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Carbon skeleton capillary gas chromatography
Ji.wr& of Chrotwography,193 (1980) 437-443 @ IZkker Ekiehk P~bIishkgCompany,Amskrdam-Printed in The Nef%erbds CEiROM.
ff678
Rd-i-
COOKE’
Dcpartmad Ek&?&J
of irrorgmri Ckmirtry,
and DAVID
JAMES
ROBERTS
University
of Bristol,
tZhtock’s
Close, Ehktol
B.!B
ITS
(Great
The simplification of environmental extracts prior to determination of organochlorine pesticide residues is nonnaily attempted via thin-layer or liquid column chromatography ++. However, this procedure is far from satisfactory especially when complex components such as polychlorinated biphenyls and polychlorinated naphthalenes are presents--7 , because the separation achieved is not complete. Simplification of the extract by chemical means rather than by physics! separation presents an alternative solution :o the problem of interferences. Perchlorination of residues to give decachiorobiphenyt or octachloronaphthaIene has recently been reported to provide a much simplified extract for analysis8*q.The consequence of perchlorination however, is that the detected species is of higher molecular weight and iower volatility than the precursor compounds necessitating more extreme chromatographic conditions. AE alternative to perchlorination is hydradechlorination, first suggested by Thompson et ~1.‘~ and subsequently applied by Ati et al.” to the determination of organochiorine residues. We have recently used the hydrodechlorination procedure for the routine determination of organochlorine compounds employing gas-solid chromatographyx2**3with packed columns. To prevent interference from other hydromrbon species a mass spectrometer was used as a selective detector. The resolution available from capillary columns permits the separation of potential inter&rents from the compounds of interest. We now report tie integration of the micro+zatalytic hydrodechIorination reaction with capsllary gas chromatography to give carbon skeleton capillary gas chromatography.
Reagents
Red&i&d hexane was used as the solvent for all standard solutions. Aroc~ors (Monsanto, Newport, Great BritXn), polychlorinated naphthalene (Bayer, Lever&en, G.F.R.) and Cereclors (KX, Macclesfield, Great- Britain) were used as receive& Standard solution concentrations were IO ppm.
438 AppCXtZhS
A Fractovap 2151 Series gas chroinatograph (Carlo Erba, MiIan, Italy) and spEit&zss injdon system fitted with an OV-I column (25 m x 0.3 mm I.D.) and &tm~ionisation detector (FID) was used. The hydrogen carrier gzs flow-rate was 2 ml/min with an injection port catalyst temperatureof. 200-~.50”. Temperature programmeparameterswere: 50” hold 3 min; increaseB”/min to 250”; the increase 8=/min to 250’; hold 2 min. Attenuation was x 16. Catalysts were preparedby publishedprocedures” with particularcare being laken to neutralisethe preparationswith I N sodium hydroxide.Catdysts werethen activated using a small oven (see Fig. 3, ref. 15) with a stream of hydrogen and gradual heating to a temperatureof 300 “C which was then maintainedfor at least 2 h. Activated catalysts wxe then packed into an injection port glass liner (see Fig. 1).
capillary callan
forcarbon skeleton capillary gaschromatography. RESULTS
AND DiSCUSSION
The reactantgas for the dechlorinationreactionis hydrogenand consequently this also acts as the carrier gas. .Tke Bow of 2 rnl/miu of hydrogen through the column has no observableeffect upon the flame of the ionization detector_The injection port of the gas chromatographedcontains a glass liner sorue 8 cm long and with an internaldiameterof 4 mm. Into the centre of this glass liner is packed the catalystwhichis retainedin -positionby quartz wool plugs (Fig. f). The lineris placed in the injection port and the operating temperatureset_ Contamination associated with the loading of the catalyst is removed by runningthe temperatureprogramme -throughwithoutan injection-Samplesmay be run without cddysis by removingthe liaer containingthe catalystand replacingit with au empty one. We haveusedthissystemto studycomplex mixturescontainingpolychlorinated biphenylsand poIychlorinatednaphthalenes.Perhapsmore sign&a&y this technique is capable of determingthe presenceof a polychlorinatedalkane residuein a sample. Polychlorinatedalkaues are widely used industriallyin place of, or in conjunction
L
4
2
I I 4 i
II I I
5 2 nlatinm
-
2
2Jzo”
/ 6* min’l .
F~2Gascfrro natograpby-FID of (A) a mixture of a polychlorinatedbiphenyl,a polycblorinated naphthakm, TDE. and a po~ychlosinatedalkane: (Bj the same mixture aftercatalysis by&la&urn; z Ez_after catiysk by platinum. I = naphth≠ 2 = biphenyl;3 = dipkyi-
;
4co
No-Es
thakne compound, IDE, and a polychlorina&d a&me mixture are psesent h this sample the positive and unambiguous identification of any one of them is a doub;ful posi$ility, Fig_ 2B is the chrornatogram obtained from the same mixture when a catahyst (375, prdladium) is present in the injection porr. Fig. ZC is obtained using a 5 % pIatinum catdyst. Peaks due to biphenyi (I), naphthalene (2), diphenylethane (3) and the hydrocarbon profile of the poiychlorinated dkane (4), are well resolved. Peak 3 is due to diphenylethane generated by reduction of TDE. Comparison of Fig. X3 and C shows, apart from the unsuitability of OV-1 for chromatographing aromatic species (note the tailing peaks), that a platinum cataIyst is more suitable for the hydrodcchIorination of alkanes and less suitable for the stripping of aromatic species than palladium. Polychlorinated alkanes are marketed in Great Britain under the tradename “cXrcc!or”. They are mzde by tbc chlorination of hydrocarbon fractions. The three dif$erent f&stocks used in the production of “Cereclor” are a C,,C, fraction, a C,,-C17 fraction and a C,-C, faction. Fig. 3A is a cbromatogram of the three basic feedstocks. Fig. 3B is the cbromatogram of three Cereclors SOLV, S52 and 54 m-=asured with an RD. A similar trace is obtained using an electroncapture detector_ On @acing a platinum catalyst in the injection port of the chromatograph and injecting the same ‘&ree chlorinated alkanes the trace shown in Fig_ 3C is obtained_ Hydrodechlorination of 50LV gives the C,,,-C, n-alkanes, of S52 gives the Cl&r7 n-alkanes. Ccreclor 54 gives the C,-C& n-alkancs. Fig. 3D is the capillary gas chromatogram of the hexane extract of a “rubber&xi” fioor tile obtained using an FID. Fig_ SE is the carbon skeleton chromatogram (5 % Pt, 200’) of the same extract. The presence of a polychlorinatezd zlkane based upon the C,,-C,, n-alkane fraction is clearly demonstrated. We have no evidence to suggest that any “scrambling” reaction leading to the formation of branched-chain alkanes takes place during the catalysis step. The mechanism of this reaction is unclear, Whereas chioro-aromatic species may adsorb onto the c&i.lyst with concommitant formation of an activated complex involving polarization of the carbon-chlorine bond 16,the absence of z-electrons precludes this possibility for alkanes. However, the non-bonding electron pairs on the chlorine atom of the carbon-chiorine bond may become loosely co-ordinatcd to the catalyst surface The mechanism depict& in Fig. 4 then becomes 2 possibility. Scrambling of the alkane chain will occur if the cleavage of the carbon-chlorine bond and formation of the carbon-hydrogen bond are not concerted_ Reformation of the transient carbonium ion to a more stable conformation may then occur to give branchedchain alkanes. The byproduct of the hydrodechlorination is. n-y, HCI. The fate of this HCl is unclear and attack upon the polymeric silicone liquid phase is a possibility. However, an OV-1 column used with a catalyst and rcgulariy programmed to 300” lzas &&raded no more rapidly than an equivafent column in conventional use. The activation and conditioning of catalysts for use in capillary gas chromate graphs is more critical than for packed columns because a signi$icant amount of volatile material may be displaced from the catalyst during the initial activation. This is particularly true for iron catalysts presumab!y because of the volatility of ferric chIoride. Ideahy therefore catalyst material should be activated before being Ioaded into the injection port to avoid contamination of the top of the cohunn
1;*i
;p
Fii_ 3. Gas cbmnatography-FID of (A) the three CerecIor feedstocks, Cm-G. &-Cm C22-c50; (B) of the threeCerec~ors5OtV, S52 and 5.4;(C) of SOLV. SSZ and 53 after catalysisby platinum; and capillary gas chromatography-FID of (D) hexme extrzct of “rubbcriscd” Roar tile; (E) the same extract after cataIysis by pWmm.
1, Activationof Czt.2fyz.t
2. Hydrcdechlorimtim.fc;-aation cf C-H hnd
-E-C-
/ \
3; Loss of HCl. re&xration of catalyst
I-&-
&E
E
-c
d-
I=@. 4. Ii possiik m&ran&i
for the catzlytic hydrode&hSmfion
of poIychlo&wxi
alkmese
CONCLUSfON
The catalytic hydrodechlorination of many environmentallysign&ant organochlorine compounds may be successfSIy achievedin the injectionport of a capiikry gas chromatograph,withoutany apparentelfectupon chromatographicperformance_ For arcmaticorganochlorinecompoundsa p&xikm catalystis recommendedbut for poIychlotitcd alkane compounds a platinum catalyst is preferred_
1 I. C. T-v EW_ _4%virua C&mm_ TotiaL, 19 (1978) 23_ 2 N. V.. Fehrkger and J. E. We&all, 3. CZrortzu~~. 57 (1971) 397. 3 N. J_ Kwseth and E M. Em& BM. Eirviizm Cuntam. ToxicoI_. 21 (1979) 213. 4 M&.wzi of A~&yzi& Qiuzby Contm~for Pesticiciesin Kwmm azzdi%v~FatmentaiMedLz, US. Enviscr~ral Protection Agency, F&may, 1976.
5 6 7 8 9
D_ E We&s aad S_ 3. Jctftnscone, JI. Cbom~_, 140 (1977) 17. D. C_ Abbatt, J. Ru. Off;c- AnaE. fZknz_, 24 (197I) 1332, V. zitko, J_ chromogr... 59 (1971) 444. C. L. Stratmr, J. M. A&m and S. A. Wkiffocic, Bun. Ewirott_ Contam. pbxko& 21(1979) 230. L. R. Kamps, W. I. Trotter, S. J. Youq, L. 3. Carson, J_A. 6. Roach, 3. A_ Sphcm,J. T_ Tanner and B. Mc~on. &dimEkvhm. Gmmm. Toxicok, 20 (1978) 589. 10 C. J_Thwpsoa, EL J_C-uC. C. Waii and EL T. R&l. &IQ& Chem., ti (i%i) k54, lt R I_ As& F. A_ Gtmkr, W. E. W&I&e and u. &vat& I. &r. Fd. C&JTI..,19 (K371) 395. 12 M. COON K. D. Khallef, G. NiWess and D. 3. Roberts, J. Chromarogr., IiS (L979) 183. !3 M. CO&Z, G. Nickless, A_ C POV~Yad D_ J_ ROE* Sci T~td. Envinm, i3 (1979) 17. 14 M. Co&e, G. Nickkss. A. M. Rcsco~ and D. J. Robds, i. Chromtogr., 156(1978) 293. 15 M. C&&e, G. X&kss and D. I. Roberts, 3. Ctrrommgr.. 187 (1980) 47. 16 R. B_ LaPkrre, L. Gni, W. L. JKranichand A. EL Weiss, A Ckzdysis, 52 (1978) 230.
ff678
Rd-i-
COOKE’
Dcpartmad Ek&?&J
of irrorgmri Ckmirtry,
and DAVID
JAMES
ROBERTS
University
of Bristol,
tZhtock’s
Close, Ehktol
B.!B
ITS
(Great
The simplification of environmental extracts prior to determination of organochlorine pesticide residues is nonnaily attempted via thin-layer or liquid column chromatography ++. However, this procedure is far from satisfactory especially when complex components such as polychlorinated biphenyls and polychlorinated naphthalenes are presents--7 , because the separation achieved is not complete. Simplification of the extract by chemical means rather than by physics! separation presents an alternative solution :o the problem of interferences. Perchlorination of residues to give decachiorobiphenyt or octachloronaphthaIene has recently been reported to provide a much simplified extract for analysis8*q.The consequence of perchlorination however, is that the detected species is of higher molecular weight and iower volatility than the precursor compounds necessitating more extreme chromatographic conditions. AE alternative to perchlorination is hydradechlorination, first suggested by Thompson et ~1.‘~ and subsequently applied by Ati et al.” to the determination of organochiorine residues. We have recently used the hydrodechlorination procedure for the routine determination of organochlorine compounds employing gas-solid chromatographyx2**3with packed columns. To prevent interference from other hydromrbon species a mass spectrometer was used as a selective detector. The resolution available from capillary columns permits the separation of potential inter&rents from the compounds of interest. We now report tie integration of the micro+zatalytic hydrodechIorination reaction with capsllary gas chromatography to give carbon skeleton capillary gas chromatography.
Reagents
Red&i&d hexane was used as the solvent for all standard solutions. Aroc~ors (Monsanto, Newport, Great BritXn), polychlorinated naphthalene (Bayer, Lever&en, G.F.R.) and Cereclors (KX, Macclesfield, Great- Britain) were used as receive& Standard solution concentrations were IO ppm.
438 AppCXtZhS
A Fractovap 2151 Series gas chroinatograph (Carlo Erba, MiIan, Italy) and spEit&zss injdon system fitted with an OV-I column (25 m x 0.3 mm I.D.) and &tm~ionisation detector (FID) was used. The hydrogen carrier gzs flow-rate was 2 ml/min with an injection port catalyst temperatureof. 200-~.50”. Temperature programmeparameterswere: 50” hold 3 min; increaseB”/min to 250”; the increase 8=/min to 250’; hold 2 min. Attenuation was x 16. Catalysts were preparedby publishedprocedures” with particularcare being laken to neutralisethe preparationswith I N sodium hydroxide.Catdysts werethen activated using a small oven (see Fig. 3, ref. 15) with a stream of hydrogen and gradual heating to a temperatureof 300 “C which was then maintainedfor at least 2 h. Activated catalysts wxe then packed into an injection port glass liner (see Fig. 1).
capillary callan
forcarbon skeleton capillary gaschromatography. RESULTS
AND DiSCUSSION
The reactantgas for the dechlorinationreactionis hydrogenand consequently this also acts as the carrier gas. .Tke Bow of 2 rnl/miu of hydrogen through the column has no observableeffect upon the flame of the ionization detector_The injection port of the gas chromatographedcontains a glass liner sorue 8 cm long and with an internaldiameterof 4 mm. Into the centre of this glass liner is packed the catalystwhichis retainedin -positionby quartz wool plugs (Fig. f). The lineris placed in the injection port and the operating temperatureset_ Contamination associated with the loading of the catalyst is removed by runningthe temperatureprogramme -throughwithoutan injection-Samplesmay be run without cddysis by removingthe liaer containingthe catalystand replacingit with au empty one. We haveusedthissystemto studycomplex mixturescontainingpolychlorinated biphenylsand poIychlorinatednaphthalenes.Perhapsmore sign&a&y this technique is capable of determingthe presenceof a polychlorinatedalkane residuein a sample. Polychlorinatedalkaues are widely used industriallyin place of, or in conjunction
L
4
2
I I 4 i
II I I
5 2 nlatinm
-
2
2Jzo”
/ 6* min’l .
F~2Gascfrro natograpby-FID of (A) a mixture of a polychlorinatedbiphenyl,a polycblorinated naphthakm, TDE. and a po~ychlosinatedalkane: (Bj the same mixture aftercatalysis by&la&urn; z Ez_after catiysk by platinum. I = naphth≠ 2 = biphenyl;3 = dipkyi-
;
4co
No-Es
thakne compound, IDE, and a polychlorina&d a&me mixture are psesent h this sample the positive and unambiguous identification of any one of them is a doub;ful posi$ility, Fig_ 2B is the chrornatogram obtained from the same mixture when a catahyst (375, prdladium) is present in the injection porr. Fig. ZC is obtained using a 5 % pIatinum catdyst. Peaks due to biphenyi (I), naphthalene (2), diphenylethane (3) and the hydrocarbon profile of the poiychlorinated dkane (4), are well resolved. Peak 3 is due to diphenylethane generated by reduction of TDE. Comparison of Fig. X3 and C shows, apart from the unsuitability of OV-1 for chromatographing aromatic species (note the tailing peaks), that a platinum cataIyst is more suitable for the hydrodcchIorination of alkanes and less suitable for the stripping of aromatic species than palladium. Polychlorinated alkanes are marketed in Great Britain under the tradename “cXrcc!or”. They are mzde by tbc chlorination of hydrocarbon fractions. The three dif$erent f&stocks used in the production of “Cereclor” are a C,,C, fraction, a C,,-C17 fraction and a C,-C, faction. Fig. 3A is a cbromatogram of the three basic feedstocks. Fig. 3B is the cbromatogram of three Cereclors SOLV, S52 and 54 m-=asured with an RD. A similar trace is obtained using an electroncapture detector_ On @acing a platinum catalyst in the injection port of the chromatograph and injecting the same ‘&ree chlorinated alkanes the trace shown in Fig_ 3C is obtained_ Hydrodechlorination of 50LV gives the C,,,-C, n-alkanes, of S52 gives the Cl&r7 n-alkanes. Ccreclor 54 gives the C,-C& n-alkancs. Fig. 3D is the capillary gas chromatogram of the hexane extract of a “rubber&xi” fioor tile obtained using an FID. Fig_ SE is the carbon skeleton chromatogram (5 % Pt, 200’) of the same extract. The presence of a polychlorinatezd zlkane based upon the C,,-C,, n-alkane fraction is clearly demonstrated. We have no evidence to suggest that any “scrambling” reaction leading to the formation of branched-chain alkanes takes place during the catalysis step. The mechanism of this reaction is unclear, Whereas chioro-aromatic species may adsorb onto the c&i.lyst with concommitant formation of an activated complex involving polarization of the carbon-chlorine bond 16,the absence of z-electrons precludes this possibility for alkanes. However, the non-bonding electron pairs on the chlorine atom of the carbon-chiorine bond may become loosely co-ordinatcd to the catalyst surface The mechanism depict& in Fig. 4 then becomes 2 possibility. Scrambling of the alkane chain will occur if the cleavage of the carbon-chlorine bond and formation of the carbon-hydrogen bond are not concerted_ Reformation of the transient carbonium ion to a more stable conformation may then occur to give branchedchain alkanes. The byproduct of the hydrodechlorination is. n-y, HCI. The fate of this HCl is unclear and attack upon the polymeric silicone liquid phase is a possibility. However, an OV-1 column used with a catalyst and rcgulariy programmed to 300” lzas &&raded no more rapidly than an equivafent column in conventional use. The activation and conditioning of catalysts for use in capillary gas chromate graphs is more critical than for packed columns because a signi$icant amount of volatile material may be displaced from the catalyst during the initial activation. This is particularly true for iron catalysts presumab!y because of the volatility of ferric chIoride. Ideahy therefore catalyst material should be activated before being Ioaded into the injection port to avoid contamination of the top of the cohunn
1;*i
;p
Fii_ 3. Gas cbmnatography-FID of (A) the three CerecIor feedstocks, Cm-G. &-Cm C22-c50; (B) of the threeCerec~ors5OtV, S52 and 5.4;(C) of SOLV. SSZ and 53 after catalysisby platinum; and capillary gas chromatography-FID of (D) hexme extrzct of “rubbcriscd” Roar tile; (E) the same extract after cataIysis by pWmm.
1, Activationof Czt.2fyz.t
2. Hydrcdechlorimtim.fc;-aation cf C-H hnd
-E-C-
/ \
3; Loss of HCl. re&xration of catalyst
I-&-
&E
E
-c
d-
I=@. 4. Ii possiik m&ran&i
for the catzlytic hydrode&hSmfion
of poIychlo&wxi
alkmese
CONCLUSfON
The catalytic hydrodechlorination of many environmentallysign&ant organochlorine compounds may be successfSIy achievedin the injectionport of a capiikry gas chromatograph,withoutany apparentelfectupon chromatographicperformance_ For arcmaticorganochlorinecompoundsa p&xikm catalystis recommendedbut for poIychlotitcd alkane compounds a platinum catalyst is preferred_
1 I. C. T-v EW_ _4%virua C&mm_ TotiaL, 19 (1978) 23_ 2 N. V.. Fehrkger and J. E. We&all, 3. CZrortzu~~. 57 (1971) 397. 3 N. J_ Kwseth and E M. Em& BM. Eirviizm Cuntam. ToxicoI_. 21 (1979) 213. 4 M&.wzi of A~&yzi& Qiuzby Contm~for Pesticiciesin Kwmm azzdi%v~FatmentaiMedLz, US. Enviscr~ral Protection Agency, F&may, 1976.
5 6 7 8 9
D_ E We&s aad S_ 3. Jctftnscone, JI. Cbom~_, 140 (1977) 17. D. C_ Abbatt, J. Ru. Off;c- AnaE. fZknz_, 24 (197I) 1332, V. zitko, J_ chromogr... 59 (1971) 444. C. L. Stratmr, J. M. A&m and S. A. Wkiffocic, Bun. Ewirott_ Contam. pbxko& 21(1979) 230. L. R. Kamps, W. I. Trotter, S. J. Youq, L. 3. Carson, J_A. 6. Roach, 3. A_ Sphcm,J. T_ Tanner and B. Mc~on. &dimEkvhm. Gmmm. Toxicok, 20 (1978) 589. 10 C. J_Thwpsoa, EL J_C-uC. C. Waii and EL T. R&l. &IQ& Chem., ti (i%i) k54, lt R I_ As& F. A_ Gtmkr, W. E. W&I&e and u. &vat& I. &r. Fd. C&JTI..,19 (K371) 395. 12 M. COON K. D. Khallef, G. NiWess and D. 3. Roberts, J. Chromarogr., IiS (L979) 183. !3 M. CO&Z, G. Nickless, A_ C POV~Yad D_ J_ ROE* Sci T~td. Envinm, i3 (1979) 17. 14 M. Co&e, G. Nickkss. A. M. Rcsco~ and D. J. Robds, i. Chromtogr., 156(1978) 293. 15 M. C&&e, G. X&kss and D. I. Roberts, 3. Ctrrommgr.. 187 (1980) 47. 16 R. B_ LaPkrre, L. Gni, W. L. JKranichand A. EL Weiss, A Ckzdysis, 52 (1978) 230.