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Abstract. Sterols were analyzed in suspended particles collected in January 1991 in the Solo River system and in the Serayu River, Java, Indonesia. Free sterols were extracted from particles larger than 0.7 #im and analyzed, after derivatization into their trimethylsilyl esters, by GC and GC/MS. Concentrations of total sterols ranged from 438 to 7922 ng/l, or from 2.4 to 183.8 ng/mg of total suspendedmatter, which varied from 3.3 to 400 and 471 mg/I, respectively in the Serayu River and at the downstream station in the Solo River. POC concentrations also varied in a wide range, from 0.91 to 4.72 and 6.13% of TSM, respectively at the above stations, and were associated with sterol/POC values ranging from 0.15 to 1.75 ag/mg. Eleven structures of C27, C 28 and C 29 stenols and associated stanols were identified. 28A 22 was only found at downstream stations in the Solo River and in the Serayu River. This unique distribution, different from that of other C 27 , C 28 and C 29 sterols, suggests a predominantly autochthonous origin for these compounds associated with an increased planktonic biosynthesis near the estuary. Concentrations of 28A 5 , 29A 5 ' 2 and 29A 5 showed similar spatial distributions and increased downstream, reflecting the significant accumulation of organic matter originating from the vegetation of the various drainage basins.Values of the autochthonous versus terrigenous sterol index, defined as 27A 5 /29A 5 ' 2 2 + 29A 5 were in the 1.4-1.9 range at upstream stations, whereas at downstream stations lower values were found, 0.4-0.6, which also corresponded to higher concentrations of TSM and lower POC values.Insofar as the stanol/stenol values can be used to estimate the bacterial activity of oxic waters, simultaneous variations of C27 and C 29 stenol/stanol pairs suggest rather different bacterial degradation capacities of autochthonous versus allochthonous organic matter. The wide differencies between the values of the stenol/stanol pairs observed in one of the main tributaries and in downstream stations of the Solo River is evidence that allochthonous organic matter is much more resistant than autochthonous matter. The low index value observed in the Serayu River indicates the highly refractory nature of both autochthonous and allochthonous organic material.

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The application of the lipid marker approach is attracting increased interest for studying the sources and the different biosynthetic pathways of organic matter, both allochthonous and autochthonous, in the chemistry of aquatic environments. The best marker candidates are stable compounds that show specific syntheses within various organisms. Fatty acids have been used extensively in organic geochemistry, but the information gained from their analysis is limited.'-3Wax esters derived from aquatic plankton have received special attention. They are currently analysed for studying the dynamics of aquatic food chains as key compounds for the storage of energy. Wax esters are also potential markers for tracing continental higher plant inputs in the marine environment because they are synthesized as components of plant cuticle^.^ Usually only the acid part obtained by transmethylation and derivatization in methyl esters has been studied.Several methods using gas chromatography/mass spectrometry (GC/MS) in the chemical ionization m~d e~.~ or liquid chromatography (LC)' have been proposed for studying intact wax esters, but localization of the double bonds is not possible. However, the position of the double bond has been determined in alkenes and methyl esters after addition of dimethyl disulphide and further GC/MS analyses of the adducts.8-15 We report here the application of this method to a complex mixture of wax esters from organic matter associated with suspensions in an arctic estuarine environment, the Lena River, in the context of a scientific programme on the Arctic Siberian Aquatorium (SPACIBA). GC/MS analyses were performed on a Nermag RlOlO quadrupole mass spectrometer coupled with a Girdel 32 gas chromatograph. The samples were injected in the splitless mode. The temperatures of the ion source and the interface R , -C t 1 0-4 961 were 150 and 250"C, respectively. The spectrometer was operated from 30 to 850 m/z with one scan per second. The electron energy was 70 eV. Mass spectral data were acquired and processed with the use of a Nermag Sidar 11 1 data system. G C analyses were performed with a fused-silica capillary column (5 m x 0.22 mm i.d.) coated with SE-54 (Chrompack) connected to the ion source via a deactivated column (1 m x 200 pm i.d.) to avoid a decrease in the vacuum when a short column is used. Lipids were extracted from a complex mixture (about 10 mg) of organic matter from Lena River suspended particles in a Soxhlet apparatus using dichloromethane for 5 h. Lipid extracts were dissolved in CH,Cl, (200 pl) and separated on a thin-layer plate (Whatman K5, 250 pm thick) pre-eluted three times with distilled methanol. Elution was effected with hexane-diethyl ether (9:1, v/v). A wax ester fraction ( R , 0.95) was obtained.Wax esters were recovered by washing the silica gel with 2 cm3 of CH,CI,, followed by 2 cm3 of CH,OH and finally with 6 cm3 of diethyl ether. The wax fraction was treated in 100 pl of CH,Cl, by addition of 100 p1 of dimethyl disulphide (DMDS) and 20 p1 of iodine solution (60 mg o...

The determination of the positions of double bonds after dimethyl disulfide (DMDS) addition is described for triunsaturated compounds (alkatrienes and an ester). Different DMDS derivatives were studied according to the numbers, n 1 and n 2 , of methylene groups separating the double bonds. When n 1 and n 2 are smaller than four, a bicyclic thioether is formed and a predictable fragmentation pathway is observed in each case after electron ionization, allowing the determination of the positions of the three double bonds and the molecular structure of the compounds.

Ce travail a consisté à analyser certains marqueurs biogéochimiques pour l'étude de paléoenvironnements d'intérêt archéologique. Le choix des molécules étudiées par chromatographie en phase gazeuse (CPG) et en couplage chromatographie- spectrométrie de masse (CPG/SM) s'est porté sur des constituants lipidiques tels que les alcanes, les acides gras (saturés, insaturés, ramifiés) et les stérols en raison de leur stabilité chimique et de leur ubiquité dans le règne végétal et animal. Certains critères nous ont permis de préciser l'impact de la dégradation bactérienne sur la matière organique étudiée (Carbon Preference Index, acides ramifiés iso et ante iso). En caractérisant l'origine des apports en matière organique, il devient alors possible d'opérer des distinctions dans les fonctions des structures archéologiques mises à jour. Il s'avère que l'utilisation de ces traceurs organiques permet d'apporter une contribution efficace à la reconstitution des de vie en milieu urbain depuis l'époque gallo-romaine.

Letter: Determination of double bond position in di-unsaturated alkadienes by means of mass spectrometry of dimethyl disulfide derivativesDear Sir The determination of the position of a double bond in unsaturated compounds using mass spectrometric methods after derivatization by dimethyl disulfide (DMDS) has been widely studied in olefins, fatty acids and wax esters.1-6 The use of DMDS addition to locate the double bonds for di-unsaturated compounds is uncommon. This method has been used with acetates, natural long chain alkadienes, 7,8 but has never been tried in a systematic way with short chain alkadienes. In this paper, compounds of the type CH 3 -CH=CH-(CH 2 ) n -CH=CH-CH 3 (n varies from zero to four and greater than four) have been studied. The structure of the DMDS adducts has been discussed with respect to the localization of the double bonds, but no consideration of stereochemistry has been given.Electron impact (EI) mass spectra were obtained on an Ion Trap Varian Saturn mass spectrometer coupled to a Varian 3400 gas chromatograph. Chemical ionization (CI) mass spectra were obtained by using ammonia as reagent gas. The samples were injected in the SPI mode. The column employed was a fused silica capillary (30 m long, 0.25 mm i.d.) coated with DB5 phase (Chrompack). The temperature increased at 2°C min -1 from 40°C to 250°C. The di-unsaturated compounds (2-6 octadiene and 2-4 octadiene) were synthesised in our laboratory by classical methods. Hexane and dimethyl disulfide were distilled. Iodine and Na 2 S 2 O 3 were used as received. Alkadiene (50 µg) was treated in 100 µl of hexane by addition of 100 µl of DMDS and 20 µl of iodine solution (60 mg of iodine in 1 ml of diethyl ether). The reaction was carried out in a closed tube for 48 h at 50°C. The excess of iodine was reduced with Na 2 S 2 O 3 solution (5% in water). The organic phase was removed and the excess of DMDS was evaporated. The dry extract was diluted with 50 µl of hexane and then analysed by CG/MS.Derivatives were formed by the addition of DMDS (Scheme 1).Depending on the values of n, a mono or a di-addition is observed and the pathway of fragmentation is different depending on the mode of addition. n = 0 (2-4 octadiene) A molecular ion (M +• = 204) is observed, confirmed by the spectrum in CI mode (Figure 1). Only one molecule of DMDS is added in 1-4 position (classical addition for conjugated diene). The allyl position of the sulfur atom only allows us to obtain the usual loss of CH 3 S or CH 3 SH from the molecular ion (m/z 157, 156, 109). It is impossible to locate the double bonds, but the spectrum is completely different from a monoalkene spectrum.The mass spectra of the DMDS derivative (Figure 2) shows a mixture, unseparated by GC, of the two mono-derivatized compounds M +• = 176 proved by CI spectra. On the contrary DMDS adducts of di-unsaturated acetates and alcohols give a di-addition. 7In each spectrum the characteristic cleavage of the bonds between the two carbon atoms linked to the sulfur atom is observed, ions at m/z 61 an...