TY - JOUR AB - Recent advances in high-throughput technologies have enabled the profiling of multiple layers of a biological system, including DNA sequence data (genomics), RNA expression levels (transcriptomics), and metabolite levels (metabolomics). This has led to the generation of vast amounts of biological data that can be integrated in so-called multi-omics studies to examine the complex molecular underpinnings of health and disease. Integrative analysis of such datasets is not straightforward and is particularly complicated by the high dimensionality and heterogeneity of the data and by the lack of universal analysis protocols. Previous reviews have discussed various strategies to address the challenges of data integration, elaborating on specific aspects, such as network inference or feature selection techniques. Thereby, the main focus has been on the integration of two omics layers in their relation to a phenotype of interest. In this review we provide an overview over a typical multi-omics workflow, focusing on integration methods that have the potential to combine metabolomics data with two or more omics. We discuss multiple integration concepts including data-driven, knowledge-based, simultaneous and step-wise approaches. We highlight the application of these methods in recent multi-omics studies, including large-scale integration efforts aiming at a global depiction of the complex relationships within and between different biological layers without focusing on a particular phenotype. AU - Wörheide, M. AU - Krumsiek, J.* AU - Kastenmüller, G. AU - Arnold, M. C1 - 60421 C2 - 49440 CY - Radarweg 29, 1043 Nx Amsterdam, Netherlands SP - 144-162 TI - Multi-omics integration in biomedical research – A metabolomics-centric review. JO - Anal. Chim. Acta VL - 1141 PB - Elsevier PY - 2021 SN - 0003-2670 ER - TY - JOUR AB - Lake sediment organic matter (OM) is composed of a variety of organic compounds differing in their biolability and origin. Sources of sediment OM can include terrestrial input from the watershed and algal/microbial metabolic byproducts residing in the water column or sediment. Dissolved organic phosphorus (DOP) is a critical component of OM in freshwater eutrophic lakes, often acting as a source for bioavailable phosphorus that fuels harmful algal and/or cyanobacterial blooms. Parallel extractions of lake sediment collected from Missisquoi Bay, a eutrophic bay in Lake Champlain, were conducted with the goal of identifying OM and organic P sediment constituents using ultrahigh-resolution mass spectrometry from various extractants. Extractants converged into two groups based on the characteristics of their extracted OM; "stronger extractants" were composed of highly acidic and alkali media, while "milder extractants" represented weaker acids and bases. Sediment treated with the strong extractants afforded highly oxygenated and unsaturated OM thought to be stable with mostly lower heteroatomic content. In contrast, milder extractants yielded highly aliphatic and saturated compounds with lower masses and greater heteroatom functionally, sharing characteristics with labile molecules. Extracted organic P molecules mirrored the bulk OM in terms of lability, mass, and oxygenation within their corresponding extractants. Milder extractants resulted in greater organic P formulae assignments than the stronger extractants, with NaHCO3 resulting in the most aliphatic organic P formulae. We recommend the use of acetic acid to probe lake sediment for overall molecular characterization, spanning the greatest ranges of O/C and H/C ratios and representing both labile and mineral-associated OM. Other extractants should be implemented for a more targeted analysis. For instance, the use of NaHCO3 for organic P characterization, while using NaOH when interested in sediment geochemistry; both of which are critical for understanding the factors contributing to internal P loading. AU - Kurek, M.R.* AU - Harir, M. AU - Shukle, J.T.* AU - Schroth, A.W.* AU - Schmitt-Kopplin, P. AU - Druschel, G.K.* C1 - 59848 C2 - 49069 CY - Radarweg 29, 1043 Nx Amsterdam, Netherlands SP - 29-38 TI - Chemical fractionation of organic matter and organic phosphorus extractions from freshwater lake sediment. JO - Anal. Chim. Acta VL - 1130 PB - Elsevier PY - 2020 SN - 0003-2670 ER - TY - JOUR AB - Urine-based metabolomics-driven strategies for the discovery of biomarkers are increasingly developed and applied in analytical chemistry. But valid, data-based recommendations for a urine sample material of choice are lacking. We investigated first and second morning urine (MU), which are the most commonly used urine specimens. Potential major factors biasing metabolomics biomarker results in these sample materials were studied. First, 35 1st and 2nd MU samples were collected from healthy, young men after an overnight fast. Subsequently, two subgroups were built, one having fast food at lunch and dinner (n = 17), the other vegetarian meals (n = 18). Again 1st and 2nd MU were collected. Non-targeted liquid chromatography-mass spectrometry was applied for analyses. More than half of the >5400 urinary ion features showed a significant difference between 1st and 2nd MU. Just two fast food meals on previous day significantly affected around 30% of all metabolites in 1st and 2nd MU. In contrast, the effects of two vegetarian meals in 2nd MU were only minor. Additionally, we describe 47 metabolites in urine, possible hits in biomarker studies, which are susceptible to the diet the day before sample collection. They should be handled with caution until validation in diet-controlled studies. Based on our results we think the second MU, ideally collected after standardized vegetarian meals and drinking only water on the previous day, is most suitable for valid analysis of biomarkers in urine. AU - Liu, X.* AU - Yin, P.* AU - Shao, Y.* AU - Wang, Z.* AU - Wang, B.* AU - Lehmann, R. AU - Xu, G.* C1 - 58734 C2 - 48268 SP - 120-127 TI - Which is the urine sample material of choice for metabolomics-driven biomarker studies? JO - Anal. Chim. Acta VL - 1105 PY - 2020 SN - 0003-2670 ER - TY - JOUR AB - In this study, we utilized elemental analyser (EA) and gas-chromatography (GC) isotope ratio mass spectrometry (IRMS) and ultra-high-performance liquid chromatography coupled to mass spectrometry (UHPLC-MS) in a comprehensive profiling approach assessing the chromatographic impurity signatures and delta C-13 and delta(15) N isotope ratios of synthetic cannabinoids from police seizures and internet test purchases. Main target of this study was the highly prevalent synthetic cannabinoid MDMB-CHMICA (methyl(2S)-2-([1-(cyclohexylmethyl)- 1H-indol-3 -yl] formamido)-3 ,3-dimethylbutaoate). Overall, 61 powder and 118 herbal blend (also called "Spice-Products") samples were analysed using both analytical techniques and evaluated in a joint model to link samples from a common source. As a key finding, three agglomerates of Spice-product samples with similar dates of purchase were identified in the IRMS data, possibly representing larger shipments of MDMB-CHMICA, each produced with the same precursor material, successively delivered to the European market. The three agglomerates were refined into multiple sub-clusters based on the impurity profiling data, each representing an individual synthesis batch. One of the agglomerates identified in the IRMS data was found to consist two groups of four subclusters, respectively, with majorly different impurity profiles, demonstrating the necessity for both analytical techniques to extract the maximum amount of information from a limited sample pool. Additionally, 31 samples containing the recently surfaced synthetic cannabinoid Cumyl-PeGaClone (5pentyl-2-(2-phenylpropan-2-yl)-2,5-dihydro-1H-pyrido[4,3-blindol-1-one) were analysed for their and delta C-13 and delta N-15 isotope ratios to put the isotopic data recorded for MDMB-CHMNICA in a more global perspective. Three building blocks of precursor chemicals (indole, tert-leucine, cumylamine) potentially used for the synthesis of the two named synthetic cannabinoids were acquired from different global vendors and measured for their delta C-13 and delta N-15 isotope ratios to better understand variations in the isotopic composition of the synthetic cannabinoids and to trace their origin. AU - Münster-Müller, S.* AU - Scheid, N.* AU - Zimmermann, R. AU - Pütz, M.* C1 - 58654 C2 - 48372 CY - Radarweg 29, 1043 Nx Amsterdam, Netherlands SP - 129-141 TI - Combination of stable isotope ratio data and chromatographic impurity signatures as a comprehensive concept for the profiling of highly prevalent synthetic cannabinoids and their precursors. JO - Anal. Chim. Acta VL - 1108 PB - Elsevier PY - 2020 SN - 0003-2670 ER - TY - JOUR AB - Formalin-fixed and paraffin-embedded (FFPE) tissue represents a valuable resource to examine cancer metabolic alterations and to identify potential markers of disease. Protocols commonly used for liquid-chromatography mass spectrometry (LC-MS)-based FFPE metabolomics have not been optimized for lipidomic analysis and pre-analytical factors, that potentially affect metabolite levels, were scarcely investigated. We here demonstrate the assessment and optimization of sample preparation procedures for comprehensive metabolomic and lipidomic profiling in FFPE kidney tissue by LC-QTOF-MS. The optimized protocol allows improved monitoring of lipids including ceramides (Cer), glycosphingolipids (GSL) and triglycerides (TAGs) while the profiling capability for small polar molecules is maintained. Further, repeatable sample preparation (CVs < 20%) along with high analytical (CVs < 10%) and inter-day precision (CVs < 20%) is achieved. As proof of concept, we analyzed a set of clear cell renal cell carcinoma (ccRCC) and corresponding non-tumorous FFPE tissue samples, achieving phenotypic distinction. Investigation of the impact of tissue fixation time (6 h, 30 h and 54 h) on FFPE tissue metabolic profiles revealed metabolite class-dependent differences on their detection abundance. Whereas specific lipids (e.g. phosphatidylinositoles, GSLs, saturated fatty acids and saturated lyso-phosphatidytlethanolamines LPED remained largely unaffected (CVs < 20% between groups of fixation time), neutral lipids (e.g. Cer and TAGs) exhibited high variability (CVs > 80%). Strikingly, out of the lipid classes assigned as unaffected, fatty acids 18:0, 16:0 and LPE 18:0 were detectable by high-resolution MALDI-FT-ICR MS imaging in an independent cohort of ccRCC tissues (n = 64) and exhibited significant differences between tumor and non-tumor regions. AU - Neef, S.K.* AU - Winter, S.* AU - Hofmann, U.* AU - Mürdter, T.E.* AU - Schaeffeler, E.* AU - Horn, H.* AU - Buck, A. AU - Walch, A.K. AU - Hennenlotter, J.* AU - Ott, G.* AU - Fend, F.* AU - Bedke, J.* AU - Schwab, M.* AU - Haag, M.* C1 - 60044 C2 - 49182 CY - Radarweg 29, 1043 Nx Amsterdam, Netherlands SP - 125-135 TI - Optimized protocol for metabolomic and lipidomic profiling in formalin-fixed paraffin-embedded kidney tissue by LC-MS. JO - Anal. Chim. Acta VL - 1134 PB - Elsevier PY - 2020 SN - 0003-2670 ER - TY - JOUR AB - In spite of demonstrated lack of accuracy and consistency, quantification of steroid hormones is still most commonly executed via immunoassays. Mass spectrometric methods with triple quadrupole instruments are well established and, because of their proven robustness and sensitivity, best suited for targeted analysis. However, recent studies have shown that high-resolution mass spectrometers, like quadrupole time-of-flight instruments (QTOF), show comparable performance in terms of quantification and can generate additional sample information via untargeted profiling workflows. We demonstrate that adequate accuracy and selectivity for estradiol and testosterone can be achieved with a QTOF by data-independent acquisition with sequential window acquisition of all theoretical fragment-ion mass spectra (SWATH). Besides potential combination of targeted quantification and untargeted profiling, SWATH offers advantages with respect to sensitivity because the reduced total number of MS/MS experiments could be used to increase accumulation time without increasing cycle time. By applying a surrogate calibrant method leading to successful validation, a reliable method for absolute steroid quantification and high potential for steroid profiling has been developed. Linear calibration was achieved in the range from 10 to 1,000 pg mL for C-estradiol and from 20 to 15,000 pg mL for C-testosterone. Results for inter-day precision (C-estradiol: 4.5-10.2%; C-testosterone: 5.1-7.8%) and inter-day accuracy (C-estradiol: 94.6-112.8%; C-testosterone: 98.2-107.7%) were found to be well acceptable. Eventually, the method has been utilized to measure clinical samples of a study in which male volunteers obtained transdermal estradiol patches and sex hormone levels were quantified in plasma. AU - Drotleff, B.* AU - Hallschmid, M. AU - Lämmerhofer, M.* C1 - 53485 C2 - 44709 SP - 70-80 TI - Quantification of steroid hormones in plasma using a surrogate calibrant approach and UHPLC-ESI-QTOF-MS/MS with SWATH-acquisition combined with untargeted profiling. JO - Anal. Chim. Acta VL - 1022 PY - 2018 SN - 0003-2670 ER - TY - JOUR AB - Urinary analyte data has to be corrected for the sample specific dilution as the dilution varies intra-and interpersonally dramatically, leading to non-comparable concentration measures. Most methods of dilution correction utilized nowadays like probabilistic quotient normalization or total spectra normalization result in a division of the raw data by a dilution correction factor. Here, however, we show that the implicit assumption behind the application of division, log-linearity between the urinary flow rate and the raw urinary concentration, does not hold for analytes which are not in steady state in blood. We explicate the physiological reason for this short-coming in mathematical terms and demonstrate the empirical consequences via simulations and on multiple time-point metabolomic data, showing the insufficiency of division-based normalization procedures to account for the complex non-linear analyte specific dependencies on the urinary flow rate. By reformulating normalization as a regression problem, we propose an analyte specific way to remove the dilution variance via a flexible non-linear regression methodology which then was shown to be more effective in comparison to division-based normalization procedures. In the progress, we developed several, easily applicable methods of normalization diagnostics to decide on the method of dilution correction in a given sample. On the way, we identified furthermore the time-span since last urination as an important variance factor in urinary metabolome data which is until now completely neglected. In conclusion, we present strong theoretical and empirical evidence that normalization has to be analyte specific in dynamically influenced data. Accordingly, we developed a normalization methodology for removing the dilution variance in urinary data respecting the single analyte kinetics. AU - Hertel, J.* AU - Rotter, M. AU - Frenzel, S.* AU - Zacharias, H.U. AU - Krumsiek, J. AU - Rathkolb, B. AU - Hrabě de Angelis, M. AU - Rabstein, S.* AU - Pallapies, D.* AU - Brüning, T.* AU - Grabe, H.J.* AU - Wang-Sattler, R. C1 - 54026 C2 - 45198 CY - Po Box 211, 1000 Ae Amsterdam, Netherlands SP - 18-31 TI - Dilution correction for dynamically influenced urinary analyte data. JO - Anal. Chim. Acta VL - 1032 PB - Elsevier Science Bv PY - 2018 SN - 0003-2670 ER - TY - JOUR AB - In analytical chemistry serum as well as plasma are recommended as sample material of choice. However, blood processing for the generation of serum or plasma is rather different. Whether plasma or serum is the preferable sample material is still controversial discussed. We performed in paired samples three UHPLC-mass spectrometry-driven metabolomics studies. In study 1 metabolite profiles of serum vs plasma were compared. 46% out of 216 identified metabolites showed significant different levels (paired Wilcoxon signed-rank test, p < 0.05, FDR <0.01) with only three metabolites (methionine, C2:0- and C3:0-carnitine) showing lower levels in serum. In study 2 comparison of three different serum blood collection tubes revealed that coagulation and associated processes distinctly alter metabolite levels depending on the tube-specific clotting process. Most pronounced differences were found for the dipeptide phenylalanine-phenylalanine (highest levels in silicate containing serum blood collection tubes). In study 3 possible adverse effects of platelets, which still remain in standard plasma even after correct processing, were investigated. No differences in a pattern of 216 metabolites were detected in the comparison of standard and platelet-free plasma (PFP). Our results give novel insights in fundamental differences between serum and plasma, thereby providing valuable information for analytical chemists for decision making to either use serum or plasma before starting complex and time-consuming analytical investigations. AU - Liu, X.* AU - Hoene, M.* AU - Wang, X.* AU - Yin, P.* AU - Häring, H.-U. AU - Xu, G.* AU - Lehmann, R. C1 - 54479 C2 - 45591 CY - Po Box 211, 1000 Ae Amsterdam, Netherlands SP - 293-300 TI - Serum or plasma, what is the difference? Investigations to facilitate the sample material selection decision making process for metabolomics studies and beyond. JO - Anal. Chim. Acta VL - 1037 PB - Elsevier Science Bv PY - 2018 SN - 0003-2670 ER - TY - JOUR AB - The comprehensive description of complex mixtures such as bio-oils is required to understand and improve the different processes involved during biological, environmental or industrial operation. In this context, we have to consider how different ionization sources can improve a non-targeted approach. Thus, the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has been coupled to electrospray ionization (ESI), laser desorption ionization (LDI) and atmospheric pressure photoionization (APPI) to characterize an oak pyrolysis bio-oil. Close to 90% of the all 4500 compound formulae has been attributed to CHO with similar oxygen class compound distribution. Nevertheless, their relative abundance in respect with their double bound equivalent (DBE) value has evidenced significant differences depending on the ion source used. ESI has allowed compounds with low DBE but more oxygen atoms to be ionized. APPI has demonstrated the efficient ionization of less polar compounds (high DBE values and less oxygen atoms). The LDI behavior of bio-oils has been considered intermediate in terms of DBE and oxygen amounts but it has also been demonstrated that a significant part of the features are specifically detected by this ionization method. Thus, the complementarity of three different ionization sources has been successfully demonstrated for the exhaustive characterization by petroleomic approach of a complex mixture. AU - Hertzog, J.* AU - Carré, V.* AU - le Brech, Y.* AU - Mackay, C.L.* AU - Dufour, A.* AU - Mašek, O.* AU - Aubriet, F.* C1 - 54675 C2 - 0 SP - 26-34 TI - Combination of electrospray ionization, atmospheric pressure photoionization and laser desorption ionization Fourier transform ion cyclotronic resonance mass spectrometry for the investigation of complex mixtures - Application to the petroleomic analysis of bio-oils. JO - Anal. Chim. Acta VL - 969 PY - 2017 SN - 0003-2670 ER - TY - JOUR AB - A new method of simultaneous redox speciation of iron (II/III), manganese (II/III), and copper (I/II) in cerebrospinal fluid (CSF) has been designed. For the separation of redox species strong cation exchange chromatography (SCX) with isocratic elution was employed. Species were detected using inductively coupled plasma sector field mass spectrometry (ICP-sf-MS), operating at medium resolution. The following parameters were optimized: analytical column, eluent composition and pH, CSF injection volume and dilution factor. Analytical column Dionex IonPac CS5A RFIC 4*250 mm was found to retain and separate species of interest the most effectively under the isocratic elution with a buffer, containing 50 mM ammonium citrate, 7.0 mM pyridine-2,6-dicarboxylic acid at pH = 4.2 and flow rate of 0.8 L min-1. Injection volume of 50 μL with CSF sample dilution of 1/3 (v/v) with the eluent was shown to result in minimal matrix suppression. For species identification, retention time matching with standards was used. The stability of metalloproteins (ferritin, transferrin, and ceruloplasmin) under elution conditions was evaluated. For the quantification of redox species, external calibration was employed. To avoid column contamination, a blank was run after measurement and all quantification values were blank subtracted. For recovery checks, species quantification data was verified against total content of an element, measured by dynamic reaction cell ICP-MS. Recoveries (sum of quantified species vs. total element determinations) were 82.5 ± 22% (Mn), 92 ± 11% (Fe), and 88.7 ± 12% (Cu). The method was tested using 38 real CSF samples. Limits of detection (3σ) for the CSF samples were 0.5 μg L-1, 0.6 μg L-1, and 0.8 μg L-1 for Fe, Mn, and Cu species, respectively. Retention time precision was 1-7.5% (as RSD), whereas peak area RSDs were in the range 5-11%, both depending on the species. AU - Solovyev, N. AU - Vinceti, M.* AU - Grill, P. AU - Mandrioli, J.* AU - Michalke, B. C1 - 50985 C2 - 42818 CY - Amsterdam SP - 25-33 TI - Redox speciation of iron, manganese, and copper in cerebrospinal fluid by strong cation exchange chromatography - sector field inductively coupled plasma mass spectrometry. JO - Anal. Chim. Acta VL - 973 PB - Elsevier Science Bv PY - 2017 SN - 0003-2670 ER - TY - JOUR AB - A novel analytical system for gas-chromatographic investigation of complex samples has been developed, that combines the advantages of several analytical principles to enhance the analytical information. Decomposition of high molecular weight structures is achieved by pyrolysis and a high separation capacity due to the chromatographic step provides both an universal as well as a selective and sensitive substance detection. The latter is achieved by simultaneously applying electron ionization quadrupole mass spectrometry (EI-QMS) for structural elucidation and [1+1]-resonance-enhanced-multi-photon ionization (REMPI) combined with time-of-flight mass spectrometry (ToFMS). The system has been evaluated and tested with polycyclic aromatic hydrocarbon (PAH) standards. It was applied to crude oil samples for the first time. In such highly complex samples several thousands of compounds are present and the identification especially of low concentrated chemical species such as PAH or their polycyclic aromatic sulfur containing heterocyclic (PASH) derivatives is often difficult. Detection of unalkylated and alkylated PAH together with PASH is considerably enhanced by REMPI-ToFMS, at times revealing aromatic structures which are not observable by EI-QMS due to their low abundance. On the other hand, the databased structure proposals of the EI-QMS analysis are needed to confirm structural information and isomers distinction. The technique allows a complex structure analysis as well as selective assessment of aromatic substances in one measurement. Information about the content of sulfur containing compounds plays a significant role for the increase of efficiency in the processing of petroleum. AU - Otto, S.* AU - Streibel, T. AU - Erdmann, S.* AU - Sklorz, M. AU - Schulz-Bull, D.* AU - Zimmermann, R. C1 - 43031 C2 - 35982 SP - 60-69 TI - Application of pyrolysis-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry with electron-ionization or resonance-enhanced-multi-photon ionization for characterization of crude oils. JO - Anal. Chim. Acta VL - 855 PY - 2015 SN - 0003-2670 ER - TY - JOUR AB - Two-stroke mopeds are a popular and convenient mean of transport in particular in the highly populated cities. These vehicles can emit potentially toxic gaseous and aerosol pollutants due to their engine technology. The legislative measurements of moped emissions are based on offline methods; however, the online characterization of gas and particulate phases offers great possibilities to understand aerosol formation mechanism and to adapt future emission standards. The purpose of this work was to study the emission behavior of two mopeds complying with different European emission standards (EURO-1 and EURO-2). A sophisticated set of online analyzers was applied to simultaneously monitor the gas phase and particulate phase of exhaust on a real time basis. The gaseous emission was analyzed with a high resolution Fourier transform infrared spectrometer (FTIR; nitrogen species) and a resonance-enhanced multiphoton ionization time-of-flight mass spectrometer (REMPI-ToF-MS; polycyclic aromatic hydrocarbons: PAH), whereas the particulate phase was chemically characterized by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS; organic, nitrate and chloride aerosol) and a multiangle absorption photometer (MAAP; black carbon). The physical characterization of the aerosol was carried out with a condensation particle counter (CPC; particle number concentration) and a fast mobility particle sizer (FMPS; size distribution in real time). In order to extract underlying correlation between gas and solid emissions, principal component analysis was applied to the comprehensive online dataset. Multivariate analysis highlighted the considerable effect of the exhaust temperature on the particles and heavy PAH emissions. The results showed that the after-treatment used to comply with the latest EURO-2 emission standard may be responsible for the production of more potentially harmful particles compared to the EURO-1 moped emissions. AU - Clairotte, M.* AU - Adam, T.W.* AU - Chirico, R.* AU - Giechaskiel, B.* AU - Manfredi, U.* AU - Elsasser, M. AU - Sklorz, M.* AU - DeCarlo, P.F.* AU - Heringa, M.F.* AU - Zimmermann, R. AU - Martini, G.* AU - Krasenbrink, A.* AU - Vicet, A.* AU - Tournié, E.* AU - Prévôt, A.S.* AU - Astorga, C.* C1 - 7416 C2 - 29712 SP - 28-38 TI - Online characterization of regulated and unregulated gaseous and particulate exhaust emissions from two-stroke mopeds: A chemometric approach. JO - Anal. Chim. Acta VL - 717 PB - Elsevier PY - 2012 SN - 0003-2670 ER - TY - JOUR AB - Atmospheric polycyclic aromatic hydrocarbons are ubiquitous environmental pollutants, which may be present both in the gaseous phase and adsorbed onto the surface of particles. Denuders are sampling devices which have been effectively employed in such partitioning applications. Here we describe and characterise a novel miniature denuder consisting of two multi-channel silicone rubber traps (each 178 mm long, 6 mm o.d. containing 22 silicone tubes), separated by a quartz fibre filter for particle phase collection. The denuder only requires a small portable personal sampling pump to provide sampling flow rates of similar to 0.5 L min(-1). Theoretical considerations indicated that the air flow through the denuder was expected to be laminar, and the linear velocity arising from longitudinal diffusion was found to be negligible. The calculated particle transmission efficiency through the denuder was found to be essentially 100% for particles > 50 nm, whilst the experimental overall efficiency, as determined by CPC and SMPS measurements, was 92 +/- 4%. The size resolved transmission efficiency was <60% for particles below 20 nm and 100% for particles larger than 200 nm. Losses could have been due to diffusion and electrostatic effects. Semi-volatile gaseous analytes are pre-concentrated in the silicone of the trap and may be thermally desorbed using a commercially available desorber, allowing for total transfer and detection of the collected analytes by GC-MS. This enhances detection limits and allows for lower sampling flow rates and shorter sampling times, which are advantageous for studies requiring high temporal resolution. AU - Forbes, P.B.C.* AU - Karg, E.W. AU - Zimmermann, R. AU - Rohwer, E.R.* C1 - 7600 C2 - 29853 SP - 71-79 TI - The use of multi-channel silicone rubber traps as denuders for polycyclic aromatic hydrocarbons. JO - Anal. Chim. Acta VL - 730 PB - Elsevier Science PY - 2012 SN - 0003-2670 ER - TY - JOUR AB - A microprobe sampling device (μ-probe) has been developed for in situ on-line photo ionization mass spectrometric analysis of volatile chemical species formed within objects consisting of organic matter during thermal processing. With this approach the chemical signature occurring during heating, pyrolysis, combustion, roasting and charring of organic material within burning objects such as burning fuel particles (e.g., biomass or coal pieces), lit cigarettes or thermally processed food products (e.g., roasting of coffee beans) can be investigated. Due to its dynamic changes between combustion and pyrolysis phases the cigarette smoking process is particularly interesting and has been chosen as first application. For this investigation the tip of the μ-probe is inserted directly into the tobacco rod and volatile organic compounds from inside the burning cigarette are extracted and real-time analyzed as the glowing front (or coal) approaches and passes the μ-probe sampling position. The combination of micro-sampling with photo ionization time-of-flight mass spectrometry (PI-TOFMS) allows on-line intrapuff-resolved analysis of species formation inside a burning cigarette. Monitoring volatile smoke compounds during cigarette puffing and smoldering cycles in this way provides unparalleled insights into formation mechanisms and their time-dependent change. Using this technique the changes from pyrolysis conditions to combustion conditions inside the coal of a cigarette could be observed directly. A comparative analysis of species formation within a burning Kentucky 2R4F reference cigarette with μ-probe analysis reveals different patterns and behaviors for nicotine, and a range of semi-volatile aromatic and aliphatic species. AU - Hertz, R.* AU - Streibel, T. AU - Liu, C.* AU - McAdam, K.* AU - Zimmermann, R. C1 - 7250 C2 - 29610 SP - 104-113 TI - Microprobe sampling - photo ionization-time-of-flight mass spectrometry for in situ chemical analysis of pyrolysis and combustion gases: Examination of the thermo-chemical processes within a burning cigarette. JO - Anal. Chim. Acta VL - 714 PB - Elsevier PY - 2012 SN - 0003-2670 ER - TY - JOUR AB - Here we developed a highly sensitive, fast and reliable liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the detection and analysis of 16 different polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs that have been identified as carcinogens and classified according to their biological potency. Comparison to standard analysis procedures based on gas chromatography-mass spectrometry (GC-MS) instrumentation demonstrated an improved easiness of sample preparation and sensitivity of detection achieved with the new LC-MS/MS method employing an atmospheric pressure photoionization (APPI) source attached to an API 4000 mass spectrometer (LC-APPI-MS/MS). The favorable outcome could be confirmed by analyzing complex mixtures such as certain Standard Reference Materials (SRMs) obtained from the National Institute of Standards & Technology (NIST), i.e., SRM 1975 and SRM 2975, and several diesel exhaust soots provided by the German automobile industry. Certified concentrations of individual analytes provided by NIST not only could be confirmed, but additional extremely potent carcinogens such as several isomeric hexacyclic dibenzopyrenes (DBPs), 5-methylchrysene (5-MC), and others have been detected in these crude samples in a concentration range down to below 1 ng g(-1) raw material. AU - Hutzler, C.* AU - Luch, A.* AU - Filser, J.G. C1 - 6602 C2 - 28968 CY - Amsterdam SP - 218-2224 TI - Analysis of carcinogenic polycyclic aromatic hydrocarbons in complex environmental mixtures by LC-APPI-MS/MS. JO - Anal. Chim. Acta VL - 702 IS - 2 PB - Elsevier PY - 2011 SN - 0003-2670 ER - TY - JOUR AB - Total yields of cigarette smoke constituents are greatly influenced by smoking behaviour, the tobacco blend as well as a variety of cigarette design parameters. Thereby, filter ventilation, i.e. diluting the smoke by providing a zone of microscopic holes around the circumference of the filter is one method to reduce the yield of 'tar' and other smoke compounds. However, little is known how these design variations influence the combustion conditions, and therefore, the overall chemical pattern of the smoke. In this paper single photon ionization-time-of-flight mass spectrometry (SPI-TOFMS) is used to characterize and compare cigarettes on a puff-by-puff basis, which differ only in filter ventilation magnitude. The research cigarettes investigated were made from Virginia tobacco and featured filter ventilations of 0% (no ventilation), 35%, and 70%. The cigarettes were smoked under two different puffing regimes, one using the puffing parameters of the conventional International Organization for Standardization (ISO) smoking regime and a more intense smoking condition. Results show that every variation entails a change of the chemical pattern, whereby, in general, cigarettes with 0% filter ventilation as well as the intense smoking regime lead to a more complete combustion compared to the ISO smoking conditions and the high ventilated cigarettes. Changes in the overall patterns can also be observed during the smoking for individual puffs. Some substances dominate the first puff, some species are more pronounced in the middle puffs, whereas others are preferably formed in the last puffs. This demonstrates the high complexity of the occurring processes. Results might help to understand the formation and decomposition reactions taking place when a cigarette is smoked and offer scope for targeted reduction strategies for specific toxicants or groups of toxicants in the smoke. AU - Adam, T. AU - McAughey, J.* AU - Mocker, C. AU - McGrath, C.* AU - Zimmermann, R. C1 - 61 C2 - 27148 SP - 36-44 TI - Influence of filter ventilation on the chemical composition of cigarette mainstream smoke. JO - Anal. Chim. Acta VL - 657 IS - 1 PB - Elsevier PY - 2010 SN - 0003-2670 ER - TY - JOUR AB - The large number of patients suffering from neurodegenerative diseases like Alzheimer's disease and Parkinson's disease motivates many research groups worldwide to investigate pathogenic factors and molecular mechanisms of these diseases. Recent studies and reviews indicate that metals are involved in these neurodegenerative processes in case their homeostasis in the brain is disturbed. Important is that the focus of these recent studies is on essential metals like Fe, Cu, Zn and Mn, but not on the well-known neurotoxic metals like Hg and Pb. Key issues for understanding metal induced neurotoxic effects are the transport processes across the neural barriers, the metal binding forms (species) and their interactions with neuronal structures. Total metal concentrations in cerebrospinal fluid were published in several studies for controls and patients, but the amount of reliable data sets is not yet sufficient for clear definition of normal and elevated levels. The need for more detailed information on metal species in CSF is highlighted in this review. However, studies on element speciation analysis, that means identification and quantification of the various binding forms of metals in cerebrospinal fluid, are rare. The major reasons therefore are difficulties in accessing cerebrospinal fluid samples, the non-covalent nature of many metal species of interest and their rather low concentrations. In spite of this, several applications demonstrate the potential of hyphenated techniques as additional diagnostic tools for cerebrospinal fluid analysis. This review shows the importance of trace element analysis and more specifically of element speciation in cerebrospinal fluid for an improved understanding of pathologic mechanisms promoting neuro-degeneration. Respective analytical techniques are also highlighted. Additionally, biochemical assays for selected high molecular mass metal species are summarized and critically discussed. Moreover additional potential techniques like direct non-invasive methods as well as mathematical modelling approaches are considered. Data on total concentrations of numerous elements in CSF as well as speciation information of elements such as Al, As, Ca, Cd, Cu, Fe, Mg, Mn, Hg, Pb, Se and Zn in CSF are summarized. AU - Michalke, B. AU - Nischwitz, V. C1 - 4408 C2 - 27629 SP - 23-36 TI - Review on metal speciation analysis in cerebrospinal fluid-current methods and results: A review. JO - Anal. Chim. Acta VL - 682 IS - 1-2 PB - Elsevier PY - 2010 SN - 0003-2670 ER - TY - JOUR AB - This study shows the detection of (N-acyl) homoserine lactones (AHLs or HSL) with monoclonal antibodies via a surface plasmon resonance (SPR)-based immunosensor in comparison to conventional microtiter plate-based enzyme-linked immunosorbent assay (ELISA). An HSL derivative, named HSL2 (Table 1), was attached to bovine serum albumin (BSA) and the conjugate (HSL2-BSA-r2) was either covalently immobilised on the SPR sensor chip surface via free amino groups or via adsorption on the ELISA polystyrene plate surface. With a newly developed rat monoclonal antibody (mAb HSL1/2 2C10), AHLs were detected sensitively in a competitive format with SPR and ELISA. Well comparable experiments between SPR and ELISA could be obtained in buffers. Moreover, the SPR sensor surface with the immobilised conjugate HSL2-BSA-r2 could be regenerated at least 340 times (regeneration cycles) without loss of activity. The measurement time per cycle was approximately 15min. The competitive detection format for SPR and ELISA allowed the detection in the μgL(-1) range. AU - Wöllner, K. AU - Chen, X. AU - Kremmer, E. AU - Krämer, P.M. C1 - 4995 C2 - 27741 SP - 113-118 TI - Comparative surface plasmon resonance and enzyme-linked immunosorbent assay characterisation of a monoclonal antibody with N-acyl homoserine lactones. JO - Anal. Chim. Acta VL - 683 IS - 1 PB - Elsevier PY - 2010 SN - 0003-2670 ER - TY - JOUR AB - An inter-laboratory exercise was performed with a yeast estrogen bioassay, based on the expression of yeast enhanced green fluorescent protein (yEGFP), for the determination of estrogenic activity in extracts of calf urine samples. Urine samples were spiked with 1 and 5 ngmL(-1) 17beta-estradiol and 17alpha-ethynylestradiol, 10 and 50 ngmL(-1) mestranol, and 100 ngmL(-1) testosterone and progesterone. Sample extracts of blank and spiked urine samples were prepared at our laboratory and sent to seven laboratories together with a reagent blank, a DMSO blank, and eight 17beta-estradiol stock solutions in DMSO ranging in concentration from 0 to 545 ngmL(-1). Sample extracts and standards were coded and tested blindly. A decision limit (CCalpha) was determined based on the response of seven blank urine samples. Signals of the negative controls, e.g. urine samples spiked with 100 ngmL(-1) testosterone or progesterone, were all below the determined CCalpha and were thus screened as compliant. Positive controls, i.e. the urine samples spiked at two levels with 17beta-estradiol, 17alpha-ethynylestradiol and mestranol, were almost all screened as suspect, i.e. gave signals above the determined CCalpha. Determined EC(50) values calculated from the 17beta-estradiol dose-response curves obtained by the seven laboratories ranged from 0.59 to 0.95 nM. AU - Bovee, T.F.H.* AU - Bor, G.* AU - Becue, I.* AU - Daamen, F.E.J.* AU - van Duursen, M.B.M.* AU - Lehmann, S.* AU - Vollmer, G.* AU - de Maria, R.* AU - Fox, J.E.* AU - Witters, H.* AU - Bernhöft, S. AU - Schramm, K.-W. AU - Hoogenboom, R.L.A.P.* AU - Nielen, M.W.F.* C1 - 870 C2 - 26385 CY - Amsterdam SP - 265-272 TI - Inter-laboratory comparison of a yeast bioassay for the determination of estrogenic activity in biological samples. JO - Anal. Chim. Acta VL - 637 IS - 1-2 PB - Elsevier Science Bv PY - 2009 SN - 0003-2670 ER - TY - JOUR AB - Neurodegenerative diseases like Alzheimer's disease and Parkinson's disease are gaining increasing relevance in our aging society. However, the complex multifactorial mechanisms of these diseases are not sufficiently understood yet. Several studies indicate that metal ions play an important role in the promotion of these diseases. Consequently, the transport pathways of metals and their species to the brain are of special interest. Following oral or inhalative uptake metals are absorbed and distributed via the blood stream in the body. Transport into the brain requires crossing of the neural barriers. Our study focuses on the investigation of the permeability of the blood-cerebrospinal fluid (CSF)-barrier for selected metals (Mn, Fe, Cu, Zn, Mg and Ca). For the first time paired human serum and CSF samples obtained from a neurological department were characterised for total metal concentrations and metal species. For CSF few data are available in the literature on total metal contents and applications of element speciation analysis in CSF samples are rare. In our study mean CSF/serum ratios (n=29) were 0.7 for Mn, 0.02 for Fe, 0.02 for Cu, 0.03 for Zn, 1.3 for Mg and 0.5 for Ca. Size exclusion chromatography (SEC) online with inductively coupled plasma mass spectrometry was further developed for the size characterisation of the metal species in CSF and serum with limits of detection of 0.4microgL(-1) for Fe, 0.01microgL(-1) for Mn, 0.2microgL(-1) for Cu, 0.2microgL(-1) for Zn, 0.6microgL(-1) for Mg and 3.8microgL(-1) for Ca in the eluate from the HPLC column. Apart from Mn the application of this technique has not been published for metal speciation in CSF, yet. In the case of some Mn species it turned out that methanol, which was contained in the mobile phase of a SEC method previously published from our group on qualitative characterisation of Mn species, was interfering with the quantification. The modified method developed in this work (with NaCl but without methanol in the mobile phase; use of internal standard) allowed reliable quantification. The results clearly indicate changes in the metal species pattern due to different permeation behaviour at the blood-CSF-barrier. As part of the method validation the relative stability of complexes of albumin, transferrin and citrate with Mn, Fe, Cu and Zn was investigated. AU - Nischwitz, V. AU - Berthele, A.* AU - Michalke, B. C1 - 2724 C2 - 25542 SP - 258-269 TI - Speciation analysis of selected metals and determination of their total contents in paired serum and cerebrospinal fluid samples: An approach to investigate the permeability of the human blood-cerebrospinal fluid-barrier. JO - Anal. Chim. Acta VL - 627 IS - 2 PB - Elsevier PY - 2008 SN - 0003-2670 ER - TY - JOUR AB - Soft single photon ionisation (SPI)-time-of-flight mass spectrometry (TOFMS) is applied for the characterisation and comparison of puff-by-puff resolved and total yields of cigarette mainstream smoke from single tobacco type cigarettes (Virginia, Oriental, Burley, and Maryland) and the 2R4F University of Kentucky research cigarette. Puff-by-puff characteristics of various smoke components within one cigarette type as well as between different cigarette types can differ tremendously. This is demonstrated by means of a few selected compounds. Puff yields vary between 15 and 106 microm for acetaldehyde, 6 and 57 microm for NO, and between 1 and 8 microm for butadiene. Thereby, cigarettes containing 100% Oriental and Burley tobacco exhibit a very unique behaviour for the first and last puff. Different cultivation and processing methods as well as burning characteristics are most likely responsible for this. Since the 2R4F cigarette contains all four tobacco types it combines features of all of them. However, for some smoke constituents, smoking of the 2R4F reference cigarette results in exceptionally high yields which might not be attributable to the four pure tobacco types, but to other factors. In addition, comparison of the different cigarettes was also carried out by normalising the yields to puff resolved particulate matter. This procedure minimises effects caused by unequal smoke formation and represents another approach in evaluating the data. AU - Adam, T.* AU - Mitschke, S.* AU - Baker, R.B.* AU - Zimmermann, R. C1 - 3870 C2 - 24073 SP - 219-229 TI - Puff-by-puff resolved characterisation of cigarette mainstream smoke by single photon ionisation (SPI)-time-of-flight mass spectrometry (TOFMS): Comparison of the 2R4F research cigarette and pure Burley, Virginia, oriental and Maryland tobacco cigarettes. JO - Anal. Chim. Acta VL - 572 IS - 2 PY - 2006 SN - 0003-2670 ER - TY - JOUR AU - Quintana, M.* AU - Klouda, A.D.* AU - Gondikas, A.* AU - Ochsenkühn-Petropoulou, M.* AU - Michalke, B. C1 - 4897 C2 - 23713 SP - 172-180 TI - Analysis of size characterized manganese species from liver extracts using capillary zone electrophoresis coupled to inductively coupled plasma mass spectrometry (CZE-ICP-MS). JO - Anal. Chim. Acta VL - 573-574 PY - 2006 SN - 0003-2670 ER - TY - JOUR AB - For the optimisation of the extraction procedures PtCl42− and PtCl62− were used as model species for extractable Pt(II)- and Pt(IV)-compounds in road dust. A previously developed ion exchange chromatography–ICP–MS method was applied for the quantification of the Pt species in the extracts. A concept in three steps was realised. First, the stability of the model species in several extractants like HCl, methionine, EDTA and thiourea was studied under variation of the concentrations of the extracting agents, the pH and the supply of energy (refluxing, exposure to microwaves, sonication). Second, spiked road dust samples were extracted with those solvents that provided good results in the first step. The results from samples spiked with a mixture of both model species were compared to analogous extractions from dust samples which were spiked with only one of the chloroplatinates. Moreover, the extractant-to-dust-ratio was optimised. Third, the optimised procedures from the second step were applied to unspiked dust samples originating from two different road tunnels in order to characterise the extractable Pt species. The results of the optimisation proved that the model species are fairly stable in the extractants in the absence of the dust matrix. However, the recoveries of PtCl42− from the spiked dust samples were significantly lower and PtCl62− could not be recovered without transformation at all. The extraction efficiencies for total Pt from the unspiked samples were below 5%. The concentrations of the model species in the extracts of these samples were below the limit of detection of the applied HPLC–ICP–MS method. For quality control mass balances of total Pt were established for all extractions. AU - Nischwitz, V. AU - Michalke, B. AU - Kettrup, A. C1 - 4909 C2 - 21888 SP - 87-98 TI - Investigations on extraction procedures for Pt species from spiked road dust samples using HPLC-ICP-MS detection. JO - Anal. Chim. Acta VL - 521 IS - 1 PY - 2004 SN - 0003-2670 ER - TY - JOUR AB - An analytical procedure for selenium speciation of analysis of selenourea (SeU), selenoethionine (SeE), selenomethionine (SeM), Se(VI), Se(IV), dimethylselenide (dMeSe) and dimethyldiselenide (dMedSe) was developed, based on two complementary liquid chromatography (LC) techniques coupled with inductively coupled plasma-mass spectrometry (ICP-MS). Specifically, strong anion exchange (SAX) chromatography coupled with ICP-MS was used for the separation and quantification of all the earlier mentioned Se compounds, except for the two methyl selenides, which could be separated and determined by reversed phase chromatography coupled with ICP-MS. This procedure was applied to a soil sample from the warm springs area of Thermopyles (Greece). For leaching the Se species from the soil sample, four extraction methods, using water at ambient temperature, hot water, methanol and 0.5 M HCl, were tested for their efficiency of extracting the different Se species. The speciation results obtained by the LC-ICP-MS methods were compared with those obtained by voltammetric techniques. The determination of total selenium in the sample was achieved by graphite furnace atomic absorption spectrometry, as well as by ICP-atomic emission spectrometry, after suitable digestion of the sediment sample. AU - Ochsenkühn-Petropoulou, M.* AU - Michalke, B. AU - Kavouras, D.* AU - Schramel, P. C1 - 10371 C2 - 20802 SP - 219-227 TI - Selenium speciation analysis in a sediment using strong anion exchange and reversed phase chromatography coupled plasma-mass spectrometry. JO - Anal. Chim. Acta VL - 478 IS - 2 PY - 2003 SN - 0003-2670 ER - TY - JOUR AB - Measurement of urinary metabolites constitutes a non-invasive method to assess exposures resulting from all routes. An immunochemical assay (enzyme-linked immunosorbent assay) was applied for the detection of metabolites excreted in urine as the result of exposure to polycyclic aromatic hydrocarbons (PAHs). Ten male subjects potentially exposed to PAHs were employed in road bituminization. Same number of referents came from university staff. The metabolites were analyzed in an indirect competitive ELISA, using a polyclonal antiserum that has been raised against pyrenebutyric acid coupled to thyroglobulin and 1-hydroxypyrene as a calibrator. Antiserum specificity was tested with several PAH metabolites. Binding was highest for 1-hydroxypyrene (100%), was acceptable for 1-hydroxypyreneglucuronide (22%) and the phenanthrols (6–32%), but was low (<1%) for 1-hydroxypyrenesulfate, 1-naphthol, and 3-hydroxybenzo(a)pyrene. No binding was observed with 9,10-dihydroxy-9,10-dihydrophenanthrene. Results given as 1-hydroxypyrene equivalents were compared to the 1-hydroxypyrene concentration as determined by off-line solid phase extraction/HPLC analysis and the sum of 1-, 2-, 3-, 4-, 9-hydroxyphenanthrenes and 1-hydroxypyrene from coupled-column HPLC analysis. All metabolite concentrations were corrected for creatinine. PAH metabolites were detected in all of the urine samples. Results obtained with the ELISA in most samples were higher than corresponding 1-hydroxypyrene concentrations and lower than the sum of phenanthrols and 1-hydroxypyrene as measured by HPLC. With both HPLC and the ELISA no significant difference in PAH metabolite excretion of exposed subjects and referents was found, whereas urinary PAH excretion was significantly higher in smokers compared to non-smokers. It is concluded that the ELISA has proved to be a useful tool for biomonitoring studies that allows an estimation of PAH urinary excretion after a simple sample dilution and without any time-consuming preliminary enzymatic hydrolysis or derivatization. AU - Knopp, D.* AU - Schedl, M.* AU - Achatz, S. AU - Kettrup, A. AU - Niessner, R.* C1 - 21138 C2 - 19179 SP - 115-126 TI - Immunochemical test to monitor human exposure to polycyclic aromatic hydrocarbons: Urine as sample source. JO - Anal. Chim. Acta VL - 399 IS - 1-2 PY - 1999 SN - 0003-2670 ER - TY - JOUR AB - The photodegradation of fenitrothion was examined in distilled water containing methanol. After 7 h of UV irradiation with a high-pressure mercury lamp, a fractionation step was carried out on a semi-preparative silica gel column. Eighty-eight fractions were collected by increasing the polarity of an eluent mixture of n-hexane—ethyl acetate (95 + 5) up to 100% ethyl acetate. Three more polar fractions in eluent mixtures of n-hexane—acetone (50 + 50), pure acetone and acetone—methanol (25 + 75) were obtained. The breakdown products formed were identified by gas chromatography—mass spectrometry with electron impact (EI) ionization. An estimate of the amount of fenitrothion degraded indicated that after 7 h of irradiation, 10% of the parent compound still remained and different oxidation, isomerization and solvolysis products were produced. The P = S group was oxidized to give fenitrooxon and trimethyl phosphate in amounts of 0.1% and 3%, respectively. Carbomethoxyfenitrothion, due to oxidation followed by solvolysis, and the isomerization products O,O,S-trimethyl phosphorothioate and the S-methyl isomer of fenitrothion were obtained as photoalteration products at 10%, 10% and 3%, respectively. Other compounds corresponded to denitrofenitrothion, carbomethoxydenitrofenitrothion, parathion-methyl and 4-nitro-m-cresol at 0.2%, 0.4%, 0.4% and 0.4%, respectively. The EI mass spectra and the structures of the ions of the different fenitrothion photolysis products are given. AU - Durand, G. AU - Mansour, M. AU - Barcelo, D. C1 - 20196 C2 - 13375 SP - 167-178 TI - Identification and Determination of Fenitrothion Photolysis Products in Water-Methanol by Gas Chromatography-Mass Spectrometry. JO - Anal. Chim. Acta VL - 262 IS - 1 PY - 1992 SN - 0003-2670 ER - TY - JOUR AB - Measurements of time-resolved photobleaching and nanosecond fluorescence decay from microscopic samples of methanogenic bacteria are reported. From cultures of Methanobacterium thermoautotrophicum and Methanosarcina barkeri, decay times of 1 ns and 3 ns were obtained for the specific coenzymes F420 and 7-methylpterin, respectively. In contrast to methylpterin, the fluorescence of F420 was bleached selectively, with a time constant of about 160 s, at an irradiation power density of 5 mW mm-2. Similar time constants were found for samples of sewage sludge containing methanogenic bacteria. Active and inactive bacterial cells could be differentiated by following the course of photobleaching. AU - Schneckenburger, H. AU - Reuter, B.W. AU - Schoberth, S.M.* C1 - 40867 C2 - 38459 SP - 249-255 TI - Time-resolved fluorescence microscopy for measuring specific coenzymes in methanogenic bacteria. JO - Anal. Chim. Acta VL - 163 IS - C PY - 1984 SN - 0003-2670 ER - TY - JOUR AU - Schramel, P. C1 - 42663 C2 - 35520 SP - 414-418 TI - The application of peak integration in flameless atomic-absorption spectrometry. JO - Anal. Chim. Acta VL - 72 IS - 2 PY - 1974 SN - 0003-2670 ER - TY - JOUR AB - Concentrations of the elements AI, Cd, Cr, Cu, Fe, Mn, Pb and V were investigated in the International Biological Standard (IBS) of Bowen, by means of atomic-absorption spectrometry with a graphite furnace. An established wet-ashing method with concentrated sulphuric acid and hydrogen peroxide was applied. For each element, a temperature programme for the graphite furnace was worked out. The influence on the absorbance of the matrix elements Ca, K, Na, P and S was tested. Considerable interferences were found in determinations of lead and vanadium. AU - Schramel, P. C1 - 42582 C2 - 35398 SP - 69-77 TI - Determination of eight metals in the international biological standard by flameless atomic-absorption spectrometry. JO - Anal. Chim. Acta VL - 67 IS - 1 PY - 1973 SN - 0003-2670 ER -