-
AuthorsD. Benanou*, D. Ben Ali, V. Boireau and J. Cigana
Anjou Recherche- Veolia Water, Analytical Research
Department
chemin de la Digue, 78600 Maisons-Laffitte, France
*(E-mail: [email protected])
Philip L. Wylie
Agilent Technologies, Inc.
2850 Centerville Road
Wilmington, DE 19808-1610
USA
Abstract
A routine method is described for quantitative determina-tion of
4-nonylphenol (NP), 4-nonylphenol monoethoxy-late (NP1EO) and
4-nonylphenol diethoxylate (NP2EO) insludge samples.
A Soxtec® extraction procedure was used to enrich target
compounds from the solid matrix. Quantitativedeterminations were
performed by high speed gas chromatography/mass spectrometry using
a short apolarfused silica column. Derivitization allows NP1EO
andNP2EO to be analyzed by gas chromatography.
The relative standard deviation was close to 5% for theanalysis
of 10 different sludges analyzed seven timeseach. Recoveries were
determined for a sludge referencematerial and were higher than 90%.
The experimentallimits of quantification were 2, 5, and 5 µg/g of
dry matter(µg/g DM), respectively, for NP, NP1EO, and NP2EO.
Determination of Alkylphenols andAlkylphenol Mono- and
Diethoxylates inSewage Sludge by High Speed Gas Chromatography/Mass
Spectrometry
Application
Good agreement was observed between results obtainedwith this
method and those obtained by our previousmethod, which used
normal-phase liquid chromatogra-phy with an aminosilica column.
This method wasapplied to different kinds of sludge collected in
Franceand showed the persistence of these contaminants.
Introduction
Sewage sludge has been used in agriculture for along time. Since
1986, the use of sewage sludge hasbeen subject to provisions
stipulated in EU Direc-tive (86/278/EWG) [1]. Presently under
revision,this Directive specifies requirements regardingsludge and
soil quality. In contrast to Directive86/278/EWG now in force, the
revised version willcover specific methods for the analysis of
sludgeand soil. Organic micro-pollutants have beenattributed even
greater importance in the environ-ment since the toxicity knowledge
of refractoryorganic compounds has grown. Thus, there is atendency
for the European Commission to set uplimit values for substances
that Europeans gener-ally find undesirable in the environment.
Specificcompound groups are mentioned in the currentversion of the
revised sludge directive along withlimit values (Table 1). Limits
are set for: halo-genated organic compounds (AOX), linear
alkyl-benzene sulfonates (LAS), di(2-ethylhexyl)-phthalate (DEHP),
nonylphenol and nonylphenolethoxylates (NPE), polyaromatic
hydrocarbons(PAH), polychlorinated biphenyls (PCB) and
poly-chlorinated dibenzodioxins/dibenzofurans(PCDD/F). From these
compound groups, onlyPAHs and PCBs are included in the current
EUDirective (86/278/EWG).
Environmental analysis, Sludge analysis
-
2
Limit valuesCompounds (mg/kg)
PCBs (Σ of 6 congeners) 0.8PAHs (Σ of 11 PAHs) 6AOX 500
DEHP 100
LAS 2600
NP + NP1EO + NP2EO 50
PCDF 100 ng TE/kg
Table 1. Limit Values for Selected Organic Contaminants
inSludge
Alkylphenol polyethoxylates (APnEO) represent animportant class
of nonionic surfactants that arewidely used in many detergent
formulations bothfor industrial and household use. Industrial
usesinclude the manufacture of plastics, textiles, paper,and
agricultural chemical products (Talmage1994)[2]. Institutional
applications include vehiclecleaning, commercial laundry products,
and hardsurface cleaners. Personal care products, contra-ceptives,
cosmetics, and household laundry prod-ucts account for the majority
of householdapplications. Nonylphenol polyethoxylates are non-ionic
surfactants symbolized by NPnEO where " n "is the number of ethoxy
groups, with 2
-
3
Experimental
Chemicals and Reagents
Hexane and acetone were obtained from Merck(Darmstadt, Germany).
The derivatization reagent,Sigma-Sil-A, was purchased from Sigma
(Milwau-kee, USA). 4-Nonylphenol, 4-nonylphenol mono-and
diethoxylates and 4-nonylphenol-d8 were pur-chased from Cluzeau
(France). Florisil cartridges(1 g, 3 mL) were obtained from Supelco
(Belle-fonte, USA). Sludge reference material wasobtained from LGC
Promochem (Molsheim,France).
Stock solutions for 4-nonylphenol, 4-nonylphenolmono- and
diethoxylates were prepared in hexaneat 300 mg/L. The stock
solution of 4-nonylphenol-d8 was prepared in hexane at 100 mg/L.
Whenstored at 4 °C, the stock solutions were stable forat least six
months. Acetic anhydride and BSTFA[N,O-bis
(trimethylsilyl)trifluoroacetamide) werepurchased from Aldrich
(USA).
Sample Collection
Sludge samples were collected in dark glass con-tainers and
stored at –80 °C for 24 hours just priorto drying by
lyophilization. The lyophilized sludgewas ground and only the
fraction below 200 µmwas analyzed.
Extraction Procedures
One gram of ground lyophilized sludge was Soxtecextracted by 100
mL of hexane (Foss, Nanterre,France). The sample was immersed in
hexane for30 minutes (boiling mode) and then rinsed for 15 minutes
(rinsing mode). Concentration of theextract to 1 mL was carried out
with a stream ofnitrogen using a Turbovap II concentrator
(ZymarkUSA). The concentrated extract was then
automatically purified over Florisil using a Rapid-Trace system
(Zymark USA). A loading volume of 1 mL of concentrated extract was
applied to aFlorisil cartridge at a flow rate of 1 mL/min.
Thesorbent was rinsed with 5 mL of a hexane/acetonemixture (70/30)
and 5 mL of hexane at 10 mL/min.NP, NP1EO and NP2EO were
selectively elutedfrom the cartridge using 5 mL of a
hexane/acetonemixture (70/30) at a flow rate of 2 mL/min.
Con-centration of the purified extract to less than 1 mLwas carried
out with a stream of nitrogen using aTurbovap LV concentrator
(Zymark USA); 20 µL oflabelled NP was added just prior to
derivatizationwith 50 µL of Sigma-Sil-A. The extract was left for30
min in darkness and was then reconstituted toa final volume of 1 mL
just prior to analysis.
Instrumental Conditions
The GC/MS system used was an Agilent 6890/5973MSD (Agilent
Technologies, Palo Alto, CA, USA)equipped with a split/splitless
inlet heated to 300 °C. The operating conditions were as
follows.Using an Agilent 7673 autosampler, 1 µL of thefinal extract
was injected in the splitless modewith the purge vent off for 1
min. Helium carriergas was run at constant flow (0.3 mL/min).
Theinlet pressure at 50 °C was 52.2 psi. The com-pounds were
separated on a 20-m × 0.10-mm id ×0.10 µm RTX5 capillary column
(Restek USA). Theoven was programmed from 50 °C (0 min) to 120 °C
at 110 °C/min then at 30 °C/min to 300 °C(5 min). A 6890 oven
insert (Part no. G2646-60500)was used in order to reduce the oven
volume,allowing the column to heat more quickly, yieldingfaster
separation and faster chromatography. MSdetection was achieved in
the selected ion moni-toring (SIM) mode for quantitative analysis
and inscan mode for qualitative analysis. The source washeated at
250 °C, the quadrupole at 150 °C, andthe transfer line at 250
°C.
-
4
40 120 200 280 360 4400
100000
200000
300000
400000
500000
m/z
Abundance221
135
263
73 193107
29255163 238
40 120 200 280 360 4400
60000
120000
180000
240000
m/z
Abundance265
30773 237
193117
149 3369155
175
217
282
40 120 200 280 360 4400
60000
120000
180000
240000
m/z
Abundance295
351
73
117135 3802071612479155 179
312
267224
330
A B C
Figure 2. Mass spectra of A) NP, B) NP1EO, and C) NP2EO after
derivatization with Sigma-Sil-A under quantitative conditions.
Tuning the Mass Selective Detector (MSD)
For qualitative analysis, the MSD was tuned usingthe autotune
macro. With this macro, the abun-dances for ions 219 and 502
relative to ion 69(using PFTBA as calibrant) are typically
around60%–100% and 3%–10%, respectively. For quantita-tive analysis
of derivatized NP, NP1EO, andNP2EO, a target tune was employed
using ions 69,219, and 414. The repeller voltage was set to givean
optimum response for ion 219. The target tuneresulted in relative
abundances (compared to ion69) of 110% and 10% for ions 219 and
414, respec-tively. Figure 2 shows the mass spectra of
thederivatized target compounds for quantitation. Formonitoring
ions in the SIM mode, 193, 207, 221,and 292 were chosen for NP,
251, 265, and 336 forNP1EO, and 295, 309, and 380 for NP2EO.
Theinternal standard (ISTD), 4-nonylphenol-d8, was monitored at m/z
300.
Method Validation
The method was validated according to the AFNORregulation XP T
90-210.
The validation consists in defining:
• The scope of linearity:The linearity was determined over seven
con-centration levels from 2 to 200 µg/L, and was
replicated five times. Calibration was doneusing the ISTD mode
with NP-d8. Linearity isachieved when the correlation coefficient
(R) is0.9990.
• The limit of quantification (LOQ): LOQ is validated when the
within-batch relativestandard deviation (RSD) is under 20% for 10
replicate samples spiked with supposedLOQs.
• The repeatability: The repeatability is expressed as a RSD (in
%)and is calculated on the basis of three repli-cates of eight
different sludge samples and mustbe less than 20%.
• The accuracy:The accuracy is expressed as recovery (in %)
ofsludge reference material and must be between80% and 120%.
• The reproducibility:The reproducibility is expressed as a %RSD
of acheck calibration standard (20 µg/g) and shouldbe under
20%.
-
5
7.504.50 5.00 5.50 6.00 6.50 7.00
20000
60000
100000
140000
180000
220000
NP1EONP
NP2EONP-d8
Abundance
7.50
NP1EO
NP
NP2EO
4.50 5.00 5.50 6.00 6.50 7.00
20000
60000
100000
140000
180000
220000
Abundance
40000
80000
120000
160000
200000
240000
NP1EONP
NP2EO
7.504.50 5.00 5.50 6.00 6.50 7.00
Abundance
A B C
NP-d8 NP-d8
Figure 4. Mixture of NP, NP1EO, NP2EO, and NP-d8 derivatized
with A) acetic anhydride, B) BSTFA, and C) Sigma-Sil A.
OH19C9
O H
n
OH19C9
O Si
n (CH3)3
TMCS: Trimethylchlorsilane
(H3C)3 Si
Cl
OH19C9
O H
n
OH19C9
O Si
n (CH3)3
HMDS: Hexamethyldisilazane
(H3C)3
SiNH
Si(CH3)3
Figure 3. Reaction of Sigma-Sil-A with NPEO
Results and Discussion
Derivatization Conditions: Optimization
Three kinds of derivatizing reagents were testedduring this
study -- acetic anhydride, BSTFA
[(N,O-bis(trimethylsilyl)trifluoroacetamide], andSigma-Sil-A which
is a 1:3:9 mixture oftrimethylchlorosilane (TMCS),
hexamethyldisi-lazane (HMDS ((CH3)3SI-NH-Si(CH3)3), and pyridine
(see Figure 3).
Acetic anhydride gave only a small response forthe target
compounds while BSTFA and Sigma-Sil-A gave complete derivatization
within 30 min-utes. As seen in Figure 4, the BSTFA and Sigma-Sil-A
gave the same chromatogram, whichcontained intense molecular ions
for NP, NP1EOand NP2EO. Sigma-Sil-A was chosen for furtherwork
because the derivatization occurred at roomtemperature while BSTFA
required heating at 90 °C.
Separation: Optimization
In some studies, capillary column GC procedureswere used for the
analysis of NPnEO either directly(Giger, 1981) [23] or after
conversion into morevolatile derivatives (Wahlberg, et al., 1990)
[24].Even though this approach was limited to ethoxy-lates with one
to five ethoxy units, this techniquewas adopted, instead of HPLC
separation becauseof the higher selectivity of the detector.
Instead ofa single eluted peak observed for each NPEO inHPLC, the
higher resolution of the capillary GCcolumn produced three groups
of peaks for deriva-tized NP, NP1EO and NP2EO resulting from
differ-ent isomers of the nonyl group. This additionalfingerprint
information is very useful for the iden-tification of these
compounds in a complex matrixsuch as sludge.
-
6
There was a desire to improve productivity byreducing the GC run
time while maintaining theelution order and selectivity of the
analyticalcolumn. Exact translation between conventionaland
high-speed chromatography was achieved byusing Agilent's dedicated
Method Translation Soft-ware (Agilent Technologies, version
2.0.a.c). Usingempirical methods, it was impossible to
maintaincolumn selectivity.
Full scan GC/MS of derivatized NP, NP1EO andNP2EO shows three
groups of peaks with retentiontimes (RTs) from 4.5 to 5 min for NP,
5.6 to 6 minfor NP1EO and from 6.5 to 6.8 min for NP2EO(Figure 3).
In this case molecular ions were avail-able for quantification. An
additional benefit ofhigh-speed chromatography was the increase
insensitivity resulting from the 10-fold reduction inpeak width
(PW). The first 10 cm of the capillarycolumn had to be removed
after each 50 injections.
Purification Conditions: Optimization
Florisil cartridges were used to clean up sludgesprior to
analysis by GC/MS. The cleanup procedurefor NP, NP1EO, and NP2EO
was optimized byadding 1 mL of hexane and 1 mL of sludge
extract(spiked with 25 µL of the target compounds inhexane) to
Florisil cartridges. Various solventswere evaluated for their
ability to elute the targetcompounds quantitatively while
separating themfrom interferences. Previous studies (Benanou,
etal., 1999, 2001) [25, 26] showed that 10 mL ofhexane allowed one
to recover PCBs, hydrocarbons
from C6 to C50, some PAHs, and LAS, but notNPEO. An additional 5
mL of a 90/10 hexane/acetone eluted only NP. With this background,
dif-ferent hexane/acetone mixtures (ranging from90/10 to 50/50)
were tested for the elution of allNPEO analogs. Quantitative and
qualitative resultsshowed that after discarding the first 10 mL
ofhexane, a 70/30 hexane/acetone mixture gave thebest results. In
fact, increasing the proportion ofacetone did not improve analyte
recovery but dra-matically increased the amount of grease in
thefinal extract. Figure 5A illustrates recovery of theNPEO
analytes while Figure 5B plots the sum ofthe total ion chromatogram
(TIC) areas as a func-tion of the solvent mixture. The 70/30
hexane/acetone mixture gave the highest recovery of theanalytes
with the least amount of co-extractedmaterial.
Quantitation of NP, NP1EO and NP2EO
Internal standard calibration was used for quanti-tation with
one labelled congener of the NP mix-ture (NP-d8) used as the
internal standard (ISTD).Each compound was quantified separately
withtwo or more different ions. In that way, even
withinterferences, it was possible to quantify the com-pounds. In
such matrices, choosing one quantify-ing ion and two or more
qualifiers is not enough.Calibration curves were prepared between 2
and200 µg/mL by injecting standards. Table 2 lists thequantifying
ions, linearity, RSD, and LOQ.
0 , 0 0 E +0 0
1 , 0 0 E +0 7
2 , 0 0 E +0 7
3 , 0 0 E +0 7
4 , 0 0 E +0 7
5 , 0 0 E +0 7
6 , 0 0 E +0 7
7 , 0 0 E +0 7
hex/ ace 90/10
hex / ace 80/20
hex / ace 70/30
hex / ace 60/40
hex / ace 50/50
0
2 0
4 0
6 0
8 0
10 0
12 0
h e x/a c e 9 0 /10
h e x/a c e 8 0 /20
h e x/a c e 7 0 /3 0
h e x/a c e 6 0/4 0
h e x/a c e 5 0 /5 0
Rec
over
y %
NP
NP1EO
NP2EO
A B
Figure 5. A) Recovery of NP and NPEO analogs after elution with
different hexane/acetone mixtures. B) Total peak area of the TICas
a function of the solvent mixture.
-
7
Table 2. Calibration Results for the Quantitative
Determinationof NP, NP1EO, and NP2EO
Performance of the Analytical Method and
ExtractionOptimization
A sludge reference material was used to verify theperformance of
this method. One g of sludge wasintroduced into a cellulose thimble
with 1 g ofsand. The sludge/sand mixture was agitated for 1 min on
a vortex mixer and the thimble was thenslurried with glass wool.
The extraction tempera-ture was 180 °C. A hexane/acetone mixture
waschosen instead of pure hexane for complete recovery of NP1EO and
NP2EO. By extracting only
with hexane, recovery was less than 20%. Soxtecextraction
performed with methanol gave satisfac-tory recovery, but methanol
is not amenable to GCanalysis. Different hexane/acetone mixtures
rang-ing from 90/10 to 50/50 and different extractiontimes ranging
from 30 to 360 min were tested.Results obtained showed the best
compromise wasan extraction time of 45 min with a 50/50
hexane/acetone mixture.
The extract was very brown compared to extrac-tions performed
with hexane only. Thehexane/acetone mixture made it possible
torecover NP1EO and NP2EO quantitatively, butmany interferences
were collected as well (Figure 6). Co-extraction of these polar and
mid-polar compounds made it necessary to perform theclean-up twice
for some sludge samples. Theextraction was improved by adding and
thoroughlymixing 1 g of Florisil and 1 g of sand to the sludgejust
prior the extraction. Analyte recoveries werenot diminished by the
addition of Florisil to thesamples and only one clean-up step was
requiredfor all sludge samples.
15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00
65.00 70.00 75.000
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
Abundance
Time (min)
15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.00
65.00 70.00 75.000
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
Abundance
Time (min)
A
B
Figure 6. Chromatogram of the same sludge sample A) without
addition of silica, and B) with addition of silica during the
extraction step.
Quantifying ions R2 RSD% LOQ µg/g
192 0.9994 5207 0.9985 12.5
NP 221 0.9989 3.7 2292 0.9997 2.2
251 0.9990 3.5 5NP1EO 265 0.9989 6.2
336 0.9999 5.3
295 0.9994 5.9 5NP2EO 309 0.9993 4.8
380 0.9996 3.6
-
8
Table 3 illustrates the recoveries obtained withthis method for
10 extractions of the sludge refer-ence material over a 1-week
period. Results,expressed in mg/kg DM, are the mean of theresults
obtained with each quantifying ion. Resultsobtained with our
previous method using Soxtecextraction with methanol (no additional
clean up)and normal phase HPLC with fluorescence detection are
listed for comparison.
NP NP1EO NP2EO(mg/kg DM) (mg/kg DM) (mg/kg DM)
Certified values 100 ±8.0 5 ±0.9 2 ±0.1
GC/MS meanconcentration 102 ±3.4 4.3 ±0.06 2.1 ±0.02
GC/MSrecovery % 102 86 105
HPLC/Fluo 87 ±9.1 6.1 ±1.0 2.5 ±0.7
HPLC/Fluorecovery % 87 122 125
Table 3. Mean Recovery Values and Uncertainties (n = 10) forNP,
NP1EO, and NP2EO Determined in Sludge Reference Material
Both techniques gave good agreement with thepublished values for
the reference material. Allrecovery values were higher than 80%
showinggood performance of the Soxtec extraction methodwith GC/MS
quantitation. However, the uncer-tainty is greater with
HPLC/fluorescence thanwith GC/MS due to the lack of specificity of
thisLC detector compared with a mass spectrometricdetection.
Sewage Sludge Analysis
This high speed GC/MS method was applied to theanalysis of
sludge samples from 10 sewage treat-ment plants (STPs) in France.
Each sludge samplewas extracted five times and results are shown
inTable 4. Results are expressed in mg/kg DM andare a mean of the
results obtained with each quan-tifying ion. Figure 7 shows
chromatograms forsludge samples 2 and 5. Some sludge samples
wereproblematic when using the m/z 207 ion as thequantifier. Some
interference appears due tocolumn bleed, which resulted in a high
backgroundat m/z 207 around the RTs of NP and NP1EO. Inthe end, NP
was only quantified with ions 193,221, and 292.
Whatever the sludge sample's origin, the sum ofNP, NP1EO, and
NP2EO was usually above thelimit value of 50 mg/kg DM indicated in
the revi-sion of the current regulation. Values ranged from8.8 to
210 mg/kg DM, with a median value of 91 mg/kg DM. NP2EO showed
higher concentra-tions than NP and NP1EO for most sludge
samples.It's contribution to the sum for sludges 1 to 6,ranged from
16% to 80% with a median value of50% (31 mg/kg DM). These values
point out thatmost of these sludges could not be applied as
fertil-izer on agricultural land once the EU approves thisrevision.
However, the contamination seems lessheavy than that observed in
STPs from Switzerland(Ahel, et al., 1994) [6]. The MSD's
specificity madeit possible to obtain satisfactory SDs for all
ofthese measurements.
1 2 3 4 5 6 7 8 9 10
NP 15.4 24.7 27.1 11.9 16.2 21.9 10 12.9 8.8 38.4
±0.6 ± 0.4 ± 0.7 ±0.4 ±0.6 ±0.7 ±0.5 0.2 0.3 3.6
NP1EO 8.7 14.6 36.0 25.3 49.9 13.3 12 12.5
-
9
2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.000
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
a
b
c
Sample 2
2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
a
b
c
Sample 5
Figure 7. Chromatograms of sludge samples 2 and 5. a) NP, b)
NP1EO, c) NP2EO.
Conclusion
High-speed GC/MS enabled rapid determination ofNP, NP1EO and
NP2EO in sludge samples. The Agilent 6890 GC was able to separate
the NP,NP1EO and NP2EO congener groups into threesets of peaks,
instead of a single peak for eachgroup as was observed when using
HPLC.
DLs were improved by working in the SIM modeand by reducing peak
widths with the 0.10-mm idGC column. The LOQs achieved with this
methodwere 2, 5, and 5 mg/kg DM for NP, NP1EO, andNP2EO,
respectively. RSDs were under 7%. Soxtecextraction followed by
Florisil cleanup resulted inrecovery values above 80% in all
cases.
Results for 10 typical sludge samples show that, inmost cases,
the sum of NP, NP1EO, and NP2EO isabove the anticipated regulatory
value of 50 mg/kgDM. Further work on NPEO will include analysis
ofthe same species in wastewater for a better under-standing of
their fate during sludge treatment.
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10
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