Determination of alkylphenol ethoxylates in industrial and environmental samples

trends in analytkalchemistty, vol.16, no.

10,

7997

Determination of alkylphenol ethoxylates in industrial and environmental samples Pim de Voogt*, Karin de Beer, Frans van der Wielen Amsterdam Research lnsfitute for Substances in Ecosys terns, Department of Environmental and Toxicological Chemistry, University of Amsterdam, Nieuwe Achtergracht 766, 1018 WVAmsterdam, The Netherlands Degradation products of nonionic surfactants, which are used in large quantities in several industrial applications, have been shown to elicit estrogenic effects in the laboratory as well as in the environment. This has prompted the monitoring of such products, in particular the alkylphenols (AP) and alkylphenol ethoxylates (APE), in the environment. This study presents a relatively simple method for the determination of AP and APE in industrial and environmental samples by HPLC and GC-MS. It discusses some of the inherent analytical issues concomitant with the determination of the complicated mixtures these analytes are composed of. The method was applied to marine and estuarine sediments as well as wastewater and sewage sludge samples taken from industrial plants. In all marine and estuarine samples APE were found with a predominance of oligomers containing l-3 ethoxylate units. 0 1997 Elsevier Science B.V.

1. Introduction Surfactants find application in industry, processing technology and science, with a major usage in detergents. Nonionic surfactants (NIS) possess specific physicochemical properties including relative ionic insensitivity and sorptive behavior [ 1 ] which make them particularly suited for use wherever interfacial effects of detergency, (de)foaming, *Corresponding

author. Tel.: + 31 (20) 525 6565;

Fax: + 31 (20) 525 6504; E-mail: uva.nl 0165-9936/97/$17.00 PtISO165-9936(97)00100-3

[email protected].

(de)emulsification, dispersion or solubilization can enhance product or process performance. The major part of the group of nonionic surfactants consists of alcohol ethoxylates (AE) and alkylphenol ethoxylates (APE). The production of nonionic surfactants in Western Europe and the USA is steadily increasing and amounts to 750000 t/a [ 2 ] including 300 000 t/a of APE. Because of the formation of persistent metabolites in the environment, the OSPARcom Member States have decided to phase out the use of nonylphenol ethoxylates (NPE) by the year 2000. In Western Europe and the USA the APE in household detergents have been completely replaced by AE. Mainly because of their lower price APE are still being used in substantial amounts in institutional and industrial applications. Environmental (bio)degradation, including sewage water treatment of APE, results in alkylphenols (AP) and short chain APE (typically l-3 ethoxylate units) which are more persistent than their parent compounds and may accumulate in food chains. These metabolites have been found to elicit weak estrogenic activities, both in laboratory [ 3,4] and in field studies [ 51. These latter findings in particular have prompted an increasing effort to survey Western European environments for the presence of APE. The analytical chemistry of AP and APE is dominated by the complexity of the mixtures which are generated as a result of the production processes applied. Typically, synthesis involves ethoxylation of branched p-octyl- or p-nonylphenols using ethylene oxide, resulting in isomers (with different branching of the alkyl moiety) and oligomers (with different numbers of ethoxylate units). The various aspects of the analytical chemistry of AP and APE have been reviewed in several monographs [ 2,6] and reviews [ 7,8]. Because of the obvious drawbacks of GC analysis (see below), HPLC has become the favored method of analysis for APE. The major advantage of HPLC is its ability to separate and quantitate the various homologues and oligomers by length of the alkyl and ethoxylate chains. Reversed-phase HPLC provides information about the alkyl chain length, 0

1997 Elsevier

Science B.V. All rights reserved.

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trends in analytical chemistry, vol. 16, no. 10, 1997

whereas normal-phase HPLC resolves the ethoxylate oligomers. LC detection of NIS can be accomplished either directly, when a chromophore is present in the molecule (APE), or by derivatization (of AE) with an appropriate reagent. APE possess a ring chromophore which enables direct UV (at 277-280 nm) or fluorescence detection using excitation and emission wavelengths of 230 and 302310 nm, respectively. For the analysis of APE in environmental samples, HPLC with fluorescence detection is the simplest and most suitable technique [ 21. Normal-phase HPLC is applied to obtain information about the etboxylate chain distribution of APE. APE are often quantitatively analyzed by normal-phase HPLC because biodegradation of APE involves stepwise shortening of the ethoxylate chain. Normal-phase HPLC enables the separation of the persistent alkylphenols and lower ethoxylated APE, whereas these may coelute in RPHPLC. A wide range of possible columns, eluents and detection techniques can be used for the analysis of APE [S]. This article presents a method for the determination of AP and APE in environmental samples by HPLC with FLU detection and its confirmation by GC-MS. Several examples of typical results obtained with actual samples from industrial wastewater treatment plants and estuarine sediments are provided.

2.2. Soxhlet extraction The wet sediment or sludge was homogenized before further treatment. Two aliquots of the wet, homogenized sample were Soxhlet extracted. A spike was added to one of the aliquots before extraction. Similarly, two blanks, with and without spike respectively, were extracted separately. The Soxhlet extraction was carried out over 16 h with basic methanol. The extract was then concentrated to approximately 20 ml. The extracts were neutralized with HCl and stored in the refrigerator (5°C) until further use. 2.3. Particle separation The Soxhlet extracts and the water samples were centrifuged at 2000 r-pm to remove solid particles. 2.4. Solid-phase

All samples were extracted and purified by solidphase extraction (SPE). A Cis SPE (Waters US, Vat 3cc) cartridge column was used to that end. The sample was introduced on the column in a matrix of water/methanol (60:40). After passing the entire sample volume, the column was eluted with 100% methanol. The first fraction ( 10 ml, containing the AP and APEO) was evaporated to dryness. 2.5. Adsorption

2. Application

of the method

2.1. Sample pfefrea tmen t Samples were taken by third parties. Typical sample sizes amounted to loo-150 g (wet weight) of sediment or sludge, loo-150 ml of waste water, and 150-500 g (wet weight) of rivet-me or estuarine sediment. Samples were preserved by adding 3% (w/w) of formalin to the wet sample. Formalin treatment is necessary to prevent changes in the oligomer composition due to biodegradation. The samples were stored in the freezer (-20°C) until analysis as soon as possible after sampling. Before analysis the samples were thawed at room temperature. Sediment and sludge samples were Soxhlet extracted prior to clean-up. Water samples were directly cleaned without Soxhlet extraction.

extraction

chromatographic

clean-up

Further clean-up of the SPE extracts was carried out with an adsorption chromatographic column consisting of (bottom to top) neutral 7 g of (5% Hz0 w/w) deactivated AlzOs, 0.6 g of AgNOs impregnated silica and lg of NazS04. The extract was redissolved in 2 ml dichloromethane/hexane 1:3 (v/v) and transferred onto the column. A first fraction was eluted with 90 ml dichloromethane/ hexane ( 1:3 ) and discarded. Next, the column was eluted with 90 ml dichloromethane / methanol ( 100: 1). This fraction, containing the analytes of interest, was concentrated by evaporation and redissolved in methanol. 2.6. Reversed-phase

HPLC analysis

The sample extracts were analyzed by RP-HPLC with fluorescence detection. Separation in this system is based on alkyl chain (e.g. Cs, C,) length. A 125X4mmC18LichrospherlOORP-18 (5pm)in

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Table 1 Composition of mobile phase and gradient elution program in normal-phase HPLC analysis Time 0

3 20 22 23

Flow (ml/min)

% n-Hexane

% 2-Propanol

1.5 1.5 1.5 1.5 1.5

98 78 50 50 0

2 20 47 47 97

Lichrocart 125-4 column was used. Fluorescence parameters comprised excitation and emission wavelengths 230 nm and 290 nm, respectively. The sample was eluted isocratically with a 80:20 (v/v) methanol/water mixture at a flow rate of 1 .O ml/ min.

2.7. Normal-phase

% Hz0

Gradient

linear linear linear

HP LC analysis

The methanol extracts were evaporated to dryness and redissolved in hexane. For the estuarine sediments the extracts in methanol were applied directly to the HPLC system. A 100X4.6 mm NP-HPLC Hypersil 3 NH2 (3 l.trn) column with fluorescence detection was used, applying the same excitation and emission wavelength as in the RP-HPLC system. Separation in the NP system is based on ethoxylate oligomers. The mobile phase composition and the gradient elution program is given in Table 1. 2.8. GC-MS

Fig. 1. Reversed-phase HPLC chromatogams of four standard mixtures of alkylphenols and alkylphenol ethoxylates. Detector: fluorescence detector. Conditions, see text. OP, p( te/t.-octyl)phenol; NP, p-nonylphenol; OP8/9E, octylphenol ethoxylates (mixture containing an average of 8-9 ethoxylate units); NPlOE, nonylphenol ethoxylates (mixture containing an average of 10 ethoxylate units).

GC-MS can be applied for the confirmation of analyte identities. This is particularly useful when both OPE and NPE may be present, because in RPHPLC some of the isomers of both groups can coelute (cf. Fig. 1). Samples and standards were analyzed by electron impact GC-MS with the HP5890 GC coupled to a HP5970 quadrupole MSD system. The 30 m X 0.32 mm DB-5 analytical column had a film thickness of 0.25 pm. Samples were redissolved in hexane and injected manually on the column. The following temperature program was applied: 100°C (20 s), lO”C/min to 320°C. The transfer line was kept at 250°C. Helium was used as the carrier gas. Groups of single ions were monitored using the principal masses given in Table 2. Each group was applied during consecutive time windows corresponding to expected retention times. Hence, group I contained masses 107, 121, 135, 149, 206 and 220, corresponding to OP and NP and was applied from t = 7-12 min; group II contained masses 45, 179, 193, 223, 237, 250, 264, 267, 281, 294, 308, 338 and 352. These masses, corresponding to OPl-3E and NPl-3E, were applied

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during t= 12-19 min. Group III contained masses 45, 267, 281, 311, 325, 352, 355, 369, 382, 397, 427,441, and so on. 2.9. identification

and quantitation

Samples analyzed by HPLC were quantified against standard solutions of mixtures of AP or APE. Standard solutions were made containing different calibration levels from which response factors were calculated. Commercially available mixtures of AP generally consist of various branched alkyl chain-containing phenols. To represent the octylphenols, a standard solution was made of commercially available paru-( tert. -octyl)phenol ( 1,1,3,3-tetramethylbutylphenol, Aldrich, B ). For nonylphenol a standard solution was prepared from a commercially available technical mixture of branched nonyl chain p-substituted phenol (Fluka, NL). For the quantitation of APE by reversed-phase HPLC two mixtures of APE were provided by the KSLA (Shell, NL). One mixture, Nonidet 140, consisted of branched chain octylphenols with an aver-

Table 2 Masses (m/z) Compound

of molecular M+

Nonylphenol

220.35

Octylphenol

206.33

NPlE NP2E NPBE NP4E NP5E NPGE NP7E NP8E NPSE NPlOE

264.41 308.46 352.51 396.57 440.62 484.67 528.73 572.78 616.83 660.89

OPl E OP2E OP3E OP4E OP5E OP6E OP7E OP8E OP9E OPl OE

250.38 294.43 338.49 382.54 426.59 470.65 514.70 558.75 602.81 646.86

ions and principal

fragments

[m-85]+

[m-71]+

(a)

(a’)

135.18 135.18 179.24 223.29 267.34 311.40 355.45 399.50 443.56 487.61 531.66 575.72

used for EIMS of AP/APE

[a-14]+ (a-CH2)

[a-28]+ (a-CO)

[a+l4]+ (a+CH2)

121.16

107.18

149.21

C15H240

121.16

107.18

149.21

C14H220

165.21 209.26

179.24 223.29 267.35 311.40 355.45 399.51 443.56 487.61 531.67 575.72

age ethoxylate chain length of 8-9. The second mixture, NP-lo-EO: KSLA 88487, consisted of branched nonylphenol ethoxylates with an average ethoxylate chain length of 10 units. Fig. 1 presents the elution profiles of these four different commercial standards when analyzed with RP-HPLC, showing the distinct elution ranges of octyl and nonyl chain-containing compounds. Two more standards of technical mixtures of NPE, viz. NP4E and NP2E, were kindly provided by Shell and ICI (UK), respectively. Quantitation was done according to a method described in the literature [ 9 1. Quantitation of the APE was based on the assumption that the average ethoxylate chain length in sediment samples was close to the ethoxylate chain length of these standard mixtures. Whether this assumption is valid can be evaluated by the normal phase HPLC results. If the average chain length in actual samples does not deviate much from that in calibration mixtures, taking into account differences in molar responses, the sum of ethoxylates found in NP-HPLC should be close to the RP-HPLC result.

193.27 237.32 281.37 325.43 369.48 413.53 467.59 501.64 545.69 589.75

CH2CH20H

Structural formula

45.06 45.06 45.06 45.06 45.06 45.06 45.06 45.06 45.06 45.06

C17H2602

45.06 45.06 45.06 45.06 45.06 45.06 45.06 45.06 45.06 45.06

C16H2602

Cd3203 C21H3604 C23H4005 C25H4406 C27H4607 C29H5206 C31H5609 C33H60010 C35H64011

C16H3003 C20H3404 C22H3605 C24H4206 C26H4607 C26H5006 C3oH5409 C32H56010 C34H62011

588

trends in analytical chemistry

3. Results of the method Table 3 presents the results calculated from RPand NP-HPLC analyses of samples taken from an industrial wastewater treatment plant. Concentrations are expressed in ltg per gram of material as received. In the water sample, reversed phase HPLC analysis showed the presence of NP and NPE ( see chromatogram A in Fig. 2) with levels of 0.008 and 0.383 (sum of NPE) l.tg/g, respectively. Normalphase analysis of NPE oligomers showed the presence of oligomers ranging from 7 to 16 ethoxylate units (cf. chromatogram C in Fig. 2). The total sum of nonylphenol ethoxylates (0.36 pg/g) is close to the concentration quantified by reversed-phase analysis. Oligomers with a lower number of ethoxylate units may be present at low levels (i.e. below 0.01 l.tg/g), but could not be identified or quantified, due to an interference in the chromatogram (see Fig. 2C) which was not removed by the cleanup procedure applied. In the sediment NP and NPE were identified by reversed-phase HPLC (see Fig. 2B) and found to be present at levels of 6.8 and 40.2 (sum of NPE) l.tg /g, respectively. Ethoxylate oligomers identified by normal-phase HPLC (see Fig. 2D) ranged from 3 to 16 ethoxylate units. Their concentrations ranged from 1.4 to 5.2 p.g /g (cf. Table 3 ). The total

vol. 16, no. 10, 1997

sum of NPE quantified by normal-phase analysis (35.5 l_tg/g) is in reasonable agreement with the value from reversed-phase analysis (40.2 pg/g ). The discrepancy can be explained by oligomers not quantified in normal phase HPLC, e.g. NP2E (see below). No octylphenol or octylphenol( 1 or 2) ethoxylates were found in the wastewater treatment plant samples. Nonylphenol( 1 or 2) ethoxylates are likely to be present in both samples, but could not be properly quantified due to the interference mentioned above, and the lack of a proper standard containing NP2E only. In particular NP2E may be present in the sediment sample (see Fig. 2D, arrow). Nonionic surfactants are applied in large quantities in the industrial cleaning of large tapestries. Cleaning is conducted e.g. by sprinkling aerosols containing a solution of the surfactant over a suction table supporting the tapestry. Air is sucked through the tapestry and the liquid is collected in a funnel mounted below the table. After application, the detergent is gradually removed by rinsing with water. Fig. 3 shows NP-HPLC chromatograms of a commercial NPE mixture applied in cleansing, the rinse water collected after 2.5 h of rinsing, and a Soxhlet extract of a treated tapestry. The chromatograms show that the detergent is a NPE containing an average of 10 ethoxylate units closely matching

Table 3 Concentrations of NP and NPE calculated from normal-phase and reversed-phase HPLC analysis of a water and a sludge sample from an industrial wasterwater plant Compound

Water RP analysis (pg/g water)

NP NP3EO NP4EO NP5EO NPGEO NP7EO NP8EO NPSEO NPlOEO NPllEO NP12EO NP13EO NP14EO NP15EO NPl6EO NPEO sum

0.008

0.383

Water NP analysis (us/g water)

Sludgea RP analysis kg/g sludge)

Sludgea NP analysis @g/g sludge)

6.822 (0.004)

0.016 0.029 0.045 0.057 0.064 0.061 0.045 0.025 0.013 0.005 0.360

40.16 (0.88)

“Standard deviation based on duplicate analyses given in parentheses.

5.13 1.47 1.71 1.51 1.78 2.25 2.55 3.20 3.23 3.06 2.75 2.40 2.39 2.04 35.48

(2.40) (0.64) (0.65) (0.48) (0.43) (0.52) (0.50) (0.56) (0.39) (0.54) (0.54) (0.58) (0.38) (0.52) (6.32)

Analytical limit of detection (ng /g sample)

0.5 1.6 1.8 2.0 2.2 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 0.5

1000 (W

1.” !

2.0

6.0

6.0

6.0

6.0

I’’

800 600

4.0

i

400.

zoo,&I\ O,-._,0.0

J

.._ _~ 2.0

-------I----,

4.0

10.0

12.0

14.0

(min)

Fig. 2. RP-HPLC (A+B) and NP-HPLC (C+D) chromatograms of wastewater (A+C) and sludge (B+D) taken from an industrial wastewater treatment plant. Detector: fluorescence detector. Conditions, see text.

the available standard. After 2.5 h rinsing, the wastewater has a concentration equivalent to about 0.1 times the concentration of the surfactant solution applied in the cleaning process.

Samples of river-me, estuarine and marine sediments from 22 locations around the North Sea were taken as a part of a large survey [ 10 1. At each location three independent samples were taken. A

590

more detailed description of this survey will be presented elsewhere. Here we show some overall results, including average data for each location, and trends that were observed. Quantitative results were calculated from RP-HPLC runs only and not from NP-HPLC because of differences in oligomer distribution between standards and samples. In all samples taken, NPE were found to be present. OP was found in 16, NP in 20, and OPE in 21 out of the total of 22 locations sampled. Levels of OP varied from below the detection limit to 2 rig/g (dry weight). No particular geographical distribution was seen. Levels of OPE varied from 0.2 to 16 rig/g,, with higher levels in the coastal areas of the southern North Sea and Irish Sea. In general, the total OPE levels were much higher (almost an order of magnitude) than total OP levels. The NP levels observed varied from 0.1 to 17 ng /g. NPE levels varied from 12 to 400 ng /g. Fig. 4 presents the mean results of OPE and NPE for each location. From the NP-HPLC analyses it appeared (results not shown here) that the majority of samples contained primarily OPE and NPE with l-3 ethoxylate units. 3.1. GC-MS Masses of molecular ions and principal fragments occurring in electron impact (EI) MS of APE are given in Table 2. The EIMS of APE is dominated by typical features such as the occurrence of the [ CHzCHzOH ]+ ion ( m/z 45 ) from the ethoxylate chain, the [m-85 ]+ and [m-7 1 ]+ ions corresponding to loss of C6Hrs or CsHi 1 fragments from the alkyl moiety. The recurring mass increment of 44 corresponds to the 1 ethoxylate (CzH40) unit difference between oligomers present in mixtures. Figs. 5 and 6 show the total ion chromatograms obtained with full scan GC-EIMS of different commercial octylphenol and nonylphenol ethoxylate mixtures. As can be seen, the octyl moiety in commercial OP and OPE mixtures is composed of only a few isomers (Fig. 5). In contrast, for the NP and NPE mixtures the complicated cluster of peaks associated with each oligomer (Fig. 6) reveals a number of isomers corresponding to differences in branching of the nonyl moiety. Fig. 7 shows the TI chromatogram from a selected ion monitoring (SIM) run of an extract of harbor sediment and the corresponding time window of the full scan TIC of an OPE standard. The

trends in analytical chemistry, vol. 76, no. 10, 1997

presence of several of the octylphenol ethoxylate oligomers in the sample is clearly demonstrated by the correspondence in retention times with OPE present in the standard mixture. The presence of some NPE oligomers was also confirmed. 3.2. Quality control Blank samples were processed according to the procedures outlined above and found to contain no or negligible amounts of NP or NPE. The recovery of the method was tested by processing and analyzing a spiked solution of NP+NPE. The recovery for NP amounted to 104%, whereas for NPE a value of 84% was found. The repeatability of the analyses was assessed by duplicate injections of the purified extracts on the pertinent HPLC system. For normal-phase HPLC a maximum deviation between duplicate injections of 16% was found. For reversed-phase HPLC the maximum deviation observed between duplicate injections was 6.9%. Analytical detection limits are given in the last column of Table 2. Practical limits of detection depend on a number of factors, including actual interferences in the sample and sample intake.

4. Precautions 4.1. Preservation

of samples

To prevent biological degradation of alkylpheno1 ethoxylates when samples are to be stored over a period of more than a few days, or transported, a combined physicochemical pretreatment procedure is recommended [ 11,12 1. This method includes addition of formaldehyde ( l%, w/w of a 37% solution of formaldehyde in water) to the sample and its subsequent freezing. Storage and transport in frozen conditions will frequently be a problem, in particular when long distances are involved. Therefore, a higher formaldehyde concentration is recommended for preservation. Storage at low temperature conditions ( < 4°C) remains compulsory, however, to prevent further breakdown of the analytes during storage and transport. It is expected that the measures proposed enable a satisfactory level of confidence when analyzing the samples for alkylphenol ethoxylates within 4-6 weeks after sampling.

591

trends in analytical chemistry, vol. 16, no. 70, 1997

250 1

A

__~,~~

250'

._

._~~~_..__~__ 4.0

6.0

6.0

4.0

6.0

6.0

10.0

12.0

--.7-p14.0

Ii.0

14.0

16.0

12.0

1;;

16.0

~_~~

r---p 16.0

(min)

(min)

B

rl 9,

n

350. 300 250 I

c

200 1 150, 100~ 50.

40;+-_A! 2.0

(mV)?.O

250.

~--.

4.0

L______---I--

--I-

6.0

6.0

10.0

.~~_

(min)

D

2004 150 I

Fig. 3. Normal-phase HPLC chromatograms of standards and samples from an industrial tapestry cleaning facility. A: Standard of NPl OE. B: 1000 x dilution of detergent (Varzapon) used for cleaning. C: Sample of washing fluid collected from tapestry cleaning process. D: Extract from a tapestry cleaned with Varzapon. 4.2. Analytical

procedure

Initially an analytical protocol was applied which made use of the solvent sublation technique,

either directly (water samples) or after Soxhlet extraction (sediments, sludge). This technique has been shown to be particularly successful in AE analysis [ 91. The majority of the extracts thus

trends in analytical chemistry, vol. 16, no. 10, 1997

rn

w

5oo

1

!

400

30

I

300

20

10

Y

0

.-(u 2s

f;rLG zmm

Fig. 4. Levels of OPE and NPE in estuarine and marine sediments from the OSPARcom area (North Sea, Irish Sea), analyzed by RP-HPLC. Left y-axis: OPE; right axis, NPE. Labels on the x-axis denote origin (country) of samples: NL = Netherlands, BE = Belgium, FR = France, IR = Ireland, UK= United Kingdom, GE = Germany, NO = Norway, SW = Sweden. Error bars represent standard deviation from triplicate sampling.

AbundanceTIC:

0621P

j

8000000~

6000000 1

Oh

I

Time--93.00

/

/

I

12.12

Abundancl e

TIC:

5e+07

0626PS.D

4

4e+07

3e+07 3 2e+07

le+07 2

I

0 Time-->

10.00

15.00

20.00

25.00

30.00

35.00

40.00

45.00

Fig. 5. Electron impact GC-MS total ion chromatograms of p( tert.-octyl)phenol late mixture (bottom). Conditions, see text.

(top) and octylphenol8:9

ethoxy-

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trends in analytical chemistry, vol.16, no. 10, 1997

Abundance~~C

062OPS

800000 600000

ITime--si Abundance

.‘OO

14:17 TIC:

0

3PS.D

6000000 NP3E

0

JL'zb

Time--s

TIC:

0624PS.D 13

6000000

NP5E h 0 Time--> Abundance

TIC:

0625PS.D

le+07 8000000 6000000

Fig. 6. Electron impact GC-MS total ion chromatograms of p( nonyl)phenol (A) and three mixtures of p( nonyl)phenol ethoxylates. Conditions, see text. 6: Mixture NP2E, containing oligomers with an average of 2 ethoxylate units. C: Mixture NP4E, containing oligomers with an average of 4 ethoxylate units. D: Mixture NPl OE, containing oligomers with an average of 10 ethoxylate units.

obtained appeared to contain chromatographic interferences. One source of these was found to be plasticizers used in rubber tubings and seals used in the laboratory, e.g. in sublation gas supply and in rotary evaporators. Cl8 SPE turned out to be a suitable alternative for circumventing contamina-

tion from plasticizers since smaller solvent volumes are used and no gas supply is needed. In AE analysis, these plasticizers may not interfere due to their different retention times or the different chromophores used.

594

trends in analytical chemistry, vol. 16, no. 10, 1997

Abundance e

TIC:

0634PS.D

1200000 1000000 800000 600000 400000 200000

h

0 Time-->-

TIC:

Abundance 5e+07

4e+07

3e+07

/

20100

15:oo

lOlO

L

b.

25100

0626PS.D

1 1 i

2e+07

le+07

1

/

0 Time-->

I

I

10.00

”

h

/ c 15.00

/

‘I””

20.00

I

25.00

”

Fig. 7. Electron impact GC-MS multiple ion chromatograms of an extract of harbor sediment (top) and a standard mixture of octylphenol 8:9 ethoxylates (bottom). Conditions, see text. Arrows indicate the presence of OPE in sediment sample.

4.3. Retention

time shifts

Retention time shifts relative to those in standard mixtures can easily occur when the composition of the sample mixture differs from the standard. To give an example, in NP-HPLC the chromatograms of a standard mixture provide just one common peak for all alkyl etboxylates with, say, 8 ethoxylate units. However, when the sample contains a mixture of octyl and nonyl octaethoxylates, with the octyl compounds more abundantly present, whereas the standard contains nonyl compounds only, a shift in retention times may be observed. The same phenomenon can occur in RP-HPLC (where, in principle, separation of OP, NP, OPE and NPE is achieved) if the ethoxylate composition of, say, the NPE peak (containing all ethoxylate oligomers containing a nonyl moiety) differs from that of a standard. In practice, these phenomena can sometimes hamper the proper identification of peaks in NP-HPLC, thereby disabling a quanti-

tative assessment. As a consequence, identification and quantitation of NIS by HPLC must be based on concomitant RP- and NP-HPLC analysis. 4.4. GC-MS A remarkable feature of the chromatograms shown in Figs. 5 and 6 is a broadening and a reduction of the response of peaks eluting later in the chromatograms. Rather than being the result of lower concentrations of the oligomers with higher numbers of ethoxylate units, this is a result of their inherently reduced volatility. For proper GC(-MS ) analysis of oligomers containing more than 5 or 6 ethoxylate units, transformation into more volatile derivatives is necessary. This can be done by silylation agents such as bis( trimethylsilyl)trifluoro acetamide or hexamethyl disilazane. Alternatively, high-temperature GC may be used although analyte degradation may then occur.

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4.5. Identification

and quantitation

It is obvious that due to the complexity of APE mixtures, precise quantitation of environmental samples is very difficult. In such samples, each of the isomers originally present within one oligomeric group may have undergone different changes as a result of processes such as weathering and (bio)degradation, which can be expected to be structure dependent. In addition, the various oligomerit groups may have been degraded (i.e. shortening of the ethoxylate chain) to different extents. Hence the actual samples taken from the environment usually contain mixtures with a composition different from that of the available standards. More accurate analysis can only be accomplished when: ( 1) individual isomer and oligomer standards of sufficient purity become available through synthesis; (2) analytical techniques with more resolving power become available. As to the latter, LC-MS using microbore columns, high-temperature GCMS, or hyphenated normal- and reversed-phase LC-FLU are techniques that need further investigation.

5. Environmental

levels

The results presented here show that levels of total NPE or OPE in estuarine and marine sediments are generally about one order of magnitude higher than the corresponding total NP or OP levels. This probably implies that the ethoxylates present in the samples have not been transformed (at least not to a great extent) to NP or OP, respectively. The distribution of the ethoxylate oligomers indicates, however, that changes in oligomer distribution compared to original sources of NIS are likely, since a predominance of O/NPE with l-3 ethoxylate units was observed. Apparently, transformation to O/NP( I-3)E is an important (first) stage in the conversion process. The ratio between NPE and OPE is also about one order of magnitude, roughly reflecting their ratio in commercial applications. The reproducibility of triplicate sampling is relatively poor (cf. Fig. 4). Although this may be the result of inhomogeneities in the field, it emphasizes the need for well-defined sampling protocols for surveys of this kind.

The results from the industrial wastewater and sludge samples show that NIS may be released in wastewaters as practically unchanged mixtures. A quantitative assessment of amounts released from the different processes involved was not made.

Acknowledgements The Dutch Ministry of Transport and Water Management, National Institute for Coastal and Marine Management supported part of this study. We thank the Shell Laboratory in Amsterdam, NL and ICI Surfactants, Middlesbrough, UK for their kind gift of standard mixtures, and Jan van der Steen, Anton Kiewiet, Pieter Slot and Hans van Zeijl for their help and comments.

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