Enhanced sensitivity in the analysis of trace organochlorine compounds by negative-ion mass spectrometry with ammonia as reagent gas

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Journl of Chromtogrphy A, 823 (1998) 73 79 Enhnced sensitivity in the nlysis of trce orgnochlorine compounds by negtive-ion mss spectrometry with mmoni s regent gs Roser Chler, Ros Vilnov, Mry

1 Journl of Chromtogrphy A, 823 (1998) Enhnced sensitivity in the nlysis of trce orgnochlorine compounds by negtive-ion mss spectrometry with mmoni s regent gs Roser Chler, Ros Vilnov, Mry Sntigo-Silv, Pilr Fernndez, Jon O. Grimlt* Deprtment of Environmentl Chemistry (CID-CSIC), Jordi Giron 18, Brcelon, Ctloni, Spin Abstrct A comprison of the performnces of mmoni nd methne s regent gses for the nlysis of trce orgnochlorine compounds by gs chromtogrphy coupled to negtive-ion chemicl ioniztion mss spectrometry is performed in the present study. Exmples of stndrd mixtures nd humn blood smples nlyzed with both regents in scn nd selected-ion monitoring mode re shown. Importnt dvntges re observed s consequence of the use of mmoni. These concern detection nd quntittion limits nd the lower dependence of sensitivity on the degree of chlorine substitution of the compounds Elsevier Science B.V. All rights reserved. Keywords: Mss spectrometry; Orgnochlorine compounds; Pesticides; Hexchlorocyclohexnes; Hexchlorobenzene; Polychlorinted biphenyls; DDT; DDE 1. Introduction the chemicl ioniztion mode nd negtive-ion recording (GC NICI-MS) tkes dvntge of the The nlysis of orgnochlorine compounds, nme- electronegtive chrcter of these compounds nd it ly pentchlorobenzene, hexchlorobenzene, hex- hs often been used when structurl informtion is chlorocyclohexnes (HCHs), DDTs nd polychloro- needed for the nlyses [3 9]. However, the high biphenyls (PCBs), t trce concentrtions in environ- differences in sensitivity relted to the degree of mentl or biologicl mtrices is still chllenging chlorintion of the compounds [10] constitute one tsk. Gs chromtogrphy (GC) coupled to electron- importnt difficulty of this ppliction. This drwcpture detection (ECD) is the current technique of bck is prticulrly importnt in environmentl nd choice [1,2] due to its specificity for electronegtive public helth studies when the purpose of the molecules. However, this technique does not provide nlyses is devoted to determine the whole comstructurl informtion of the chemicl species. Like- position of orgnochlorine species. wise, it does not llow the selective nlysis of GC In the present pper, it is shown tht GC NICIcoeluting compounds. MS using mmoni s regent gs provides more GC coupled to mss spectrometry (GC MS) in even response mong liphtic nd romtic orgnochlorine compounds substituted by three seven * Corresponding uthor. chlorine toms. Furthermore, this regent gs gives / 98/ $ see front mtter 1998 Elsevier Science B.V. All rights reserved. PII: S (98)

2 74 R. Chler et l. / J. Chromtogr. A 823 (1998) rise to better sensitivities for most of the species nlyzed. The results re compred with those obtined with methne becuse this regent gs is the most common ionising gent in generl purpose NICI pplictions. Tble 1 Mss-ion progrmme for the chemicl ioniztion mss spectrl quntittion of orgnochlorine compounds with methne nd mmoni Time Compound Mss ions (min) m/z 4 7 Pentchlorobenzene Hexchlorocyclohexnes 71, Experimentl Hexchlorobenzene PCB No , 255 PCB No , p, p9-dde 318 PCB No Stndrds PCB No PCB No All PCB congeners were purchsed from Promo p, p9-ddt 71, 283 chem (Wesel, Germny). g-hch nd p, p9-dde PCB No were from Aldrich-Chemie (Steinheim, Germny), PCB No nd d-hchs were from Promochem (Ntionl When two ions re indicted, the first ws used for quntittion. Physicl Lbortory, Teddington, UK) nd b-hch, p, p9-ddt nd HCB were from Dr. Ehrenstorfer (Augsburg, Germny). All stndrd mixtures were prepred in isooctne. 3. Results nd discussion 3.1. Mss spectr 2.2. Instrumentl nlysis Severl representtive spectr of NICI-MS using All GC NICI-MS nlyses were performed using mmoni s regent gs re shown in Fig. 1. The Fisons MD 800 instrument (qudrupole detector, spectr displyed in this figure re dominted by the Thermo Instruments, Mnchester, UK). The gs moleculr mss frgment resulting from the incorpochromtogrph ws equipped with nonpolr fused- rtion of therml electrons produced by the modertsilic cpillry column HP-5-MS (30 m30.25 mm ing effect of mmoni. The stbility of the moleculr I.D., 0.25-mm film thickness). Helium ws used s ion depends on the mount of chlorine toms bound crrier gs (1.1 ml/min). The oven temperture ws to romtic crbons. Thus, the NICI spectr of the progrmmed from 808C (1 min) to 1208C t 158C/ tetr-, pent-, hex- nd heptchlorobiphenyl commin nd then to 3008 t 48C/min with finl holding pounds considered in this study (PCB Nos. 52, 101, time of 10 min. The smples were injected in split/ 118, 138, 153 nd 180) re dominted by the splitless mode (48 s) t 2808C (hot needle technique) moleculr ion. In the lower substituted biphenyls, nd dt cquisition strted fter solvent dely of 4 e.g. PCB No. 28, the spectr is dominted by other min. Ion source nd trnsfer line tempertures were frgments, e.g. m/z 221 (Tble 1). 150 nd 2808C, respectively. Methne nd mmoni Comprison of the hexchlorobenzene nd PCB were used s regent gses. Ion source pressure mss spectr displyed in Fig. 1 with those obtined (currently 1.6 Torr) ws djusted to mximize the with methne s regent gs [11 13] shows higher perfluorotributylmine ions (m/z 312, 452, 633 nd frgmenttion with mmoni. Thus, the reltive 671) (1 Torr P). Ion repeller ws 1.5 V. bundnces of the [M-Cl1H] ions (c %) re Dt were scnned from m/z 50 to 450 t 1 s per considerbly higher thn those reported with decde. Dt were lso cquired in selected-ion methne (5 16%; [11 13]), even those obtined t monitoring mode with dwell time nd spn of 0.06 high ion source tempertures, e.g. 2508C [13]. These s nd 0.10 u, respectively. The ion windows used in differences re consistently observed despite the this second cse re described in Tble 1. differences in frgmenttion ssocited with the use

3 R. Chler et l. / J. Chromtogr. A 823 (1998) Fig. 1. Negtive-ion chemicl ioniztion mss spectr of hexchlorobenzene, p, p9-dde nd polychlorobiphenyl congeners Nos. 138 nd 180 using mmoni s regent gs.

4 76 R. Chler et l. / J. Chromtogr. A 823 (1998) of different instruments, tht hve been reported for methne NICI MS [11]. A dominnce of the moleculr ion is lso observed in the nlysis of p, p9-dde with mmoni NICl-MS (Tble 1). In this molecule the double bond is conjugted with the benzene rings nd ll chlorine substituents re ttched to romtic crbons. Agin, this spectrum exhibits higher frgmenttion thn tht obtined with methne NICl-MS. Wheres the m/z 262 nd 281 frgments hve reltive intensity of 80% in the former cse (Fig. 1), the intensities of these frgments re 1 nd 15%, respectively, with methne [12,13]. However, in this second cse the frgmenttion pttern hs high dependence on the ion source temperture nd no moleculr ion is observed t 2508C by methne NICI-MS. Conversely, the NICI-MS of p, p9-ddt is dominted by the Cl2 ion (Tble 1). In this molecule, no conjugtion is possible nd only two of the five chlorine toms re bound to romtic crbons. The Cl2 mss frgment lso domintes the NICl-MS of Fig. 2. Scn profiles (m/z t 1 s) of stndrd mixture of hexchlorocyclohexnes (Tble 1). In this cse, ll orgnochlorine compounds recorded by gs chromtogrphy chlorine toms re linked to liphtic crbons. negtive-ion chemicl ioniztion mss spectrometry using Despite the differences in degree of frgmenttion, methne nd mmoni s regent gses. (1) Pentchlorobenzene the use of both gses give rise to the sme mss ions. (160 pg), (2) -HCH (190 pg), (3) hexchlorobenzene (160 pg), (4) b-hch (310 pg), (5) g-hch (240 pg), (6) d-hch (220 pg), Thus, the use of one or the other gs for the nlysis (7) PCB No. 28 (170 pg), (8) PCB No. 52 (160 pg), (9) PCB No. of orgnochlorine compounds does not require 101 (160 pg), (10) p, p9-dde (260 pg), (11) PCB No. 118 (170 chnges in the ions selected for identifiction or pg), (12) PCB No. 153 (210 pg), (13) p, p9-ddt (230 pg), (14) quntittion. PCB No. 138 (190 pg), (15) PCB No. 180 (230 pg) GC MS profiles 118, 153 nd 138 is higher thn in the methne profile which is essentilly dominted by hexchloro- The scn profiles (m/z t 1 s) obtined by benzene nd PCB No In ddition to this GC NICl-MS nlysis of mixture of orgnochlor- difference, smll chromtogrphic peks correine stndrds with mmoni nd methne s regent sponding to orgnochlorine compounds with lower gses re shown in Fig. 2. Consistently with previous degree of chlorine substitution (e.g., PCB Nos. 28, studies [10 12], both profiles show higher re- 52 nd 101 nd p, p9-dde) cn be observed in the sponse for the compounds with higher degree of mmoni GC NICl-MS record. These compounds chlorintion in romtic rings. Thus, compounds re hrdly detectble in the methne ioniztion contining five (pentchlorobenzene, PCB No. 118), profile. The use of mmoni s regent gs gives rise six (hexchlorobenzene, PCB Nos. 138 nd 153) or to chromtogrphic trces with lower compound seven (PCB No. 180) chlorine substituents in ben- discrimintion thn chemicl ioniztion with zene or biphenyls stnd out in the mixture. methne. Similr differences between the two gses Nevertheless, the GC profile generted by ioniz- re observed in selected-ion monitoring mode. tion with mmoni exhibits more uniform re- The difference in sensitivity between methne nd sponse. Thus, the reltive proportion of the peks mmoni is probbly due to the buffer cpcity of corresponding to pentchlorobenzene nd PCB Nos. the two gses to decrese the energy of the electrons

5 R. Chler et l. / J. Chromtogr. A 823 (1998) emitted by the mss spectrl filment to ner-therml vlues. Thus, experiments of electron decy in pulse irrdited mixtures of CCl4 nd diverse moderting gses showed tht the CCl4 electron ttchment rte 29 constnt in the presence of mmoni, 5.9?10 ml/ s, ws bout seven times higher thn in the presence of 210 methne, 8.6?10 ml/ s [14]. Likewise, the unit 28 pressure thermliztion time of mmoni, 2.8?10 s Torr, ws bout seven times shorter thn tht of 27 methne, 2.0?10 s Torr [14]. p, p9-ddt nd HCHs show lower reltive bundnces when both methne nd mmoni re used. The lck of stbiliztion of the moleculr ion in the bsence of sufficient number of chlorine substituents to romtic crbons is not only reflected in high frgmenttion but lso in low ion bundnces. Thus, these compounds exhibit low reltive responses even when they re nlyzed by selected-ion monitoring (SIM) using the m/z frgment progrm of Tble 1 tht includes m/z 71 s their specific mss ion. Among ll HCHs, the b-isomer is the one ex- Fig. 3. Selected-ion monitoring profile of humn blood extrct of hibiting the lowest signl/ response rtio with both orgnochlorine compounds recorded by gs chromtogrphy gses. The low sensitivity of this HCH isomer on negtive ion chemicl ioniztion mss spectrometry using methne nd mmoni s regent gses (m/z ion-monitoring progrm s nlysis by methne GC NICl-MS or even electrondescribed in Tble 1, the GC profiles re normlized t the cpture detection is known [15]. The different ioni- mximum pek of ech window). Pek identifiction s in Fig. 2. ztion rte of this isomer probbly reflects its higher stbility nd lower dipole moment thn the other HCHs. mmoni results in obvious dvntges in the pres- The strong differences in reltive re bundnces ence of interfering compounds such s those occurshown in Fig. 2 re significnt for the nlysis of rel ring in biologicl smples. smples such s humn blood extrcts (Fig. 3) which contin trce mounts of orgnochlorine compounds 3.3. Detection nd quntittion limits (in the order of few ng/ml). These concentrtions require high instrumentl sensitivity since the current The detection nd quntittion limits of the smple mounts vilble for nlysis re in the orgnochlorine compounds included in Figs. 2 nd 3 order of 1 ml. Smple extrction nd clen up re reported in Tble 2. They hve been obtined procedures for the preprtion of these extrcts re from the nlysis of stndrd mixtures by selecteddescribed elsewhere [15]. ion monitoring s described in Tble 1. Severl At this low mount of orgnochlorine compounds, clibrtion curves were generted by progressive e.g. low pg rnge, only hexchlorobenzene nd PCB dilution of stndrd mixtures nd subsequent in- No. 180 give detectble signls by methne GC strumentl nlysis. The vlues reported in Tble 2 NICl-MS. Conversely, PCB congeners (Nos. 118, correspond to those determined with the stright 153 nd 138) nd p, p9-dde re recorded in ddition lines closer to the lowest detectble concentrtion to the methne-detected compounds when mmoni rnge. is used. The contrst between the two ioniztion In nerly ll cses, the limits of detection nd gents is even higher thn tht observed with stn- quntittion re lower when mmoni is used s drd mixtures (Fig. 2) illustrting tht the use of regent gs. The contrst is prticulrly remrkble

6 78 R. Chler et l. / J. Chromtogr. A 823 (1998) Tble 2 Detection nd quntittion limits (in pg) of orgnochlorine compounds by chemicl ioniztion mss spectrl nlysis using methne nd mmoni s regent gses Compound Ammoni Methne Limit Limit of Limit of Limit of detection quntittion detection quntittion (pg) (pg) (pg) (pg) Pentchlorobenzene Hexchlorobenzene Hexchlorocyclohexne b-hexchlorocyclohexne g-hexchlorocyclohexne d-hexchlorocyclohexne PCB congener No PCB congener No PCB congener No p, p9-dde PCB congener No PCB congener No PCB congener No PCB congener No Not determined. mong the PCB congeners nd p, p9-dde (five to ten tion rections. Despite the differences in frgmenttimes) which, s outlined in Fig. 2, give rise to tion ptterns ssocited to these two regent gses, significnt differences for the determintion of the use of one or the other does not require chnges orgnochlorine compounds in rel smples. in the compound-specific ions selected for the SIM In the cse of HCHs, the differences re smller mode. lthough the limits re generlly lower with mmoni thn with methne. b-hch does not exhibit significnt differences from the use of one or the other regent. Likely the use of mmoni does not Acknowledgements involve ny significnt dvntge for enhnced ioniztion in this compound. We thnk Esther Mrco for her vluble help in the preprtion of stndrds. R.V. thnks the Spnish Ministry of Eduction for Ph.D. fellowship. M.S.- 4. Conclusions S. thnks FAPESP Foundtion for Support to Scientific Reserch of the So Pulo Stte (Brzil) for The use of mmoni s regent gs in GC NICl- post-doctorl fellowship. Finncil support from the MS provides lower limits of detection nd quntit- Spnish Ministry of Helth (FISS Project No. 93/ tion thn methne for most orgnochlorine comis 0006) nd the Europen Union (ENV4-CT ) pounds. These lower limits llow the detection nd cknowledged. quntittion of species with three nd four chlorine substituents in romtic rings which re difficult to determine t trce levels when methne is used s regent gs. The use of mmoni s regent gs lso References fcilittes the quntittion of the DDT derivtives. [1] J.S. Wid, PCBs nd the Environment, CRC Press, Boc The mss spectr obtined with mmoni nd Rton, FL, methne correspond to the moleculr incorportion [2] M.D. Erickson, Anlyticl Chemistry of PCBs, Lewis, Boc of therml electrons rther thn true chemicl ioniz- Rton, FL, 1991.

7 R. Chler et l. / J. Chromtogr. A 823 (1998) [3] J.R. Hss, M.D. Friesen, D.J. Hrvn, C.E. Prker, Anl. [11] E.A. Stemmler, R.A. Hites, B. Arbogst, W.L. Budde, M.L. Chem. 50 (1978) Deinzer, R.C. Dougherty, J.W. Eichelberger, R.L. Foltz, C. [4] A. Cvllro, G. Bndi, G. Invernizzi, L. Lucini, E. Grimm, E.P. Grimsrud, C. Skshit, L.J. Sers, Anl. Chem. Mongini, G. Gorni, Environ. Sci. 5 (1982) (1988) 781. [5] E. Lewis, W.D. Jmieson, Int. J. Mss Spectrom. Ion Phys. [12] E.A. Stemmler, R.A. Hites, Biomed. Environ. Mss Spec- 48 (1983) 303. trom. 17 (1988) 311. [6] M. Oehme, P. Kirschmer, Anl. Chem. 56 (1984) [13] E.A. Stemmler, R.A. Hites, Electron Cpture Negtive-ion [7] J.-A.B. Cmpbell, D.A. Griffin, M.L. Deinzer, Org. Mss Mss Spectr of Environmentl Contminnts nd Relted Spectrom. 20 (1985) 122. Compounds, VCH, New York, 1988, 390 p. [8] M. Oehme, D. Stockl, H. Knoppel, Anl. Chem. 58 (1986) [14] J. Wrmn, M.R. Suer Jr., J. Chem. Phys. 62 (1975) [15] R. Otero, M. Sntigo-Silv, J.O. Grimlt, J. Chromtogr. A [9] L. Cnton, J.O. Grimlt, Chemosphere 23 (1991) (1997) 87. [10] R.B. Westerberg, S.L. Alibrndo, F.J. vn Lenten, J. Chromtogr. 284 (1984) 447.

Problem 22: Buffer solutions 1. The equilibrium, which governs the concentration of H + within the solution is HCOOH! HCOO + H + + Hence K

Problem 22: Buffer solutions 1. The equilibrium, which governs the concentration of H + within the solution is HCOOH! HCOO + H + + Hence K Problem : Buffer solutions. The equilibrium, hich governs the concentrtion of H ithin the solution is HCOOH! HCOO H [HCOO ] 4 Hence. [HCOOH] nd since [HCOOH] 0.00 M nd [HCOO ] 0.50 M -4 0.00 4..8 M 0.50