Characterisation of dissolved organic compounds in hydrothermal fluids by stir bar sorptive extraction - gas chomatography - mass spectrometry. Case study: the Rainbow field (36°N, Mid-Atlantic Ridge)

Table 1 Summary of the groups of compounds detected (+) and not detected (nd) in fluids from the Rainbow hydrothermal field over 3 years and in the deep seawater extract

Compound	Log(K _o/w )	2005	2007	2008	Deep seawater
n-alkanes (C_9-19)	5.5-8.2	C_9-14	C₁₁	C₁₀	C₁₁
branched saturated alkanes (C_9-12)	5.0-6.8	+	nd	+	nd
cycloalkanes (C_9-11)	4.9-6.0	+	nd	nd	one C₉
phenol	1.5	+	nd	+	nd
toluene	2.7	+	+	+	+
ethylbenzene	3.2	+	nd	+	nd
xylene	3.2*	+	nd	+	+
styrene	2.7	+	+	+	+
other alkylated benzenes (C_9-12)	3.7-5.0	nd	?	?	one C₉H₁₂
naphthalene	3.4	+	+	+	+
methyl and dimethyl naphthalenes	> 3	+	+	+	nd
PAHS (C_12-16)	4.2-5.2	+	+	+	nd
n-fatty acids (C_8-18)	3.4-8.2	C_9-18	C_8-10	C_9-16	C₆ and C_14-16

* [38].
(?) stands for compounds for which further investigation is needed to confirm their presence. Results were identical for the two samples in 2007 with respect to the compounds listed in this table, therefore it appears only one column for 2007. C_n is the carbonated chain length of the identified compounds. Additionally, ranges of Log(K_o/w) values at 25°C for pure water are given. These values are meant to give a rough estimate only. The reader should bear in mind that the partition between seawater or hydrothermal fluids and PDMS will somewhat differ from these values. Precise identification of isomers was not possible without the use of synthetic standards so that ranges of values have been determined based on log(K_o/w) values for compounds with the same raw formula. Values were obtained from the SciFinder® data base.

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