Document 6533389

Environmental Toxicology and Chemistry, Vol. 15, No. 11, pp. 1937–1944, 1996
q 1996 SETAC
Printed in the USA
0730-7268/96 $6.00 1 .00
EVALUATION OF THE GOULDEN LARGE-SAMPLE EXTRACTOR FOR ACIDIC
COMPOUNDS IN NATURAL WATERS
JOHN V. HEADLEY,*† LESLIE C. DICKSON,† CHRIS SWYNGEDOUW,‡ BOB CROSLEY§ and GERRY WHITLEY\
†National Hydrology Research Institute, Environment Canada, 11 Innovation Boulevard, Saskatoon, Saskatchewan S7N 3H5, Canada
‡Chemex Labs Alberta Ltd., 2021 41st Avenue Northeast, Calgary, Alberta T2E 6P2, Canada
§Ecological Research Division—Prairie and Northern Region, Environment Canada, 220 4th Avenue Southeast,
Calgary, Alberta T2G 4X3, Canada
\Water Resources Division, Indian and Northern Affairs Canada, 345-300 Main Street, Whitehorse, Yukon Territory Y1A 2B5, Canada
(Received 9 November 1995; Accepted 20 May 1996)
Abstract—The Goulden Large-Sample Extractor has received extensive use for monitoring and surveillance surveys of natural
waters impacted by pulp and paper mills and agricultural runoff water. However, there are concerns about whether this sampler,
which was originally developed for extractions of hydrophobic polycyclic aromatic hydrocarbons, polychlorinated biphenyls,
and other organochlorines, is suitable for sampling polar acidic compounds. The sampler was evaluated for recovery of surrogates
for resin acids, fatty acids, herbicide acids, and chlorophenols from natural waters. Performance tests conducted in this work
indicated that three surrogate compounds with Kp (CDCM/Cwater pH 2) values from 16,700 to 1,260 were extracted from pH 2-adjusted
20-L water samples with an average recovery of 83.6%. The surrogate compounds with Kp values less than 1,000 were extracted
with significantly lower recoveries. The variability ranged from 10 to 36% relative standard deviation. Recoveries and variability
compared favorably with reported recoveries and variabilities for neutral pesticide surrogates. Specific performance criteria
(percent recoveries 6 standard deviation, number of determinations in parentheses) observed for the surrogates 2,4,6-tribromophenol, heptadecanoic acid, O-methylpodocarpic acid, dichlorophenylacetic acid, and 4-bromophenol were 89.5 6 24.0 (17),
82.8 6 21.7 (18), 78.4 6 14.8 (18), 41.9 6 8.5 (16), and 22.1 6 8.1 (19), respectively. Low recoveries of the 4-bromophenol
surrogate may be due in part to side reactions with diazomethane. As a result, 4-bromophenol is not recommended as a surrogate.
These values can be used to provide guidelines for acceptable surrogate recoveries and validation of extractions of polar acidic
compounds.
Keywords—Water
Large-volume extraction
Organic acids
part of any analytical protocol used in site characterization
studies.
Part of any assessment of a polluted aquatic environment
is the preparation of a list of relevant contaminants selected
using a combination of BSA and TIE procedures. The analytical protocol must be able to extract and identify a broad
spectrum of substances rather than a limited list of priority
pollutants [5]. Samoiloff et al. [3] and Onley et al. [6] have
demonstrated that toxicity in aquatic environments is rarely
associated with priority pollutants. Since it is not possible a
priori to predict which class(es) of compounds will be consistently toxic at a given site, BSA techniques are needed that
can extract and identify a large portion of the dissolved bioavailable fraction and do so in a predictable manner based on
measured physical and chemical parameters or on quantitative
structure–property relationships [7]. Thus, large-volume techniques that can extract polar acidic compounds in addition to
the usual suite of hydrophobic neutral compounds play an
important role in site characterization studies.
Organic contaminants are often present at picogram-per-liter
to nanogram-per-liter levels in environmental water. To obtain
sufficient quantities for chemical analysis or bioassays, it is
necessary to extract or concentrate very large volumes of water
[8,9]. For analysis by gas chromatography–mass spectrometry
(GC–MS), a concentration factor of about 50,000 is needed,
while GC–MS–MS and high-performance liquid chromatography–mass spectrometry (HPLC–MS) techniques require a
concentration factor of 100,000 [10]. Biological testing protocols requiring long-term exposures for chronic toxicity eval-
INTRODUCTION
The Goulden Large-Sample Extractor (GLSE) has been
used extensively for monitoring natural waters for organochlorines, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and other hydrophobic base/neutral-extractable organic compounds. In western Canada the GLSE has been used
in monitoring and surveillance surveys of natural waters impacted by pulp and paper mills and agricultural runoff. The
performance of the GLSE has been well characterized for these
situations. However, there is concern about whether GLSE is
suitable for monitoring polar acidic compounds such as resin
acids, fatty acids, herbicide acids, and chlorophenols in target
analyses. There is also concern about using GLSE as an extraction method for use with broad-spectrum analyses (BSAs)
and toxicity-based identification and evaluation (TIE) studies.
Polar acidic compounds, especially those in pulp mill effluents, are associated with toxic effects on communities in
the receiving waters. The acute toxicity of pulp mill effluents
are primarily due to resin and fatty acids [1], especially dichlorodehydroabietic acids [2] and diterpene resin acids [3].
Resin acid toxicity is associated with elevated bilirubin levels,
smaller erythrocytes, and lower cell hemoglobin contents in
laboratory toxicity studies on fish [1]. Resin acids have bioconcentration factors in the range of 80 to 800 and depurate
quickly with a half-life of less than 4 d [1,4]. Detection of
these compounds in aquatic organisms is an indication of recent exposure to pulp mill effluent [4] and thus is an important
* To whom correspondence may be addressed.
1937
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Environ. Toxicol. Chem. 15, 1996
uations or requiring many large test species may need milligram-to-gram quantities of material [8].
The techniques available to concentrate and isolate organic
compounds from water have been reviewed [8,11,12]. Jolley
[8] organized the available methods into two groups, concentration methods and isolation methods. Concentration methods
include freeze concentration, lyophilization, vacuum distillation, reverse osmosis, and ultrafiltration. Isolation methods
include solid-phase extraction (SPE), solvent liquid–liquid extraction (LLE), precipitation, centrifugation, and gas stripping.
Solid-phase extraction and LLE are the most commonly used
methods for extracting organic contaminants from large volumes of water.
Solid-phase extraction, which uses solid sorbants to accumulate organic compounds from water, has been the subject
of many reviews [13–16]. A variety of materials has been used
as sorbants for SPE, including synthetic polymeric macroreticular resins [8,17–19], graphitized carbon black [20,21], and
bonded silica sorbants [9]. While the most common application
of SPE is the extraction of hydrophobic base/neutral compounds, SPE has also been used to isolate acidic compounds
from water [17–21].
Liquid–liquid extraction uses a water-immiscible solvent to
extract organics from water. Small volumes (,4 L) can be
batch-extracted in separatory funnels or in glass bottles, but
for larger samples a continuous extraction technique is preferred. Goldberg et al. [22] described a counter-flow LLE with
three extraction stages which could use either lighter-thanwater or heavier-than-water solvents. A continuous LLE using
flow through a Teflont helix to mix immiscible phases has
been developed by Suffet and coworkers [10,23,24]. This system uses an integrated phase separator and an evaporative
concentrator to recover solvent for recycling and to concentrate
the extract for further analysis. Another approach to continuous
LLE is the mixer–settler design [25,26]. A fixed volume of
heavier-than-water solvent is mixed with a continuous stream
of water entering the extractor body. Phase separation can take
place within the extractor body [25] or in separate compartments [27]. The GLSE is an example of the latter design of
continuous LLE.
The GLSE was originally developed to extract neutral hydrophobic compounds with Kow values $10,000 at nanogramper-liter levels from Great Lakes water onboard ship [28,29].
The original design, which extracted 50 L of water at rates up
to 1 L/min with 200 ml of dichloromethane (DCM), has been
modified into several different versions, each optimized for
particular situations [27,30,31]. The GLSE has been used to
sample a variety of environmental waters [29,32–36].
No one concentration method is adequate for isolating all
the organic constituents of interest from an aqueous sample
[37]. Each method has advantages and limitations, so the
choice of method will depend on the specific sampling situation and the objectives of the study. For this study we wished
to take advantage of the many strengths of the GLSE for BSA
and TIE approaches to site characterization. The GLSE has
the advantages of having very low blanks and low artifactual
toxicity, predictable extraction efficiencies, high flow rates,
and high capacity.
It is important for BSA and TIE studies to be able to keep
background contamination and toxicity to a minimum. Solvents can be purchased with very low levels of contamination,
and they can be easily distilled to further reduce contamination.
The use of DCM for LLE of contaminants in water for sub-
J.V. Headley et al.
sequent toxicity studies has been criticized because these solvents have a high background toxicity even after dilution, and
unacceptable losses can occur during solvent exchange [16].
However, Durhan et al. [38] have shown that it is possible to
exchange DCM extracts into methanol without significant
losses of semivolatile components. Solid-phase extraction materials, however, can impart very high levels of contaminants
and artifactual toxicity to extracts unless they are extensively
cleaned and properly stored [14]. Artifacts can be generated
because of poor cleaning procedures, fractured beads, and
slowly diffusing contaminants. The level of contamination is
a function of resin cleaning and reuse, storage conditions, elution conditions, and exposure to large volumes of environmental water samples which may contain reactive components.
By using LLE with lower levels of contamination and artifactual toxicity, a more reliable evaluation of the nature and
level of pollutants in an environmental water sample can be
made.
Predictable extraction efficiencies are an advantage in BSA
because it is not possible to predict a priori which compounds
or compound classes are going to be present at a given site.
It is necessary to be able to estimate the extraction efficiencies
of compounds not included in the surrogate mixture or in lists
of priority pollutants so that the true concentrations of contaminants can be estimated. The extraction efficiency of the
GLSE for organic contaminants in water can be predicted from
solute properties and thermodynamic theory. As described by
Foster and Rogerson [32], for continuous extraction an analyte
will partition between the water and DCM phases, assuming
no losses of the analyte through chemical transformations,
sorption, or volatilization, according to Equation 1:
E 5 KpV2 /V1(1 2 exp[2V1/KpV2])
(1)
V2 5 volume of DCM,
V1 5 volume of water (i.e., sample volume), and
Kp 5 DCM/water partition coefficient.
During extraction, the solvent volume V2 is kept constant; in
this study V2 was 0.3 L. In situations where dissolved organic
matter (DOM) is expected to have a significant effect on predicted extraction efficiencies, the extraction equations can be
modified to account for interactions between the solutes and
DOM [39].
In contrast, extraction efficiences for solutes using SPE are
much less predictable. Extraction efficiences in SPE are a complex function of sorbant characteristics (resin type and functionality, surface polarity, surface area, pore size, particle size,
and resin preparation procedures), water parameters (pH, ionic
strength, and temperature), and solute properties (size, molar
volume, polarity, polarizability, partition coefficient, and solubility) [18]. While the extraction efficiency for a single compound in isolation can be determined using frontal chromatography, it is difficult for mixtures. The extraction of a given
analyte can be strongly affected by specific and nonspecific
competetive adsorption by other solutes.
The design of the GLSE is flexible enough to allow a wide
range of sampling flow rates, from 35 ml/min to over 1 L/min.
Using high flow rates, a 50-L volume of water can be collected
in under 1 h, which allows short-term changes in contaminant
composition to be monitored [31]. Low flow rates can be used
to produce time- and volume-integrated samples over an extended time. Solid-phase extraction methods are usually limited to lower flow rates seldom exceeding a few hundred milliliters per minute.
Extraction of acidic compounds in natural waters
It is important in large-volume extraction methods that the
measured concentration of contaminants in water be independent of the sampled volume so that the detection limit will
decrease in inverse proportion to the sampled volume. Both
GLSE and SPE methods can suffer from decreases in apparent
concentration of solutes with increasing sample volume. In the
GLSE this is due to emulsion formation, the presence of high
levels of DOM, suspended solids and colloids, and unfavorable
partition coefficients [31]. The decrease in concentration can
be countered by using lower flow rates, using a larger solvent/
water ratio, and prefiltering the sample. In SPE this effect can
be attributed to lack of absorption capacity, competitive nonspecific adsorption by DOM and other matrix components, and
clogging of pores by humic acids and suspended material.
When the capacity of the SPE resin is exceeded and breakthrough occurs, the resulting extracts can be biased toward the
hydrophobic compounds in the water sample [18].
In spite of these advantages, there is legitimate concern
whether the use of the GLSE for major sampling and surveillance programs which need to include polar acidic compounds is appropriate. For the more water-soluble polar acidic
compounds with values of Kp , 1,000, one would predict low
extraction efficiencies. There is a lack of performance data for
these compounds. Only one other study has investigated the
recovery of acidic pesticides from water [36]. Recoveries of
2,3,6-tribromobenzoic acid and Picloram from acidified
groundwater were below 5%. Since batch DCM/water solvent
extraction tests of these compounds predicted higher extraction
efficiencies, the authors of the study speculated that the low
results might be due to analyte decomposition, inadequate solvent extraction conditions, or incorrect preparation of the standards.
Therefore, as part a collaborative study to define the baseline
levels of organic contaminants in northern rivers and to develop tools for BSA, this study was done to determine whether
the use of the GLSE could be extended to include ultratrace
levels of acidic organic contaminants in natural waters and, if
so, to select suitable field and laboratory surrogates and establish performance criteria using operational conditions similar to current practice in the field for water surveys. This
report presents the results of performance tests using surrogates for resin acids, fatty acids, herbicide acids, and chlorophenols and recommendations for performance criteria.
METHODS
Apparatus
The GLSE-95 was manufactured by Lasalle Scientific,
Guelph, ON, Canada (Fig. 1). Detailed descriptions of the
apparatus and procedures for operation and optimization for
hydrophobic compounds with Kow values $10,000 can be
found in the literature [29,32].
Stainless-steel pressure containers of 20-L capacity used to
collect and store samples were purchased from Spartanburg
Steel Products, Spartanburg Challanger, VA, USA. Containers
were equipped with stainless-steel quick-disconnect hose connections. Corrugated Teflon flexible hose (Penntube CT Flex
#400) for transfer of water and extract was purchased from
Dixon Industries.
A Hewlett-Packard (HP) Model 5892a gas chromatograph
was equipped with an HP Model 7673 injector and an HP
Model 5970 mass selective detector (MSD). The gas chromatograph was fitted with a 30-m 3 0.25-mm inner diameter
Environ. Toxicol. Chem. 15, 1996
1939
Fig. 1. Schematic of Goulden Large-Sample Extractor apparatus.
DB-5.625 (0.25-mm film thickness) fused silica capillary column (J & W Scientific).
Reagents and materials
Several polar acidic target compounds were selected based
on ready availability in the laboratory and historical occurrence
in natural waters impacted by pulp and paper mills and agricultural runoff water. The selection of surrogates was based
on commercial availability and similarity to the target compounds of interest. The surrogate and target compounds are
listed in Table 1.
Pesticide-grade DCM, isooctane, and methanol were used
without further cleanup. Concentrated sulfuric acid was preextracted with DCM before use. Anhydrous sodium sulfate was
heated at 4008C for 4 h, then allowed to cool in a desiccator
before use.
Standards and solutions
Primary stock solutions of each target and surrogate compound (2.5 g/L) were prepared by accurately weighing about
25 mg of substance into a 10-ml volumetric flask and diluting
to volume with methanol.
A composite solution of target compounds (50 mg/L) was
prepared by accurately transferring 0.50 ml of each primary
stock solution to a 25-ml volumetric flask and diluting to volume with methanol. This solution was also used as a highlevel field spike solution. A low-level field spike solution (0.5
mg/L) was prepared by accurately transferring 250 ml of composite solution to a 25-ml volumetric flask and diluting to
volume with methanol. A 1.00-ml volume of one of the two
field spike solutions was added to a 20-L sample of water (2.5
or 0.025 mg/L final concentration) for field spike recovery
studies.
Composite surrogate solutions (100 mg/L) were prepared
by accurately transferring 1.00 ml each of the appropriate primary stock solutions to a 25-ml volumetric flask and diluting
to volume with methanol. The surrogate spiking solution was
prepared by accurately transferring 100 ml of the composite
surrogate solution to a 100-ml volumetric flask and diluting
to volume with methanol.
A primary stock solution of the anthracene-d10 internal standard (2 g/L) was prepared by accurately weighing about 20
mg of substance into a 10-ml volumetric flask and diluting to
volume with methanol. A working solution (200 mg/L) was
prepared by accurately transferring 2.50 ml of primary stock
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Environ. Toxicol. Chem. 15, 1996
J.V. Headley et al.
Table 1. Surrogate and target compounds used in this study
Class
Surrogate compounds
Resin acids
O-methylpodocarpic acid
Fatty acids
Heptadecanoic acid
Herbicide acids
Dichlorophenylacetic acid
Chlorophenols
4-Bromophenol
2,4,6-Tribromophenol
solution to a 25-ml volumetric flask and diluting to volume
with isooctane.
Sampling and storage
Water samples were collected from potable and natural waters along the Athabasca River, surface water from the Bow
River in Calgary, and surface waters from upstream and downstream of Whitehorse. Precleaned 20-L stainless-steel cans
with noncontaminating fittings were filled with grab samples
of water taken using a pail. In some cases, the water in the
can was spiked with one of two matrix field spike solutions.
Samples were then transported to the laboratory without preservation and stored at 48C. The samples were acidified with
sulfuric acid to pH 2 in the laboratory prior to extraction.
Extraction procedure
Prior to use, the extractor was washed with soap and water,
followed by three rinses with deionized water. A blank extraction of 20 L of deionized water was run before using the
extractor and after each batch of three samples. The extractor
was initially charged with 300 ml DCM. The sample was
pumped from the stainless-steel can by a positive displacement
pump at 250 ml/min and warmed to room temperature in the
heating chamber. After about 300 ml of sample had been
pumped, the stirrer was started. The surrogate spiking solution
was continuously mixed into the sample using a metering
pump. According to conventional field use, DCM lost to the
system by dissolution (1.6% by volume) was replenished from
a fresh supply using a positive displacement pump at 4 ml/min.
Solvent was not recovered from the effluent water. All liquids
were allowed to contact only glass, Teflon, stainless steel, or
ceramic surfaces. Each pump was calibrated before use, and
volume deliveries were determined from the time of operation.
The DCM extracts were dried using anhydrous sodium sulfate and were reduced in volume to 10 ml by rotary evaporation
under reduced pressure. Isooctane (10 ml) was added to the
extracts to function as a keeper, and this combined extract was
reduced to 10 ml. The extract was treated with diazomethane
in ether to derivatize the acids and phenols. After standing for
0.5 h, the derivatized extracts were further concentrated to 1
ml under a gentle stream of nitrogen. A 125-ml aliquot of the
internal standard working solution was added to the extract
just prior to chromatographic analysis. Samples of 1 ml were
injected into the GC–MSD using an autosampler.
Target compounds
Sandaracopimaric acid
Dehydroabietic acid
12,14-Dichlorodehydroabietic acid
Hexadecanoic acid
Octadecanoic acid
Oleic acid
9,10-Dichlorostearic acid
2,4-Dichlorophenoxyacetic acid
Diclofop-methyl
2,4-Dichlorophenol
2,4,6-Trichlorophenol
2,3,4,6-Tetrachloropheol
Pentachlorophenol
Chromatographic analysis
The GC operating conditions were splitless injector 2508C;
septum purge flow, 3 ml/min; inlet purge flow, 50 ml/min;
injector purge time, 0.5 min; helium carrier gas flow, 25 cm/s;
column temperature program: initial temperature 758C (hold
3 min), ramp at 108C/min to 2008C, then ramp at 208C/min to
2708C (hold 11 min); and transfer line, 2708C. The MSD operating conditions were ion source temperature, 2508C and
electron energy, 70 eV, with mass calibration, peak widths
(typically 0.5 mass units), and electron multiplier voltage (typically 1,400 to 1,600 V) set during the AUTOTUNE automatic
calibration procedure using pentafluorotributylamine. Selected
ion monitoring (SIM) data were acquired from the MSD by
an HP Unix A.01.03 data system using an HP Series 300
computer and Target 1.12 software. Retention times and quantification ion masses were determined by full-scan analysis of
a solution containing target, surrogate, and internal standard
compounds. Quantification parameters are given in Table 2.
Calibration
Quantification was accomplished using internal standard calibration on selected ions. A series of six calibration solutions
was prepared by combining the appropriate volumes of composite target solution, composite surrogate solutions, and internal standard solution to 25-ml volumetric flasks. Each combined solution in the flasks was treated with diazomethane in
ether to derivatize the acids and phenols. After standing for
0.5 h the ether was evaporated, and the solutions were diluted
to 25 ml with isooctane. Final concentrations ranged from
0.025 to 1.00 mg/L for target compounds, 4.00 to 9.00 mg/L
for surrogate compounds, and 1.00 mg/L for the internal standard.
Calibration curves were constructed for each target and surrogate compound by injecting 1 ml of each calibration solution
into the GC–MSD.
Batch determination of DCM/water (pH 2) partition
coefficients
Partition coefficients were determined for heptadecanoic
acid, O-methylpodocarpic acid, 4-bromophenol, 2,4-dichlorophenylacetic acid, and 2,4,6-tribromophenol. A stock solution containing the five surrogate standards at a nominal concentration of 1 g/L was prepared in 10 ml DCM. A 0.01 N
sulfuric acid solution (pH 2) was prepared using Milli-Qt
water in a 50-ml volumetric flask. A series of five calibration
Environ. Toxicol. Chem. 15, 1996
Extraction of acidic compounds in natural waters
1941
Table 2. Quantification parameters
Method
detection
Retention Massb
level
time
(dal- Response
(ng/L)
(min)
tons)
factorc
No.
Compounda
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
4-Bromomethoxybenzene (S)
2,4-Dichloromethoxybenzene
2,4,6-Trichloromethoxybenzene
Dichlorophenylacetic acid methyl ester (S)
1,2,3,4-Tetrachloromethoxybenzene
2,4,6-Tribromomethoxybenzene (S)
2,4-Dichloropohenoxyacetic acid methyl ester
Pentachloromethoxybenzene
Anthracene-d10 (IS)
Hexadecanoic acid methyl ester
Heptadecanoic acid methyl ester (S)
Oleic acid methyl ester
Octadecanoic acid methyl ester
Sandaracopimaric acid methyl ester
O-methylpodocarpic acid methyl ester (S)
Dehydroabietic acid methyl ester
Diclofop-methyl
9,10-Dichlorostearic acid methyl ester
12,14-Dichlorodehydroabietic acid methyl ester
9.07
10.52
11.18
13.66
13.96
15.23
15.37
16.38
17.25
18.12
18.84
19.35
19.51
20.65
20.97
21.24
21.59
22.55
25.83
186
176
195
159
246
346
199
280
188
74
74
55
74
121
227
239
253
74
307
13.50
3.57
3.59
2.44
4.59
7.15
5.84
7.40
–
2.27
2.15
7.16
2.62
6.02
4.89
5.88
12.28
12.24
15.46
–
1
1.5
–
1
–
1.25
1
–
1
–
1.5
1
1
–
1
2
10
10
S 5 surrogate; IS 5 internal standard.
Mass monitored during selected ion monitoring.
c Relative to anthracene-d
10 internal standard.
a
b
solutions were prepared by serial dilution from the stock solution covering the range of 10 to 0.26 mg/L.
The partition coefficients were determined in quadruplicate
according to the method of Foster and Rogerson [32]. In brief,
1 ml of the DCM stock surrogate solution was shaken with 5
ml of pH 2 water in an 8-ml screw-capped vial for 24 h, then
left to separate overnight. A 4-ml aliquot of the water solution
was extracted 3 3 2 ml with ethyl acetate. The extract was
dried over anhydrous sodium sulfate and concentrated to 2 ml.
A 10-ml aliquot of the DCM solution was diluted to 2 ml with
ethyl acetate. Solutions were treated with diazomethane in
ether, concentrated to less than 1 ml, and exchanged into iso-
Fig. 2. Control chart showing percent recovery of 2,4,6-tribromophenol. UCL, upper control limit (average 13 SD.); UWL, upper
warning limit (average 12 SD); AVG, average recovery; LWL, lower
warning limit (average 22 SD); LCL, lower control limit (average
23 SD). C, quality control samples; m, Yukon River upstream of
Whitehorse; m, Yukon River downstream of Whitehorse; l, Bow
River; ●, Athabaska River, * outlier data point not included in calculation of average and control values.
octane; final volume was 1 ml. Concentrations of the surrogate
compounds were determined by GC as described above. Gas
chromatography–mass spectrometry full-scan analyses of the
10-mg/L standard, a water phase extract, and a DCM phase
were performed to confirm peak assignments and identify potential interferences.
RESULTS AND DISCUSSION
Surrogate recoveries
Control charts showing the recoveries of the candidate surrogates compounds are presented in Figures 2 through 6. The
mean and standard deviation of the recoveries are presented
in Table 3, along with determined Kp values and predicted
extraction efficiencies calculated from the Kp values using
Equation 1. The results are from analyses of field samples
(11), method blanks (4), spiked method blanks (3), and du-
Fig. 3. Control chart showing percent recovery of heptadecanoic acid.
Abbreviations and symbols defined Figure 2 legend.
1942
Environ. Toxicol. Chem. 15, 1996
J.V. Headley et al.
Fig. 4. Control chart showing percent recovery of O-methylpodocarpic acid. Abbreviations and symbols defined in Figure 2 legend.
Fig. 6. Control chart showing percent recovery of 4-bromophenol.
Abbreviations and symbols defined in Figure 2 legend.
plicates (1). The standard deviation of the predicted extraction
efficiencies is based on the standard deviation of the determined Kp values. These results are from experiments in which
the surrogates were added throughout the continuous extraction of the 20-L water samples.
The water quality characteristics of the sampling sites are
given in Table 4. No correlations were observed between recovery values and the water quality characteristics. However,
one sample from the Bow River had anomalously high recoveries for 2,4,6-tribromophenol and heptadecanoic acid. Likewise, a method blank and a spiked blank had high recoveries
of dichorophenylacetic acid and 4-bromophenol.
The candidate surrogate compounds heptadecanoic acid, Omethylpodocarpic acid, and 2,4,6-tribromophenol were extracted from pH 2-adjusted water samples with an average
recovery of 83.6%. The variability ranged from 10 to 36%
relative standard deviation (RSD); the average RSD was
23.1%. These surrogates had Kp values greater than 1,000 and
predicted extraction efficiencies of 96.7 to 99.8%. These values
compare favorably with recoveries of surrogates for neutral
pesticides from surface water. Foster et al. [34] reported mean
percentage recoveries of 72, 54, and 78% for surrogate compounds cynazine, lindane, and methylparathion, respectively.
The variability ranged from 15 to 40% RSD. The average
recovery for the neutral pesticide surrogates was 67.5%, with
an average RSD of 21%.
These surrogate recoveries were lower than the predicted
extraction efficiencies. Since the aim of this study was to establish performance criteria for the use of the GLSE for acidic
compounds using conditions similar to current practice in the
field for water surveys, the operation of the GLSE was not
optimized for recovery of these compounds. To maximize recoveries of acidic compounds, improvements could include
but not be limited to lower water flow rates and recovery of
DCM lost during the extraction procedure.
The other acidic surrogates, dichlorophenylacetic acid and
4-bromophenol, had recoveries less than 50%, much lower
than predicted from the Kp values. The lower-than-expected
extraction efficiency for dichlorophenylacetic acid was attributed to volatility losses during extraction and sample preparation [34].
Additional experiments were also performed in which 4-bromophenol was added to the methylene chloride extract obtained from the extractor to monitor the losses from the solvent
concentration step in the laboratory and illustrate the utility
of laboratory surrogates. No significant difference was observed between the recoveries of 4-bromophenol when added
on-line or to the DCM extract, despite the use of isooctane as
a keeper.
In addition to volatility losses, the low recovery of 4-bromophenol may be due in part to side reactions with diazo-
Table 3. Recoveries and predicted extraction efficiencies of
surrogate compounds
Compound
2,4,6-Tribromophenol
Heptadecanoic acid
O-Methylpodocarpic acid
Dichlorophenylacetic acid
4-Bromophenol
Fig. 5. Control chart showing percent recovery of dichlorophenylacetic acid. Abbreviations and symbols defined in Figure 2 legend.
a
b
% Recovery
(mean 6 SD)
K pa
6
6
6
6
6
1,260
16,700
3,160
125
275
89.5
82.8
78.4
41.9
22.1
24.0
21.7
14.8
8.5
8.1
Kp 5 CDCM/CWater(pH 2).
Calculated from Kp using Equation 1.
Predicted
extraction
efficiencyb
(mean 6 SD)
96.7
99.8
98.9
75.4
88.7
6
6
6
6
6
2.02
0.02
0.21
7.52
1.01
Environ. Toxicol. Chem. 15, 1996
Extraction of acidic compounds in natural waters
Table 4. Water quality characteristics of sampled natural waters
River
pH
Yukon
Bow
Athabaska
7.7
8.2
8.2
Nonfilterable
Alkalinity Hardness residue
(mg/L) (mg/L)
(mg/L)
42
135
139
44
170
231
,10
,1
4
Total
organic
carbon
(mg/L)
,0.5
3
4.5
methane. A GC–MS full-scan analysis of a methylated standard mixture of surrogates used in the partitioning study
showed that 4-bromoethoxybenzene and unreacted 4-bromophenol were also present along with the expected 4-bromomethoxybenzene. The peak height of the methoxy compound
was about 56% of the sum of the peak heights of the methoxy,
ethoxy, and phenol compounds, accounting for part of the low
recovery of 4-bromophenol. As a result, 4-bromophenol is not
recommended as a surrogate.
Field spikes of water in the reservoir
Extractions were performed in a controlled laboratory environment by an analyst after a familiarization period. Extreme
care was required to minimize carryover from field spikes
made directly into the 20-L stainless-steel reservoir. Incidences
of carryover were observed even after extensive solvent rinsing of the stainless-steel reservoir after field spikes. This may
preclude this method of spiking for target analytes directly to
the stainless-steel reservoir for field spikes or field surrogates
for polar acidic compounds.
Impurities in the surrogate standards
A potential problem observed with the candidate surrogates
for fatty acids is the compromise of the method detection limit
for fatty acids present as impurities in the surrogate standards.
The heptadecanoic acid surrogate contained hexadecanoic
acid, octadecanoic acid, and oleic acid impurities which resulted in background levels in the method blanks (20 L pure
water plus surrogate compounds) of 282 to 1,260 ng/L, 167
to 1,150 ng/L, and 153 to 922 ng/L, respectively. As a result,
the detection limits listed in Table 2 for these compounds were
compromised by a factor of 150 to 1,200.
Criteria for valid field extractions
For the purpose of providing some guidelines for the surrogate recoveries in this work, a recovery within the upper
and lower warning limits of 62 SDs was adopted for the
criteria to validate field extractions for acidic polar compounds.
CONCLUSIONS
Contrary to concerns of inadequate extraction efficiencies,
the GLSE gave acceptable recoveries of acidic polar contaminants with Kp values greater than 1,000 for pH 2-adjusted
20-L water samples. Recoveries of acidic surrogate compounds
compared favorably with reported recoveries of surrogates for
neutral pesticides from surface water. Low recoveries of the
4-bromophenol surrogate may be due in part to side reactions
with diazomethane reagent. As a result, 4-bromophenol is not
recommended as a surrogate.
Acknowledgement—This work was partially funded by Indian and
Northern Affairs Canada under the Arctic Environmental Strategy.
1943
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