Analysis Of N-alkanes Research Articles

Two drying methods of bovine faeces for estimating n-alkane concentration, intake and digestibility: A comparison

An experiment was completed to evaluate effects of two drying methods applied to faecal and herbage samples on estimation of n-alkane concentration and the calculated dry matter (DM) intake, faecal output (FO) and apparent in vivo DM digestibility (DMD). Four Holstein–Friesian steers (182±12.1kg initial body weight) housed in individual pens were fed at 8:30 and 16:30h with ryegrass (Lolium perenne L.) hay for 18d. Refusals were removed and weighed every day at 8:30h before morning feeding. From days 9 to 18, the steers were dosed twice a day at feeding time, with cellucotton stoppers containing C32 (88.49mg/pellet) and C36 (87.12mg/pellet). During the last 5d of dosing, total collection of faeces was completed using harnesses. For the n-alkane analysis, faecal (n=64) and offered hay (n=4) samples were subdivided into two subsamples and prepared for two alternative drying methods: oven-drying at 60°C (OD) or freeze-drying (FD). The n-alkane profiles of the offered and refused hay oven-dried at 60°C did not differ. In offered hay subsamples, concentrations of n-alkanes were not affected by drying method. In faecal subsamples, drying method affected (P<0.05) concentrations of all n-alkanes, except for C23, C25 and C35, as well as the ratios C32:C31 and C32:C33. There were no differences between estimated and measured values when DM intake and apparent in vivo DMD were estimated based on the ratio C32:C33. In contrast, when the ratio C32:C31 was used, estimated values either differed (P<0.02) or tended to differ (P<00.09) from measured values for OD and FD subsamples, respectively. Estimates of FO from subsamples OD and FD did not differ from measured values. Faecal recovery increased with increasing carbon-chain length in both drying methods. Results show that oven-drying at 60°C could replace freeze-drying for sample dehydration to estimate DM intake and apparent in vivo DMD when ratio C32:C33 was used. However, due to the low number of replicates, further studies should be conducted before use of C32:C33 ratio in oven-dried samples can be recommended.

Analyses of n-alkanes degrading community dynamics of a high-temperature methanogenic consortium enriched from production water of a petroleum reservoir by a combination of molecular techniques

Despite the knowledge on anaerobic degradation of hydrocarbons and signature metabolites in the oil reservoirs, little is known about the functioning microbes and the related biochemical pathways involved, especially about the methanogenic communities. In the present study, a methanogenic consortium enriched from high-temperature oil reservoir production water and incubated at 55 °C with a mixture of long chain n-alkanes (C(15)-C(20)) as the sole carbon and energy sources was characterized. Biodegradation of n-alkanes was observed as methane production in the alkanes-amended methanogenic enrichment reached 141.47 μmol above the controls after 749 days of incubation, corresponding to 17 % of the theoretical total. GC-MS analysis confirmed the presence of putative downstream metabolites probably from the anaerobic biodegradation of n-alkanes and indicating an incomplete conversion of the n-alkanes to methane. Enrichment cultures taken at different incubation times were subjected to microbial community analysis. Both 16S rRNA gene clone libraries and DGGE profiles showed that alkanes-degrading community was dynamic during incubation. The dominant bacterial species in the enrichment cultures were affiliated with Firmicutes members clustering with thermophilic syntrophic bacteria of the genera Moorella sp. and Gelria sp. Other represented within the bacterial community were members of the Leptospiraceae, Thermodesulfobiaceae, Thermotogaceae, Chloroflexi, Bacteroidetes and Candidate Division OP1. The archaeal community was predominantly represented by members of the phyla Crenarchaeota and Euryarchaeota. Corresponding sequences within the Euryarchaeota were associated with methanogens clustering with orders Methanomicrobiales, Methanosarcinales and Methanobacteriales. On the other hand, PCR amplification for detection of functional genes encoding the alkylsuccinate synthase α-subunit (assA) was positive in the enrichment cultures. Moreover, the appearance of a new assA gene sequence identified in day 749 supported the establishment of a functioning microbial species in the enrichment. Our results indicate that n-alkanes are converted to methane slowly by a microbial community enriched from oilfield production water and fumarate addition is most likely the initial activation step of n-alkanes degradation under thermophilic methanogenic conditions.

Oil families and their inferred source rocks in the Barents Sea and northern Timan-Pechora Basin, Russia

A geochemical study of 34 oil samples was conducted to understand the types and distributions of effective source rocks and evaluate the geographic extent of the petroleum systems in the Barents Sea and northern Timan-Pechora Basin. Taxon-specific, age-related, and source-related biological markers (biomarkers) and isotope data provided information on the depositional environment of the source rock, source input, and source age of the oil samples. A relationship between biomarker and diamondoid concentration was used to identify mixed oils having both oil window and highly cracked components. Compound-specific isotope analyses of diamondoids and n-alkanes were used to deconvolute cosourced oils and identify deep source rocks in the basin. Results suggest five major source rocks in the Barents Sea and the northern Timan-Pechora Basin: Upper Jurassic shale, Lower–Middle Jurassic shale, Triassic carbonate and shale, Devonian marl, and Devonian carbonate. The Upper and Lower–Middle Jurassic source rocks are dominant in the Barents Sea. Triassic source rock consists of carbonate in the onshore part of northern Timan-Pechora Basin and marine shale in the Barents Sea. The Devonian Domanik Formation carbonate source rock extends offshore into the southern Barents Sea. The high-maturity Domanik Formation could also be a secondary source rock for most of the mixed oils in the northern Timan-Pechora Basin. This detailed geochemical study provides a new and detailed understanding of petroleum systems in the Barents Sea and northern Timan-Pechora Basin.

Last glacial vegetation reconstructions in the extreme-continental eastern Asia: Potentials of pollen and n-alkane biomarker analyses

The current study presents quantitative reconstructions of tree cover, annual precipitation and mean July temperature derived from the pollen record from Lake Billyakh (65°17′N, 126°47′E, 340 m above sea level) spanning the last ca. 50 ka (ca. 50,000 cal yrs). The reconstruction of tree cover suggests presence of woody plants through the entire analyzed time interval, although trees played only a minor role in the vegetation around Lake Billyakh prior to 14 ka BP (<5%). This result corroborates low percentages of tree pollen and low scores of the cold deciduous forest biome in the PG1755 record from Lake Billyakh. The reconstructed values of the mean temperature of the warmest month ∼8–10 °C do not support larch forest or woodland around Lake Billyakh during the coldest phase of the last glacial between ∼32 and ∼15 ka BP. However, modern cases from northern Siberia, ca. 750 km north of Lake Billyakh, demonstrate that individual larch plants can grow within shrub and grass tundra landscape in very low mean July temperatures of about 8 °C. This makes plausible the hypothesis that the western and southern foreland of the Verkhoyansk Mountains could provide enough moist and warm microhabitats and allow individual larch specimens to survive climatic extremes of the last glacial. Reconstructed mean values of annual precipitation are about 270 mm during the last glacial interval. This value is almost 100 mm higher than modern averages reported for the extreme-continental north-eastern Siberia east of Lake Billyakh, where larch-dominated cold deciduous forest grows at present. This suggests that last glacial environments around Lake Billyakh were never too dry for larch to grow and that the insufficient summer warmth was the main factor, which limited tree growth during the last glacial interval. The n-alkane analysis of the Siberian plants presented in this study demonstrates rather complex alkane distribution patterns, which challenge the interpretation of the fossil records. In particular, extremely low n-alkane concentrations in the leaves of local coniferous trees and shrubs suggest that their contribution to the litter and therefore to the fossil lake sediments might be not high enough for tracing the Quaternary history of the needleleaved taxa using the n-alkane biomarker method.

Biomarkers, carbon isotopic composition and source rock potentials of Awgu coals, middle Benue trough, Nigeria

Coal and carbonaceous shale samples were collected from two boreholes (BH 94 and BH 120) in Awgu formation of Middle Benue Trough, Nigeria. Source rock potentials of the samples were studied using biomarkers and carbon isotopic composition. Biomarkers in the aliphatic fractions in the samples were studied using Gas Chromatography–Mass Spectrometry (GC–MS). The Carbon isotope analysis of individual n-alkanes in the aliphatic fraction was performed using Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometer (GC–IRMS). The abundance of hopanes, homohopanes (C31–C35), and C29 steranes in the samples indicate terrestrial plant, phytoplankton and cyanobacteria contributions to the organic matter that formed the coal. High (Pr/Ph) ratio (3.04–11.07) and isotopic distribution of individual alkanes showed that the samples consisted of mixed terrestrial/marine organic matter deposited under oxic condition in lacustrine–fluvial/deltaic depositional environment. The maturity parameters derived from biomarker distributions showed that the samples are in the main phase of oil window.

Organic matter compounds as source indicators and tracers for marine pollution in a western Mediterranean coastal zone

Complex organic compounds found in oil and sediments linked with a particular source (such as algae, bacteria or vascular plants) are defined as biomarkers and are useful dating indicators in organic geochemistry. This paper presents the composition of the organic matter (OM) on marine surface sediments from a degraded Tunisian coast analysed by pyrolysis and gas chromatography-mass spectrometry (GC-MS). High total OM contents (0.3-4.2%) were detected with high levels of saturated linear hydrocarbons. The aliphatic lipids had contributed with up to 11.7% of the total OM, and their distribution had consisted of resolved compounds (n-alkanes and fatty acid (FAs)) and an unresolved complex mixture. Hydrocarbons, primarily n-alkanes, were ranged from 368 to 3,886 μg g(-1). The FAs (674-2,568 μg g(-1)) were dominated by derived primary production, and the short chain FAs (C16 and C18) were the most abundant throughout. The ubiquitous presence of petroleum contamination, mainly from offshore oil exploration, discharge of pollutants from rivers, shipping activities and atmospheric deposition was found in all samples. The Gabès littoral seems to be quite to very polluted near the industrial zone of Ghannouch. The C/H ratio (generally around 5.9), the thermal analysis and GC-MS of n-alkanes and FAs showed that the OM in the studied area was composed of anthropogenic/petrogenic, marine and continental sources. Our study represents an innovative approach to assessing environmental pollution. The evaluation of organic matter by examination of sterols, alkanes and fatty acids allows the identification of source, both anthropogenic and natural.

Distribution and sources of aliphatic and polycyclic aromatic hydrocarbons in suspended particulate matter in water from two Brazilian estuarine systems

The levels of selected organic markers, including 17 polycyclic aromatic hydrocarbons (PAHs), 16 of which are classified as priority pollutants by the US-EPA and perylene, aliphatic hydrocarbons (total and linear alkanes) and petroleum biomarkers (hopanes and steranes), were measured in suspended particulate matter (SPM) of the Mundaú–Manguaba estuarine-lagoon system (MMELS) in northeastern Brazil and the Paraíba do Sul River (PSR) estuary in southeastern Brazil, both of which are affected by sugarcane agriculture and urbanization. A total of 33 surface water samples of SPM were collected (22 from the MMELS and 11 from the PSR). The ∑16PAH ranged from 221 to 1243 ng g −1 in the MMELS and from 228 to 1814 ng g −1 in the PSR. Hopane and sterane concentrations in the PSR were higher than in the MMELS due to the input from petrogenic sources in PSR. The contributions of higher plants were also observed by n-alkane analyses. The PAH isomeric ratios indicated that the SPM from MMELS showed characteristics of combustion from biomass or petroleum and PSR was associated to petrogenic input, either from combustion or from unburned petroleum. Three sampling sites located near to the sugarcane plant and mouth of the rivers showed higher PAH concentrations and may largely be considered as highly contaminated. However, levels of n-alkanes and petroleum biomarkers in both study areas were relatively low.

Revisiting petroleum systems in the Gippsland Basin using new geochemical data

The Gippsland Basin is one of the most prolific petroleum provinces in Australia, yet the understanding of source, migration and secondary alteration of petroleum is often based on data and concepts that have been developed decades ago. For instance, the Gippsland Basin is commonly cited as an explicit example of a province dominated by oil from coal, yet there is no literature using molecular and isotope geochemistry explicitly demonstrating that generation and expulsion has been from the coal seams and not the intervening carbonaceous mudstones. In this study we will present insights from the evaluation of quantitative analyses of aromatic hydrocarbons, which will be evaluated together with low molecular weight hydrocarbon distributions from whole oil gas chromatography and aliphatic biomarker distributions of the oils. Oils are commonly incrementors of different charge events, and hence extending molecular and isotopic information from a wide molecular weight range offers a more detailed insight into the charge history of an oil field. Oil-bearing fluid inclusions are additional archives that hold keys to the fill history of petroleum reservoirs, and this contribution will also present new data on the distribution and composition of palaeo-oils trapped in fluid inclusions. Lastly, examples will be presented of how modern tools for analysis such as compound specific isotopic analysis (CSIA) of n-alkanes and isoprenoids as well as how understanding relationships between organic facies and source rock kinetics can contribute to refining our understanding of petroleum systems in the Gippsland Basin.

The Use of Herbage N-alkanes as Markers to Estimate the Diet Composition of Yaks on the Qinghai-Tibetan Plateau

The chemical components in plant cuticular wax can be used as markers to estimate the species composition of the diet of grazing animals. In this experiment, composition of the diet of yak on the Qinghai-Tibetan plateau was estimated using n-alkane analysis. During the grazing period. samples of whole plants of the species present, plus fecal samples voided by the yak, were collected. air-dried and ground prior to the extraction of cuticular wax n-alkanes. The species composition of the yak diets was estimated by relating fecal alkane contents to those of the plant species, using the 'EATWHAT' software package. The results showed that the n-alkane technique can detect the main dietary components selected by yak, The diet consumed by yak contained 33% Kobresia humilis. 67% Stipa aliena in summer pasture: 26% Potentilla anserine, 74% Carex qinghaiensis in autumn pasture 52% Carex qinghaiensis. 32% Heteropappus bowerii and 16% Saussurea semifasciata in winter pasture and 5% Carex qinghaiensis. 95% Achnatherum splendens in spring pasture. The apparent selection for forbs is likely to be a reason for nutritional constraint of yak inhabiting alpine environments.

Dynamic control of split flow in packed column supercritical fluid chromatography using dual resistively heated restrictors

Remote control of the vent/detector split flow ratio in packed column supercritical fluid chromatography (pSFC) with flame ionization detector (FID) is demonstrated using a dual heated restrictor method. Restrictors stemming from a Tee at the separation column outlet were, respectively, fixed into an FID and a vent port, and their individual temperatures were controlled using resistively heated wires. Subsequently, both system pressure and split flow could be manipulated. For example, for applied restrictor temperatures examined up to 600 degrees C, corresponding vent/FID split flow ratios between 2 and 7 were observed depending on the port heated. As well, column pressures around 16-23 MPa were also achievable over the same range. Conversely, isobaric altering of the split flow ratio was possible when opposing positive and negative temperature gradients were applied at the two restrictors. Under these conditions, the system pressure varied less than 1% RSD over a 10 min period. As an application, the method was used to establish stable detector operation in the analysis of n-alkanes under pSFC-FID conditions that initiated flame instability. Results indicate that this technique could be a relatively simple and inexpensive means of controlling system pressure and detector split flow ratios in pSFC-FID.

N-Alkanes as Indicators of Natural and Anthropogenic Organic Matter Sources in the Siak River and its Estuary, E Sumatra, Indonesia

Along the Siak River and its estuary a total of 100 sediment and 57 plant samples were taken for the analysis of n-alkanes from 2003 to 2005. Sediment n-alkanes exhibit in the majority of samples a pronounced odd over even predominance with maxima at C29 and C31 indicative of a plant origin. Plant n-alkanes analysed have chain lengths up to C39. These compounds are also present in the river sediments. In some plants the Carbon Preference Index (CPI) has extremely low values normally only found in petroleum-contaminated samples. A distinction between vegetation- and petroleum-derived n-alkanes is therefore only possible by a combination of CPI and and the absence/presence of a prominent unresolved complex mixture. Based on these criteria only a limited number of the 100 sediments analysed exhibit clear indications of a petroleum contamination.

Biomarkers and compound-specific stable carbon isotope of n-alkanes in crude oils from Eastern Llanos Basin, Colombia

Representative samples of crude oils from Cusiana, Cupiagua, Apiay, Castilla and Chichimene fields in the Eastern Llanos Basin of Colombia were analyzed to determine its compound-specific stable carbon isotope composition (CSIA) using gas chromatography–isotopic ratio–mass spectrometry (GC–IRMS). GC–IRMS analyses of n-alkanes allowed differentiating between Cretaceous and Cretaceous/Tertiary oil samples. Cretaceous sourced samples have δ13C-enriched values than Cretaceous/Tertiary sourced samples; the heavier isotope composition of these samples is due to their major terrigenous organic matter input. Their isotope distribution patterns suggest significant algal and/or bacterial contribution (marine origin). The analysis of the n-alkane fractions by GC–IRMS confirms that the organic matter has marine origin in those samples from Cusiana, Cupiagua and Apiay while Castilla and Chichimene have marine origin with terrestrial inputs. The results were confirmed by gas chromatography/FID and gas chromatography/mass spectrometry (GC/MS). Basic geochemical composition show that samples from Cupiagua/Cusiana fields and Apiay/Castilla/Chichimene fields in the Llanos basin, Colombia present different characteristics reflecting a specific for each depositional environment.

Characterization and source identification of polycyclic aromatic hydrocarbons (PAHs) in river bank soils

Elevated PAH concentrations were detected in bank soils along the Mosel and Saar Rivers in Germany. Information on the identification of PAH sources in this area however remains unclear. This study was able to characterize the PAH sources by application of several approaches, including consideration of the distribution patterns of 45 PAHs (including 16 EPA PAHs and some alkyl PAHs), specific PAH ratios, distribution patterns of n-alkanes and principal component analysis (PCA). In addition, the efficiency of the tested approaches was assessed. The results from the application of the various source identification methods showed that pyrogenic PAHs dominate soil samples collected upstream of the confluence of the Mosel and Saar Rivers, and petrogenic and pyrogenic PAHs dominate samples downstream of the confluence. Based on the analysis of reference materials and organic petrography, the petrogenic input was found to be dominated by coal particles. More detailed information on the petrogenic sources was provided by the n-alkane analyses. The current study concludes that to accurately determine the origin of PAHs, several identification methods must be applied.

Improved compound‐specific δ13C analysis of n‐alkanes for application in palaeoenvironmental studies

We present an optimized method for compound-specific stable carbon isotope (delta(13)C) analysis of n-alkanes. For sample preparation, the traditionally used Soxhlet extraction was replaced by accelerated solvent extraction (ASE). delta(13)C values of individual n-alkanes--measured using gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS)--were first drift-corrected with regularly discharged pure CO(2) pulses as reference gas and, secondly, corrected for the amount dependence of the delta(13)C values by co-analyzing standards with varying analyte concentrations. Finally, the delta(13)C values were calibrated against two internal standards. The improved method was applied to selected sediment samples from a palaeoenvironmental study in subtropical NE Argentina. The measured delta(13)C values of all long-chain n-alkanes (nC(27), nC(29), nC(31) and nC(33)), representing biomarkers for terrestrial plants, correlate significantly with the delta(13)C of bulk organic matter (delta(13)C(TOC)). The latter is hence corroborated as a proxy for C3-C4 vegetation changes. Furthermore, the delta(13)C variations reveal higher amplitudes for nC(31) and nC(33) than for nC(27) and nC(29), indicating that the former n-alkanes mainly derive from C3 and/or C4 grasses, whereas the latter homologues mainly derive from C3 plants (trees and shrubs). Except for the lowermost part of the sediment core, the delta(13)C values of the mid-chain alkanes nC(23) and nC(25) do not reflect the terrestrial delta(13)C pattern, thus indicating that they are probably mainly of lacustrine origin.

Semi Volatile Organic Compounds in Ambient PM2.5. Seasonal Trends and Daily Resolved Source Contributions

Concentrations of ambient semivolatile organic compounds (SVOC) in the PM2.5 fraction of Augsburg, Germany, have been monitored on a daily basis from January 2003 through December 2004. Samples were taken in a large garden in the city center. Quantitative analysis of n-alkanes, alkanones, alkanoic acid methylesters, long chain linear alkyl benzenes and toluenes, hopanes, polycyclic aromatic hydrocarbons (PAH) and oxidized PAH, and some abietan type diterpenes was done. All compounds showed distinct seasonal variations in concentration. Most compounds showed highest concentrations during the cold seasons, but some n-alkanones and 6,10,14-trimethylpentadecanone showed maximum concentration during summer. Changes in patterns between and within compound classes were obvious, e.g., the hopane pattern exhibited a strong seasonal variation. The main source related contributions to changes observed were discussed. Using positive matrix factorization (PMF) for the statistical investigation of the data set, five factors have been separated. These factors are dominated by the pattern of single sources or groups of similar sources: factor 1, lubricating oil; factor 2, emissions of unburned diesel and heating oil consumption; factor 3, wood combustion; factor 4, brown coal combustion; and factor 5, biogenic emissions and transport components. Like the SVOC, the factors showed strong seasonality with highest values in winter for factors 1-4 and in summer for factor 5.

Protocol for the analysis of n-alkanes and other plant-wax compounds and for their use as markers for quantifying the nutrient supply of large mammalian herbivores

Plant-wax markers can be used for estimating forage intake, diet composition and supplement intake in grazing livestock, wild ruminants and other mammals. We describe protocols for using the saturated hydrocarbons (alkanes) of plant wax as markers for estimating fecal output, intake and digestibility. Procedures for investigating digestion kinetics are also discussed. Alkanes can also be used to estimate diet composition and the procedures required to do this are also described, including the special case where supplementary feed is treated as a component of the diet composition estimate. The long-chain alcohols (LCOHs) and very long-chain fatty acids (VLCFAs) of plant wax show particular promise for discriminating a greater number of species in the diet. The use of all these plant-wax markers in nutrition studies depends on having quantitative, repeatable and mutually compatible assay procedures for alkanes, LCOHs and VLCFAs; we present protocols for these assays in detail. Analysis of a single sample of feces or plant material for all these plant-wax markers can be completed within 2 days; however, it is possible to process up to 50 samples (analyzed in duplicate) per week.

Compound-specific δ13C and δ2H analyses of plant and soil organic matter: A preliminary assessment of the effects of vegetation change on ecosystem hydrology

Here we present δ 13C and δ 2H data of long-chained, even-numbered (C 27–C 31) n-alkanes from C3 (trees) and C4 (grasses) plants and from the corresponding soils from a grassland–woodland vegetation sequence in central Queensland, Australia. Our data show that δ 13C values of the C4 grassland species were heavier relative to those of C3 tree species from the woodland ( Acacia leaves) and woody grassland ( Atalaya leaves). However, n-alkanes from the C4 grasses had lighter δ 2H values relative to the Acacia leaves, but showed no significant difference in δ 2H values when compared with C3 Atalaya leaves. These results differ from those of previous studies, showing that C4 grasses had heavier δ 2H values relative to C3 grasses and trees. Those observations have been explained by C4 plants accessing the more evaporation-influenced and isotopically heavier surface water and tree roots sourcing deeper, isotopically lighter soil water (“Two-layered soil–water system”). By comparison, our data suggest that ecosystem changes (vegetation “thickening”) can significantly alter the soil hydrological characteristics. This is shown by the heavier δ 2H values in the woodland soil compared with lighter δ 2H values in the grassland soil, implying that the recent vegetation change (increased tree biomass) in the woodland had altered soil hydrological conditions. Estimated δ 2H values of the source-water for vegetation in the grassland and woodland showed that both trees and grasses in open settings accessed water with lighter δ 2H values (avg. −46‰) compared with water accessed by trees in the woodland vegetation (avg. −7‰). These data suggest that in semi-arid environments the “two-layer” soil water concept might not apply. Furthermore, our data indicate that compound-specific δ 2H and δ 13C analyses of n-alkanes from soil organic matter can be used to successfully differentiate between water sources of different vegetation types (grasses versus trees) in natural ecosystems.

Analysis of n-alkanes in water samples by means of headspace solvent microextraction and gas chromatography

A simple and efficient headspace solvent microextraction (HSME) was developed for the simultaneous determination of the trace concentrations of some n-alkanes in water samples. Therefore, a microdrop of an organic solvent was extruded from the needle tip of a gas chromatographic syringe to the headspace above the surface of the solution in a sealed vial. Then the volatile organic compounds are extracted and concentrated in the microdrop. Next, the microdrop was retracted into the microsyringe and injected directly into the gas chromatograph. Experimental parameters which control the performance of HSME such as the type of microextraction solvent, organic drop and sample volume, sample stirring rate, sample solution and microsyringe needle temperatures, salt addition and exposure time profiles were investigated and optimized. Finally, the enrichment factor, dynamic linear range (DLR), limit of detection (LOD) and precision of the method were evaluated. Using optimum extraction conditions, good linearity with correlation coefficients in the range of 0.995 < r 2 < 0.999, suitable precision (%2.3 < R.S.D. < %7.2) and low detection limits (0.1–4.0 μg/l) were achieved. The HSME was performed for determination of n-alkanes in different types of natural water samples and acceptable recoveries were obtained. The results demonstrated that HSME is a rapid, accurate and effective sample preparation method and could be successfully applied for the determination of n-alkanes in water samples.

Effect of method of conservation on the n-alkane C31 concentration of two legumes and three temperate grasses

SummaryThe objective of this study was to compare five methods of forage preservation (ice, dry ice, liquid-N, drying in newspaper, and sundried) on the concentration of the n-alkane C31 in Medicago sativa cv Puebla 76 (lucerne/alfalfa), Trifolium repens latum (white clover), Lolium perenne (perennial ryegrass), Pennisetum clandestinum (kikuyu grass) and Dactylis glomerata (orchardgrass/cocksfoot). The sampled forages in ice and dry ice were kept in hermetically sealed plastic bags in a plastic cooler. The deep frozen samples were put into small plastic bags and submerged in liquid-N. The samples dried in newspaper were placed between sheets of newspaper, and put into hermetically sealed plastic bags. All these samples were taken to the laboratory and freeze-dried approximately 24 h later. The sun-dried samples were taken to the laboratory in newspaper and sun-dried for 48 h. The forage samples were ground and worked on in triplicate, extracted by the Soxhlet method (C34 n-alkane was used as standard and n-heptane as solvent), saponified, separated, purified and injected into a gas chromatograph. The data were analysed for variance as a randomised factorial (n=74). The comparison between means was by the Boneferroni test (P&lt;0.05). The interaction between forage and method of conservation was significant P&lt;0.0001). There were no differences between methods of conservation for white clover (mean 26mg C31/kg DM) or orchardgrass/cocksfoot (mean 31 mgC31/ kgDM). In comparison with liquid-N, (261 mgC31/kgDM), the other methods reduced the concentration of n-alkane in kikuyu grass by 27-35%. Sun and newspaper dried samples increased the concentration of C31 in alfalfa/lucerne by 6 and 15% respectively in comparison with freezing with liquid-N (291 mgC31/kgDM), while that frozen on ice reduced C31 by about 8%. This method, however, increased the ryegrass n-alkane by 12% in relation to liquid-N (169 mgC31/kgDM), but sun drying reduced it by about 40%. It is concluded that drying in liquid-N is the most reliable method for the conservation of samples for n-alkane analysis.

In-injection port thermal desorption and subsequent gas chromatography–mass spectrometric analysis of polycyclic aromatic hydrocarbons and n-alkanes in atmospheric aerosol samples

The traditional approach for analysis of aerosol organics is to extract aerosol materials collected on filter substrates with organic solvents followed by solvent evaporation and analytical separation and detection. This approach has the weaknesses of being labor intensive and being prone to contamination from the extracting solvents. We describe here an alternative approach for the analysis of aerosol alkanes and polycyclic aromatic hydrocarbons (PAHs) that obviates the use of solvents. In our approach, small strips of aerosol-laden filter materials are packed into a GC split/splitless injector liner. Alkanes and PAHs on the filter are thermally desorbed in the injection port and focused onto the head of a GC column for subsequent separation and detection. No instrument modification is necessary to accommodate the introduction of the aerosol organics into the GC–MS system. Comparison studies were carried out on a set of 16 ambient aerosol samples using our in-injection port thermal desorption (TD) method and the traditional solvent extraction method. Reasonably good agreement of individual alkanes and PAHs by the two methods was demonstrated for the ambient samples. The in-injection port thermal desorption method requires much less filter material for detecting the same air concentrations of alkanes and PAHs.