Global occurrence and heterogeneity of the Roseobacter-clade species Ruegeria mobilis.

Tropodithietic acid (TDA)-producing Ruegeria mobilis strains of the Roseobacter clade have primarily been isolated from marine aquaculture and have probiotic potential due to inhibition of fish pathogens. We hypothesized that TDA producers with additional novel features are present in the oceanic environment. We isolated 42 TDA-producing R. mobilis strains during a global marine research cruise. While highly similar on the 16S ribosomal RNA gene level (99-100% identity), the strains separated into four sub-clusters in a multilocus sequence analysis. They were further differentiated to the strain level by average nucleotide identity using pairwise genome comparison. The four sub-clusters could not be associated with a specific environmental niche, however, correlated with the pattern of sub-typing using co-isolated phages, the number of prophages in the genomes and the distribution in ocean provinces. Major genomic differences within the sub-clusters include prophages and toxin-antitoxin systems. In general, the genome of R. mobilis revealed adaptation to a particle-associated life style and querying TARA ocean data confirmed that R. mobilis is more abundant in the particle-associated fraction than in the free-living fraction occurring in 40% and 6% of the samples, respectively. Our data and the TARA data, although lacking sufficient data from the polar regions, demonstrate that R. mobilis is a globally distributed marine bacterial species found primarily in the upper open oceans. It has preserved key phenotypic behaviors such as the production of TDA, but contains diverse sub-clusters, which could provide new capabilities for utilization in aquaculture.

Direct µ-flow injection isotope dilution ICP-MS for the determination of heavy metals in oil samples.

The determination of trace elements in oil samples and their products is of high interest as their presence significantly affects refinery processes and the environment by possible impact of their combustion products. In this context, inductively coupled plasma mass spectrometry (ICP-MS) plays an important role due to its outstanding analytical properties in the quantification of trace elements. In this work, we present the accurate and precise determination of selected heavy metals in oil samples by making use of the combination of µ-flow direct injection and isotope dilution ICP-MS (ICP-IDMS). Spike solutions of (62)Ni, (97)Mo, (117)Sn and (206)Pb were prepared in an organic solvent, mixed directly with the diluted oil samples and tested to be fit for purpose for the intended ID approach. The analysis of real samples revealed strong matrix effects affecting the ICP-MS sensitivity, but not the isotope ratio measurements, so that accurate results are obtained by ICP-IDMS. Typical relative standard deviations were about 15% for peak area and peak height measurements, whereas the isotope ratios were not significantly affected (RSD < 2%). The developed method was validated by the analysis of a metallo-organic multi-element standard (SCP-21, typically applied as a calibration standard) and the standard reference material SRM1084a (wear metals in lubricating oil). The obtained results were in excellent agreement with the certified values (recoveries between 98% and 102%), so the proposed methodology of combining µ-flow direct injection and ICP-IDMS can be regarded as a new tool for the matrix-independent, multi-element and reliable determination of trace elements in oil and related organic liquids.

Sulfur trace determination in petroleum products by isotope dilution ICP-MS using direct injection by thermal vaporization (TV-ICP-IDMS).

An accurate, sensitive, and fast method for direct determination of total sulfur in petroleum products after thermal vaporization of an isotope-diluted sample was developed by using ICP-MS. (34)S-labelled dibenzothiophene spike was used for the isotope dilution step. The isotope-diluted sample was injected into a thermal vaporizer which was directly connected by a heated transfer line to the plasma torch. Sample transport was achieved by using a helium gas flow, and the isotope ratio (34)S/(32)S was determined within seconds after injection. No other sample preparation other than the simple and fast isotope dilution step, which enables accurate and sensitive determination of sulfur at high sample throughputs, is necessary. Thus, this technique fits all needs for routine analyses. Validation of the TV-ICP-IDMS method was carried out by analyzing the certified gas oil reference materials BCR672 and BCR107. Comparison of results for noncertified low- and high-boiling samples, obtained from an ICP-IDMS microwave-assisted digestion method, also resulted in very good agreement. The low detection limit of 40 ng/g and the large dynamic range of TV-ICP-IDMS fulfill all necessities to allow analysis of sulfur in different petroleum products, e.g., even at the low concentration level of 'sulfur-free' gasoline.

Development of a species-unspecific isotope dilution GC-ICPMS method for possible routine quantification of sulfur species in petroleum products.

Inductively coupled plasma mass spectrometry (ICPMS) hyphenated with capillary gas chromatography was applied for sulfur multispecies determination in petroleum products by species-unspecific isotope dilution mass spectrometry (IDMS). To guarantee a stable and continuous addition of the spike into the GC-ICPMS system, a special dosing unit was designed and synthesis of a (34)S-labeled dimethyldisulfide spike from (34)S-enriched elemental sulfur in the milligram range was developed. The sample was mixed with an internal standard for spike mass flow calibration. From the mass flow chromatogram obtained by species-unspecific GC-ICP-IDMS, determination of all separated sulfur species and of the total sulfur content was possible without any matrix influence by coeluting hydrocarbons. The accuracy of the developed method was evaluated by determining reference material SRM-2296 certified for three sulfur species and by comparison of results obtained by species-specific GC-ICP-IDMS. The total sulfur concentration determined for all separated species agreed well with the sulfur content in the original samples which demonstrated that all sulfur species have been covered. Structural characterization of sulfur species was carried out by corresponding sulfur standards and by applying electron ionization ion trap mass spectrometry. The low detection limit of 9 ng sulfur per gram sample, independent of results on coeluting hydrocarbons, and the robust instrumental design of the continuous spike flow dosing unit qualifies this species-unspecific GC-ICP-IDMS method for accurate and sensitive sulfur multispecies determinations also on a routine basis.

Development of a species-specific isotope dilution GC-ICP-MS method for the determination of thiophene derivates in petroleum products.

A species-specific isotope dilution technique for accurate determination of sulfur species in low- and high-boiling petroleum products was developed by coupling capillary gas chromatography with quadrupole ICP-MS (GC-ICP-IDMS). For the isotope dilution step 34S-labeled thiophene, dibenzothiophene, and mixed dibenzothiophene/4-methyldibenzothiophene spike compounds were synthesized on the milligram scale from elemental 34S-enriched sulfur. Thiophene was determined in gasoline, 'sulfur-free' gasoline, and naphtha. By analyzing reference material NIST SRM 2296, the accuracy of species-specific GC-ICP-IDMS was demonstrated by an excellent agreement with the certified value. The detection limit is always limited by the background noise of the isotope chromatograms and was determined for thiophene to be 7 pg absolute, which corresponds to 7 ng sulfur/g sample under the experimental conditions used. Dibenzothiophene and 4-methyldibenzothiophene were determined in different high-boiling petroleum products like gas oil, diesel fuel, and heating oil. In this case a large concentration range from about < 0.04 to more than 2,000 microg g(-1) was covered for both sulfur species. By parallel GC-ICP-MS and GC-EI-MS experiments (EI-MS electron impact ionization mass spectrometry) the substantial influence of co-eluting hydrocarbons on the ICP-MS sulfur signal was demonstrated, which can significantly affect results obtained by external calibration but not those by the isotope dilution technique.

Development of an accurate, sensitive, and robust isotope dilution laser ablation ICP-MS method for simultaneous multi-element analysis (chlorine, sulfur, and heavy metals) in coal samples.

A method for the direct multi-element determination of Cl, S, Hg, Pb, Cd, U, Br, Cr, Cu, Fe, and Zn in powdered coal samples has been developed by applying inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) with laser-assisted introduction into the plasma. A sector-field ICP-MS with a mass resolution of 4,000 and a high-ablation rate laser ablation system provided significantly better sensitivity, detection limits, and accuracy compared to a conventional laser ablation system coupled with a quadrupole ICP-MS. The sensitivity ranges from about 590 cps for (35)Cl+ to more than 6 x 10(5) cps for (238)U+ for 1 microg of trace element per gram of coal sample. Detection limits vary from 450 ng g(-1) for chlorine and 18 ng g(-1) for sulfur to 9.5 pg g(-1) for mercury and 0.3 pg g(-1) for uranium. Analyses of minor and trace elements in four certified reference materials (BCR-180 Gas Coal, BCR-331 Steam Coal, SRM 1632c Trace Elements in Coal, SRM 1635 Trace Elements in Coal) yielded good agreement of usually not more than 5% deviation from the certified values and precisions of less than 10% relative standard deviation for most elements. Higher relative standard deviations were found for particular elements such as Hg and Cd caused by inhomogeneities due to associations of these elements within micro-inclusions in coal which was demonstrated for Hg in SRM 1635, SRM 1632c, and another standard reference material (SRM 2682b, Sulfur and Mercury in Coal). The developed LA-ICP-IDMS method with its simple sample pretreatment opens the possibility for accurate, fast, and highly sensitive determinations of environmentally critical contaminants in coal as well as of trace impurities in similar sample materials like graphite powder and activated charcoal on a routine basis.

Isotope dilution ICP-MS with laser-assisted sample introduction for direct determination of sulfur in petroleum products.

Inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) with direct laser-assisted introduction of isotope-diluted samples into the plasma, using a laser ablation system with high ablation rates, was developed for accurate sulfur determinations in different petroleum products such as 'sulfur-free' premium gasoline, diesel fuel, and heating oil. Two certified gas oil reference materials were analyzed for method validation. Two different 34S-enriched spike compounds, namely, elementary sulfur dissolved in xylene and dibenzothiophene in hexane, were synthesized and tested for their usefulness in this isotope dilution technique. The isotope-diluted sample was adsorbed on a filter-paper-like material, which was fixed in a special holder for irradiation by the laser beam. Under these conditions no time-dependent spike/analyte fractionation was only observed for the dibenzothiophene spike during the laser ablation process, which means that the measured 34S/32S isotope ratio of the isotope-diluted sample remained constant-a necessary precondition for accurate results with the isotope dilution technique. A comparison of LA-ICP-IDMS results with the certified values of the gas oil reference materials and with results obtained from ICP-IDMS analyses with wet sample digestion demonstrated the accuracy of the new LA-ICP-IDMS method in the concentration range of 9.2 microg g(-1) ('sulfur-free' premium gasoline) to 10.4 mg g(-1) (gas oil reference material BCR 107). The detection limit for sulfur by LA-ICP-IDMS is 0.04 microg g(-1) and the analysis time is only about 10 min, which therefore also qualifies this method for accurate determinations of low sulfur contents in petroleum products on a routine level.

Accurate determination of sulfur in gasoline and related fuel samples using isotope dilution ICP-MS with direct sample injection and microwave-assisted digestion.

Inductively coupled plasma isotope-dilution mass spectrometry (ICP-IDMS) with direct injection of isotope-diluted samples into the plasma, using a direct injection high-efficiency nebulizer (DIHEN), was applied for accurate sulfur determinations in sulfur-free premium gasoline, gas oil, diesel fuel, and heating oil. For direct injection a micro-emulsion consisting of the corresponding organic sample and an aqueous 34S-enriched spike solution with additions of tetrahydronaphthalene and Triton X-100, was prepared. The ICP-MS parameters were optimized with respect to high sulfur ion intensities, low mass-bias values, and high precision of 32S/34S ratio measurements. For validation of the DIHEN-ICP-IDMS method two certified gas oil reference materials (BCR 107 and BCR 672) were analyzed. For comparison a wet-chemical ICP-IDMS method was applied with microwave-assisted digestion using decomposition of samples in a closed quartz vessel inserted into a normal microwave system. The results from both ICP-IDMS methods agree well with the certified values of the reference materials and also with each other for analyses of other samples. However, the standard deviation of DIHEN-ICP-IDMS was about a factor of two higher (5-6% RSD at concentration levels above 100 mircog g(-1)) compared with those of wet-chemical ICP-IDMS, mainly due to inhomogeneities of the micro-emulsion, which causes additional plasma instabilities. Detection limits of 4 and 18 microg g(-1) were obtained for ICP-IDMS in connection with microwave-assisted digestion and DIHEN-ICP-IDMS, respectively, with a sulfur background of the used Milli-Q water as the main limiting factor for both methods.