Anal. Chem. 1994,66, 4483-4489
Centrifugal Partition Chromatographic Extraction of Phenols and Organochlorine Pesticides from Water Samples Yan Liu, Viorica Lopez=Avila,*and Marcela Alcaras
Midwest Research Institute, California Operations, 625-8Clyde Avenue, Mountain View, California 94043 Tammy L. Jones
U.S. Environmental Protection Agency, Environmental Monitoring System Laboratory, 944 East Harmon Avenue, Las Vegas, Nevada 891 19
As part of an ongoing evaluation of new sample prepara-
Centrifugal partition chromatography (CPC) is one form of countercurrent chromatography. In CPC, the liquid stationary phase is retained in discrete and interconnected partition channels of a series of disks by the action of a centrifugal force. The mobile phase is pumped continuously through the liquid stationary phase in the form of microdroplets. The sample components are partitioned between the mobile and the stationary liquid phases, and are separated from each other on the basis of dserences in their partition coefficients. After a known volume of sample has passed through the CPC column, the flow direction is reversed, and fresh extraction solvent is pumped in to displace the liquid stationary phase containing the components of interest. CPC has been used to fractionate and purify a broad range of natural and synthetic chemical compounds such as alkaloids, htty acids, proteins, polyphenols, antibiotics, et^.^ CPC seems to be a straightforward technique for extracting organic compounds from a relatively large volume of aqueous sample. Its full potential, however, has not yet been established for extracting environmentally significant organic compounds from aqueous mattices. When CPC is used in the extraction mode, the aqueous sample is carried into the CPC column by reagent water saturated with the extraction solvent, and after a known volume has passed through the CPC column, the flow direction is reversed, and fresh organic solvent saturated with reagent water is pumped in to displace the “contaminated” solvent containing the analytes of interest. Recently, Menges and co-workers reported the use of CPC in the extraction mode to extract nonylphenol ethoxylate (NPEO), a nonionic surfactant, from simulated wastewater^;^ they found that more than 86% of the NPEO was recovered when 20 L of a simulated wastewater sample (concentration 16.5 mg/L) was Countercurrent chromatography is a liquid-liquid partition extracted with 30 mL of ethyl acetate at a flow rate of 5 mL/min. chromatographic technique in which a centrifugal or gravitational As part of an ongoing evaluation of new sample preparation force is used to retain the liquid stationary phase in devices such methods conducted by the US. Environmental Protection Agency as a coil or a train of partition chambers. This technique has been (EPA) through the Environmental Monitoring Systems investigated extensively since it was first introduced by Ito and Laboratory-Las Vegas (EMSLLV),especially those methods that co-workers in 1966.’ The apparatus, theory, and applications of minimize waste solvent generation, we investigated the feasibility countercurrent chromatography have been reviewed e l ~ e w h e r e . ~ - ~ of using CPC to extract parts-per-billion levels of phenols and organochlorine pesticides from aqueous samples. In this paper, (1) Ito, Y.; Weinstein, M. A; Aoki, I.; Harada, R; Kimura, E.; Nunogaki, K. we report on the optimization of a CPC extraction technique for
tion methods conducted by the U.S. Environmental Protection Agency through the Environmental Monitoring Systems Iaboratory-Ias Vegas, especiallythose meethods that minimize waste solvent generation, we investigated the feasibility of using centrifugal partition chromatography (CPC) to extractparts-per-billionlevels of phenols and organochlorine pesticides (OCPs) from aqueous samples. In this paper, we report on the optimization of a CPC extraction technique, discuss the effects of five variables (Le,, extraction solvent, sample loading flow rate, volume of displaced extraction solvent, ionic strength, and presence of humic materials in the aqueous sample) on the extraction of 13 phenols and 20 OCPs, and present recovery data for these analytes from spiked reagent water and spiked wastewater samples. Our results indicate that methylene chloride is more effective than hexane in extracting phenols but only slightly better than hexane in extracting OCPs. CPC appears to perform much better than conventionalliquid-liquid extractionfor phenols but not for OCPs, and our results also show that the target compounds are extracted into a very small volume of solvent, which means that the CPC technique can be used to concentrate such compounds from a relatively large volume of aqueous matrix (e.g., 100 mL) into a small volume of solvent (e.g., 2 mL). Therefore, the CPC technique reduces extraction solvent consumption and eliminates additional sample workup.
Nature 1966,212, 985-987. (2) Mandava, N. B.; Ito, Y., Eds. Countercurrent Chromatography: Theory and Practice; Dekker: New York, NY, 1988. ( 3 ) Conway, W. D. Countercurrent Chromatography, Apparatus, Theory & Practice; VCH Publishers: New York, NY, 1990. 0003-2700/94/0366-4483$04.50/0 0 1994 American Chemical Society
(4) Foucault, A P. Countercurrent Chromatography, Anal. Chem. 1991,63,
569A-579A (5) Menges, R A.; Menges, T. S.; Bertrand, G. L.; Armstrong, D. W.; Spino, L. AJ. Liq. Chromatogr. 1992,15, 2909-2925.
Analytical Chemistty, Vol. 66,No. 24, December 15, 1994 4403
Table 1. Phenols and Organochlorine Pestlcldes Investigated In This Study.
compd name
no.
4 5 6 7 8 9 10 11 12 13
14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
e
28 500 93 OOO 2 100
.g p (aaturatrd with reagent water)
NA 800
5 600 16 000 183 128 14 0.2-0.7 0.2-0.7 8.6-31 5.7-12 0.056-0.18 0.017-0.18 0.35 0.056-1.85 0.15-0.6 0.006-0.009 0.14-0.20 0.001-0.12 0.23 0.07-0.28 0.02-0.09 NA
0.12-0.22 0.001-0.004 NA
0.1-0.25
(I
these compounds, discuss the effects of five variables (i.e., extraction solvent, sample loading flow rate, volume of displaced extraction solvent collected, ionic strength, and presence of humic materials in the aqueous sample) on the extraction of 13 phenols and 20 organochlorine pesticides (OCPs), and present recovery data for these analytes from spiked reagent water and spiked wastewater samples. EXPERIMENTAL SECTION Reagents and Materials. Analytical reference standards of the 13 phenols (compounds 1-13) and 20 OCPs (compounds 14-33,Table 1) were purchased as two separate composite solutions (concentration 2 mg/mL per compound) from Supelco, Inc. (Bellefonte, PA). Hexane and methylene chloride used in the CPC extraction were distilled-in-glasspesticide grade and were obtained from Baxter Scientifc (McGaw Park, IL). All other reagents and solvents used in this study were of analytical grade. The spiking solution and the working calibration standards were prepared by serial dilution of one of the two composite stock solutions containing either the phenols or the OCPs. Wastewater samples were collected from an industrial wastewater discharge well in Mountain View, CA Analytical Chemistry, Vol. 66, No. 24, December 75, 7994
Sample coilectlon vial Waate
'fa
Sample loop
BP
-r
NAc
4 500 3 990
=p Switchlng valve
'
CAS registry no.
The compounds included in this table are listed in the order of elution from the gas chromatographic column. The water solubility data for phenols and OCPs are adopted from refs 7 and 8, respectively. The water solubility data were determined at 20-25 "C. NA, information not available.
4484
CPC operation ~
Phenolic Compounds 9557-8 108952 88755 2,4dimethylphenol 10567-9 2,ddichlorophenol 120-852 2,6dichlorophenol 87-650 khloro-5methylphenol 59-50-7 2,4,6trichlorophenol 88062 2,4dinitrophenol 51-285 4-nitrophenol 100-01-7 2,3,4,6tetrachlorophenol 5890-2 4,&dinitrc-2-methylphenol 534-52-1 pentachlorophenol 87-865 Organochloride Pesticides a-BHC 319-857 /3-BHC 319-857 6-BHC 319-868 Y-BHC 5889-9 heptachlor 76-448 aldrin 309-00-2 heptachlor epoxide 102457-3 ychlordane 5103-742 endosulfan4 959-988 achlordane 5103-71-9 dieldrin 60-52-1 4,4'-DDE 72-559 endrin 72-20-8 endosulfan-I1 72-20-8 4,4'-DDD 33213-659 endrin aldehyde 7421-363 endosulfan sulfate 1031-07-8 4,4DDT 50-29-3 endrin ketone 53494-70-5 methoxychlor 72-43-5
1 Bchlorophenol 2 phenol 3 2-nitrophenol
Sample
descending mode
Figure 1. Block diagrams of the CPC system in the descending mode. Table 2. CPC Operatlng Conditions
parameter
value
CPC system
Sanki Series lo00 high-performancecentrifugal partition chromatographs (250-mLinner volume) equipped with an Isco Model 2350 pump CPC rotational 700 rpm speed CPC flow rate 1-7.5 mL/min (typically 5 mL/min) stationary hexane or methylene chloride (saturated with the aqueous carrier solution) phase mobile phase aqueous d e r solution (saturated with hexane or methylene chloride) sample volume 25 or 100 mL extract volume varied (collected in 2-or 5mL fractions)
CPC Jktradion System. A block diagram of the CPC system assembled in this study is shown in Figure 1 (only the descending mode is shown). The CPC system consisted of an Upchurch Model V-250 six-way stream selection valve (Upchurch Scientifc, Oak Harbor, WA), an Isco Model 2350 HPLC pump (Isco, Inc., Lincoln, NE), two Rheodyne Model 9010 six-port valves (Rheodyne, Inc., Cotati, CA), and a Sanki Series 1000 CPC column module (Sanki Laboratories, Inc., Nagaokakyo, Kyoto, Japan). The Sanki CPC column module consisted of two partition disk packs, each containing six partition disks connected in series. Each partition disk had 178 interconnected channels (approximately 20 mL of total internal volume per disk); the CPC column had a total of 2136 partition channels and an internal volume of approximately 250 mL. The typical operating conditions for the CPC system used in this study are summarized in Table 2. We used a rotor speed of 700 rpm, which resulted in a CPC column pressure drop of 700 psi for hexane and 610 psi for methylene chloride at a mobile phase flow rate of 5.0 mL/min. There are no special safety precautions to be taken when using the CPC equipment other than monitoring of rotational speeds and flow rates to avoid pressure buildup in the system; follow the manufacturer's instructions when setting up the system. CPC Extraction Procedure. The aqueous carrier solution (reagent water) of the desired ionic strength and pH together with the extraction solvent (either hexane or methylene chloride) were first mutually saturated by shaking them vigorously for 20 min. The extraction solvent (saturated with the aqueous carrier solution) was then pumped into the CPC column, with the CPC centrifuge rotor turned off. After the CPC column was filled with the extraction solvent, the centrifuge rotor was turned on, and the aqueous carrier solution (saturated with the extraction solvent) was pumped into the CPC column to equilibrate the system. When using hexane, the aqueous carrier solution was pumped into the CPC column in the descending mode (Le., the direction
100.0
i
Q)
60.0 --
0
d
s
40.0
--
20.0 --
0.0
I 0
__c___/
1
2
3
4
5
6
7
8
Sample loading flow rate, mLlmin Figure 2. Effect of sample loading flow rate on the CPC recoveries of a- (m), p- (U),y- (0),and 6-BHC (+) and dieldrin (A).The sample was 25 mL of reagent water containing 0.14 g of NaCl and spiked with OCPs at 20 ,ug/L; hexane was used as the extraction solvent.
of flow was from the top of the CPC column to the bottom of the column, as shown in Figure 1). When methylerk chloride was used, the aqueous carrier solution was pumped into the CPC column in the ascending mode (i.e., the direction of flow was from the bottom of the CPC column to the top of the column). At equilibrium, the volume of extraction solvent in the CPC column was 220 mL for hexane and 190 mL for methylene chloride; the remaining volume was aqueous. At this point, a known volume (25-100 mL) of the aqueous sample to be extracted was pumped directly into the column or was loaded into the column through a sample injection loop. After all of the aqueous sample had passed through the CPC column, the flow direction was reversed, and fresh extraction solvent (saturated with the aqueous carrier solution) was introduced into the CPC column to displace the "contaminated" extraction solvent, which contained the analytes of interest. The displaced solvent was collected in 2- or 5mL fractions; the various fractions were dried with anhydrous magnesium sulfate and then analyzed. Conventional Liquid-Liquid EMraction Procedures. Conventional liquid-liquid extraction of phenols was performed as follows. Reagent water (100 mL), spiked with phenolic compounds listed in Table 1 at 2.5 mg/L, was adjusted to pH > 11 with 0.5 N NaOH and then extracted with methylene chloride (10 mL) using magnetic stirring for 3 min. This was repeated once with another portion of fresh methylene chloride (10 mL). The organic layers from both extractions were discarded. The pH of the aqueous layer was adjusted to 2 with 0.5 N HCl, NaCl was added to the acidified sample, and the sample was extracted twice with fresh methylene chloride (10 mL each) using magnetic stirring. The extracts were combined and filtered through a column of anhydrous sodium sulfate, and the solvent was exchanged to hexane prior to GC/MS analysis.6 The liquid-liquid extraction of OCPs from reagent water spiked with OCPs at 2.0 pg/L was performed with hexane (10 (6) Young, R; Lopez-Ada, V. Evaluation and Improvement of Quick-Turnaround
mL) using magnetic stirring and was repeated once with fresh hexane (10 mL). The hexane extracts were combined, filtered through a column of anhydrous sodium sulfate, and concentrated to 1.0 mL prior to GC/ECD analysis. Analysis of CPC-Generated Extracts. The analyses of the extracts containing the 13 phenols or the 20 OCPs were performed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/electron capture detection (GC/ECD) , respectively. For phenols, we used an HP 5890 Series I1 gas chromatograph (Hewlett Packard, Wilmington, DE) interfaced to an HP Model 597lA mass spectrometer MSD/DOS Chemstation and equipped with an HP Model 7673A automatic sample injector and a split/splitless injection inlet. Samples were introduced via a 30m-length x 0.25"-i.d. x 0.25pm-film thickness DB-5 fused-silica open-tubular column U&W Scientiiic, Folsom, CA) with helium carrier gas at a flow rate of 1.0 mL/min. The column temperature was held at 40 "C for 4 min and then programmed at 8 "C/min to a final temperature of 300 "C, where it was held for 10 min. The injection volume was 1pL, and the injector temperature was 250 "C. The injector was set in the splitless mode for 1min after the injection. The electron energy was set at 70 eV, and the electron multiplier voltage was set at 2270 V. Spectral data were acquired at a rate of 1.25 s/scan (scanning range was 40-500 amu). For OCPs, we used an HP 5890 Series I1 gas chromatograph equipped with an HP Model 7673A automatic sample injector, an electronic pressure control, a split/splitless injection inlet, and an ECD. Samples were introduced via a 30-m-length x 0.32-mm4.d. x 0.25pm-film thickness DB-5 fused-silica open-tubular column a&W Scient&) with helium carrier gas at a flow rate of 3.7 mL/ min. The injection volume was 1pL, and the injector temperature was 250 "C. The column temperature was programmed from 140 to 190 "C (2-min hold) at 12 "C/min and then to 275 "C at 4 "C/ min. The detector temperature was 320 "C.
Methods; EPA 540/X-94/501; 1994. (7) Water Related Environmental Fate of 129 Priority Pollutants, Vols. I and II; EPA 440/7-790296; US. Government Printing Office: Washington, DC,
1979.
(8) Chau, A S. Y.; Afghan, B. IC Analysis of Pesticides in Water, Vol. II; CRC Press Inc.: Boca Raton, FL, 1982.
Analytical Chemistry, Vol. 66, No. 24, December 15, 1994
4485
a Methylene chloride
100.0
80.0
Hexane
'
.
f a >
60.0
0 0
a
cc
40.0 .
8
2 Chlorophenol
Phenol
2-N~trophenol
2.4. Dimethylphenol
2.4. Dichlorophenol
2.6. Dichlorophenol
4.Chloro-3. methylphenol
2.4.62.3.4.6Trlchlorophenol Tetrachlorophenol
Compound 100.0
80.0
R
8
40.0
1 n enc
0
BHC
I
6 . BHC
I. BHC
Haplachlor
Aldrln
Heptachlor epoxlde
.
y Endosulfan4 Chlordana
a.Chlordane Dteldrtn
Endrm
Endo.
sulfan.ll
4.4'.DDD
Endrln aldehyde
Endosullen sullale
Endrvn ketone
Compound Figure 3. Effect of extraction solvent on the CPC recoveries of (a, top) phenolic compounds and (b, bottom) OCPs. The samples were either 50 mL of reagent water containing 0.29 g of NaCl and spiked with OCPs at 2.0 pg/L or 50 mL of reagent water (pH 2) containing 0.29 g of NaCl and spiked with phenols at 4.0 mg/L.
RESULTS AND DISCUSSION We investigated the effect of sample loading flow rate (i.e.,
the mobile phase flow rate) on the CPC extraction using five OCPs as the test analytes and hexane as the extraction solvent. The results (Figure 2) show that recoveries of these five OCPs remained essentially the same when the sample loading flow rate was varied from 1.0 to 7.5 mWmin. High mobile phase flow rates are desirable to gain high extraction efficiencies and to reduce the extraction time. High flows, however, result in increased column pressure drop (the operating pressure limit of the Sanki CPC column is 870 psi). Therefore, in most experiments, we used a mobile phase flow rate of 5 mL/min. Two extraction solvents (hexane and methylene chloride) were investigated by extracting nine phenols and 17 OCPs from aqueous samples. The recovery data for the nine phenols from spiked reagent water samples (Figure 3a) indicate that methylene chloride is a much more effective solvent than hexane (except 4486 Analytical Chemistry, Vol. 66, No. 24, December 15, 7994
for 2,4,&trichlorophenol, where recoveries were identical for the two solvents); Z-chlorophenol, phenol, 2,4dimethylphenol, and khloro-3-methylphenol were quantitatively extracted (recovery > 95%) with methylene chloride, but not recovered or barely recovered with hexane; recoveries of 2-nitrophenol, 2,4dichlorophenol, 2,6dichlorophenol, and 2,3,4,&tetrachlorophenol were 23-43% higher with methylene chloride than with hexane. The recovery data for the 17 OCPs from spiked reagent water samples (Figure 3b) indicate that, with three exceptions, methylene chloride is a better extraction solvent than hexane; for aldrin and y- and a-chlordane, recoveries were slightly higher when hexane was used. Therefore, methylene chloride was used as the extraction solvent in subsequent experiments. To establish the volume of fresh solvent needed to displace the "contaminated" solvent from the CPC column, we determined the concentration profiles of the analytes of interest by collecting
100.0 I
80.0 1
Q)
I
40.0
I
.j
20.0
I
~
a - BHC
- BHC
6 - BHC
y - BHC
Dieldrin
I
Heptachlor Endosulfan-I epoxide
Endrin
Endosulfan4
Endrin aldehyde
-4L
Endosulfan sulfate
-
1
Endrin ketone
Compound mFrtlCtjon1 =Fraction2
mFmction3 =Fraction4
flFraction5
I
‘tl 1:
0 .! -
d2.4-
2.4-
2.6methylphenol
-. .
Tlicbloropbcrd
Compound Figure 4. Concentration profiles of (a, top) OCPs and (b, bottom) phenolic compounds in the displaced CPC extraction solvent. The samples were either 50 mL of reagent water containing 0.29 g of NaCl and spiked with OCPs at 2.0 pg/L or 50 mL of reagent water (pH 2) spiked with phenols at 4.0 mgL; methylene chloride was used as the extraction solvent.
2- or 5mL fractions of the displaced solvent. Figures 4a and 4b show the concentration profiles for 11 phenols and 12 OCPs, respectively. The results (Figure 4a) indicate that the first 2-mL fraction contained the full amount of each phenolic compound [except for phenol and 4-nitrophenol, which were recovered in subsequent fractions (see Figure 5), and except for small amounts of 2chloropheno1,2,4dimethylphenol,and khloro-3-methylphe nol, which were found in fraction 21. Of the extractable amounts of the OCPs, nearly all appeared in the first fraction (Figure 4b). Figure 5 shows the recovery data for phenol and 4nitrophenol in nine 2-mL fractions; phenol was found in fractions 4-9, and
4nitrophenol was found in fractions 4-6. The broad concentration profiles of phenol and 4-nitrophenol are likely due to their higher solubilities in water (the solubilities of phenol and 4-nitrophenol in water are 93 OOO and 16 OOO mg/L, respectively). Table 3 summarizes the CPC recoveries of 13 phenols (compounds 1-13) from reagent water (with and without NaCI) and from an industrial wastewater; the recoveries are compared with those obtained by conventional liquid-liquid extraction with methylene chloride. Using CPC with methylene chloride as the stationary phase, we obtained quantitative recoveries (>80%) for almost all of the phenolic compounds, regardless of the matrix. Analytical Chemistry, Vol. 66, No. 24, December 15, 1994
4487
40 Fraction 1
35
Fraction 2
'
I
30
6>
25
0
20
0
a
I
I
Fraction 4
I
Fraction 5
I
I
' Fraction 6
1
'
Fraction 7
i I
K
8
._ Fraction 3
Fraction 8
II
15
10
'
5
.
i
Fraction 9
I mend
4-Nitrophenol
Compound Figure 5. Concentration profiles of phenol and 4-nitrophenol in the displaced CPC extraction solvent. The sample was 50 mL of reagent water (pH 2) spiked with phenols at 4.0 mg/L; methylene chloride was used as the extraction solvent. Table 3. Average Recoveries (YO)of Phenols from Spiked Aqueous Samples.
compound
no. 1 2 3 4 5 6
7 8 9 10 11 12 13
name 2chlorophenol phenol 2-nitrophenol 2.4dimethylphenol 2.4dichlorophenol 2,6dichlorophenol khloro-3-methylphenol 2,4.~trichlorophenol 2.4dinitrophenol 4nitrophenol 2,3.4,6-tetrachlorophenol 4.6-dinib-o-2-methylphenol pentachlorophenol
reagent wate$ average RSD recovery (%)
102 91 97 105 104 103 104
96 83 67 91 96 78
9 7 10 9 12 9 10 6 27 10 10 15 13
CPC extraction reagent water containing NaCIc average RSD recovery (%)
89 99 95 96 90 87 94 99 74 86 96 71 59
8 9 3 5 3 24 2 2 10 11 10 1 5
industrial wastewate+ average RSD recovery (%)
88 95 94 95 95 86 105 97 89 95 91 105 80
5 14 4 2 9 9 9 8 17 21 20 34 26
liquid-liquid extraction reagent watef average RSD recovery (W
69 54 58 70 82 NAf 91 86 91 40 83 92 94
20 24 7 2 4 NA 2 2 5 33 2 1
2
a All samples were adjusted to pH 2 with 6 M HCI prior to the extraction; methylene chloride was used as the extraction solvent. The number of determinations was three. The sample was 50 mL of reagent water spiked with phenols at 2.0 mg/L. The sample was 50 mL of reagent water containing 0.29g of NaCl and spiked with phenols at 4.0 mg/L The sample was 50 mL of industrial wastewater sample containing 0.29 g of NaCl and spiked with phenols at 4.0 mg/L. The sample was 100 mL of reagent spiked with phenols at 2.5 mg/L f NA, not available.
There were a few exceptions, however, including LGnitrophenol (67%recovery) and pentachlorophenol (78%recovery) from spiked reagent water and 2,4dinitrophenoi (74%recovery), 4,6dinitre2methylphenol (71%recovery), and pentachlorophenol (59%recovery) from spiked reagent water containing NaCI. Nonetheless, CPC appears to perform much better than conventional liquidliquid extraction, where only seven of the 12 compounds gave recoveries above 80%,and three compounds exhibited recoveries ranging from 40 to 58%. Table 4 summarizes the CPC recoveries of 20 OCPs (compounds 14-33) from spiked reagent water (with and without NaCI), industrial wastewater, and a humic acid solution (prepared in our laboratory) and recoveries obtained by conventional liquidliquid extraction. When the spiked reagent water was extracted by CPC, six OCPs had recoveries ranging from 60 to 79%, seven OCPs from 30 to 59%, and seven OCPs below 30%. When NaCl was added to the aqueous sample, we noticed a slight improve4488 Analytical Chemistry, Vol. 66, No. 24, December 15, 1994
ment in recoveries (three OCPs had recoveries above 80%, eight OCPs had recoveries ranging from 60 to 79%,four OCPs from 30 to 59%, and five OCPs below 30%). In the case of the spiked industrial wastewater (no OCPs were detected in the unspiked sample), two compounds had recoveries above 80%,six OCPs had recoveries ranging from 60 to 79%,five OCPs from 30 to 59%, and seven OCPs below 30%. Recoveries seem to follow about the same trend for the humic acid solution. When comparing the CPC recoveries to those achieved by conventional liquid-liquid extraction with hexane, we found that CPC recoveries were much lower (see Table 4), especially for compounds with water solubilities in the range of 0.001-0.02 mg/L (e.g., aldrin, achlordane, 4,4'-DDE, and 4,4'-DDT). It is possible that these compounds are not completely dissolved in the reagent water that is loaded to the CPC column and get lost in the injection loop even before reaching the CPC column. The repeatability of the CPC technique (as determined from the percent relative standard deviations in Table
Table 4. Average Recoveries 1%) of Organochlorine Perticides from Spiked Aqueous Sample8
compound no. 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
name
a-BHC
j3-BHC 6-BHC )/-BHC heptachlor aldrin heptachlor epoxide y-chlordane endosulfan-I a-chlordane dieldrin 4,4'-DDE endrin endosulfan-I1 4,4'-DDD endrin aldehyde endosulfan sulfate 4,4'-DDT endrin ketone methoxychlor
reagent water reagent watef with NaC1-Id ~ average FSD average RSD recovery
67 79 76 74 23 9 51 11
46 21 65
(%)
recovery
(%)
7
74 83 81
13
4 7 6 26 40 24 2 22 33 23
