Anal. Chem. 1995, 67, 4409-4415
Trace Analysis of Ethoxylated Nonionic Surfactants in Samples of Influent and Effluent of Sewage Treatment Plants by High-Performance Liquid Chromatography Anton T. Kiewiet,* Jan M. D. van der Steen, and John R. Parsons Department of Environmental and Toxicological Chemistly, Amsterdam Research Institute for Substances in Ecosystems, University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands
An analytical procedure is presented for the routine
determination of trace amounts of ethoxylated nonionic surfactants in samples of raw and treated wastewater of sewage treatment plants. The alcohol ethoxylates were isolated by solvent sublation and Soxhlet extraction. Interferences were removed by open-column alumina chromatography. Following sample cleanup, the nonionic surfactants were derivatized with phenyl isocyanate and analyzed with RP-HPLCwith UV detection. Sodium azide was used for presening the environmental samples. Although the nonionic surfactants were isolated from the sampleswithh 7 days, substantial losses (17-81%)were observed during transport and storage of the wastewater samples. Analytical recoveries of standard additions were '80%. The limit of determination of the procedure for effluent samples was 3.0 pg/L. The concentrations of alcohol ethoxylates in samples of influent wastewater fluctuated between 1.0 and 5.5 mg/L, whereas concentrations between 13.0and 12 pg/L were found for efnuent samples. Nonionic surfactants are used in a broad spectrum of household products and industrial applications. The group of nonionic surfactants consists mainly of ethoxylated substances. The annual consumption of alcohol ethoxylates in Western Europe and the United States amounts about 750 000 tonnes.' According to the Dutch Soap Association, the consumption in the Netherlands was 9700 tonnes in 1994. Over 80%of all nonionic surfactants used in detergents in the Netherlands are based on alcohol ethoxylates. The most commonly used alcohol ethoxylates contain a linear and partially a-methyl-branched hydrocarbon chain consisting of between 12 and 18 carbon atoms and an ethoxylate (poly[ethylene glycol]) chain of between 2 and 20 ethoxylate units. The linear and a-methylated branched alcohol ethoxylates easily pass ready biodegradibility tests, but there is environmental concern because of their high abundance in household wastewater. In general, chronic aquatic toxicity is observed at levels above 100 pg/L.2 To assess the environmental risk of nonionic surfactants, their exposure concentrations must be known. However, most of the available analytical procedures for the analysis of nonionic surfactants in environmental samples are not suf(1) Holt, M. S.; Mitchell, G . C.: Watkinson J. R The Handbook ofEnvironmental Chemisfy;Springer-Verlag: Berlin, 1992: Vol. 3, pp 89-144. (2) Lewis, M. A. Water Res. 1991,25, 101-113.
0003-2700/95/0367-4409$9.00/0 0 1995 American Chemical Society
ficiently sensitive and selective to determine nonionic surfactants at the microgram per liter level in these complex matrices. The colorimetric analytical procedures based on complex formation with tetraiod~bismuthate,~ ammonium cobalt~thiocyanate,~ or picrate anion5 do not meet the criteria of specificity and sensitivity. The current chromatographic procedures, which employ gas chromatography (GC)a7or high-performance liquid chromatograpy (HPLC),8s9give information on alkyl or ethoxylate distribution but still lack the appropriate sensitivity. Only the recently published method of Evans et a1.,I0based on liquid chromatography coupled to mass spectrometry, is highly selective and sensitive, and it is currently considered the benchmark method. This method, however, has been validated only for effluent samples and requires very expensive and not readily available equipment, which makes it less suitable for routine applications. This study reports an improved analytical procedure for the reversed-phase HPLC derivatization m e t h ~ d . The ~ , ~ optimization of the analytical procedure was focused on the sample pretreatment. Characteristic features of the present method are the separate extraction of liquid and solid phases and the chromatographic cleanup. The current method was developed for routine measurements and provides a good estimate of the true concentration of nonionic surfactants in environmental samples. The method was applied to samples of raw and settled influent and effluent of seven representative municipal sewage treatment plants (STPs) in the Netherlands. The sampling was camed out as part of a monitoring program executed by the Dutch Soap Association 0and the Dutch authorities. A detailed publication on the outcome of this monitoring study is in preparation.11 EXPERIMENTAL SECTION
Apparatus. The HPLC system consisted of a Waters 600-E system controller, a Waters 600 fluid unit, and a Rheodyne injector (3) Wickbold, R. Tenside, Sutfactants, Deterg. 1972,9,173-177. (4) Boyer, S. L.; Guin, IC F.: Kelley, R M.; Mausner, L. M.; Robinson, H. F.; Schmitt, T. M.; Stahi, C. R.; Setkom, E. A. Environ. Sei. Technol. 1976,10, 1167-1171. (5) Favretto, L.; Stancher, B.; Tunis, F. Analyst 1978a,103, 955-962. (6) Wee, V. T. Adv. Identif:Anal. Org. Pollut. Water 1981,I , 467-469. (7) Fendinger, N. J.; Begley, W. M.; McAvoy, D. C.; Eckhoff, W. S. Environ. Sci. Technol. 1995,29, 856-8153. (8) Allen, M. C.; Linder, D. E. J. Am. Oil Chem. Soc. 1981,58, 950-957. (9) Schmitt, T. M.; Allen, M. C.; Brain, D. IC;Guin, IC F.; Lemmel, D. E.; Osbum, 9. W. J. Am. Oil Chem. Soc. 1990,67,103-109. (10) Evans, K. A; Dubey, S. T.; Kravetz, L.; Gumulka, J.; Mueller, R; Stork, J. R. Anal. Chem. 1994,66,699-705. (11) Matthijs, E.; Holt, M. S.; Kiewiet. A. T.; Rijs, G. Submitted to Environ. Sci. Technol.
Analytical Chemistry, Vol. 67, No. 23, December 1, 1995 4409
(Model 7125) with a 20 pL loop. Detection was performed with a Waters 484 tunable UV detector. Prepacked Lichrocart 1254, 5 pm C18 columns were supplied by Merck (Darmstadt, Germany). Reagents and Materials. The commercial surfactant Neodol 25/9 was supplied by Procter & Gamble (Strombeek-Bever, Belgium). Neodol25/9 is a mixture of linear alcohol ethoxylates with alkyl chain length ranging from 12 to 15 and an ethoxylate chain length between 2 and 20. n-Decyl alcohol (98%), lauryl alcohol (99%), 1-hexadecanol (99%), poly(oxyethy1ene 5decyl ether) (C10E5), poly(oxyethy1ene 3-lauryl ether) (C12E3), poly(oxyethylene gmyristyl ether) (C14E8), and poly(oxyethy1ene k e t y l ether) (C16E5) were all purchased from Sigma (St. Louis, MO) . 1-Undecanol (99%), 1-tridecanol (97%),1-tetradecanol (97%), l-pentadecanol(gg+%), l-heptadecanol(98%), l-octadecanol (99%), and 1-eicosanol (98%) were obtained from Aldrich (Steinheim, Germany). Phenyl isocyanate (98+%) and neutral alumina, Brockmann I, standard grade, 150 mesh (58 A) were obtained from Aldrich. The alumina was deactivated with 5% (w/w) demineralized water before use. Sodium azide (99%)was supplied by Janssen Chimica (Geel, Belgium); sodium chloride (99.7+%) was Jozo kitchen salt from Akzo (Amersfoort, The Netherlands). Sodium hydroxide (99+%) and sodium sulfate were obtained from Merck. HPLC methanol, hexane, and dichloromethane were purchased from Rathbum (Walkerburn, Scotland). These solvents were glass distilled grade. Ethyl acetate was obtained from Janssen Chimica and glass distilled in our laboratory. The water for HPLC elution was purif3ed by a Barnstead Nanopure system. Glass microfiber filters GMF 150 (diameter 47 and 90 mm) and GF/F (diameter 47 and 90 mm) were purchased from Whatman (Maidstone, England). The water columns in the influent and effluent sublator were diameter 7 cm, height 28 cm and diameter 10 cm, height 62 cm, respectively. Sample Collection and Preservation. Samples of raw, settled, and treated sewage were collected during three consecutive days at seven representative activated sludge treatment plants in the Netherlands: de Meern, Kralingseveer, Lelystad, Hostermeer, Eindhoven, de Stolpen, and Steenwijk. Every 24 h, flow proportional samples were taken by automatic samplers. The samples were preserved on site with 0.01 M sodium azide. The preservation agent was added to the sampling bottles prior to the collection of the samples. The samples were cooled on site and stored at 4 "C. Sample preparation was done on all samples within 7 days after collection. Uncontaminated surface water which was not influenced by human or industrial activity was sampled from the nature reserve Lake Naardermeer. Isolation and Concentration. Representative samples of raw influent (100 mL), settled influent (200 mL), and effluent (4.7 L) were separated into liquid and solid phases by glass microfiber filtration. The solid phase was stored at -20 "C until extraction. The liquid phase of the influent sample was diluted to 1 L with demineralized water and extracted four times with 50 mL of ethyl acetate by solvent sublation for 10 min, as recommended by Boyer et aL4 The solvent sublation technique is based on the tendency of the surfactants to accumulate at interfaces (e.g., the air/water interface). In this technique, tine bubbles of an inert gas (typically nitrogen or helium) are dispersed through the aqueous sample, thereby transferring the nonionic surfactants to an overlaying ethyl acetate layer. The ethyl acetate layer is replaced several times to enhance the extraction efficiency. The liquid phase of the 4410 Analytical Chemistry, Vol. 67, No. 23, December 1, 1995
effluent sample was extracted four times with 100 mL of ethyl acetate by solvent sublation for 20 min. The ethyl acetate extract was dried by filtration over 5 g of sodium sulfate, concentrated to 5 mL by rotary vacuum evaporation, and evaporated to dryness on a water bath using a gentle stream of nitrogen. The solid phase was transferred to a glass Soxhlet thimble. After the addition of 0.2 g of sodium hydroxide to the thimble, the contents were extracted with methanol over 16 h. The extract was evaporated to leave a volume of 25 mL, diluted to 1 L with demineralized water, and subsequently extracted by solvent sublation following the same procedure as described for the influent liquid phase extraction. The ethyl acetate extract was evaporated to dryness with rotary evaporation and nitrogen and either added to the liquid phase extract or analyzed separately. Cleanup and Derivabtion. A glass column (length 20 cm, diameter 1cm) provided with a plug of solvent-washed glass wool was dry packed with 7 g of alumina (previously deactivated as purchased with 5% (v/v) demineralized water). The residue of the previous step was emulsified in 1 mL of hexane/dichloromethane (1:l v/v) and transferred to the column. The vial was rinsed with two additional washes of 1 mL of hexane/dichloromethane. The column was then eluted with 90 mL of hexane/ dichloromethane (1:l v/v), followed by 90 mL of methanol/ dichloromethane (1:100 v/v). The former fraction was discarded, and the latter fraction, which contained the nonionic surfactants, was evaporated to dryness by rotary evaporation and nitrogen. The residue was transferred to a 10 mL vial using dichloromethane. Before derivatization, 3 pg of 1-eicosanol was added to the residue as the internal standard. Next, 10pL of phenyl isocyanate and 250 pL of dichloromethane were added and mixed. The mixture was heated for 45 min at 55 "C with the cap loose on the vial.7 Following derivatization, the residue was dissolved in 250 pL of the HPLC mobile phase and analyzed by RP-HPLC. RP-HPLCAnalysis and Quantification. Twenty microliters of the sample was injected into the HPLC system. The chromatographic separation was performed with a gradient of methanol/ water (8:2 v/v) to 100%methanol in 25 min using a Lichrocart RP-18 column and a flow rate of 2 mL/min. The alcohol ethoxylates were detected with UV absorption at 235 nm. Identification of the alcohol ethoxylates was made by comparison with a series of ClO-Cl8 alcohols, using 1-eicosanol (C20-OH) as the internal standard. Quantification was made versus Neodol 25/9 with alkyl chain length ranging from C12 to C15 and an average ethoxylate chain length of 9. The total area of the alcohol ethoxylate peaks within the C12 alcohol to the C15 or C18 alcohol retention time window was used for quantification. A four-point calibration curve was made with concentrations ranging from 0.68 to 2.72 mg/mL. The blanks consisted of 0.1, 0.2, and 4.7 L of demineralized water, which was taken through the entire analytical procedure. The results of the measurements were corrected for the blank analysis. Limit of Determination and Quality Control. The limit of determination of the analytical procedure was calculated from the standard deviation of the blanks. Blanks and standard addition of alcohol ethoxylates were used in the analysis for every series of environmental samples. To check the efficiency of the sample preservation during sampling, transport, and storage, standard additions of Neodol 25/9 were performed on site, directly after
Separate Extraction of Liquid and Solid Phases. Due to the hydrophobic nature of nonionic surfactants, a large fraction of the compounds present in aqueous environmental samples are expected to be associated to particulate matter. When separate analysis of the liquid and the solid phases was not applied, a consistent decrease of recoveries as a function of the hydrocarbon chain length was observed (Table 1). The data presented in Table 1were obtained by standard additions of pure alcohol ethoxylates to uncontaminated surface water. When the liquid and solid phases were extracted separately, the recoveries of the standard additions appeared to be independent of the length of the hydrocarbon chain. The most probable explanation of this phenomenon is that sorption of linear alcohol ethoxylates caused an inefficient sublation extraction when working with a total environmental sample. However, solvent sublation was chosen as the extraction technique for the liquid phase because of its selectivity and its capacity for handling sample volumes up to 5 L. The nonionic surfactants from the solid phase were isolated using Soxhlet extraction. Soxhlet extraction has already been proven to be successful in the extraction of alkylphenol ethoxylates from sediments.I2 Cleanup. Ion exchange is frequently used as a cleanup method prior to the analysis of nonionic surfactant~.~.8J~ In the ion exchange step, anionic and cationic substances, which interfere in the colorimetric detection, are removed from the sample.
However, nonionic materials (e.g., triglycerides) also interfere with the analysis of nonionic surfactants. The current procedure employs alumina chromatography, which eliminates both ionic and a large number of nonionic interferences. Open-column alumina chromatography is a widely used technique for the cleanup of organic compounds.13 Alumina adsorbs polar s u b stances via interactions with the surface -OH and =O moieties. Nonpolar analytes will not be retarded and elute earlier than polar analytes. Figure 1 shows chromatograms of samples of 1 L of uncontaminated surface water concentrated by sublation without further cleanup (A), with ion exchange (B), and with alumina cleanup (C). The combination of solvent sublation with polar open-column alumina and It€-HPLC chromatography eliminates an important number of interferences, which makes the analysis of nonionic surfactants selective. Identitication and Quantitication. Because It€-HPLC separates alcohol ethoxylates by hydrocarbon chain length, a characteristic pattern of peaks can be expected in the chromatograms of the environmental samples. This pattern is due to Neodol or Dobanol, which are commercial mixtures of alcohol ethoxylates that are used in high amounts in Western Europe. The chromatogram of Neodol25/9 shows a set of peaks, each of which corresponds to alcohol ethoxylates with alkyl chain length from C12 to C15 and an ethoxylate distribution from 2 to 20 (Figure 2A). The chromatogram of Neodol25/9 shows peak broadening due to the ethoxylate chain length distribution. The small front peak is most likely due to the presence of a-methyl-branched alcohol ethoxylates. This was confirmed by LC/MS. A suitable choice of a combination of solvents and stationary phase might further reduce the influence of the ethoxylate chain on reversed phase HPLC. This was, however, beyond the scope of this study. Due to the influence of differences in the ethoxylate distribution, the retention times of the alcohol ethoxylates are not reproducable. Therefore, a mixture of C10-C18 alcohols with an internal standard of eicosanol (C20-OH) was used for the calibration of the retention times (Figure 2B). In addition, the retention times of the alcohol ethoxylates in the environmental samples (Figure 2C,D) were very similar to the retention times of the series of alcohols. The characteristic Neodol25/9 pattern appears in the influent samples but not as such in the effluent samples. This might result from the fact that the measurements of the effluent samples were close to the limit of determination. The peaks in the chromatograms of the effluent samples which elute earlier than the C12 alcohol ethoxylate were identified with thermospray LC/MS as the plasticiser tris(2-butoxyethyl) phosphate (Tris) and nonylphenol ethoxylate (NPE), respectively (Figure 2D). The nonylphenol ethoxylate coelutes with the C11 alkyl homologue of the alcohol ethoxylates. Quantification was carried out using the total area of the peaks in the chromatograms of the environmental samples within the retention time window of the C12-Cl5 or C18 alcohols. Neodol 25/9 was used for calibration. This assumes that the primary degradation mechanisms are mainly via central cleavage or oxidation of the alkyl chain.' With these two degradation routes, the ethoxylate chain length stays intact. If degradation occurs via the shortening of the ethoxylate chain, the molar response of the alcohol ethoxylates in the environmental samples will be different from that of Neodol25/9. Recent work conducted with thermospray LC/MS1' has shown that the avarage ethoxylate
(12) Marcomini, A.; Giger, W. Anal. Chem. 1987,59, 1709-1715.
(13) De Voogt, P. Trends Anal. Chem. 1994, 13, 389-397.
Table 1. Recoveries of Spikes from 1 L of Uncontaminated Surface Water Spiked with a Range of Representative Alcohol Ethoxylates.
separation of phases (%) sublation of component whole sample (%) liquid phase solid phase total C10E5 C12E3 C14E8 C16E5
91 81 34 22
42 54 24 5
23 37 65 70
65 91 89 75
Worked up solely by sublation extraction or by separate extraction of liquid and solid phases (spike, 8 pg/component).
sampling. Peak identification was validated by thermospray LC/ MS. Thermospray LC/MS Analysis. The HPLC separation was carried out on a Milton Roy CM 4000 using a Chrompak Spherisorb ODS column (length 10 cm, diameter 3 mm) and employing gradient elution from 50% acetonitrile (HPLC grade, Promochem) in Milli-Q water to 100%acetonitrile in 25 min at a flow rate of 0.6 mL/min. To aid ionization efficiency, a LKB 2150 was used for postcolumn addition of 1.2 mL/min of 0.1 M ammonium formate (Sigma). The mass spectrometer was a Finnigan MAT TSQ 700 with thermospray TSP2 interface. The thermospray vaporizer was operated at 95 "C and without discharge. The repeller voltage was 20. The mass spectrometer source temperature was 250 "C. For identification purposes, the rf-only daughter mode was used with a scan time of 1 s, a scan range of m/z 70-1100, and alternating per scan cutoff mass 71 with collision offset -6 V and cutoff mass 70 with collision offset -20 V. The collision gas used was 2.3 mTorr argon, and no MS/ MS correction was applied. RESULTS AND DISCUSSION
Analytical Chemistv, Vol. 67, No. 23, December 1, 1995
4411
Table 2. Means and Standard Devlations of the Concentrations (pg/L) of C12-ClS and C12-C18 Alcohol Ethoxylates in the Blanks and the Limits of Determination of the Samples with Different Volumes
mean i sd, 100 mL blank (n = 5) mean f sd, 200 mL blank (n = 3) mean f sd, 4.7 L blank (n = 7) limit of determination, 100 mL sample limit of determination, 200 mL sample limit of determination, 4.7 L sample
I
I
I
I
1
5
10
15
20
25
Minutes
B
5
10
15
20
25
Minutes
C
C12-Cl5
C12-Cl8
9 5 i 64 48 i 27 3.0 f 1.0 192 81 3.0
153 i 59 68 f 24 4.1 f 1.2 177 72 3.6
is also observed in this chromatogram. The same pattem was observed in samples from surface water from a nature reserve which was unaffected by human activities (results not shown). The means and the standard deviations of the total analytical responses within the C12-Cl5 and C12-Cl8 alkyl chain length window as measured in the blanks are presented in Table 2. A linear decrease of the response as the the sample volume increases is observed. This indicates that a small amount of alcohol ethoxylates is present in the blanks, which is independent of the volume of the blank sample. Therefore, these alcohol ethoxylates cannot arise from demineralized water. Although the level of alcohol ethoxylates in the blanks was significantly reduced by using glass-distilled solvents, alcohol ethoxylate-free detergent, and preextraction of filters and glassware, blanks still showed a detectable level of alcohol ethoxylates. Further reduction of the blank levels could possibly be achieved by cleaning glassware at high temperatures (>300 "C) for every new set of samples and preextracting of all chemicals used. However, it was decided not to implement these inconvenient measures, as the blank levels were much lower than those in the effluent samples. The (theoretical) limit of detection, CL or q L , is defined as14
C, (or 43 = 3s,/S
5
10
15
20
25
Minutes Figure 1. Reversed phase HPLC chromatograms of a sublation extract of 1 L of uncontaminated surface water without further cleanup (A), treated with with anion and cation exchange chromatography (E), or treated with additional alumina cleanup (C). PIC, phenyl isocyanate; C20-OH, 1-eicosanol.
chain length of alcohol ethoxylates in effluent samples is only a little smaller than that of Neodol 25/9. Blank Analysis and Limit of Determination. Blanks consisted of 0.1, 0.2, and 4.7 L of demineralized water, which correspond to the sample volumes of raw and settled influent and effluent samples as used in the methodology developed. A chromatogram of a 4.7 L blank is shown in Figure 2E. The characteristic alkyl chain length pattem of the alcohol ethoxylates 4412 Analytical Chemistry, Vol. 67, No. 23, December 1, 1995
where CLor q L , SB, and S are the concentration or amount, the standard deviation of the blank measurements, and the sensitivity of the method, respectively. The limit of determination is defined here as 3 times the standard deviation of the concentration of alcohol ethoxylates quantified in the blanks. This is a practical limit of determination rather than a limit of detection based on the noise of the analysis. The calculated limit of determination of an effluent sample of 4.7 L is 3.0 pg/L. In a comparable study with U S , a similarly defined limit of detection of 8 pg/L was found.15 Based on the expected effluent concentrations, the method is sufficiently sensitive for the determination of alcohol ethoxylates in samples from sewage treatment plants. Recoveries. To check the accuracy of the method and the preservation efficiency of the samples during transport and subsequent storage, recovery experiments were performed both in the laboratory and at the STP. The analytical recoveries (standard addition in the laboratory) were determined by the addition of 4.5 mg/L, 2.25 mg/L, and 27-73 pg/L of a mixture of pure and C14E8 to samples of raw influent, settled influent, and effluent, respectively, prior to filtration of the samples. Total (14) Analytical Methods Committee. Analyst 1987,112. 199-204. (15) Feijtel, T. C. J.: Matthijs, E.; Rottiers, A,: Rijs, G. B. J.; Kiewiet, A T.: de Nijs. A. Chemosphere 1995,30,1053-1066.
1
I
....... PIC product
Cl2.AE
B
C20-OH
10
5
r-
A
20
15
5
25
15
10
20
25
Minutes
Minutes ....... PIC product
D
1 r--
PIC producc
i
CIZ-AE
i
CZO-OH
h
C 13-AE
I
I
I
5
10
15
I
r
I
20
5
25
I 10
I 15
I 20
I
25
Minutes
Minutes C20-OH
E
C14-AE
5
10
15
20
25
Minutes Figure 2. Reversed phase chromatograms of Neodol 25/9 (A), a series of C10-C18 and C20 alcohols (B), influent (C) and effluent (D) samples from a wastewater treatment plant, and 4.7 L of demineralized water blank (E). PIC, phenyl isocyanate; AE, alcohol ethoxylate; C20OH, 1-eicosanol.
recoveries (standard addition of Neodol 25/9 on site) were determined by addition of 3 mg/L and 30 pg/L Neodol25/9 to the (raw and settled) influent and effluent samples, respectively, of different STPs which were selected for the Dutch surfactant monitoring study. Recoveries were calculated by subtracting the peak areas present in the C12 and C14 alkyl homologues window (analytical recovery) and the Neodol 25/9 chromatographic window (total recovery) of the unspiked sample from that of the spiked samples. The results of the analytical and total recoveries are shown in Table 3. The results of the analytical standard additions show consistently high recoveries. The results of the recovery experiments performed on site show losses of 17-43% and 33-81% for the influent and effluent samples, respectively. Because of the limited
Table 3. Analytical and Total Recoveries of Alcohol Ethoxylates from Raw Sewage, Settled Sewage, and Effluent'
raw sewage settled sewage effluent
analytical recovery (%)
total recovery (%)
102 i 3 (n = 3) 100 f 6 (n = 3) 84 f 9 (n = 3)
58-72 (n = 4) 64-83 (a = 4) 19-77 (a = 7)
Analytical recoveries: spike of 4.5 mg/L, 2.25 mg/L C12E8 and C14E8 to raw sewage, settled sewage and 27-73 g/L to effluent, respectively. Total recoveries: spike of 3 mg/L NE8DOL 25/9 to the raw and settled sewage and 30 pg/L to effluent.
preservation efficiency of 0.01 M sodium azide and storage at 4 "C, the nonionic surfactants were isolated from the aqueous Analytical Chemistiy, Vol. 67, No. 23, December 1, 1995
4413
Table 4. Concentrations of C12-C15 and C12-C18 Alcohol Ethoxylates in Raw Influent, Settled Influent, and Effluent from Seven Sewage Treatment Plants, Corrected for Blanks.
STP de Meem Lelystad
A B C A
B C
Kralingseveer A B C
Hostermeer
A B
Eindhoven
A B
de Stolpen
A B
C
Steenwiik
C
C A B C
raw influent
settled influent
(mg/L)
(mg/L) c12- c12C15 C18
c12C15
c12C18
2.41 2.63 2.85 4.56 4.67 4.81 1.91 1.19 1.69 5.50 3.81 3.03 2.38 1.69 1.71 1.54 3.21 3.07 3.39 4.31 2.18
3.05 3.22 3.51 5.01 5.10 5.50 2.20 1.48 1.97 6.35 4.43 3.53 2.64 1.92 1.99 1.82 3.59 3.39 3.83 4.76 2.43
1.82 2.31 2.05 -
1.71 1.02 1.45 3.44 2.79 2.31 1.84 1.43 1.26 -
2.59 1.77 1.45
2.57 2.77 2.39 1.96 1.24 1.84 3.93 3.28 2.69 2.06 1.64 1.38 -
2.93 1.99 1.68
effluent WL) c12-
c12C15
C18
~3.0 3.1 ~3.0 5.0 3.5 3.4 4.3 4.5 5.8
