Anal. Chem. 1002, 64, 3161-3167
9161
Quantitative Determination of Sulfonated Aliphatic and Aromatic Surfactants in Sewage Sludge by Ion-Pair/ Supercritical Fluid Extraction and Derivatization Gas ChromatographyIMass Spectrometry Jennifer A. Field,'JJ David J. Miller,s Thomas M. Field,? Steven B. Hawthorne) and Walter Gigert Swiss Federal Institute for Water Resources and Water Pollution Control (EAWAG), CH-8600 Diibendorf, Switzerland, and Energy and Environmental Research Center, University of North Dakota, Grand Forks, North Dakota 58202
Secondary alkenesulfonate (SAS) and linear alkylbenzene sulfonate (LAS) surfactants were quantltatlvely (>go%) extracted from sewage sludges as their tetrabutylammonlum Ion palrs wlng 400 atm of supercrltlcal C 0 2 for 5 mln of static extractlon followed by 10 mln of dynamlc extractlon at 80 OC. Ion palrs of SAS and LAS quantltatlvely formed butyl esters In the lnjectlon port of the gas chromatograph and were determlnd by gas chromatography/mam smrometry wtthout clam fractlonatlon of the sewage sludge extracts. Concentratlons of SAS and LAS In sludges from five different sewage treatment plants ranged from 0.27 to 0.80 g/kg of dry sewage sluge and from 3.83 to 7.51 g/kg, respectlvely. Good reproduclblllty was achleved wtth RSDs of typlcally 5 % for replicate extractlons and analyses. Homologue and Isomer dlstrlbutlons of SAS In sewage dudge lndlcated an enrlchment of the more hydrophoblc componentsIn sewage sludge durlng sewage treatment.
INTRODUCTION Supercritical fluid extraction (SFE) has gained attention
as a viable technique for combining derivatization reactions with extraction for the determination of polar and ionic organic compounds in solid samples. Coupling derivatization reactions with sample extraction and concentration reduces sample handling and analysis time. Hawthorne et ala1 reported SFE of polar analytes (e.g., 2,4-dichlorophenoxyacetic acid, phospholipid-derived fatty acids, and phenols) using trimethylphenylammonium hydroxide as an ion pair and methylating reagent. Hills et al.2 combined silylation reactions with SFE for extracting oxalic acid, dicarboxylic acids, and alcohols from roasted coffee. Important classes of amphiphilic compounds used in laundry and cleaning products are linear alkylbenzenesulfonate (LAS) surfactants with 1.8 X lo6 tons consumed worldwide in 1987.3 Although it has been shown that LAS removal from the aqueous phase varies from 80 to 98% depending on the type of sewage treatment? LAS generally + Swiss Federal Institute for Water Resources and Water Pollution Control. t Current address: Department of Agricultural Chemistry, Oregon State University, Corvallis, OR 97331. f Energy and Environmental Research Center. (1)Hawthorne, S.B.; Miller, D. J.; Nivens, D. E.; White, D. C. Anal. Chem. 1992,64,405-412. (2)Hills, J. W.; Hill, H. H.; Maeda, T. Anal. Chem. 1992,63,2152-
2155. (3)Berth, P.; Jeschke, P. Tenside, Surfactants, Deterg. 1989,26,7579. 0003-2700/92/0364-3161$03.0010
accumulates in sewage sludges.58 Concentrations of LAS in sewage sludge and sediment have been determined using various extraction methods including refluxing in methanol: sonication using methanol? and ion-pair extraction using methylene blue.6 It also has been shown that LAS is quantitatively extracted from sewage sludge using SFE with methanol as modifer.10 Secondary alkanesulfonates (SAS) are surfactants with a European SAS production capacity of approximately 1.5 X lo5 tons/yearl1 and are potentially present in sewage sludge and extractable using LAS extraction methods. LAS can be determined using HPLC with UV absorption12 or fluorescence13-15 detection, but SAS lack a chromophore and is therefore not amenable to HPLC methods using photometric detectors. Because SAS and LAS are ionic, nonvolatile analytes, derivatization is required prior to their determination by GC. Previously reported derivatization procedures for LAS, including formation of sulfonyl chlorides,6JB-l8 methyl esters,16J*21 and trifluoroethyl esters,9922 are not directly amenable for coupling with extraction techniques and typically require multiple preparative steps and the use of hazardous reagents (e.g. diazomethane). However, Heywood et al.19 reported high-temperature esterification of p-dodecylbenzenesulfonicacid from its tetramethylammonium ionpair form. As previously reported,' ion-pair extraction under (4)Rapaport, R. A.; Eckhoff, W. S. Enuiron. Toxicol. Chem. 1990,9, 1245-1257. (5)McEvoy, J.; Giger, W. Naturwissenschaften 1985,72,429-431. (6)McEvoy, J.; Giger, W. Enuiron. Sci. Techno 986,20,376-383. (7)Giger, W.; Alder, A. C.; Brunner, P.; Mar omini, A.; Siegrist, H. Tenside Surfactants Deterg. 1989,26,95-100. (8) Matthijs, E.; DeHenau, H. Tenside, Surfactants,Deterg. 1987,4, 193-199. (9)Trehy, M.; Gledhill, W. E.;Orth, R. G. Anal. Chem. 1990,62,25812586. (10)Hawthorne, S.B.; Miller, D. J.; Walker, D. D.; Whittington,D. E.; Moore, B. L. J . Chromatogr. 1991,541,185-194. (11)Personal communication, Hds AG, Marl, Germany, 1991. (12)Marcomini, A.; Giger, W. Anal. Chem. 1987,59,1709-1715. (13)Castles, M. A.;Moore, B. L.; Ward, S. R. Anal. Chem. 1989,61, 2534-2540. (14)Nakae, A.; Tsuji, K.; Yamanaka, M. Anal. Chem. 1980,52,22752277. (15)Kikuchi, M.; Tokai, A.; Yoshida, T. Water Res. 1986,20,643-650. (16)Parsons, J. S. J. Gas Chromatogr. 1967,May, 254-256. (17)Watanabe,S.;Nukiyama,M.;Takagi,F.;Lida,K.;Kaise,T.;Wada, Y. J . Food Hyg. SOC.Jpn. 1975,16,212-217. (18)Hon-nami, H.; Hanya, T. J . Chromatogr. 1978,161,205-212. (19)Heywood, A.;Mathias, A.; Williams, A. E. Anal. Chem. 1970,42, 1272-1273. (20)Imaida, M.; Sumimoto, T.; Yada, M.; Yoshida, M.; Koyama, K.; Kunita, N. J. Food Hyg.SOC.Jpn. 1975,16,218-224. (21)Kirkland, J. 3. Anal. Chem. 1960,32,1388-1393. (22)Field, J. A.;Leenheer, J. A.; Thorn, K. A.; Barber, L.; Roatad, C. E.; Macalady, D.L.; Daniel, S. R. J. Contam. Hydrol. 1992,9,55-78.
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ANALYTICAL CHEMISTRY, VOL. 64, NO. 24, DECEMBER 15, 1992
SFE conditions using tetraalkylammonium ion-pair reagents can be coupled with ion-pair derivatization, thereby minimizing analysts exposure to hazardous reagents as well as reducing the number of sample preparation steps and time. This paper describes an ion-pair/SFE and injection-port derivatization method for determining SAS and LAS in sewage sludges. SAS and LAS are coextracted from sewage sludge and unambiguously determined by gas chromatography/mass spectrometry (GUMS)without class fractionation of the SFE extract. The ion-pair/SFE method presented in this paper reduces total sample preparation and analysis time to less than 1 h.
EXPERIMENTAL SECTION Samples. Three anaerobically stabilized sewage sludges and two fresh (untreated) sludges were collected from mechanicalbiological sewage treatment plants in the area of Ztirich, Switzerland. Sewage sludge samples were dried at 80 "C for 72 h, finely ground, and stored in amber bottles. Chemicals and Reagents. Commercial mixtures of SAS (Hostapur 60; Hoechst AG, Frankfurt, Germany) and LAS (Dobane 113;Shell) were obtained through the Lever Co. (Port Sunlight, England) for use as standards. Primary alkanesulfonates(C12-SASand C18-SAS)were purchased from Lancaster Synthesis Ltd. (Lancaster, England) for use as SAS surrogates and 4-octylbenzenesulfonicacid (C8-LAS)was purchased from Aldrich Chemical (Milwaukee,WI). The Clz-SAS,ClB-SAS, and Cs-LAS surrogates were chosen for this study because they do not occur in commercialSASand LAS mixtures and are therefore suitable for evaluating the efficiency of SAS and LAS extraction and alkylation. Reagent grade ion-pair reagents were prepared as 0.5 M methanolic solutions except where noted. Reagents tested included tetrabutylammonium hydrogen sulfate (TBA;Aldrich Chemical),tetraethylammonium hydrogen sulfate (TEA; Fluka AG, Buchs, Switzerland), tetramethylammonium hydrogen sulfate (TMA;Aldrich Chemical), trimethylphenylammonium hydroxide (0.2 M) (TMPA; Pierce, Rockford, IL), and (trifluoromethy1)phenylammoniumhydroxide (0.2 M) (TFMPA;Alltech, Deerfield, IL). A preliminary survey of ion-pair reagents was first conducted to determine the most efficient reagent for ion-pair extraction and derivatization of SAS using water as the sample matrix. Reagent evaluation based on liquid-liquid extraction of aqueous SAS standard solutions was performed at room temperature by adding 0.5 mL of each 0.5 M ion-pair reagent to separate vials containing 3 mL of 15 pg/mL C12-SAS standard. Standard solutions were extracted a total of three times with 2 mL of chloroform by shaking for 30 s. The chloroform extracts were combined and concentrated to 1 mL under nitrogen. Samples for this preliminary investigation of ion-pair reagents were analyzedusing a Hewlett Packard Model 5890 GC equipped with a HP-5 column (20-m X 0.2-mm X 0.17-pm film thickness; Hewlett-Packard) with flame ionization detection (FID). Injection conditions included a split ratio of 1:15,a glass inlet liner packed with silanized glass wool, and an inlet injection temperature of 300 "C. The GC oven was ramped from an initial temperature of 100 to 250 "C at 10 "C/min. Ion-Pair/Supercritical Fluid Extraction. All extractions were performedusing an ISCO 260D pump and SFX 210 extractor (Lincoln, NE) and SFC grade COz (Scott Specialty Gases, Plumsteadville, PA). Lengths (10 cm) of 30-32-pm-i.d. fused silica (Polymicro Technologies, Phoenix, AZ) were attached to the extractor outlet and used to obtain dynamic extraction flow ratesof 0.74.9 mL/min measured as liquid COz flow at the pump. Extracts were collected by placing the end of the restrictor in 3-4 mL of chloroform. Chloroform was periodically added to the collection vials to compensate for evaporative losses during the extraction. During the dynamic extraction step, the restrictor was constantly warmed with a heat gun to maintain constant flow by minimizing restrictor plugging. Ion-pair/SFE, a two-step procedure, was applied using a static extraction step during which an ion-pair reagent is permitted to mix with the sewage sludgesample under supercritical conditions,
followed by a dynamic extraction step to recover the extracted analytes. Unless otherwisenoted, the followingprocedures were used for extracting sewage sludgesunder ion-pair/SFE conditions. First, a 0.45-pm glass-fiber filter (Gelman Sciences, Ann Arbor, MI) was placed over the outlet frit of a 2.5-mL ISCO extraction cell end cap to minimize restrictor plugging by the finely ground sewage sludge. The extraction cell body was attached and dry sewage sludge (100 mg) was then weighed directly into the cell followed by addition of 25 pL of 2 pg/mL each SAS and LAS surrogates and 1 mL of ion-pair reagent. Finally, the cell was placed into the extractor (maintained at 80 "C) and immediately pressurized to 400 atm of COz for 5 min of static extraction by opening the inlet valve and keeping the exit valve closed. After 5 min, the exit valve was opened for 10min of dynamic extraction. The cell was removed from the extractor and allowed to cool to room temperature. Secondand third extractions were conducted by adding additional SAS and LAS surrogates and 1mL of ionpair reagent to the cooled cell and repeating the extraction procedure. Sewage sludge extracts were concentrated to ca. 1 mL under a gentle stream of nitrogen and transferred to GC autosampler vials. The sewage sludge extracts required no additional fractionationor cleanup steps prior to GC/MS analysis. Conventional Liquid Solvent Extraction of Sewage Sludge. Liquid solvent extraction of sewage sludge using 0.02 M TBA in methanol was performed using a sewage sludge collected from the Ziirich-Glatt sewage treatment plant. Three 100-mgsamples of sewage sludge were weighed into 15-mLglass vials with Teflon-lined screw caps. TBA (5 mL) was added to each vial, and the mixtures were sonicated for 30 min at room temperature. The vials were centrifuged for 10min, after which the methanol supernatant was decanted. Each sewage sludge sample was extracted a total of three times by adding 5 mL of fresh TBA prior to each extraction. The three extracts for each sewage sludge sample were combined, spiked with SAS and LAS surrogates, and concentrated to approximately 0.5 mL for GC/ MS analysis. Gas Chromatography/Mass Spectrometry. Gas chromatographicseparationswere performedwith a Hewlett-Packard Model 5890 GC equipped with a HP-5 column (20-m X 0.2-mm i.d. x 0.33-pm film thickness; Hewlett-Packard) with helium as carrier gas. For SAS and LAS determinations, the oven was ramped at 10 "C/min from an initial temperature of 110 to 220 "C, followed by a second ramp of 6 "C/min to 300 OC where the temperature was held for 3 min. Injection-port conditions for SAS and LAS included a split ratio of 1:7,an injector temperature of 300 "C, and a glass inlet liner with a plug of silanized glass wool. Inlet liners were routinely replaced every 20-25 injections. Each sewage sludge extract injection was followed by a 1-pL injection of TFMPA to minimize any potential sample carryover into the next injected sample. For TFMPA injections the GC oven was ramped at 20 W m i n from 110to 300 "C. Mass spectral detection was performed with a Hewlett-Packard 5971A massselective detector with electron impact ionization (70 eV). The mass spectrometer was operated in both full scan (50-400 amu) and in selected ion mode (SIM) using a dwell time of 50 ms for each mass. GC/MS Quantitation of SAS and LAS. Commercial preparations of Hostapur 60 and Dobane 113 were used to construct SAS and LAS quantitation curves,respectively. Glass vials containing aqueous solutions of 50-1000 pg of SAS and from 500 to 1500pg of LAS were each spiked with 50 rg each of Clz-SAS, ClB-SAS, and Cs-LAS. To each vial, 0.5 mL of 0.5 M TBA in methanol was added and shaken to allow ion-pair formation. Each sample was then extracted a total three times with 2 mL of chloroform each for 30 s. The chloroform extracts were combined and evaporated to 0.5 mL. For quantitation, the peak areas of the ([M - 138]'+) ions at m/z 196,210,224,and 238 corresponding to the C14-, C16-, C16-, and C17-SAS homologues, respectively, were ratioed to the area of the ([M - 138]'+)ion at mlz 168of the C12-SASsurrogate. The correlation between peak area and total SAS concentration was determined by linear regression, typically with r2 = 0.997. SAS homologue distributions were determined by summingall isomers for each homologue and calculating their percent of the total. Quantitation of LAS was based on the sum of the ion currents correspondingto mlz 91,171,and 185. ALAS quantitation curve
ANALYTICAL CHEMISTRY, VOL. 64, NO. 24, DECEMBER 15, 1992
Table I. Relative Efficiency of CltSAS Derivatization ion-pair alkyl group added 7% SAS retained by reagent by the inlet linerb reagents' TBA butyl nd TEA ethyl 40 TMA methyl 50 TFMPA methyl 20 TMPA methyl 10
3183
(A) 6.C14.SAS
~~
Jo,lc~~lrcH, H-lCHJrC
H,C-lCH,],-C
H,
[M-138It*
TBA tetrabutylammoniumhydrogen sulfate. TEA: tetraethylammonium hydrogen sulfate. TMA: tetramethylammoniumhydrogen sulfate. TFMPA: (trifluoromethy1)phenylammoniumhydroxide. TMPA: trimethylphenylammoniumhydroxide. * % SAS retained by the inlet liner is determined by comparing the peak area in the first injection to that observed for a subsequent injection of 1p L of TFMPA. nd: not detected. 0
.
~
~
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~
was constructed by ratioing the area of the LAS standard to that of the Ca-LAS surrogate. The correlation between total LAS and Ca-LAS surrogate peak area and total LAS concentration was determined by linear regression, typically with r2 = 0.994. High-PerformanceLiquid Chromatography. HPLC with fluorescence detection was used to independently determine whether alkylation occurred under SFE or injection-port conditions. The butyl ester of the Ca-LAS surrogate (C8-LAS-Bu) was prepared by an alternative method to ion-pair derivatization by first convertingCa-LASto ita sulfonylchloride derivative with phosphorus pentachloride, followed by substitution to the butyl ester using butanol. Formation of C8-LAS-Bu was verified by GC/MS. Prederivatized Cs-LAS-Buwas then spiked intoextracts of both a LAS commercialmixture, extracted from water at room temperature, and a sewage sludge extracted under ion-pair/SFE conditions. Underivatized Cs-LAS surrogate had been added to eachsample prior to extraction. Extrack were analyzed by HPLC before and after spiking with Cs-LAS-Bu. HPLC separations were performed with a liquid chromatograph (Hewlett-Packard 1090) equipped with a dual grating fluorescencespectrophotometer (Hewlett-Packard1046A). The fluorescence detector was operated at an excitation wavelength of 225 and an emission wavelength of 295 nm, with a spectral band-pass of 2 nm. The volume of the detector flow cell was 5 pL. For reversed-phase separations, a Hypersil ODS (120-mm x 2.1-mm i.d.) column (Hewlett-Packard) was operated at ambient temperature with a flow rate of 0.4 mL/min. Gradient elution was performed with a binary solution of methanol and 0.1 M ammonium acetate buffer (pH 6.5) using a linear gradient from 35/65 methanol/buffer to 90/10 methanol/buffer in 25 min. One minute of 35/65 methanol/buffer was used to reestablish initial conditions.
RESULTS AND DISCUSSION
Ion-Pair Reagent Evaluation. Ion-pair reagents served two purposes in this study. First, ion-pair reagents enhanced the extraction of sulfonatedsurfactants into supercriticalCO2 by decreasing their polarity. Second, surfactant ion pairs underwent derivatization in the GC injection port to form sulfonate alkyl esters. Since different ion-pair derivatization reagents were available and since derivatization efficiency may depend upon the reagent selected, ion-pair reagents were evaluated for their reaction with SAS to form alkyl esters under injection-portconditions (Table I). Of the five reagents tested, only TBA indicated no retention of SAS by the inlet liner. In addition, SAS butyl esters formed quantitatively from SAS ion pairs with TBA under injection-portconditions, as demonstrated by the fact that the peak area for the Cl2SAS surrogate was between 90 and 107% of the predicted response. Gas ChromatographyIMass Spectrometry of SAS a n d LAS. Mass spectral fragmentation (Figure 1A)for SASunder electron impact ionization was consistent with fragmentation
~
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60
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120
~
140
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160
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180
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z
117
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150
200
MI2
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250
300
Flgure 1. Mass spectra of (A) 6CI4-SAS and (6) 3C111AS.
previously reported for alkyl esters of alkane sulfonates.23 Although the commercial SAS standard was reported to contain mono-, di-, and polysulfonates, only monosulfonated SAS were detected using GCIMS. All SAS components give an intense homologue-specific ion of ([M- 138]*+),corresponding to the loss of HS03C4H9 (sulfonate butyl ester). Therefore, the ([M - 138]*+)ions of mlz 168, 196, 210, 224, and 238 were used for quantitating the C12-SAS surrogate, native C14-SAS,C1&3AS, CI~-SAS, and Ci,-SAS, respectively. Since preliminary work indicated that C13-SASand Cls-SAS, found at trace levels in the SAS commercial mixture, were not detectable in sewage sludge extracts; their ([M - 1381*+) ions were excluded from subsequent analyses. Electron impact ionization spectra of LAS were characteristic of the aromatic nature of LAS (Figure 1)with intense peaks typically at mlz 91 (tropylium ion) or rnlz 171 or 185, corresponding to CnH&6H4S03H where n = 1 or 2.24 For purposes of locating individual LAS homologues and their isomers, the [M - 551+ ions of mlz 299, 313, 327, and 341 arising from the loss of C4H7, were characteristic of Cia-LAS, Cll-LAS, C12-LAS,and Ci3-LAS, respectively. The sum of theLASionsat m/z91,17l,and 185wereusedforquantitating the C8-LAS surrogate and native C10-C14-LAS in ion-pairl SFE extracts of sewage sludge. Total ion current chromatograms for extracts of sewage sludge demonstrated the complexity of the sample extracted (23) Truce, W. E.; Campbell, R. W.; Madding, G. D. J. Org. Chem. 1967,32,308-317. (24) Agozzino, P.; Ceraulo, L.; Ferrugia, M.; Caponetti, E.; Intravaia, F.; Triolo, R. J. Colloid Interface Sci. 1986, 26-31.
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ANALYTICAL CHEMISTRY, VOL. 64, NO. 24, DECEMBER 15, 1992
4
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t 50
-e 0
0 0
L L
I
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I
14
16
18
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I
22
24
1
20
time, min Flgure 2. Total ion current chromatogramfor the unfractlonatedionpair/SFE extractof sewage sludge with the retentiontimes of surrogate and native SAS and LAS indicated.
&AS (m/z 196)
A
C1$AS
(m/z 224)
100 50
C17SAS (m/z 238) -
LA
100 50
sample support filter filter filter glass wool glass wool
% SAS recovery extract 1 extract 2 extract 3 92 5 3 93 5 2 92 5 3 75 19 6 75 18 7
Recoveries based on three sequentialextractions of sewage sludge from the Ziirich-Glatt sewage treatment plant where 100%recovery is defined as the s u m of three sequential extractions.
d
CllLAS (m/z313)
C12LAS
Flgure 4. HPLC chromatogramsof (A) commercial LAS standard and Ce-LASsurrogate extractedfrom water at room temperature,(e) ionpair/SFE extract of sewagesludge wtth C&S and nativeLASIndicated, and (C) ion-pair/SFE extract of sewage spiked wlth C8-LAS-Bu. For chromatographic conditions see the Experimental Section.
sample size, mg 250
A
CloLAS (m/z 299)
20
Table 11. Effect of Sample Size and Support Material on Native SAS Recovery from Sewage Sludge.
C15SAS (m/z 21 0)
1
s
..
1
(m/z 327)
C13LAS (m/7 341)
rI A
I
15.00 16:OO 17100 18:OO 19:OO 20.00 2i.00 22.00 23.00
Time Imin) Flgure 3. Selected Ion chromatogramsfor homologuesof SAS using [M - 138]'+ ions at m/z 196, 210, 224, and 238 and of LAS using [M - 55]+ ions at m/z 299, 313, 327, and 341 in an unfractionated Ion-palr/SFE extract of sewage sludge.
by ion-pair/SFE (Figure 2). Owing to their high concentrations in sewage sludge, LAS peaks were observed in the full scan chromatogram of the unfractionated sewage sludge extract. Although native SAS were not easily distinguished from the many other components in the total ion chromatogram, selected ion monitoring (SIM) yielded relatively simple chromatograms for both SAS and LAS (Figure 3). Although SAS and LAS overlap in retention time, SAS and LAS were easily distinguished from one another and from other matrix components using SIM analysis without class fractionation of the ion-pair/SFE extract.
Verification of Ion Pairs in Ion-Pair/SFE Extracts Using HPLC. HPLC with fluorescence detection was used to determine whether alkylation occurred already under ionpair/SFE conditions in the SFE apparatus or later in the GC injection port. The HPLC chromatogram (Figure 4A) of a commercial C1O-CI4-LAS mixture and Ca-LAS surrogate ion pairs, extracted from water using TBA in liquid methanol at room temperature, showed typical reversed-phase chromatographic behavior. The selected conditions for HPLC separation of LAS resulted only in partial separation of the CloC13-LASisomers (Figure 4). Retention times identical to that of the commercial LAS extract were observed for the C8-LAS surrogate and native LAS in a HPLC chromatogram for an unspiked ion-pair/SFE sewage sludge extract (Figure 4B), demonstrating that LAS ion pairs are present in SFE extracts. Further evidencethat ion-pair/SFE extracts contain ion pairs and not butyl esters was shown by spiking the ion-pair/SFE extract with prederivatized C8-LAS-Bu. The CB-LAS-BU was detected as a later-eluting peak (Figure 4C), compared to the Cs-LAS ion pair, further indicating that the butyl ester of Ca-LAS is chromatographically different from the ion pair. Having shown that CS-LASexists as an ion pair in the ionpair/SFE extract and not as a butyl ester proves that derivatization occurs under the high-temperature conditions of the GC injection port and not in the SFE extraction apparatus. Ion-Pair/Supercritical Fluid Extraction of Sewage Sludge. Initial experiments were performed to demonstrate ion-pair formation and extraction under SFE conditions using surrogates spiked onto sand, a relatively simple sample matrix.
ANALYTICAL CHEMISTRY, VOL. 64, NO. 24, DECEMBER 15, 1992
Table 111. Recovery of SAS and LAS from Sewage Sludges aewage treatment planto Glatt Seegraben Niederglatt SWa-uetikon Opfikon
extract 1 93 94 89 91 90
% SAS recovery extract 2 extract 3 5 2 5 1 9 2 7 2 7 3 % LAS recovery
sewage treatment plant Glatt
Seegraben Niederglatt
extract 1
extract 2
extract 3
91 91 86
6
3 1 4
8 10
0 Sewage treatment planta in the Zivich area. The area of three sequential extractions is defined as 100% recovery.
Table IV. Concentration of SAS and LA9 in Sewage Sludge concn, g/kg of dry sludge0 sewage treatment plant SAS LAS (A) Ztirich-Glattb 0.78 f 0.02 5.54 f 0.06 0.80 f 0.05c 5.39 f 0.llC (B)Ztirich-Glattb (C) Opfikon-Klotenb 0.80 f 0.04 7.51 f 0.23 (D)Niederglattb 0.27 f 0.01 3.98 f 0.25 (E) Seegrabend 0.37 f 0.01 3.83 f 0.31 (F) SWa-uetikond 0.51f 0.02 4.90 f 0.26 0 Concentrations determined from four replicate samples except for B and F with three replicate samples. Anaerobically stabilized sewage sludge. Determined by liquid solvent extraction. Fresh sewage sludge.
The SAS surrogates spiked onto sea sand were recovered quantitatively (>975% ) usingTBA as an ion-pair reagent under SFE conditions of 150 OC with 30-min static followed by 15min dynamic extraction times. In a separate experiment, quantitative recovery (93-94 % ) of SAS and LAS surrogates, spiked onto 250 mg of sewage sludge instead of sea sand, demonstrated quantitative ion-pair formation and extraction from sewage sludge, a complex organic-rich matrix. Because spiking solid samples with surrogate standards is potentially problematic,two separate sets of experimentswere conducted in order to validate the use of surrogate standards for quantitating native SAS and LAS in sewage sludge extracts. First, exhaustive extraction of native SAS and LAS was determined by ratioing the total amount of native analyte recovered in sequential extractions to the CIZ-SAS and CgLAS surrogate standards, which were shown to be quantitatively recovered in a single extraction. Second, the total concentrations of native SAS and LAS determined by ionpair/SFE were compared directly with those obtained by liquid ion-pair extraction. For both methods, Cu-SAS and C8-LAS were used as surrogate internal Standards. The dependence of native SAS recoveryfromsewage sludge on extraction temperature was investigated by varying the extractor temperature between 150 and 80 OC. Although no dependence on recovery with temperature was observed,the use of lower temperatures was more convenient with less time required to cool the extraction cells to room temperature in between additions of TBA. In addition, no change in the recovery of native SAS was observed by decreasing the static extraction time from 30 to 5 min or the dynamic extraction time from 15to 10 min. Therefore, an extraction temperature of 80 OC and a 5-min static extraction followed by a 10-mim dynamic extraction were used as standard conditions for ionpair/SFE.
3165
Table V. Distributions of SAS Homologues for Sewage Sludges and a Commercial Product SAS homologue distributiona sewage treatment plant CI~ ClS ClS c17 Zivich-Glattb
Zivich-Glattc Opfikon-Klotenb Niederglattb Seegribenb SWa-uetikonb
19 f 1.5 15 f 0.1 18 f 1.8 19 f 1.6 20 f 1.0 20 f 1.0
30 f 1.0 32 f 0.1 31 f 0.6 28 f 0.6 28 f 0.6 28 f 0.4
17 f 0.5 19 f 0.3 18 f 0.3 22 f 1.1 16 & 0.8 15 f 0.6
commercial product (Hostapur 60P
40f 0.3 32 f 0.2 19f 0.2
9f0.2
35 f 0.3 34 f 0.3 34 f 0.9 31 f 1.2 35 f 0.8 37 f 0.7
As percent of t ~ t a SAS. l Determined from ion-pair/SFE. Determined from liquid solvent extraction.
Sincemethanol-modified COZis known to extract LAS from sewage sludge,"%e recovery of native SAS from sewage sludge extracted under supercritical fluid conditions using TBA was compared to that extracted using methanol. Two 100-mg samples of sewage sludge were extracted under standard conditions with either 1mL of pure methanol or 1mL of 0.5 M TBA in methanol added to the extraction cell containing sewage sludge. The methanol-only extract was analyzed by adding TBA prior to GUMS analysis. The advantage of ion-pair/SFE extraction over that using only the methanol modifier was demonstrated by a 2.5-fold increaein the amount of native SAS extracted from sewage sludge samples using ion-pair reagent (TBA)compared to that extracted using only methanol. To investigate the dependence of native SAS recovery on sample size and the number of extractions required for quantitative recovery, three samples each of 50,100, and 250 mg of sewage sludge from the ZcUich-Glatt sewage treatment plant were extracted using three sequential extractions under standard ion-pair/SFE conditions. Recoveries of native SAS from all three sample sizes were essentially identical (e.g., 92-93 9% , 5-6 % , and 2-3 % for the first, second, and third extractions, respectively (Table 11)). Consistent recovery of >92% in the first extract indicated that only one extraction was required for essentially quantitative extraction of native SAS from sewage sludge, regardless of sample size. Since no dependence of recovery on sample size was observed, 100 mg was arbitrarily selected for subsequent extractions. The effect of support material covering the extraction cell outlet frit on native SAS recovery and overall extraction performance was tested by replacing the 0.45-pm glass-fiber filter with a plug of silanized glass wool. Decreased dynamic extraction flow rates and restrictor blocking occurred frequently when using glass wool, suggesting incomplete retention of sewage sludge particles inside the extraction cell. In addition, native SAS recovery from sewage sludge supported by glass wool decreased to 75 % in the first extract compared to 92% using the glass-fiber filter (Table 11)so the fiiter was used as the sample support for all subsequent extractions. The ability of the ion-pair/SFE method to quantitatively extract SAS and LAS from different types of sewage sludges also was tested by performing three sequential extractions each on four additional sewage sludges collected from sewage treatment planta in the region around Ziirich (Table 111). Native SAS recovery varied in the first extract between 89 and 94% with an additional 5-9% and 1-3% in the second and third extracts,respectively. Sewagesludge extracts from three of the samples were also analyzed for LAS. Between 86 and 913'% of native LAS was recovered in the first extract followed by an additional 6 1 0 % in the second extract and 1-4 5% in the third extract. Consistent recovery of 1 8 97% for SAS and 286% for LAS in the first extract indicated that
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ANALYTICAL CHEMISTRY, VOL. 64, NO. 24, DECEMBER 15, 1992
-
1
isomeric positions
2
2
1k
l " " 1
17
" " I " " I " " I " '
18
time,
-
17
16
min
Flgurr 5. Selected ion chromatograms for CI5-SAS (m/z 210) and CI&S an Ion-palr/SFE extract of a sewage sludge.
only a single extraction was required for the reproducible and quantitative recovery of SAS and LAS from different sludges. Quantitative of SAS and LAS in Sewage Sludge. Concentrations of SAS and LAS in sewage sludge were determined from the extraction and analysis of four replicates of each sewage sludge sample extracted by ion-pair/SFE (Table IV). Concentrations of SAS in the five sewage sludge samples ranged from 0.27to 0.80 g/kg and LAS concentrations ranged between 3.83 and 7.51 g/kg. The method gave good relative standard deviations (typically 57% ) for both SAS and LAS. The reproducibility of the injection-port derivatization, calculated from four replicate injections of a single sewage sludge extract, gave a relative standard deviation of 4 7 % for both SAS and LAS. However, when samples of very high concentrations preceded samples containing low levels of SAS and LAS, traces of SAS were observed in the sample of low concentration but could be eliminated by changing the inlet liner. Concentrations of LAS found in sewage sludge using ionpair/SFE and injection-port derivatization are comparable to those previously reported for sludges collected from municipal sewage treatment plants in Switzerland,5.6 Germany! and the United States.4 Ion-pair/SFE was further validated by comparing SAS and LAS concentrations in sewage sludge from the Zijrich-Glatt treatment plant using a conventional liquid solvent extraction with TBA as the ionpair reagent aa described above (Table IV). The concentration of SAS in sewagesludge,obtained by liquid solvent extraction, was 0.76 g/kg compared to 0.80g/kg by ion-pair/SFE. Liquid solvent extraction gave a LAS concentration of 5.39 g/kg compared to 6.54 g/kg obtained by ion-pair/SFE. Excellent agreement between SAS and LAS concentrations in sewage sludge determined by the two methods proved that ion-pair/ SFE is quantitative while requiring only 15 min for complete extraction. In contrast, the time needed to prepare sewage sludge extracts wing conventional liquid solvent extraction was a minimum of 2 h. Homologue and Isomer Distributions for SAS in SewageSludge. Quantitative information on the homologue and isomer composition of SAS mixtures in sewage sludge also was available by integrating the individual SAS peaks
18
time,
min
(m/z 327) Isomers In (A) standard commerclal mlxtures and In (B)
shown in Figure 3. Homologuedistributions were determined for each sewage sludge by summing the individual isomers for C14-C1,homologues of SAS. Table V also gives the homologue distribution determined for the commercial SAS standard. Unfortunately, no published information on the homologue composition of the commercial SAS standard was available. However, comparison of SAS homologue distributions for sewage sludge and the commercial mixture demonstrated a relative enrichment of the longer-chain SAS homologues by sewage sludge (Table V). As shown in Figure 5,isomers with the sulfonicacid group located near the middle of the alkyl chain (internal isomer) elute first followed by those with the sulfonic acid group attached to the end of the chain (external isomers). Selected ion chromatograms of C15SAS and C12-LAS for sewage sludge both gave isomeric patterns that demonstrated a relative enrichment of the more hydrophobic (external) isomers relative to the standard mixture (Figure 5). Selective enrichment of the more hydrophobic homologues and isomers of LAS has been previously reported for sewage sludges6 and sediments.25
CONCLUSIONS Ion-pair/SFE and injection-port derivatization is a simple, fast, and quantitative alternative for determining both aliphatic and aromatic sulfonated surfactants in sewagesludge by GUMS. Although SAS lack a chromophore necessary for selective and sensitive detection by HPLC, they can be determined in the presence of aromatic surfactants (LAS) without prior class fractionation or sample cleanup of sewage sludge extracts using GC/MS. Ion-pair/SFE improves upon a previous SFE methodlo for extracting LAS from sewage sludge by reducing the total extraction time from 30 to 15 min. In addition, ion-pair/SFE does not require modification of existing instrumentation or a second pump for delivering a high percent of methanol modifier. Ion-pair derivatization requires a minimum number of preparative steps and does not involve hazardous reagents. Although this report illustrates ion-pair/SFE for sulfonated surfactants, it can be applied to other sulfonated chemicals. Ongoing work in our (25)
Hand,V. C.; Williams, G. K.Enuiron. Sci. Technol. 1987, 21,
370-373.
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laboratories indicates that sulfonated stilbene and biphenyl derivatives, used as optical brighteners in laundry detergents, are also present in the ion-pair/SFE extracts of sewage sludge. By combining ion-pair extraction with derivatization, the number of analytss that can be determined simultaneously is increased while the time and cost of sample extraction and analysis is reduced.
ACKNOWLEDGMENT This work is part of a cooperativeresearch project between the Commission for the Promotion of Scientific Research, SwissDepartment of Public Economy, Lever AG, Switzerland,
3107
and Carlo-Erba SA, Switzerland. As partners in the Rhine Basin Program, we gratefully acknowledge the donation of the GUMS equipment by the Hewlett Packard Co. Additional support came from Umweltbundesamt, Berlin, Shell Development Corp. (Houston, TX) and the U.S. Department of Energy. We thank Thomas Poiger for providing the HPLC chromatograms. Sewage sludges were collected by the sewage treatment plant operators in the region of Ziirich, Switzerland. RECEIVEDfor review May 20, 1992. Accepted September 14, 1992.
