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Int J Mol Sci. 2010; 11(4): 1434–1457.
Published online 2010 March 31. doi:  10.3390/ijms11041434
PMCID: PMC2871125

Origin and Distribution of Thiophenes and Furans in Gas Discharges from Active Volcanoes and Geothermal Systems


The composition of non-methane organic volatile compounds (VOCs) determined in 139 thermal gas discharges from 18 different geothermal and volcanic systems in Italy and Latin America, consists of C2–C20 species pertaining to the alkanes, alkenes, aromatics and O-, S- and N-bearing classes of compounds. Thiophenes and mono-aromatics, especially the methylated species, are strongly enriched in fluids emissions related to hydrothermal systems. Addition of hydrogen sulphide to dienes and electrophilic methylation involving halogenated radicals may be invoked for the formation of these species. On the contrary, the formation of furans, with the only exception of C4H8O, seems to be favoured at oxidizing conditions and relatively high temperatures, although mechanisms similar to those hypothesized for the production of thiophenes can be suggested. Such thermodynamic features are typical of fluid reservoirs feeding high-temperature thermal discharges of volcanoes characterised by strong degassing activity, which are likely affected by conspicuous contribution from a magmatic source. The composition of heteroaromatics in fluids naturally discharged from active volcanoes and geothermal areas can then be considered largely dependent on the interplay between hydrothermal vs. magmatic contributions. This implies that they can be used as useful geochemical tools to be successfully applied in both volcanic monitoring and geothermal prospection.

Keywords: heteroaromatics, geothermal fluids, volcanic fluids, furans, thiophenes

1. Introduction

Chemical constituents released from gas discharges in active and quiescent volcanic complexes and geothermal systems can be related to: 1) primary (magma degassing) and 2) secondary (gas-water-rock interactions occurring at relatively shallow depth) sources. The ratio between magmatic vs. hydrothermal contributions is generally indicative of the state of activity of a volcanic system and is a basic parameter in terms of volcanic surveillance [14]. Magma degassing produces highly acidic and corrosive gas compounds that may affect the geothermal potential of a hydrothermal reservoir. Hydrothermal fluid composition is constituted by water vapor and CO2 and show significant concentrations of reduced gas species, such as H2S, H2 CO and CH4 [5,6]. Magmatic-related fluid contributions, although mainly consisting of the same gases dominating hydrothermal fluids, i.e., water vapor and CO2, can unequivocally be recognized in thermal discharges by the presence of highly acidic compounds, especially SO2 [79]. Secondary interactions, such as gas scrubbing processes within shallow aquifers [10,11], are able to strongly affect this highly soluble and reactive gas compounds, frequently masking any clue of magmatic-related fluid contribution at surface. The behaviour of hydrocarbons in natural fluid discharges has recently been considered as a potential tool to investigate the thermodynamic conditions controlling fluid reservoirs feeding fumarolic exhalations in volcanic and geothermal systems [1215]. These investigations have demonstrated that light hydrocarbons, especially the C2–C4 alkenes-alkanes pairs, play an important role in both geochemical surveillance of volcanic systems and geothermal prospection. On the contrary, little attention was devoted to heavier organic compounds for similar purposes.

In the present work, 139 gas emissions from active volcanoes and geothermal systems set in different geodynamical environments were analysed for the determination of non-methane VOC (Volatile Organic Compound) composition, especially that of heteroaromatic and aromatic compounds. On the basis of this dataset, the main goals were to: 1) assess the origin of thiophenes and furans in naturally discharged fluids and 2) evaluate the possible use of these compounds as geochemical tracers to discriminate different fluid source regions in volcanic-hydrothermal environment.

2. Results and Discussion

2.1. Chemical Composition of the Main Gas Species

A representative composition of the main gas components in fluid discharges from the volcanic and geothermal systems investigated in the present study is listed in Table 1. Gas concentrations are expressed in μmol/mol and referred to the dry gas phase. Gas samples from Teide (Spain), Turrialba (Costa Rica), Vulcano (Italy), Lascar and Tacora (Chile) volcanoes have outlet temperatures varying in a wide range (from 72 to 405 °C) and show a chemical composition dominated by CO2 and characterised by variable amounts of SO2 (from 1.2 to 569394 μmol/mol).

Table 1.
Chemical composition of the main gas species. Concentrations are in μmol/mol.

Such features, coupled with relatively low concentrations of CH4 (<690 μmol/mol) and high concentrations of HCl (from 351 to 74540 μmol/mol) and H2 (up to 32591 μmol/mol), indicate that the gas chemistry of these systems is strongly controlled by magma degassing [16]. This hypothesis is in agreement with previous studies [1720] that investigated the source of fluids produced by the intense fumarolic activity recently observed at these volcanic systems. A different chemistry characterises gases from (1) El Tatio (Chile), Larderello (Italy) and Tendaho (Ethiopia) geothermal systems [2123] (samples #48–64), and (2) volcanoes whose degassing activity is considered to be mainly related to boiling of extended hydrothermal reservoirs (Copahue, Argentina; Deception, Antarctica; El Chichon, Mexico; Ischia, Pantelleria, Phlegrean Fields and Vesuvio, Italy; Nisyros, Greece; Tatun, Taiwan; Yellowstone, USA) [2431] (samples #65–139). This group shows SO2 below the instrumental detection limit (≈0.01μmol/mol: samples #48–138), relatively low outlet temperatures <118 °C, high CH4 concentrations (up to 64103 μmol/mol), and HCl not exceeding 500 μmol/mol.

2.2. VOC Composition

Up to 129 different non-methane VOCs, pertaining to the alkane (27 compounds), aromatic (21 compounds), cyclic (17 compounds), alkene (15 compounds), Cl-bearing (13 compounds), O-bearing (ketones, aldehydes, organic acids and alcohols; 36 compounds) and heteroaromatic (7 compounds) groups, were determined (Table 2; gas concentrations are expressed in ppb by volume and referred to the dry gas phase). The total VOC concentrations in gases with a dominating magmatic contribution (samples #1–47, hereafter M gases) are relatively low (from 61 to 1664 ppbv), whereas they range from 180 to 1235942 ppbv (Table 2) in those gases (#48–141) characterised by prevalent hydrothermal contribution (hereafter H gases). Hydrothermal reservoirs, even when associated with volcanic systems, are commonly recharged by fluids circulating within organic-bearing sedimentary rocks. This organic source is then transformed into VOCs through biogenic and thermogenic processes [32]. Therefore, relatively high VOC concentrations in the H gases are expected. On the contrary, the organic-rich component constitutes a minor fraction of the M gases, since it is generally destroyed by high-temperature, oxidizing fluids released from the magmatic melts [13]. The relative percentages (mean values) of the different groups of VOCs can provide preliminary indications to distinguish the M and H gases: in the M gases, alkane, Cl-bearing, aromatic, heteroaromatic and alkene compounds are present in almost comparable amounts (31, 28, 16, 16 and 9% of total VOCs, respectively), whereas cyclic and O-bearing species represent a small VOC fraction (<0.04%) (Figure 1a). The organic fraction of the H gases is largely dominated by alkanes and aromatics (54 and 24%, respectively) with minor cyclic, alkene, heteroaromatic and O-bearing compounds (from 0.7 to 1.4%), and traces (<0.04%) of Cl-bearing compounds (Figure 1b). These evidences are consistent with recent investigations that have highlighted a recurrent relation between VOC speciation and thermodynamic conditions at the fluid source in gas discharges from volcanic and geothermal systems [3336]. Predominance of alkanes and aromatics in both the M and H gases was considered to reflect the proceeding of “reforming” processes, which in geothermal areas, as well as in hydrothermal systems commonly surroundings active volcanoes, are favoured by the large availability of catalytic agents, such as free acids, allumosilicates and sulphur gas species [37,38]. Pyrolysis of organic material was found to produce mostly alkanes and, secondarily, aromatics [39,40], whereas Fischer-Tropsch reactions were invoked for the production of light alkanes and, at a minor extent, alkenes [41]. The presence of halocarbons in volcanic gas emissions was attributed to either the product of pyrolysis of adjacent vegetation [42,43] or, alternatively, air contamination [44,45]. Conversely, organic geochemical evidence supported a pristine abiogenic origin by high-temperature gas-phase radical reactions [46,47].

Figure 1.
Relative concentrations, expressed as % of the total VOC abundances, of alkane, aromatic, cyclic, alkene, Cl-bearing, O-bearing and heteroaromatic compounds in (a) M and (b) H gases.
Table 2.
Composition of main VOC groups. Concentrations are in ppbv.

2.3. Distribution and Origin of the Heteroaromatic Compounds

Concentrations (in ppbv, referred to the dry gas phase) of C4H4O, 3-C5H6O, C4H8O, 2-C5H10O, C4H4S, 3-C5H6S and 2,5-C6H8S, and those of the simplest aromatics (C6H6 and C7H8), are reported in Table 3. In the M gases, the concentrations of furans tend to be higher than those of thiophenes (their sum ranging from 1.9 to 35 and from 0.2 to 26 ppbv, respectively); C4H4S is largely the most abundant S-bearing compound (up to 1.9 ppbv), whereas C4H4O (up to 31 ppbv) dominates the furan composition. Conversely, the H gases have relatively high concentrations of C4H4S and 3-C5H6S (up to 191 and 121 ppbv, respectively), minor 2,4-C6H8S (up to 13 ppbv), and no furans, with the only exception of those from Deception, Nisyros, Vesuvio, Copahue and El Chichon volcanoes. As shown in Figure 2, in the H gases thiophenes are strongly related to H2S, (in hydrothermal environment SO2 concentrations are the below detection limit; Table 1). This correlation would imply that the formation of the S-bearing heteroaromatics intimately depends on sulphur fugacity (fS) at the fluid source, and likely occurs within deep fluid reservoirs where H2S is also produced. This hypothesis is consistent with the composition of fluids from carbonate reservoirs affected by thermochemical sulphate reduction: the higher the H2S fugacity, the higher content of organic sulphur compounds in the coexisting hydrocarbon phase [48,49]. Moreover, sulphidation of organic matter giving rise to thiophenes was found to be associated with gold mineralization deriving from hydrothermal fluids [50,51]. According to these considerations, it is reasonable to suppose that thiophenes can efficiently be produced in a hydrothermal reservoir, this environment being commonly characterised by reducing conditions, relatively high fS and temperature <350 °C [5,6]. Production of C4H4S by reaction of light alkenes, such as C2H4, with FeS2 and H2S was invoked to explain their presence in the volcanic gases emitted from Mt. Etna [52].

Figure 2.
(H2S + SO2) vs. (C4H4S + 3C5H6S + 2,4C6H8S) binary diagram. Green triangle: H gas; red circle: M gas.
Table 3.
Composition of heteroaromatics, C6H6 and C7H8. Concentrations are in ppbv.

On an industrial scale thiophene is synthesized through the following catalytic processes: 1) reaction of C4+ alcohols or carbonyls with CS2 over alkali-promoted alumina; 2) reaction of unsaturated aldehydes with H2S over an alkali-promoted alumina; 3) reaction of C4+ alkyl hydrocarbons or olefins with CS2, S, and H2S over alkali-promoted alumina; 4) catalytic dehydrogenation of tetrahydrothiophene; 5) synthesis from furan and H2S over alumina [5356]. The thiophene Paal-Knorr synthesis involves the reaction of 1,4-diketones with H2S as sulphurising agent [57]. Generally speaking, in gases from natural fluid discharges, the most reliable genetic mechanism for the formation of thiophene is through the addition of H2S to dienes in the presence of H+ and metal catalysts (Scheme 1).

Scheme 1.
Synthesis of C4H4S from butadiene.

In the M gases heteroaromatics and inorganic sulphur-bearing gases, the latter being constituted by SO2 and H2S at comparable concentrations (Table 1), are apparently showing an inverse correlation (Figure 2). This suggests that thiophenes, which are less reactive than other five-membered heteroaromatics, including furans, serving as dienes during Diels-Alder reactions [58], tend to be destroyed when fluid reservoirs are affected by conspicuous contribution from magmatic degassing.

The C4H4S concentrations and those of 3-C5H6S (Figure 3a) and C6H6 (Figure 3b) show a positive correlation in both H and M gases. This supports the following hypotheses: 1) at hydrothermal conditions mono-aromatics and thiophenes are efficiently produced by similar genetic processes; 2) all these compounds have a similar behaviour in response to thermodynamic conditions caused by presence of oxidizing and high temperature (>400 °C) magmatic fluids.

Figure 3.
(a) 3-C5H6S vs. C4H4S and (b) C6H6 vs. C4H4S binary diagrams. Symbols as in Figure 2.

It is worth noting that the H gases have higher 3-C5H6S/C4H4S and C7H8/C6H6 ratios than the M ones (Figure 4). This may be caused by the large availability of CH4 (Table 1) and light hydrocarbons (Table 2) that at hydrothermal conditions can produce free and halogenated radicals that favour the production of 3-C5H6S from C4H4S, as well as that of C7H8 from C6H6. Attach of XCH3+ (X = F or Cl), whose formation likely occurs in both geothermal and volcanic fluid reservoirs where halogenated species are abundant [69], on thiophene may give rise to the corresponding methylated derivatives [59]. It is worthy of noting that 3-C4H4S is the only methyl-thiophene recognized in both geothermal and volcanic gases (Table 3), although electrophilic methylation of thiophene is able to produce different isomers. This may be explained by the occurrence of secondary isomerization of methylated thiophenes favouring 3-C4H4S that results the thermodynamically most stable isomer in natural environments. Alternatively, 3-C4H4S may be produced through H2S adding to dienes, such as 2-methylbutadiene originated by isomerization of 1.3-pentadiene (Scheme 2). Double methylation seems to be favoured when methyl substitutions are stabilized at positions 2 and 4 (Table 3).

Figure 4.
3-C5H6S/C4H4S vs. C7H8/C6H6 binary diagram. Symbols as in Figure 2.
Scheme 2.
3-Methylthiophene production from 2-methylbutadiene.

In the M gases, C4H4O is inversely correlated to C4H4S (Figure 5). This suggests that the production of C4H4O is particularly efficient in a magmatic-related environment, where thermodynamic conditions promote the destruction of thiophenes and aromatics.

Figure 5.
C4H4O vs. C4H4S binary diagram. Symbols as in Figure 2.

The main mechanism of formation of C4H4O may be related to the Paal-Knorr synthesis (Scheme 3), which is efficient under acidic conditions, such as those determined by the huge amounts of highly acidic gas species (HF, HCl and SO2) occurring in the M gases (Table 1).

Scheme 3.
Paal-Knorr synthesis of C4H4O.

As shown in Figure 6, the H and M gases can also be clearly distinguished on the basis of the relative concentrations of furans: C4H8O is dominant in the H gases, whereas C4H4O is the most abundant O-bearing heteroaromatic species in the M gases. This suggests that reducing conditions and relatively low temperature (<350 °C), typical of hydrothermal environments, tend to favour the consumption of C4H4O to produce C4H8O through catalytic hydrogenation (Scheme 4) [60,61].

Figure 6.
C4H4O-C5H6O-C4H8O triangular diagram. Symbols as in Figure 2.
Scheme 4.
Furan hydrogenation to form C4H8O.

3. Experimental Section

3.1. Gas Sampling Method

Gas samples for the determination of the main gas species were collected into pre-evacuated 60 mL glass flasks filled with 20 mL of a 4N NaOH and 0.15 M Cd(OH)2 suspension. Quartz-glass dewar tubes and a plastic funnel were used to convoy the gas into the sampling flasks from 1) fumarolic vents and 2) boiling pools, respectively. During sampling, CO2, SO2 and HCl dissolved into the alkaline solution, water vapour condensed, and H2S reacted with Cd2+ to form insoluble CdS, allowing the residual gases (N2, CH4, Ar, O2, H2, and light hydrocarbons) to be concentrated in the head-space [6264]. Gas samples for the determination of VOC composition were collected with the same devices used for the conventional gas sampling, and stored into pre-evacuated 12 mL glass vials equipped with pierceable rubber septum (Labco Exetainer®).

3.2. Analytical Methods

Nitrogen, Ar, O2 and H2 were analysed with a Shimadzu 15A gas-chromatograph equipped with Thermal Conductivity Detector (TCD) and a 9 m, 5A molecular sieve column. Methane and C1–C4 alkanes and alkenes were analysed with a Shimadzu 14a gas-chromatograph equipped with Flame Ionization Detector (FID) and a 10 m long stainless steel column ([var phi] = 2 mm) packed with Chromosorb PAW 80/100 mesh coated with 23% SP 1700. The alkaline solution, separated from the solid precipitate by centrifugation at 4,000 rpm for 30 min, was used for the determination of: 1) CO2 as CO32− by titration with 0.5 N HCl solution; 2) SO2 as SO42−, after oxidation with H2O2, by ion-chromatography (Metrohm Compact 761); 3) HCl, as Cl by ion-chromatography. The solid precipitate was oxidized by H2O2 to determine H2S as SO42− by ion-chromatography [63,64]. The analytical error is <5%.

The VOCs were pre-concentrated and transferred from the sampling vials into the column headspace of a Thermo Trace GC Ultra gas chromatograph by using a manual SPME (solid-phase micro-extraction) device introduced through the silicon membrane of the glass vial to expose the gas mixtures to a divinylbenzene (DVB)-Carboxen-polydimethylsiloxane (PDMS), 50/30 μm, 2 cm long fibre assembly (Supelco; Bellefonte, PA, USA) for 15 min [65]. The usefulness of the SPME method [66] for the VOC analysis has widely been demonstrated [6769]. The DVB-Carboxen-PDMS fibre was selected by its high retentive properties, a feature that is particularly appropriate for analysis aimed to the determination of the organic compounds of interest for the present paper. A Thermo Trace GC Ultra gas chromatograph coupled with a Thermo DSQ Quadrupole Mass Spectrometer was used for analytical separation and detection. The mass spectrometer operated in full scan mode, in the mass range 40–400 m/z. The transfer-line temperature was set at 230 °C. The mass detector was equipped with EI set at 70 eV. The source temperature was 250 °C. The gas chromatograph was equipped with a split/splitless injection port operating in the splitless mode with a dedicated SPME liner (0.75 mm i.d.). Analytes were desorbed from the SPME fiber through direct exposure for 2 min in the GC injection port, heated at 230 °C. The chromatographic column was a 30 m × 0.25 mm i.d. 0.25 μm film thickness TV1-MS fused silica capillary column (Thermo). The carrier gas was helium set to a flow-rate of 1.3 mL/min in constant pressure mode. The column oven temperature program was the following: 35 °C (hold 10 min), rate 5.5 °C/min to 180 °C (hold 3 min), rate 20 °C/min to 230 °C (hold 6 min) [65]. Compounds were identified by comparison of the mass spectra with those of the NIST05 library (NIST, 2005).

The VOCs identified by mass spectrometry were quantified using an external standard calibration procedure performed on the basis of calibration curves created by analyzing gaseous standard mixtures of the main VOC groups, i.e., alkanes, alkenes, aromatics, cyclics, chlorofluorocarbons, ketones, aldehydes and heteroaromatics. The values of the Relative Standard Deviation (RDS), calculated from seven replicate analyses of a gaseous mixture in which the compounds of interest were present at a concentration of 2 ppmv, are <7%. Eventually, the detection limits were determined by linear extrapolation from the lowest standard in the calibration curve using the area of a peak having a signal/noise ratio of 5 [68].

4. Conclusions

The distribution of thiophenes and furans in gases from hydrothermal and magmatic-hydrothermal systems have been revealed to be strongly dependent on the physical-chemical conditions acting on fluid reservoirs, where VOCs are produced via a complex series of catalytic processes, involving organic matter buried in sedimentary formations. Thiophene seems to be efficiently produced at hydrothermal conditions and tend to be destroyed in presence of hot, highly oxidizing fluids from a magma source. On the contrary, the formation of C4H4O seems to be favoured at highly acidic and oxidizing conditions that are determined by the presence of fluids from magmatic degassing. Methylated and hydrogenated heteroaromatics are also preferentially associated with hydrothermal conditions. According to these considerations, the composition of O- and S-bearing heteroaromatics can be utilized in both volcanic and geothermal systems to evaluate contributions of fluids produced in different “natural dominions”, i.e., hydrothermal and magmatic. These results may imply useful applications in volcanic monitoring and geothermal prospection, although the existing dataset should be expanded to better constrain the behaviour of these new geochemical tracers. Experimental runs, able to test the mechanisms of formation and stability of heteroaromatics at temperature, redox and catalytic conditions resembling those of a volcano-hydrothermal environment, would probably useful to better constrain their behaviour.


Many thanks are due two anonymous reviewers who improved an early version of the manuscript. This work partly benefited from the financial support of the Laboratories of CNR-IGG and Department of Earth Sciences of Florence (Italy).


Sample Availability: Available from the authors.

References and Notes

1. Fischer TP, Arehart GB, Sturchio NC, Williams SN. The relationship between fumarole gas composition and eruptive activity at Galeras Volcano (Colombia) Geology. 1996;24:531–534.
2. Giggenbach WF. The origin and evolution of fluids in magmatic-hydrothermal systems. In: Barnes HL, editor. Geochemistry of Hydrothermal Ore Deposits. 3rd ed. Wiley; New York, NY, USA: 1997. pp. 737–796.
3. Hirabayashi J, Kusakabe M. A review on the chemical precursors of volcanic eruptions. Bull Volcanol Soc Jpn. 1985;30:171–183. (in Japanese).
4. Martini M, Giannini L, Buccianti A, Prati F, Cellini Legittimo P, Iozzelli P, Capaccioni B. Ten years of geochemical monitoring at Phlegrean Fields, Italy. J. Volcanol. Geotherm. Res. 1991;48:161–171.
5. Chiodini G, Marini L. Hydrothermal gas equilibria: The H2O-H2-CO2-CO-CH4 system. Geochim. Cosmochim. Acta. 1998;62:2673–2687.
6. Giggenbach WF. Geothermal gas equilibria. Geochim. Cosmochim. Acta. 1980;44:2021–2032.
7. Gerlach TM, Nordlie BE. The C–O–H–S gaseous system. Part II: Temperature, atomic composition and molecular equilibria in volcanic gases. Am. J. Sci. 1975;275:377–394.
8. Giggenbach WF. Redox processes governing the chemistry of fumarolic gas discharges from White Island, New Zealand. Appl. Geochem. 1987;2:143–161.
9. Giggenbach WF. Chemical composition of volcanic gases. In: Scarpa M, Tilling RJ, editors. Monitoring and mitigation of Volcanic Hazards. Springer; Heidelberg, Germany: 1996. pp. 221–256.
10. Doukas MP, Gerlach TM. Sulfur dioxide scrubbing during the 1992 eruptions of Crater Peak, Mount Spurr Volcano, Alaska. In: Keith TEC, editor. The 1992 Eruptions of Crater Peak Vent, Mount Spurr Volcano, Alaska. Vol. 2139. US Geol Surv Bull; Mount Spurr Volcano, AK, USA: 1995. pp. 47–57.
11. Symonds RB, Gerlach TM, Reed MH. Magmatic gas scrubbing: Implications for volcano monitoring. J. Volcanol. Geotherm. Res. 2001;108:303–341.
12. Capaccioni B, Mangani F. Monitoring of active but quiescent volcanoes using light hydrocarbon distribution in volcanic gases: The results of 4 years of discontinuous monitoring in the Campi Flegrei (Italy) Earth Planet. Sci. Lett. 2001;188:543–555.
13. Taran YA, Giggenbach WF. Geochemistry of light hydrocarbons in subduction-related volcanic and hydrothermal fluids Volcanic, Geothermal, and Ore-Forming Fluids: Rulers and Witnesses of Processes within the Earth, Spec Publ, 10; Simmons SF, Graham IJ, editors. Soc Econ Geol; Littleton, CO, USA: 2003. 61–74.74
14. Tassi F, Vaselli O, Capaccioni B, Giolito C, Duarte E, Fernandez E, Minissale A, Magro G. The hydrothermal-volcanic system of the Rincon de la Vieja volcano (Costa Rica): A combined (inorganic and organic) geochemical approach to understanding the origin of the fluid discharges and its possible application to volcanic surveillance. J. Volcanol. Geotherm. Res. 2005;148:315–333.
15. Tassi F, Vaselli O, Capaccioni B, Montegrossi G, Barahona F, Caprai A. Scrubbing process and chimica equilibria controlling the composition of light hydrocarbon in natural fluid discharges: An example from the geothermal fields of El Salvador. Geochem. Geophys. Geosys. 2007;8:Q05008.
16. Giggenbach WF. Chemical composition of volcanic gases. In: Scarpa M, Tilling RJ, editors. Monitoring and Mitigation of Volcanic Hazards. Springer; New York, NY, USA: 1996. pp. 221–256.
17. Chiodini G, Cioni R, Marini L, Panichi C. Origin of the fumarolic fluids of Vulcano Island, Italy, and implications for volcanic surveillance. Bull. Volcanol. 1995;57:99–110.
18. Gottsmann J, Wooller L, Martí J, Fernández J, Camacho AG, González PJ, García A, Rymer H. New evidence for the reawakening of Teide volcano. Geophys. Res. Lett. 2006;33:L20311.
19. Tassi F, Aguilera F, Vaselli O, Medina E, Tedesco D, Delgado Huertas A, Poreda R, Kojima S. The magmatic- and hydrothermal-dominated fumarolic system at the Active Crater of Lascar volcano, northern Chile. Bull Volcanol. 2009;71:171–183.
20. Tassi F, Vaselli O, Barbosa V, Fernandez E, Duarte E. Fluid geochemistry and seismic activity in the period 1998–2002 at Turrialba Volcano (Costa Rica) Ann. Geophys. 2004;47:1501–1511.
21. Duchi V, Minissale A, Manganelli M. Chemical composition of natural deep and shallow hydrothermal fluids in the Larderello geothermal field. J. Volcanol. Geotherm. Res. 1992;49:313–328.
22. Endeshaw A. Current status (1987) of geothermal exploration in Ethiopia. Geothermics. 1988;17:477–488.
23. Tassi F, Martinez C, Vaselli O, Capaccioni B, Viramonte J. Light hydrocarbons as redox and temperature indicators in the geothermal field of El Tatio (northern Chile) Appl. Geochem. 2005;20:2049–2062.
24. Chiodini G, Marini L, Russo M. Geochemical evidence for the existence of high-temperature hydrothermal brines at Vesuvio volcano, Italy. Geochim. Cosmochim. Acta. 2001;65:2129–2147.
25. Duchi V, Campana ME, Minissale A, Thompson M. Geochemistry of thermal fluids on the vulcanic isle of Pantelleria, southern Italy. Appl. Geochem. 1994;9:147–160.
26. Fiebig J, Chiodini G, Caliro S, Rizzo A, Spangenberg J, Hunziker JC. Chemical and isotopic equilibrium between CO2 and CH4 in fumarolic gas discharges: Generation of CH4 in arc magmatic-hydrothermal systems. Geochim. Cosmochim. Acta. 2004;68:2321–2334.
27. Hurwitz S, Lowenstern JB, Heasler H. Spatial and temporal geochemical trends in the hydrothermal system of Yellowstone National Park: Inferences from river solute fluxes. J. Volcanol. Geotherm. Res. 2007;162:149–171.
28. Inguaggiato S, Pecoraino G, D’Amore F. Chemical and isotopical characterization of fluid manifestations of Ischia Island (Italy) J. Volcanol. Geotherm. Res. 2000;99:151–178.
29. Lee HF, Yang TF, Lan TF. Fumarolic gas composition of the Tatun Volcano Group, northern Taiwan. TAO. 2005;15:843–864.
30. Taran Y, Fischer TP, Pokrovsky B, Sano Y, Armienta MA, Macias JL. Geochemistry of the volcano-hydrothermal system of El Chichon volcano, Chiapas, Mexico. Bull. Volcanol. 1998;59:436–449.
31. Tedesco D, Sabroux JC. The determination of deep temperatures by mean of the CO-CO2-H2-H2O geothermometer: an example using the fumaroles in the Campi Flegrei, Italy. Bull. Volcanol. 1987;49:381–387.
32. Mango FD. The origin of light hydrocarbons. Geochim. Cosmochim. Acta. 2000;64:1265–1277.
33. Capaccioni B, Martini M, Mangani F, Giannini L, Nappi G, Prati F. Light hydrocarbons in gas-emissions from volcanic areas and geothermal fields. Geochem. J. 1993;27:7–17.
34. Capaccioni B, Tassi F, Maione M, Mangani F, Vaselli O. Organics in volcanic gases: A review on their distribution and applications to volcanic surveillance Eos Trans AGU 2005. 86, Abstract B23D-03.
35. Darling WG. Hydrothermal hydrocarbon gases: 1. Genesis and geothermometry. Appl. Geochem. 1998;13:815–824.
36. Tassi F. Fluidi in Ambiente Vulcanico: Evoluzione Temporale dei Parametri Composizionali e Distribuzione Degli Idrocarburi Leggeri in Fase Gassosa. Ph.D. Thesis, Univ. of Florence: Florence, Italy, 2004
37. Capaccioni B, Martini M, Mangani F. Light hydrocarbons in hydrothermal and magmatic fumaroles: hints of catalytic and thermal reactions. Bull. Volcanol. 1995;56:593–600.
38. Mango FD, Hightower JH, James AT. Role of transition- metal catalysis in the formation of natural gas. Nature. 1994;368:536–538.
39. Tannenbaum E, Kaplan IR. Low-Mr hydrocarbons generated during hydrous and dry pyrolysis of kerogen. Nature. 1985;317:708–710. [PubMed]
40. North FK. Petroleum Geology. Allen & Unwin; Boston, MA, USA: 1985.
41. Stockwell DM, Bianchi D, Bennett CO. Carbon pathways in methanation and chain growth during the Fischer-Tropsch synthesis on Fe/Al2O3. J. Catal. 1988;113:13–25.
42. Gerlach TM. Evaluation of volcanic gas analyses from Kilauea volcano. J. Volcanol. Geotherm. Res. 1980;7:295–317.
43. Lobert JM, Warnatz J. Emissions from the combustion processes in vegetation. In: Crutzen PJ, Goldammer JG, editors. Fire in the Environment: The Ecological, Atmospheric, and Climate Importance of Vegetation Fires. Wiley; Hoboken, NJ, USA: 1993. pp. 15–37.
44. Gaffney JS. Volcanic CFCs. Environ. Sci. Technol. 1995;29:A8. [PubMed]
45. Jordan A, Harnisch J, Borchers R, Le Guern FN, Shinohara H. Volcanogenic halocarbons. Environ. Sci. Technol. 2000;34:1122–1124.
46. Rasmussen RA, Rasmussen LE, Khalil MAK, Dalluge RW. Concentration distribution of methyl chloride in the atmosphere. J. Geophys. Res. 1980;85:7350–7356.
47. Schwandner FM, Seward TM, Gize AP, Hall PA, Dietrich VJ. Diffuse emission of organic trace gases from the flank and crater of a quiescent active volcano (Vulcano, Aelian Islands, Italy) J. Geophys. Res. 2004;109:D04301.
48. Manzano BK, Fowler MG, Machel HG. The influence of thermochemical sulphate reduction on hydrocarbon composition in Nisku reservoirs, Brazeau river area, Alberta, Canada. Org. Geochem. 1997;27:507–521.
49. Richard L, Neuville N, Sterpenich J, Perfetti E, Lacharpagne J-Cl. Thermodynamic analysis of organic/inorganic reactions involving sulfur: Implications for the sequestration of H2S in carbonate reservoirs. Oil Gas Sci. Technol. 2005;60:275–285.
50. Kettler RM, Waldo GS, Penner-Hahn JE, Meyer PA, Kesler SE. Sulfidation of organic matter associated with gold mineralization, Pueblo Viejo, Dominican Republic. Appl. Geochem. 1990;5:237–248.
51. Xiao J, Zhang A. Discovery of thiopene-type compounds in Jinya gold deposit of Guangxi and its significance. Chin. Sci. Bull. 1997;42:1009–1011.
52. Jordan A. Natural Production of Organohalogen Compounds. Part P. Vol. 3. Springer Berlin Heidelberg; New York, NY, USA: 2003. pp. 121–139.
53. Li Q, Xu Y, Liu C, Kim J. Catalytic synthesis of thiophene from reaction of furan and hydrogen sulphide. Catal Lett. 2008;122:354–358.
54. Rivers TJ, Hudson TW, Schmidt CE. Synthesis of a novel, biodegradable electrically conducting polymer for biomedical applications. Adv. Funct. Mater. 2002;12:33–37.
55. Southward BWL, Fuller LS, Huctchings GJ, Joyner R, Stewart R. Comments on the mechanism of the vapor-phase catalytic synthesis of thiophenes. Catal. Lett. 1998;55:207–210.
56. Tomov A, Fajula F, Moreau C. Vapor-phase synthesis of thiophene from crotonaldehyde and carbon disulfide over promoted chromia on g-alumina catalysts. Appl. Catal. A. 2000;192:71–79.
57. Campaigne E, Foye WO. The synthesis of 2,5 diarylthiophenes. J. Org. Chem. 1952;17:1405–1412.
58. Jursic BS. Suitability of furan, pyrrole and thiophene as dienes for Diels-Alder reactions viewed through their stability and reactions barriers for reactions with acetylene, ethylene and cycloporpene. An AM1 semiempirical and B3LYP hybrid density functional theory study. J. Molecul. Struct. 1998;454:105–116.
59. Angelini G, Lilla G, Speranza M. Gas-phase heteroaromatic substitution. 3. Electrophilic methylation of furan and thiophene by CHXCH (X = fluoro, chloro) ions. J. Am. Chem. Soc. 1982;104:7091–7098.
60. Wojcik BH. Catalytic hydrogenation of furan compounds. Ind. Eng. Chem. 1948;40:210–216.
61. Reddy BM, Reddy GK, Rao KN, Khan A, Ganesh I. Silica supported transition metal-based bimetallic catalysts for vapor phase selective hydrogenation of furfualdehyde. J. Mol. Catalys. A: Chem. 2007;265:276–282.
62. Giggenbach WF, Gougel RL. Method for the Collection and Analysis of Geothermal and Volcanic Water and Gas Samples Chem. Div. Report, no. 2387, Petone, New Zealand DSIR: 1989. 1–53.53
63. Montegrossi G, Tassi F, Vaselli O, Buccianti A, Garofalo K. Sulfur species in volcanic gases. Anal. Chem. 2001;73:3709–3715. [PubMed]
64. Vaselli O, Tassi F, Montegrossi G, Capaccioni B, Giannini L. Sampling and analysis of volcanic gases. Acta Volcanol. 2006;18:65–76.
65. Tassi F, Buccianti A, Capecchiacci F, Vaselli O, Montegrossi G, Minissale A. Metodo d'analisi e di riconoscimento dei composti organici volatili (COV) in gas vulcanici, idrotermali e del suolo Internal Report CNR-IGG, n°1/2008, Florence, Italy: 2008. 1–12.12
66. Arthur CL, Pawliszyn J. Solid phase microextraction with thermal desorption using fused silica optical fibers. Anal. Chem. 1990;62:2145–2148.
67. Davoli E, Gangai ML, Morselli L, Tonelli D. Characterization of odorants emissions from landfills by SPME and GC/MS. Chemosphere. 2003;51:357–368. [PubMed]
68. Mangani G, Berloni A, Maione M. “Cold” solid-phase microextraction method for the determination of volatile halocarbons present in the atmosphere at ultra-trace levels. J. Chromatogr. A. 2003;988:167–175. [PubMed]
69. Mangani G, Berlani A, Capaccioni B, Tassi F, Maione M. Gas chromatographic-mass spectrometric analysis of hydrocarbons and other neutral organic compounds in volcanic gases using SPME for sample preparation. Chromatographia. 2004;58:1–5.

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