The Sea Journal of the Korean Society of Oceanography Vol. 12, No. 3, pp. 244 250, August 2007 [Note] Membrane Inlet Mass Spectrometer (MIMS) ts } r š r } ld 1 * x 1 rs 1 qt 2 x 3 1 x ff, 2, 3 p x / mn Dissolved Methane Measurements in Seawater and Sediment Porewater Using Membrane Inlet Mass Spectrometer (MIMS) System SOONMO AN 1 1 1 *, JINAM KWON, JEAHYUN LIM, YUNJUNG PARK 2 AND DONG-JIN KANG 3 1 Division of Earth Environmental System/Marine Science Major, Pusan National University, Busan 609-735, Korea 2 Department of microbiology, Pukyung National University, Busan Korea 3 School of Earth & Environmental Sciences/Research Institute of Oceanography, Seoul National University, Seoul 151-742, Korea MIMS edšp k~ e p ns d r r pn l m, l l m r l sq ns ˆ r n l. rp r p Žk o l, l k p ˆ l k~ e t mp p MIMS edšp r m. r p ns ~p q p m. rp t m p 0.13~0.9% r m. p edšp pn l k p p ns ˆ r, ns ˆp p rp n sn ppp k pl. MIMS systemp pn l, p ns ˆ p p l pl. e l MIMS edšp inlet p ˆ ˆ rq l r pl n s ˆp r pl. Membrane inlet mass spectrometer (MIMS) has been used to accurately quantify dissolved gases in liquid samples. In this study, the MIMS system was applied to measure dissolved methane in seawater and sediment porewater. To evaluate the accuracy of the measurement, liquid samples saturated with different methane partial pressure were prepared and the methane concentrations were quantified with the MIMS system. The measured values correspond well with the expected values calculated from solubility constants. The standard error of the measurements were 0.13~0.9% of the mean values. The distribution of dissolved methane concentration in seawater of the South Sea of Korea revealed that the physical parameters primarily control the methane concentration in sea water. The MIMS system was effective to resolve the small dissolved methane difference among water masses. The probe type inlet in MIMS system was proven to be effective to measure porewater methane concentration. Keywords: Methane, MIMS, Dissolved Gas, Porewater, Methane Hydrate, Probe 2007 4o, ol r oo (IPCC) v m p p ˆ pp m. v m r e mp f, me ~ (CO 2, CH 4, N 2O, CFCs, O 3, v )p o, p, r p ~p ˆl l l ep kv p (Cicerone and Oremland, 1988; Middleburg et al., 2002; Bange, 2006). p tl ˆ *Corresponding author: sman@pusan.ac.kr d(ch 4) CO 2l kp rp, me p p CO 2 l l k 20 r pp, r~ me p 15% r k r p (Cicerone and Oremland, 1988;, 1995). t CH 4p p r v r 2003 l 1790 ppbp, l v pp 1990 p k 5 ppb r p (WMO, 2005). rv rp CH 4p p l 535 Tg(CH 4)l pt 70% porp op 30% ql rp opl p k r p (, 2002). kp ˆp o(source)p l v pp kp v k (5~50 Tg; Cicerone and Oremland, 1988; Middleburg et al., 244
Membrane Inlet Mass Spectrometer (MIMS) edšp pn r ns ˆp r 245 2002). k tl lkvlp ˆ l tn p k v pp, q, vl e r l l n s p (Jones and Mullholland, 1998; Middleburg et al., 2002). v m l l ˆp t n k, l v qop ˆ (methane hydrate) p t p k r,, p m p l ~ ˆp r r p n r. ˆ p l v qop p tn k, v m rl kp p(positive feedback)p qn l, v m eˆ p qqrp o v vr m (Damm et al., 2005). v v m v l m kv, p p ˆp ˆp d ˆ tl o, v ˆl p me ƒr, v m p. v m rp ˆ qo ˆ kp ˆ l l l pl, ns ˆp ˆp r r n p kv p. p rp ns ˆp rp p lv, ~w ns ˆp ˆ d ~ ˆ m pp d r p. ns ˆp d l t d pd(headspace) pn, purge-trappingp pn, equilibrator pn p n l (Middleburg et al., 2002; Seifert et al., 1999). p ˆp flame ionization detector(fid) q d Š photo-acoustic infrared detector(middleburg et al., 2002)l r. tp ˆ n p pl, e p mm p r, r l n (detector)p p r p l, p rp r m rp p. d pd purge-trappingp n e p } l e p k, ns d l p r l lv (An and Joye, 1997). rl n e p k 50~600 ml p p r ƒ rp e p l npp (Middleburg et al., 2002). tp ns d r r o l v edšp Membrane inlet mass spectrometer (MIMS) l l kl pn p (Kana et al., 1994; An et al., 2001; Vrana, 2005; Sheppard et al., 2005; Tortell, 2005; Demeestere et al., 2007). MIMS system l e p pl v p l, k~e l kp ns d VOC (volatile organic carbon), quadrapole v (mass spectrometer) pn l r (Kana et al., 1994; An et al., 2001). k~e r e p e n l v ˆ ov l p k~ e ns d. d d r v l op l r l ns dp l p e p mm p o}rp, m l l d pp pp pn p f rp r p p p (Kana et al., 1994). MIMS system p rl n e p kp r, p e p l rp r ns d rl l qrp v p. l MIMS systemp l, tl q rp MIMS system(underwater membrane introduction/quadrupole mass filter system; Short et al., 2005)p lp, membrane inlet system p l, r p p ns d p (Sheppard et al., 2005; Hartnett and Seitzinger, 2003) l l MIMS systemp pn l, ns ˆ dp p kk m. l m m ˆp ks l eˆ t nkp mp, pp rp MIMS systemp pn ns ˆ rp r p k k k. er rp m lk l pl ns ˆ r l, p l ns ˆp k. pm ˆ (probe) ˆp inlet system p pn l r p ns ˆ r m. m MIMS system l l n MIMS systemp r e p s l 2 v ns ~ edš(membrane inlet)p n l (Fig. 1). k~ e p n v ˆl p, 0.75 mm( 0.15 mm) p 20 mmp e pn l ns d l (Fig. 1A). k~ e r pn l d p d (n : 0.75 mm, 0.5 mm)p op, d p d p v p p T-q ƒ kl e m pl v k~e e v e p n s ~. ns ~ k~e d p d p r v. T-q ƒ kl ns ~ r o k~v p, p r o quadrapole v op (Kana et al., 1994; An et al., 2001). w edšp r l p p ns ˆ r o n l. p edšl d p d l e q e p rl mp, rp e p kyp d p d m v edš l m (Fig. 1B). r~ v p 2 mm r mp, p r l vr p l, p ns ~ e l v p ov MIMS system l ˆp r m. ns d rl Pfeiffer vacuump gas analyzer(pfeiffer QMA 200) pn l. pm dp v : r (massto-charge ratio; m/z) t r d( ˆ m/z=15, m/z=32, k m/z=40) p v :r ˆ m. ˆ d(ch 4)p e (m/z=16)l pm (O m/z=16)l p (interference) p sq l, CH 3 +(m/z=15)p kp r m, ˆ CH 3 + sp p k r p (Benstead and Lloyd, 1994; Sheppard et al., 2005). ˆ e p k l t nk(20 o C, 0 pptm 20 o C, 30 ppt) ˆ l.
246 k Ë v Ëpq Ë orë v Fig. 1. Inlet diagram of MIMS system showing membrane inlet for liquid samples (A), and porewater sample (B). h o m ko ~o l m m s l nkp e t m (Table 1). m 0 ppt p nkp v 2 v m (20 o Cm 30 o C) ov m sl 48e p l, l p m (S 0T 20, S 0T 30). nk p m k e 30 ml o n l lr. v m p 0, p 35 ppt t l 48e p l e p p headspace lp n l }o. p r t pn l 10 mlp headspace l, 23 ppm p t ˆ(23 ppm CH 4, N 2 balanced) tp (S 0T 20C, S 0T 30C, S 35T 20C, S 35T 30C, S 35T 20CH, S 35T 30CH), (S 35T 20A, S 35T 30A) 30 C ov m o }o l. p k~ e 20 Cm o sl 48e l, headspace p ˆ p m. pm l k~ l p sq p ns dp kp tp o l, d k 20 (bubbling) eˆ pl om p } l, l p sq ns dp m k (S 35T 20CH, S 35T 30CH). m e, p 95% p p ns d l r lpp k d k k pl. r~ 10 v s p t e t lp, s p e 3 j l r l (Table 1). m ~o 2005 9o ks ˆk s t (34~34.30 N, 128~129 E)p 6 s rr(station 1~6)l e ns ˆ rp p lr (Fig. 2). s rrp ep 30~80 m r Niskin-rosette } pn l 5~10 m p }, m k e 30 ml o n l p Table 1. Saturated water samples in various salinity and temperature for dissolved methane analysis. Sample ID Salinity (ppt) Temperature ( o C) Headspace (10 ml) Degassing with Helium S 0T 20 0 20 none n S 0T 30 0 30 none n S 0T 20C 0 20 23ppm CH 4 n S 0T 30C 0 30 23ppm CH 4 n S 35T 20C 35 20 23ppm CH 4 n S 35T 20CH 35 20 23ppm CH 4 y S 35T 20A 35 20 Air n S 35T 30C 35 30 23ppm CH 4 n S 35T 30CH 35 30 23ppm CH 4 y S 35T 30A 35 30 Air n Fig. 2. Study sites for vertical profiles of dissolved methane.
Membrane Inlet Mass Spectrometer (MIMS) edšp pn r ns ˆp r 247 ZnCl 2(vol/vol 50%, 0.1 ml)p l p p rve m. e e e rm MIMS systemp pn l r m. ˆn ko ~o 2005 9o ˆ (probe) ˆ lv membrane inlet system p pn l r ns ˆp rp p lr (Fig. 1B). p l v 10 cm, p 25 cmp r l } e e rm q m l, rp p lr (Fig. 1B). r p ˆ e p t nk(20 o C, 0 pptm 20 o C, 30 ppt) ˆ l. ko ~o 10 v s p ns e p ˆ 2~3.4 nmp o m (Table 2). tl eˆ 4 v e t ˆ 1.9 ppm r(bange et al., 1994) m m r n (Bunsen solubility coefficient; Yamamoto et al., 1976) f ~ p p m (Fig. 3). v k tl eˆ S 0T 20, S 0T 30 p m p m (Fig. 3). ˆl tpeˆ, r e (S 35T 20A, S 35T 30A)l r p l p ˆ, p e headspacep k p k kr p. rl t m 0.004~0.027 nm e p CH 4 p 0.13~0.9% n r rp m (Table 2). e l 23 ppm t ˆ ~ eˆ nkl l eˆ nkl ns ˆ kk o l, e p ˆ e k e m ˆ l (Fig. 4). p m 20 Cm o 30 o C, kl nk (S 0T 20, S 0T 30) tp k e l l l p p l ˆ e (excess methane signal) v p v m (Fig. 4). Headspace }n e (S 35T 20A, S 35T 30A)p Fig. 3. Measured and calculated methane concentrations in saturated water samples of various temperature and salinity conditions. See Table 1. for the saturation conditions. n pl ˆp llp, CH 4:Arp pp S 0T 20, S 0T 30m p p m. 23 ppm t ˆ ~ headspacel tp e p n n p k m. n t ~l ˆ v d sq v tn d p k~ e headspace lp p. t ~ tp e l k 82%, 92% m. n rp d l ns d r pl, t ˆ d tp e (S 35T 20CH)l v k t ˆ d tp e m p o k, m, p 23 ppm t ˆ dl k sq v kk, p mpp k pl. k m ˆp p l k - ˆ ep pl ˆp 2.4~3.3 nml p. e l 23 ppm p v t d p Table 2. Methane and argon signal (mbar) and concentration (nm) in saturated water samples of various salinity and temperature. See Table 1. for the saturation conditions. Sample ID Methane Signal (mbar) Argon Signal Methane Concentration (nm) Excess Methane Average SE (mbar) mean 1 SE Signal (mbar) S 0T 20 1.93 10-11 1.73 10-13 1.74 10-10 3.067 0.027-0.033 S 0T 30 1.58 10-11 1.97 10-13 1.44 10-10 2.511 0.031-0.002 S 0T 20C 2.11 10-11 1.29 10-14 1.58 10-11 3.665 0.002 3.373 S 0T 30C 1.84 10-11 6.28 10-14 1.39 10-11 2.931 0.010 2.976 S 35T 20C 1.85 10-11 6.86 10-14 1.38 10-11 2.943 0.011 2.989 S 35T 20CH 1.82 10-11 6.90 10-14 7.38 10-12 2.898 0.011 3.071 S 35T 20A 1.46 10-11 1.06 10-13 1.39 10-10 2.328 0.017-0.091 S 35T 30C 1.54 10-11 3.14 10-14 1.52 10-11 2.452 0.005 2.471 S 35T 30CH 1.54 10-11 2.58 10-14 6.89 10-12 2.445 0.004 2.627 S 35T 30A 1.27 10-11 2.51 10-14 1.20 10-10 2.021 0.004-0.022
248 k Ë v Ëpq Ë orë v Fig. 4. Argon versus methane signal of MIMS measurement in saturated water samples. See Table 1. for the saturation conditions. n mp, v t ˆ d pn l op e p ee, s r rp p. ~o 2005 9o p lp ns ˆ 2~3 nmp o m. s p o lk p ns ˆ o(4~150 nm; Middleburg et al., 2002)l p p. v l ˆp p p p (Jones and Mullholland, 1998), s vlp lkp p m p vr rp vlp k r rp p p mp p, ovl n rr l rr p p m. e ns ˆp, l p p p 40~60 m v pr p p mk el 60 m p l kv p m. p p r rp lt rp rrp rr 5p el ns ˆp m, m Fig. 5l ˆ l. p rrl el m m p v e k 50~60 m l o mk p tep (Fig. 5). ns ˆp p p r p q m l, l r pr p p, mk k l Fig. 5. Depth profile of dissolved methane concentration in station 5. Water temperature and salinity were also shown together. kv p ˆ. p rp p ns ~p n op r op l n rp np rp npl p sr. rp npp ~p n r m m p n rp qn l p ~l n r. t ~p n m m p p ~p n. p t ml p m p m l p m ˆ. n s ˆp nl mp 1 p m 1 ppt l k 4 r n l m p t. m n s ˆ p (Fig. 6), r rp l ltl p vlp ns ˆp rp npl p p rp sr p p p r pp, MIMS systemp pn ns ˆ rp n p l qp p p rp n p. ˆn ko r m, k r p k 1cml kp 1 10-11 mbar p, kp 1%l p l, p l (Fig. 7). r o 1 cml ˆ k 5 nmpl r - l 8 nm r v m, p r pl
Membrane Inlet Mass Spectrometer (MIMS) edšp pn r ns ˆp r 249 Fig. 6. Relation between water temperature and dissolved methane concentration measured by MIMS. Fig. 7. Dissolved methane concentration (nm) and oxygen signal strength (mbar) during MIMS probe measurement of sediment porewater. Negative depth denotes water above the sediment surface. v l 1 cm p l 12 nm n ˆ. r p 3.5 cml perp v m pm l ns ˆp 9 nm r mp 5 cm v p ov l. 3.5 cm pl v ˆp opp q p lp, r p p sq l p p lp p p (Aller 1980). MIMS probe pn ˆp rp ~ ( ) k Šk l l r l (Sheppard et al., 2005), q l 1500~2500 nm n p p ˆ l. e } r l r q lp, p ˆp t n o(source)p l v pl(kelly et al., 1995; Middelburg et al., 2002) r pl p mp, l 2~3 p l ~. p rp p ˆ p r(methanogenesis)p kp t rp r p m o r prp, m o r j p pl pl k r p (Capone and Kiene, 1988). s l r r pl ˆp l p l, tl lp p p. ˆ ˆp MIMS systemp pn l, r ns ˆp rp e mp, r Žk p rl m p t r npp Žk pp p. p ns ˆ r s p p p ˆv r o r p f p rp pp p. r ns ˆp p ˆ lk l ˆp l p p rp ˆp k(flux)l l m p v, tn r r p (Frans- Jaco et al. 1998). kh MIMS systemp rl n e p kp r, pe p l rp ns d rl l qrp v pl, l l kl pn p. l l l m m m s ˆp ks l eˆ t nkp mp, p p rp MIMS systemp p n ns ˆ rp sd p pl. p m l, lk, r p ˆ r m. k m, m, ˆ dp k s l eˆ ns e rl ns ˆ s l n f m q p p m. rl t m 0.004~0.027 nm k~ e p ns ˆ p 0.13~0.9 % sd n r r rp m. 2005 9o p lp ns ˆ 2~3 nmp o m. e ns ˆp, l p p p 40~60 m v pr p p 60 m p l kv p m. p rp n p l q p p p MIMS systemp rp n pp k pl. r l p ns ˆ d p, r o 1 cm l ˆ k 5 nmpl r - l 8 nm r v m, p r pl v l 1 cm p l 12 nm n p ˆ. r p ns ˆp r p f r l tp
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