified with greater selectivity, thus reducing spectral complexity and enhancing MS detection.

Detection of volatile organic compounds in breath using thermal desorption electrospray ionization-ion mobility-mass spectrometry.

A thermal desorption unit has been interfaced to an electrospray ionization-ion mobility-time-of-flight mass spectrometer. The interface was evaluated using a mixture of six model volatile organic compounds which showed detection limits of <1 ng sample loaded onto a thermal desorption tube packed with Tenax, equivalent to sampled concentrations of 4 microg L(-1). Thermal desorption profiles were observed for all of the compounds, and ion mobility-mass spectrometry separations were used to resolve the probe compound responses from each other. The combination of temperature programmed thermal desorption and ion mobility improved the response of selected species against background ions. Analysis of breath samples resulted in the identification of breath metabolites, based on ion mobility and accurate mass measurement using siloxane peaks identified during the analysis as internal lockmasses.

High-throughput ultra-high-performance liquid chromatography/tandem mass spectrometry quantitation of insulin-like growth factor-I and leucine-rich alpha-2-glycoprotein in serum as biomarkers of recombinant human growth hormone administration.

Insulin-like growth factor-I (IGF-I) is a known biomarker of recombinant human growth hormone (rhGH) abuse, and is also used clinically to confirm acromegaly. The protein leucine-rich alpha-2-glycoprotein (LRG) was recently identified as a putative biomarker of rhGH administration. The combination of an ACN depletion method and a 5-min ultra-high-performance liquid chromatography/tandem mass spectrometry (uHPLC/MS/MS)-based selected reaction monitoring (SRM) assay detected both IGF-I and LRG at endogenous concentrations. Four eight-point standard addition curves of IGF-I (16-2000 ng/mL) demonstrated good linearity (r(2) = 0.9991 and coefficients of variance (CVs) <13%). Serum samples from two rhGH administrations were extracted and their uHPLC/MS/MS-derived IGF-I concentrations correlated well against immunochemistry-derived values. Combining IGF-I and LRG data improved the separation of treated and placebo states compared with IGF-I alone, further strengthening the hypothesis that LRG is a biomarker of rhGH administration. Artificial neural networks (ANNs) analysis of the LRG and IGF-I data demonstrated an improved model over that developed using IGF-I alone, with a predictive accuracy of 97%, specificity of 96% and sensitivity of 100%. Receiver operator characteristic (ROC) analysis gave an AUC value of 0.98. This study demonstrates the first large scale and high throughput uHPLC/MS/MS-based quantitation of a medium abundance protein (IGF-I) in human serum. Furthermore, the data we have presented for the quantitative analysis of IGF-I suggest that, in this case, monitoring a single SRM transition to a trypsin peptide surrogate is a valid approach to protein quantitation by LC/MS/MS.

Serum biomarker profiling in cancer studies: a question of standardisation?

Companion animals are exposed to similar environmental conditions and carcinogens as humans. In some animal cancers, there also appears to be the same genetic changes associated as in humans. However, little work has been carried out in cancer biomarker identification in animals. The recent dramatic advances in molecular medicine, genomics, proteomics and translational research will allow biomarker identification, which may provide the best strategies for veterinarians and clinicians to combat disease by early diagnosis and administration of effective treatments. Proteomics may have important applications in cancer diagnosis, prognosis and predictive clinical outcome that could directly change clinical practice by affecting critical elemen-ts of care and management. This review summarizes the advances in proteomics that has propelled us to this exciting age of clinical proteomics, and highlights the future work that is required for this to become a reality. In this review, we will discuss the available proteomic technologies and their limitations, and highlight the key areas of research and how they have been used to discover cancer biomarkers. The principles described here are equally applicable to human and animal disease, but implementation of 'omic' technologies requires stringent guidelines for collection of clinical material, the application of analytical techniques and interpretation of the data.

Electrospray mass spectrometry for the identification of MHC class I-associated peptides expressed on cancer cells.

Electrospray ionisation (ESI) mass spectrometry (MS) has been used extensively for the detection of peptides presented by major histocompatibility complex (MHC) molecules. This review focuses on the optimisation of electrospray mass spectrometry and the use of tandem mass spectrometry to sequence MHC class I peptides. We review the isolation of MHC class I peptides from the surface of cells with particular reference to tumour cells. In addition, we also discuss the advantages and disadvantages of the methods available to concentrate and fractionate the peptides prior to analysis by electrospray mass spectrometry.

Direct evidence that leukemic cells present HLA-associated immunogenic peptides derived from the BCR-ABL b3a2 fusion protein.

The BCR-ABL oncogene is central in the pathogenesis of chronic myeloid leukemia (CML). Here, tandem nanospray mass spectrometry was used to demonstrate cell surface HLA-associated expression of the BCR-ABL peptide KQSSKALQR on class I-negative CML cells transfected with HLA-A*0301, and on primary CML cells from HLA-A3-positive patients. These patients mounted a cytotoxic T-lymphocyte response to KQSSKALQR that also killed autologous CML cells, and tetramer staining demonstrated the presence of circulating KQSSKALQR-specific T cells. The findings are the first demonstration that CML cells express HLA-associated leukemia-specific immunogenic peptides and provide a sound basis for immunization studies against BCR-ABL.

FTIR sensing of inhomogeneous systems using immobilized organometalcarbonyl probe groups.

Tricarbonyl(eta 5-cyclohexadienyl)iron(0) and dicarbonyl(triphenylphosphine)(eta 5-cyclo-hexadienyl)iron(0) were derivatized by attachment of an aminopropylsilyl link and covalently attached to fumed silica particles. The fumed silica was coated onto the ZnSe element of an attenuated total reflection (ATR) cell for Fourier transform infrared (FTIR) spectroscopic analysis. The immobilized organometalcarbonyl probe groups are shown to retain their capacity to function as a key element of a molecular sensor assembly and the nu(CO) bands of the two probe groups were interrogated to calibrate the responses for 0-5% levels of dodecane in cyclohexanol to within +/- 0.1%. The potential for dual sensing is described and the simultaneous monitoring of two discrete regions of a dynamically varying inhomogeneous system is reported for the determination of dodecane in cyclohexanol as solutions mix across a permeable barrier in the ATR cell.

In-membrane preconcentration/membrane inlet mass spectrometry of volatile and semivolatile organic compounds.

The on-line determination of volatile and semivolatile organic compounds (SVOCs) is reported using membrane inlet mass spectrometry with in-membrane preconcentration (IMP-MIMS). Semivolatile organic compounds in aqueous samples are preconcentrated in a flow-through silicone hollow-fiber membrane inlet held in a GC oven. The sample stream is replaced with air, and the SVOCs are thermally desorbed into the mass spectrometer by rapid heating of the membrane. The method is evaluated for the on-line determination of 4-fluorobenzoic acid, 3,5-difluorobenzoic acid, 2-chlorophenol, p-tert-butylphenol, and dimethyl sulfoxide (DMSO) in water. The selectivity of the IMP-MIMS technique for SVOCs in the presence of VOCs is demonstrated. Cryotrapping and a rapid gas chromatographic separation step were added between the membrane and the mass spectrometer ion source for the determination of SVOCs in complex mixtures. The procedure is demonstrated for the determination of dimethyl sulfoxide (DMSO) in equine urine, using internal standardization with DMSO-d6. Full-scan electron ionization (EI) mass spectrometric detection showed good linearity (R = 0.998) and RSDs, relative to the internal standard, of 2.2% for desorption only and 4.6% for desorption and cryotrapping.

Nano-electrospray and microbore liquid chromatography-ion trap mass spectrometry studies of copper complexation with MHC restricted peptides.

The formation of copper/peptide complex ions by nano-electrospray and microbore HPLC-electrospray mass spectrometry has been investigated for major histocompatibility complex (MHC) class I and class II restricted peptides. Post-column addition of copper(II) acetate following microbore HPLC-MS separation was carried out using a mixing T-piece or via the sheath flow inlet of the electrospray source. Optimal analytical conditions for copper complex ion formation were determined by variation of copper concentration, pH, nebulization gas supply and spray voltage. Tandem mass spectrometry of copper/peptide complex ions provides peptide sequence information and insight into the peptide chelation sites. Copper associated y fragment ions dominate the product ion spectrum for non-histidine containing peptides, but both b and y copper complex ions were observed for the histidine containing MHC class I associated peptide gp70.

PCB and PCDD/DF concentrations in egg and poultry meat samples from known urban and rural locations in Wales and England.

A survey was undertaken of PCB and PCDD/DF congeners in eggs and poultry meat from a smallholding close to a chemical waste incinerator, other sites in the surrounding district, and three rural locations. The concentrations from the site close to the incinerator were appreciably greater than those found elsewhere, although the contrast was less marked for poultry meat than eggs. All types of poultry produce displayed noticeable variations in congener composition when the samples were grouped according to geographical origin. These results support the view that the environment in which poultry live does influence the PCB and PCDD/DF characteristics of their products. Exposure calculations indicated that consumption of eggs from the site close to the incinerator would constitute a substantial proportion of recommended daily intakes for such contaminants and at the present time these products are not being eaten.

Immunoaffinity chromatography combined on-line with high-performance liquid chromatography-mass spectrometry for the determination of corticosteroids.

On-line coupled immunoaffinity chromatography-reversed-phase high-performance liquid chromatography (IAC-HPLC) with detection by quadrupole ion trap mass spectrometry using a particle beam interface has been developed for the determination of the steroids, dexamethasone and flumethasone. HEMA (polyhydroxyethylmethacrylate) was evaluated as a support material for the anti-dexamethasone antibodies used in IAC. Antibody cross-reactivity and non-specific binding have been investigated for the HEMA bound anti-dexamethasone IAC column. The on-line IAC-HPLC-MS determination of dexamethasone and flumethasone in post-administration equine urine samples showed precisions (R.S.D.) of 8.0 and 7.1%, respectively, with limits of detection in the range 3-4 ng/ml.

Organometallic flavonoid derivatives as spectroscopic probes.

Derivatives of naringenin have been synthesized with organometalcarbonyl reporting groups for IR spectroscopy attached at C-2, C-3', or C-6, and the products have been tested for the induction of nod gene expression using a Rhizobium leguminosarum strain which contains the Escherichia coli lacZ (beta-galactosidase) gene fused to nodABC. Derivatives with an OMe substituent within the reporting group moiety showed residual gene induction activity.

Validation of a congener specific method for ortho and non-ortho substituted polychlorinated biphenyls in fruit and vegetable samples.

An on-line procedure has been developed and validated for the clean-up and fractionation of ortho and non-ortho-PCBs in fruit and vegetable samples. The procedure combines silica/acid and carbon/glass fibre columns with gas chromatography-mass spectrometry. Chromatography on carbon/glass fibre allowed collection of mono-ortho/di-ortho and non-ortho-PCB fractions, which were determined separately by GC-MS. The method was validated by replicate analyses and by inter-laboratory comparison of data for PCB congeners determined in fruit and vegetable samples collected in South Wales. The concurrent determination of ortho and non-ortho substituted PCBs is reported with recoveries ranging from 55-95% and a mean intra-laboratory precision (%COV) of 9.5% for apple extracts.

Particle beam-mass spectrometric analysis of difluorophenyl triazole compounds using normal phase-HPLC.

Normal phase liquid chromatography combined with particle beam mass spectrometry has been applied to the analysis of fluconazole, an anti-fungal agent, [2-(2,4-difluorophenyl)-1,3-bis(1H-1,2,4-triazol-1-yl)-propan-2-ol] and a related intermediate, UK-51060 [2-(2,4-difluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-ethan-2-one]. Electron ionisation and chemical ionisation have been investigated in combination with quadrupole ion trap and magnetic sector mass spectrometers and the spectra obtained compared with those for direct probe analysis. A novel method for the introduction of the chemical ionisation reagent gas via the interface is described for particle beam-magnetic sector mass spectrometry. Multi-stage scan routines have been implemented on the ion trap for the selective storage of analyte species and removal of solvent ions. Detection limits for both spectrometers have been determined and are discussed in terms of interface geometry and analyte transport characteristics. Normal phase HPLC on silica provided a good separation of the intermediate from the later eluting fluconazole peak.

PCB and PCDD/DF congeners in locally grown fruit and vegetable samples in Wales and England.

A survey was undertaken of PCB and PCDD/DF congeners in fruit and vegetables grown in an urban areas close to a chemical waste incinerator and three rural locations. All of the concentrations detected were low and there was considerable overlap between those found in urban and rural samples. Some similarities with the congener composition of air samples were identified and concentrations in apple skin were noticeably higher than those in the flesh of the fruit. These results suggest that atmospheric deposition was an important contamination pathway. Assessments using the highest concentrations found indicated that consumption of such fruit and vegetables would represent an additional 3% of the normal dietary intake for PCBs and 8% for PCDD/DFs.

Levels of selected ortho and non-ortho polychlorinated biphenyls in UK retail milk.

Nineteen pooled samples of retail cow's milk were analysed for ortho (PCBs 28, 52, 101, 118, 138, 153 and 180) and non-ortho (PCBs 77, 126 and 169) polychlorinated biphenyls. Concentrations of individual congeners in whole milk were in the ranges 2 to 95 ng/kg for ortho substituted PCBs (51 to 2440 ng/kg fat) and 0.05 to 0.6 ng/kg for non-ortho substituted PCBs (1.3 to 15.4 ng/kg fat). These values provide a preliminary estimate of background contamination levels for polychlorinated biphenyls in UK milk. Results expressed in TEQs, using the recently proposed WHO/IPCS TEFs, averaged 0.06 ng TEQ/kg whole milk.