ANALYTICAL CHEMISTRY, VOL. 51, NO. 14, DECEMBER 1979
2329
Determination of Poly(oxyethylene)alkylphenyl Ether Nonionic Surfactants in Water at Trace Levels by Reversed Phase Adsorption Liquid Chromatography and Field Desorption Mass Spectrometry Akira Otsuki" and Hlroaki Shiraishi Division of Chemistry and Physics, National Institute for Environmental Studies, P.O. Yatabe, Tsukuba, Ibaraki 300-2 1, Japan
Poly(oxyethylene)alkylphenyl ether nonionic surfactants in water were adsorbed on an octadecyltrichiorosilanebonded glass bead packed column and eluted by gradient elution from water to 100% methand In the order octylphenyl, nonylphenyl and dodecylphenyl ethers. The recovery from fortified water samples was more than 96% at 1 mg/L level and 71 YO at 50 pg/L level, respectively. Field desorption mass spectrometry (FDMS) was applied to confirm these compounds In the fraction collected and to determine the degree of polymerization of ethylene oxide. Tables for identification of poly(oxyethy1ene)alkylphenyl ethers by FDMS were constructed from field desorption mass spectra of standard samples.
With the increasing need t o develop methods for concentrating, isolating, and identifying nonextractable and relatively high molecular weight organic compounds in natural waters, the combination of liquid chromatography and field desorption mass spectrometry (FDMS) is receiving considerable attention with some advantages of F D M S over gas chromatographymass spectrometry ( I ) . The use of XAD resins for adsorption and separation of the nonextractahle and high molecular weight organic compounds in water is becoming the common technique in place of activated carbon because of reproducible recovery ( 2 ) . On the other hand, adsorption liquid chromatography with high pressure liquid chromatograph and solvent programming techniques offers a great possibility for concentration and separation of a wide variety of organic compounds in water with the development of chemically bonded stationary phases. In the present study, the reversed phase adsorption chromatography was applied to the concentration and separation of trace amounts of poly(oxyethy1ene) (POE)alkylphenyl ethers in water (3). POE alkylphenyl ethers, which are one of the important nonionic surfactants, are widely used as emulsifiers, wetting agents, and detergents. The use of the POE alkylphenyl ethers in place of anionic surfactants is increasing ( 4 ) . However, the biodegradability of these compounds is not well known. Sheldon and Hites first reported the presence of POE octylphenyl ethers in river water (5),and presented mass spectral characteristics of ethylene oxide derivatives by electron impact mode (6). Since the biodegradation of POE alkylphenyl ethers is not well understood, their environmental hazards cannot he ruled out. This paper describes a reversed phase adsorption chromatographic procedure for concentration and separation of POE alkylphenyl ethers from water, and FDMS for identification and determination of the degree of polymerization of ethylene oxide. EXPERIMENTAL Apparatus. A Waters ALCIGPC-204 liquid chromatograph equipped with two 6000A pumps, a Model 660 solvent program0003-2700/79/0351-2329$01.00/0
mer, a U6K injector and a Model 440 UV detector operating a t 280 nm was used. A 120 cm X 2 mm i.d. column, packed with Bondapak C-l8/Corasil (Waters Associates), was used. FDMS was performed on a JEOL JMS 01SG2 double focusing mass spectrometer with a combined field desorption/field ionization/electron impact ion source, JMS-2000 data analysis system (Japan Electronic and Optics Laboratory, Japan), and an emitter current programmer (7)which was constructed with minor modifications according to Maine et al. (8). The emitter was tungsten wire (10 pm in diameter) with carbon needles (20--40 pm) made in a manner similar to that of Schulten and Beckey (91, with a MS-FDA01 activator (JEOL, Japan). The anode potential was 10 kV and the cathode potential -3 kV. The emitter current was linearly increased by the emitter current programmer at a rate of 3 mA/min. The samples were loaded by the microsyringe technique (10). FD mass spectra were obtained by integration of repetitive scans over the range from 100 to 820 m / z at an interval of 12 s (the individual FD mass spectrum obtained by repeated scans during an emitter current programming was integrated more than 15 times by computer). Materials. POE tert-octylphenyl ethers (Igepal CA-CO 630, GAF), POE nonylphenyl and dodecylphenyl ethers (Noigen EA 80 and EA 83, Daiichiseiyaku, Japan) were technical grade and used without further purification. Methanol (Mallinckrodt) was nanograde and pure water was prepared by passing distilled water through a Milli-Q system (Millipore). A standard solution was prepared by dissolving each reagent in methanol to give R concentration of each 1 pgJpL. Procedure. (A) While pure water was pumped through the column a t 3 mL/min, 1 to 20 pL of the standard solution was injected and the POE alkylphenyl ethers were retained on the C-l8/Corasil column. After the flow rate was changed to 1 mL/min, a gradient elution was started on the Mode 2 in the Waters programmer. When mobile phase composition became 50 to 50 water-methanol, the gradient was held for 5 to 20 min, and then continued further to 100% methanol. The programming time was for 10 min excluding the time of holding process. The column regeneration effected between two successive runs was always carried out under the same condition. The regeneration time was 5 min. Calibration graphs were made by this procedure (A). (B) Glass fiber filtered sample solution containing 1 to 20 kg of POE alkylphenyl ethers had been passed through the column a t 3 mL/min, the column was washed with pure water for 10 min and then gradient elution was started after the flow rate was changed to 1 mL/min as described above. Fractions were then collected as needed. All experiments were done at ambient temperature.
RESULTS Reversed Phase Adsorption Chromatography. Figure 1 shows a typical liquid chromatogram of the separation of POE octylphenyl, nonylphenyl, and dodecylphenyl ethers obtained by gradient elution with a holding process. After holding the mobile phase composition of 50 to 50 watermethanol, POE alkylphenyl ethers were eluted by a further initiation of the gradient in the order octylphenyl, nonylphenyl, and dodecylphenyl ethers, indicating that the retention time was related to the number of alkyl carbon atoms. Although the efficiency of adsorption was nearly constant in the C 1979 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 14, DECEMBER 1979
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Figure 1. Typical liquid chromatogram of the separation of POE octylphenyl, nonylphenyl, and dodecylphenyl ethers by gradient elution with a holding process. C-8, C-9 and '2-12 correspond to POE octylphenyl, nonylphenyl, and dodecylphenyl ethers, respectively. Flow rate in elution: 1 mL/min 300
500
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658
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Figure 4.
FD mass spectrum of
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400
500
600
700
800
M Z
Table I. Recovery from Fortified Tap Water recoveries concentration in fortified sample POE octylphenyl ethers POE nonylphenyl ethers sample volume taken
1 . 2 5 mg/L 100, 98%
0.05 mg/L
96, 97% 10 mL
7 1 , 75% 200 mL
78, 94%
range from 1to 4 mL/min, sensitivity increased with decrease in flow rate of gradient elution. Thus 1 mL/min was used in gradient elution. Holding time in gradient elution showed no effect on retention time for 20 min in the mobile phase composition of 50 to 50 water-methanol. Calibration graphs of POE octylphenyl and nonylphenyl ethers with a full scale range of 0.05 absorbance unit were linear between 0 and 20 pg. Since POE dodecylphenyl ethers used as a standard contained a considerablely high content of impurities as later shown in FD mass spectrum, accurate determination of POE dodecylphenyl ethers was impossible. T h e results of recovery tests from fortified, filtered tap water are given in Table I. At the 1mg/L level, the recovery was more than 96% using 10-mL samples and at the 50 pglL level it was more than 71% using 200-mL samples. FDMS f o r Identification a n d Confirmation. Figure 2 shows the FD mass spectrum of POE octylphenyl ethers. Each peak is due to each molecular ion with a different degree of polymerization of ethylene oxide because any fragment in the range of less than 100 mlz was not observed. The difference between two peaks corresponds to the difference of molecular weight of ethylene oxide, 44 mlz. The peak a t 602 mlz is equivalent to POE octylphenyl ether with the degree of po-
Figure 5. FD mass spectrum of Triton X-100
lymerization of 9 of ethylene oxide. The other small peaks would be due to impurities having different alkyl group or dialkyl groups. The peaks a t 484,528, 572,616,660, 704, and 748 mlz may be due to POE nonylphenyl ethers because of the difference of 14 mlz by methylene group. I t is possible that the other peaks a t 450,494,538,582,626,670,714, and 758 mlz are due to POE dioctylphenyl ethers. Figure 3 shows the FD mass spectrum of POE nonylphenyl ethers. The peak a t 528 m / z corresponds to POE nonylphenyl ether with the degree of polymerization of 7 of ethylene oxide. The other small peaks a t 366,410,454,498,542,586, and 630 mlz may be due to POE decanylphenyl ethers as an impurity because of the difference of 14 m l e by methylene group. The FD mass spectrum of POE dodecylphenyl ethers is shown in Figure 4. This spectrum suggests that this reagent contains a considerably high content of impurities such as POE undecylphenyl and tridecylphenyl ethers, and when the reagent is used as a standard material, purification is necessary. The peak a t 570 m / z corresponds to POE dodecylphenyl ethers with the degree of polymerization of 7 of ethylene oxide. From the FD mass spectra of standard samples, a table for identification of POE alkylphenyl ethers and determination of the degree of polymerization of ethylene oxide was constructed as shown in Table 11. n is the number of alkyl carbon atoms and m is the degree of polymerization of ethylene oxide. When the FD mass spectrum having the peak pattern with the difference of 44 m / z was obtained such as the peaks a t 484,528,572,616, and 660 mlz, Table I1 would tell that those peaks are due to POE nonylphenyl ethers with the degree of
ANALYTICAL CHEMISTRY, VOL. 51, NO. 14, DECEMBER 1979
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Table 11. Table for Identification of Poly(0xyethylene)Alkylphenyl Ethers from FD Mass Spectra C,H*,+ ;C,H,.O(C2H,O), m n
6 7 8 9 10 11
12 13
4 354 368 382 396 410 424 438 452
5 398 412 426 440 454 468 482 496
6 442 456 47 0 484 498 512 526 540
7 486 500 514 528 542 556 570 584
H
8
9
10
11
12
13
530 544 558 572 586 600 614 628
574 588 602 616 630 644 658 672
618 632 646 660 674 688 702 716
662 676 690 704 718 732 746 760
706 720 734 748 762 776 790 804
750 764 778 792 806 820 834 848
-
14 794 808 822 836 830 864 87 8 892
15 838 852 866 880 894 908 922 936
16 882 896 910 924 938 952
14 85 8 906 934 962 990 1018 1046 1074
15 922 950 978 1006 1034 1062
966
980
Table 111. Table for Identification of Poly(0xyethylene)dialkylphenyl Ethers from FD Mass Spectra 2(CnH?,- ,).C,H;.O( C,H,O),II m n 6
7 8 9 10 11
12 13
3 394 422 450 478 506 534 562 590
4 438 466 494 522 550 578 606 634
5 482 510 538 566 594 622 650 678
666
694 722
7 570 598 626 654 682 710 738 766
8 614 642 670 698 726 I54 782 810
9 658 686 714 742 770 798 826 854
10
11
702 730 758 786 814 842 870 898
746 774 802 830 858 886 914 942
12 790
13 834 862 890 918 946 974 1002 1030
818
846 874 902 930 958 986
1090 1118
5!4
44a
1
6 526 554 582 610 638
484
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1001
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400
500
600
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m z Figure 6. FD mass spectrum of the fraction containing POE octylphenyl and nonylphenyl ethers separated by gradient elution 0-
polymerization of 6 to 10 of ethylene oxide. Table I11 also shows the identification of POE dialkylphenyl ethers and determination of the degree of polymerization of ethylene oxide based on calculations of the molecular weight. Figure 5 shows the FD mass spectrum of Triton X-100 as an example of identification of POE alkylphenyl ethers. From Table 11, the peaks a t 426, 470, 514, 558, 602, and 646 m / z become clear to be due to POE octylphenyl ethers with the degree of polymerization of 3 to 12 of ethylene oxide. The other peaks a t 538, 582, 626, 670, 714, 758, and 802 m / z indicate the presence of POE dioctylphenyl ethers with the degree of polymerization of a t least 5 to 11 of ethylene oxide. This result demonstrates that the main component in Triton X-100 is POE octylphenyl ethers with the degree of polymerization of 3 to 12 of ethylene oxide and it also contains POE dioctylphenyl ethers with the degree of polymerization of a t least 5 to 11 of ethylene oxide. Figure 6 shows the FD mass spectrum of the concentrate of the fraction containing POE octylphenyl and nonylphenyl ethers separated by gradient elution with a 10-min holding process after adsorption of standard mixture sample. I t is apparent that POE octylphenyl and nonylphenyl ethers in water can be recovered by reversed phase adsorption chromatography. Application. An example of the application of the present method to an environmental sample is demonstrated. After sampling from the Sanno River, a small stream polluted by
I
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20 30 10 Time min
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40
Figure 7. Liquid chromatogram of organic compounds adsorbed from polluted stream water sample by gradient elution. Adsorption condtion: 3 mL/min; flow rate in elution: 1 mL/min; sample volume: 390 mL
mainly domestic wastes, the sample was filtered through a Whatman GF/C filter and then the filtrate was pumped through the C-18 packed column a t 3 mL/min for 130 min to concentrate and separate POE alkylphenyl ethers. Figure 7 shows a liquid chromatogram of the separation of organic compounds eluted by gradient elution with a 13-min holding process. Most organic compounds were eluted during the holding process and several peaks appeared during further gradient elution to 100% methanol. A fraction containing two peaks, the retention time of the first peak corresponded t o t h a t of POE nonylphenyl ethers, was collected and concentrated to one tenth under reduced pressure. Figure 8 shows the FD mass spectrum of the concentrate. Nine peaks a t 440, 484, 528, 572, 616, 660, 704, 748, and I92 m / z with the difference of 44 m / z were confirmed to be due to POE nonyl-
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ANALYTICAL CHEMISTRY, VOL. 51, NO. 14, DECEMBER 1979
Y
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compound is alkylbenzene sulfonates, but they are not adsorbed on the C-18 column because the sodium sulfonate group has strong hydrophilic property. The most important thing would be the use of glass fiber filter instead of membrane filter because some membrane filters may contain POE alkylphenyl ethers as a wetting agent (15).
As pointed out by Shiraishi et al. (7),the integration of each FD mass spectrum from each repeated scan during an emitter U/Z
Flgure 8. FD mass specbum of the concentrate of a fraction separated from polluted stream water sample
phenyl ethers with the degree of polymerization of 5 to 13 or more of ethylene oxide from Table 11. The peak height of the P O E nonylphenyl ethers corresponded to 7 pg and consequently the concentration was determined to be 24 kg/L.
DISCUSSION Although there are several studies on the chromatographic separation of POE alkylphenyl ethers by the difference in the degree of polymerization of ethylene oxide (11-141, the separation of mixtures of POE alkylphenyl ethers with a different alkyl group has not been reported. In the present study, mixtures of POE alkylphenyl ethers were separated by the affinity between the chain length of the alkyl group in the POE alkylphenyl ethers and the octadecyl group of the bonded stationary phase, and the solubility to the solvent at the mobile phase composition during gradient elution. This reversed phase adsorption chromatography involves injection of the sample either by direct injection (maximum 2 mL) or by pumping a certain volume through the column. The choice depends on whether the sample contains high levels of POE alkylphenyl ethers. In case of the sample containing more than 1 mg/L, direct injection should be used. In the application of the present method to environmental water samples, the reason for selecting a hyperbolic programming and for introducing a holding process during gradient elution was to elute most organic compounds adsorbed from water sample in the early stage of the gradient to avoid overlapping of the peaks of the POE alkylphenyl ethers eluted in the later stage. In our experience, most organic compounds adsorbed from filtered natural water samples and having an absorbance near 280 nm were eluted during a holding process of about 15 min when using a mobile phase composition of 50 to 50 watermethanol. As far as we know, interfering compounds in environmental samples may be dialkyl phthalate esters having more than eight carbon atoms in an alkyl group and an absorbance near 280 nm such as di-2-ethylhexyl phthalate, but the peak can be confirmed by FDMS. The other possible
current programming was essential to get a reproducible FD mass spectrum of multicomponents or mixtures because fractional desorption occurs with increase in emitter current. In the integrated FD mass spectrum, the peak pattern would indicate relative abundance of POE alkylphenyl ethers with each degree of polymerization of ethylene oxide. Therefore, the concentrations of each POE alkylphenyl ether with a different degree of polymerization of ethylene oxide would be estimated from total concentration determined by the peak height in liquid chromatogram. It is interesting to note that, as pointed out by Sheldon and Hites ( 5 ) ,environmental occurrence of POE derivatives may be a common phenomenon, and FDMS can be a powerful tool for identification and determination of POE alkylphenyl ethers.
ACKNOWLEDGMENT POE octylphenyl ethers (Noigen EA-80) and POE dodecylphenyl ethers (Noigen EA-83) were kindly supplied by Daiichikogyo-seiyaku, LTD, Japan.
LITERATURE CITED e.g., H.-R. Schutten and H. D. Beckey, J . Chromatogr., 81, 315 (1973). P. V. Rossum and R. G. Webb, J . Chromatogr., 150, 381 (1978). A. Otsuki, J . Chromatogr., 133, 402 (1977). G. F. Longman, Talanta, 22, 621 (1975). L. S. Sheldon and R. A Hites, Environ. Sci. Techno/., 12, 1188 (1978). L. S. Sheldon and R. A. Hites, Sci. Total Environ., 11, 279 (1979). H. Shiraishi, A. Otsuki, and K. Fuwa, Bull. Chem. SOC.Jpn. 52, 2903 (1979). J. W. Maine, B. Sotlmann, J. F. Holland, N. D. Toung, J. N. Qrber, and C. C. Sweeley, Anal. Chem., 48, 427 (1976). H.-R. Schutten and H. D.Beckey. Org. Mass Spectrom., 8, 885 (1972). H. D. Beckey, A. Heindrichs, and H. U.Winkler, Int. J. Mass Sepctrom. Ion Phys., 3, 11 (1970). H. G. Nadeau, D. M. Oaks, W. A. Nichols, and L. P. Carr, Anal. Chem.. 36, 1914 (1964). K. J. Bombaugh, W. A. William, and R. F. Levangie, J . Chromatogr. Sci., 7 . 42 (1969). L. Favretto and B. Stancher, J . Chromatogr., 108, 183 (1975). B. Stancher, L. FavrettoGabrielli, and L. Favretto, J. Chromatogr., 111, 459 (1975). A. Otsuki and K. Fuwa, Talanta, 24, 584 (1977).
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RECEIVED for review June 13,1979. Accepted August 31,1979. This paper was presented at the joint meeting of the American Chemical Society and the Chemical Society of Japan, Honolulu, Hawaii, April 3, 1979.
