Kansas Water Science Center
 PUBLICATIONSDATA CENTER
WATER DATA & STUDIES
INFORMATION CENTER
ABOUT KANSAS WSCUSGS IN YOUR STATEUSGS Water Science Centers are located in each state. 
|
U.S. Geological Survey
|
| Multiply | By | To obtain |
|---|---|---|
| ounce (oz) | 0.02957 | liter |
| pound (lb) | 453.6 | gram |
| pound per square inch (lb/in²) | 6.895 | kilopascal |
| Miscellaneous Abbreviations | |
|---|---|
| cubic centimeter (cm³) gram (g) mass-to-charge ratio (m/z) meter (m) micrometer (mm) milliabsorbance units (mAU) milligram (mg) millimeter (mm) millimole (mM) millisecond (ms) minute (min) nanogram (ng) nanometer (nm) volt (V) |
|
| Abbreviated Water-Quality Units | |
| liter (L) liter per minute (L/min) microgram per liter (mg/L) microliter (mL) milligram per milliliter (mg/mL) milliliter (mL) milliliter per minute (mL/min) nanogram per microliter (ng/mL) |
Analytical methods using high-performance liquid chromatography-diode array detection (HPLC-DAD) and high-performance liquid chromatography/mass spectrometry (HPLC/MS) were developed for the analysis of the following chloroacetanilide herbicide metabolites in water: acetochlor ethanesulfonic acid (ESA), acetochlor oxanilic acid (OXA), alachlor ESA, alachlor OXA, metolachlor ESA, and metolachlor OXA. Good precision and accuracy were demonstrated for both the HPLC-DAD and HPLC/MS methods in reagent water, surface water, and ground water. The mean HPLC-DAD recoveries of the chloroacetanilide herbicide metabolites from water samples spiked at 0.25, 0.50, and 2.0 mg/L (micrograms per liter) ranged from 84 to 112 percent, with relative standard deviations of 18 percent or less. The mean HPLC/MS recoveries of the metabolites from water samples spiked at 0.05, 0.20, and 2.0 mg/L ranged from 81 to 125 percent, with relative standard deviations of 20 percent or less. The limit of quantitation (LOQ) for all metabolites using the HPLC-DAD method was 0.20 mg/L, whereas the LOQ using the HPLC/MS method was 0.05 mg/L. These metabolite-determination methods are valuable for acquiring information about water quality and the fate and transport of the parent chloroacetanilide herbicides in water.
The chloroacetanilide herbicides-acetochlor, alachlor, and metolachlor-are an important class of herbicides in the United States. Together with the triazine compounds, chloroacetanilide herbicides compose the majority of pesticides applied in the Midwestern United States for control of weeds in corn, soybeans, and other row crops (Gianessi and Anderson, 1995). Alachlor and metolachlor have been used extensively for more than 20 years, whereas acetochlor application is relatively recent, having been applied extensively since March 1994 (Kolpin, Nations, and others, 1996). Chloroacetanilide herbicides have been shown to degrade more rapidly in soil than other herbicides, with half-lives from 15 to 30 days, whereas triazine half-lives are typically 30 to 60 days (Leonard, 1988).
Recent studies have reported the occurrence of chloroacetanilide metabolites in surface and ground water (Aga and others, 1996; Kolpin, Thurman, and Goolsby, 1996; Thurman and others, 1996; Kolpin and others, 1998). Kolpin and others (1998) found that metabolite concentrations in ground water may be at similar or even higher concentrations than the parent compounds, whereas in surface water the parent compounds are more abundant in the spring after application and are replaced gradually by metabolites during the remaining growing season. In understanding the fate and transport of parent compounds, reliable methods for the analysis of metabolites are vital. These methods also are important for analytical verification of the metabolites in toxicological studies.
High-performance liquid chromatography (HPLC) is needed for the analysis of chloroacetanilide herbicide metabolites because they are ionic compounds and are not sufficiently volatile for analysis by gas chromatography. HPLC-diode array detection (DAD) may be used in determining metabolite concentrations, especially when the water sample is relatively free of humic materials and ionic surfactants that can cause chromatographic interference. Coupling HPLC with mass spectrometry (MS) yields more qualitative data and lower detection limits than HPLC-DAD analysis alone.
This report describes the development of reliable HPLC-DAD and HPLC/MS methods for the analysis of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of acetochlor, alachlor, and metolachlor in surface water and ground water. The HPLC-DAD method was derived from an analytical method for the analysis of alachlor ESA and alachlor OXA as reported by Macomber (1992). For application to the acetochlor and metolachlor metabolites, several modifications to that method were necessary to achieve chromatographic separation of metabolite peaks. The HPLC/MS method was derived from Ferrer and others (1997), with a minor modification to resolve co-eluting peaks on the chromatogram, and was reported in Hostetler and Thurman (1999). Similarly, the analysis of the ESA and OXA metabolites of the newly registered acetanilide herbicide dimethenamid could be added to these methods of analysis, but performance data for these compounds are not included in this report. These methods supplement other methods of the U.S. Geological Survey (USGS) and have been implemented by the USGS Organic Geochemistry Research Group in Lawrence, Kansas.
The HPLC-DAD method of analysis described in this report has been assigned the method number "O-2133-00." This unique code represents the HPLC-DAD automated method of analysis for organic compounds as described in this report and can be used to identify the method.
The HPLC/MS method of analysis described in this report has been assigned the method number "O-2134-00." This unique code represents the HPLC/MS automated method of analysis for organic compounds as described in this report and can be used to identify the method.
This report provides a detailed description of the methods, including the apparatus, reagents, instrument calibration, and the solid-phase extraction (SPE) procedure required for sample analysis. Estimated method detection limits, recoveries, and relative standard deviations for six chloroacetanilide herbicide metabolites for the HPLC-DAD and the HPLC/MS methods are presented.
HPLC-DAD is suitable for the determination of low concentrations (in micrograms per liter) of chloroacetanilide metabolites in natural water samples (table 1). Suspended particulate matter is removed from the samples by filtration, so this method is suitable only for dissolved-phase metabolites.
Metabolites were selected for analysis because of the extensive use of their parent herbicides in the United States and their importance to current (1999) studies being conducted by the USGS. The HPLC-DAD method is suitable for concentrations ranging from 0.2 to 3.0 mg/L without dilution.
Water samples are filtered at the collection site using baked, glass-fiber filters with 0.7-mm pore diameter to remove suspended particulate matter. In the laboratory, filtered water samples are passed through a preconditioned C-18 column. The C-18 column is rinsed with ethyl acetate to remove interferring compounds. The adsorbed chloroacetanilide metabolites are removed from the C-18 with methanol. The eluted solution is spiked with an internal standard, evaporated under nitrogen, and reconstituted. The sample components are separated, identified, and measured by injecting an aliquot of the concentrated extract into an HPLC equipped with a DAD. Compounds eluting from the LC columns are identified by comparing their retention times obtained by the measurement of control samples under the same conditions used for the collected samples. The concentration of each identified compound is measured by relating the DAD response produced by that compound to the DAD response produced by the internal standard.
Samples with high concentrations of humic materials and ionic surfactants may cause chromatographic interference. Compounds that elute from the LC at the same time and are detected at the same wavelengths as the metabolites of interest also may interfere.
Following USGS protocol, sampling methods capable of collecting water samples that accurately represent the water-quality characteristics of the surface water or ground water at a given time or location are used. Detailed descriptions of sampling methods used by the USGS for obtaining depth- and width-integrated surface-water samples are given in Edwards and Glysson (1988) and Ward and Harr (1990). Similar descriptions of sampling methods for obtaining ground-water samples are given in Hardy and others (1989).
Briefly, sample-collection equipment are free of tubing, gaskets, and other components made of nonfluorinated plastic material that might leach interferences into water samples or sorb the pesticides and metabolites from the water. The water samples from each site are composited in a single container and filtered through a 0.7-mm glass-fiber filter using a peristaltic pump. Filters are leached with about 200 mL of sample prior to filtration of the sample. The filtrate for analysis is collected in baked 125-mL amber glass bottles with Teflon-lined lids. Samples are chilled immediately and shipped to the laboratory within 3 days of collection. At the laboratory, samples are logged in, assigned identification numbers, and refrigerated at 4±2 °C until extracted and analyzed.
LC performance is evaluated by background absorbance readings, peak shape, and pressure. Background absorbance signals should remain balanced and low and indicate that the columns have equilibrated with the mobile-phase flow and the absence of interferents. If peak shape deteriorates, the columns may need to be replaced. If the pressure reading is high, there may be a clog in the mobile-phase flow path, or the column compartment thermostat may not have reached the required temperature yet. A variable DAD background signal indicates that the lamp may need replacement.
(1),See table 2 for an example of retention times and relative retention times.
RRTc = RTc/RTi,
where RTc = uncorrected retention time of the selected compound, and
where RTi = uncorrected retention time of the internal standard (2,4-dichlorophenoxyacetic acid).
Two automated extraction systems are used in the laboratory. One method uses an automated Millilab lA workstation (Waters, Milford, Massachusetts), and the SPE cartridges (Sep-Pak) are obtained from Waters (Milford, Massachusetts). The SPE cartridges contain 360 mg of 40-µm C-18- (C18H37) bonded silica.
An alternate SPE procedure used to extract samples is a Tekmar six-position AutoTrace (Tekmar-Dohrmann, Cincinnati, Ohio) and SPE cartridges (Vac C-18 6 mL) obtained from Waters Corporation (Milford, Massachusetts). These vacuum cartridges contain 500 mg of 55- to 105-µm C-18- (C18H37) bonded silica. The same manufacturer of C-18-bonded silica is used for both SPE procedures, but the different automation systems require different cartridge formats. The differing quantities of C-18-bonded silica and the different automation systems require minor differences in solvent volumes used in the extraction. The data in this report were produced using the automated Millilab lA workstation, but the Tekmar six-position AutoTrace procedure is listed in Appendix 1.
(2),
RT = (RRTc) (RTi) ,
where RT= expected retention time of the selected metabolite,
where RRTc = relative retention time of the selected metabolite, and
where RTi = uncorrected retention time of the internal standard.
(3),
DF = (123/123 - Vmp) (123/123 + Va) ,
where DF= dilution factor,
where Vnp = volume not pumped = volume, in mL, not pumped through the SPE column, and
where Va volume added = volume, in mL, of distilled water added to a sample that contains less than 123 mL.
The dilution factor is incorporated into the calculation for determining the final concentration in the sample.
(4),
C = ((Hc/Hi) (m) + y) (DF) ,
where C = concentration of the selected metabolite in the sample, in micrograms per liter;
where Hc= peak height, in milliabsorbance units, for the selected metabolite identified;
where Hi = peak height, in milliabsorbance units, for the internal standard;
where m = slope of correlation curve between the selected metabolite and the internal standard from the original calibration data;
where y = y intercept of correlation curve between the selected metabolite and the internal standard from the original calibration data; and
where DF = dilution factor as calculated in equation 3.
Chloroacetanalide herbicide metabolites are reported in concentrations ranging from 0.2 to 3.0 µg/L. If the concentration is greater than 3.0 µg/L, the sample is re-extracted with a 1:10 (sample:distilled water) dilution and re-analyzed for those compounds that were greater than 3.0 µg/L. Linearity experiments have been conducted showing linear response curves from 0.2 to 10 µg/L.
A reagent-water sample, a surface-water sample collected from Poison Creek in Valley County, Idaho, and a ground-water sample collected from a well in Valley County, Idaho, were used to test the method performance. The surface- and ground-water samples were collected in 45-L carboys and were split into twenty-one 123-mL samples. One set of seven samples was spiked with 0.25 µg/L of each chloroacetanalide metabolite of interest, one set with 0.50 µg/L, and the other set of seven samples was spiked with 2.0 µg/L. In addition, unspiked samples of surface and ground water were extracted and analyzed to determine background concentrations of the pesticides. All subsamples were analyzed in one laboratory (the USGS Organic Geochemistry Research Laboratory in Lawrence, Kansas) using one HPLC-DAD system. Each sample set was extracted and analyzed on different days from November 1998 through January 1999, so comparison of different matrices and concentrations included bias from day-to-day variation. Method recoveries from the analyses are listed in tables 3, 4, and 5.
Corrections for background concentrations: Neither surface- nor ground-water samples required correction for background concentrations of metabolites. All unspiked reagent-water samples also had no detections of metabolites.
Method detection limits (MDL's): An MDL is defined as the minimum concentration of a substance that can be identified, measured, and reported with a 99-percent confidence that the compound concentration is greater than zero. MDL's were determined according to procedures outlined by the U.S. Environmental Protection Agency (1992). Seven replicate samples of reagent water were spiked with 0.25 µg/L of each of the metabolites of interest and analyzed to determine MDL's (table 6). Each sample was analyzed on different days during November 1998 through January 1999, so day-to-day variation is included in the results.
The MDL was calculated using the following equation:
(5),
MDL = (S) (t(n-1, 1-a=0.99) ) ,
where S = standard deviation of replicate analysis, in micrograms per liter, at the spiked concentration;
where t(n-1, 1-a=0.99) , = Student's t-value for the 99-percent confidence level with n-1 degrees of freedom (U.S. Environmental Protection Agency, 1992); and
where n = number of replicate analyses.
The estimated mean MDL's ranged from 0.09 to 0.17 µg/L (table 6). According to the U.S. Environmental Protection Agency (1992) procedure, the spiked concentrations should be no more than five times the estimated MDL. The spiked concentrations were within five times the MDL.
Mean recovery: Mean recovery in reagent-, surface-, and ground-water samples was determined by comparing the mean calculated concentration (see "Quantitation" section) from seven replicate samples to the spiked concentration. Mean recoveries were highest in reagent water spiked at 0.25 µg/L (table 3). Acetochlor OXA and alachlor OXA generally exhibited the lowest recoveries regardless of matrix. The mean recoveries of all compounds spiked at the concentrations in table 3 were combined to calculate the mean recovery for reagent-water samples. The mean recovery in reagent water at all spiked concentrations was 99.6 percent.
Extraction absolute recovery: Absolute recovery of each chloroacetanalide metabolite was determined by comparing samples processed using the aforementioned procedure versus solvent spiked with the metabolites injected directly into the HPLC-DAD. Metabolite peak heights were compared to internal-standard peak heights. Absolute recoveries are listed in table 7. Absolute recovery is different than mean recovery listed in tables 3, 4, and 5 in that mean recovery is calculated from an initial calibration curve that is processed in the same manner as the samples, thus correcting for routine analyte losses.
Method discussion: SPE and recovery for chloroacetanilide metabolites have been discussed in previous work (Aga and others, 1994; Thurman and others, 1996; Ferrer and others, 1997). In those studies, chromatographic separation was achieved only for a few of the herbicide metabolites specified in this report. In the work described in this report, each control surface- and ground-water sample was spiked with a standard containing all the ionic chloroacetanilide metabolites of interest. For purposes of accuracy and precision, chromatographic separation of the metabolites was essential.
The phosphate buffer supplied sodium as a counter ion to the anionic metabolites, creating neutral species that interact with the column. Coupling two columns and maintaining the columns at 60 °C yielded enough metabolite-peak resolution for peak-height quantitation. In this case, it is not known exactly why using two columns with different particle diameters (5 µm and 3 µm) and column diameters (3 mm and 4.6 mm) gave better metabolite separation than using two identical columns. One hypothesis is that water capacity of the column is related to the particle diameter, giving rise to subtle differences in ionic interactions. The columns were configured so that the larger particle column was positioned before the smaller particle column for effective backpressure regulation (smaller phase thickness gives higher backpressure). The analytical wavelength was set at 210 nm, and DAD spectra were stored for every integrated peak with a peak height greater than 0.5 mAU. Figure 1 shows a typical HPLC-DAD chromatogram of a 2.0-µg/L control reagent-water sample.
The HPLC/MS is suitable for the determination of low concentrations (in micrograms per liter) of chloroacetanilide metabolites in water samples (table 1). Suspended particulate matter is removed from the samples by filtration, so this method is suitable only for dissolved-phase metabolites.
Metabolites were selected for analyses because of the extensive use of their parent herbicides in the United States and their importance to current (1999) studies being conducted by the USGS. The HPLC/MS method is suitable for concentrations ranging from 0.05 to 5.0 µg/L without dilution.
Water samples are filtered at the collection site using baked, glass-fiber filters with 0.7-µm pore diameter to remove suspended particulate matter. In the laboratory, filtered water samples are passed through a preconditioned C-18 column. The C-18 column is rinsed with ethyl acetate to remove interferring compounds. The adsorbed chloroacetanilide metabolites are removed from the C-18 with methanol. The eluted solution is spiked with an internal standard, evaporated under nitrogen, and reconstituted. The sample components are separated, identified, and measured by injecting an aliquot of the concentrated extract into an HPLC equipped with a DAD and a mass spectrometer detector. Compounds eluting from the LC columns are identified by comparing their retention times obtained by the measurement of control samples under the same conditions used for the collected samples. Compounds are identified further by selected fragment ions for compounds that can produce fragment ions. The concentration of each identified compound is measured by relating the MS response produced by that compound to the MS response produced by the internal standard.
Compounds that elute from the LC at the same time and have identical ions as the metabolites of interest may interfere. Samples with considerable humic materials can cause interference with the ionization of the internal standard if they are eluting from the LC column at the same time.
Following USGS protocol, sampling methods capable of collecting water samples that accurately represent the water-quality characteristics of the surface water or ground water at a given time or location are used. Detailed descriptions of sampling methods used by the USGS for obtaining depth- and width-integrated surface-water samples are given in Edwards and Glysson (1988) and Ward and Harr (1990). Similar descriptions of sampling methods for obtaining ground-water samples are given in Hardy and others (1989).
Briefly, sample-collection equipment are free of tubing, gaskets, and other components made of nonfluorinated plastic material that might leach interferences into water samples or sorb the pesticides and metabolites from the water. The water samples from each site are composited in a single container and filtered through a 0.7-µm glass-fiber filter using a peristaltic pump. Filters are leached with about 200 mL of sample prior to filtration of the sample. The filtrate for analysis is collected in baked 125-mL amber glass bottles with Teflon-lined lids. Samples are chilled immediately and shipped to the laboratory within 3 days of collection. At the laboratory, samples are logged in, assigned identification numbers, and refrigerated at 4 ±2 °C until extracted and analyzed.
LC performance is evaluated by background absorbance readings, peak shape, and pressure. Background absorbance signals should remain balanced and low and indicate that the columns have equilibrated with the mobile-phase flow. If peak shape deteriorates, the columns may need to be replaced. If the pressure reading is high, there may be a clog in the mobile-phase flow path, or the column compartment thermostat may not have reached the required temperature yet. A variable DAD background signal indicates that the lamp may need replacement.
Two automated extraction systems are used in the laboratory. One method uses an automated Millilab 1A workstation (Waters, Milford, Massachusetts), and SPE cartridges (Sep-Pak) obtained from Waters (Milford, Massachusetts). The SPE cartridges contain 360 mg of 40-µm C-18- (C18H37) bonded silica.
An alternate SPE procedure used to extract samples is a Tekmar six-position AutoTrace (Tekmar-Dohrmann, Cincinnati, Ohio) and SPE cartridges (Vac C-18 6 mL) obtained from Waters Corporation (Milford, Massachusetts). These vacuum cartridges contained 500 mg of 55- to 105-µm C-18-(C18H37) bonded silica. The same manufacturer of C-18-bonded silica is used for both SPE procedures, but the different automation systems require different cartridge formats. The differing quantities of C-18-bonded silica and the different automation systems require minor differences in solvent volumes used in the extraction. The data in this report were produced using the automated Millilab 1A workstation, but the Tekmar six-position AutoTrace procedure is listed in Appendix 1.
(6),
C = ((Ac/Ai) (m) + y) (DF) ,
where C = concentration of the selected metabolite in the sample, in micrograms per liter;
where Ac= peak area of the quantitation ion for the selected metabolite;
where Ai = peak area of the quantitation ion for the internal standard;
where m = slope of correlation curve between the selected metabolite and the internal standard from the original calibration data;
where y = y intercept of correlation curve between the selected metabolite and the internal standard from the original calibration data; and
where DF = dilution factor as calculated in equation 3.
Chloroacetanalide herbicide metabolites are reported in concentrations ranging from 0.05 to 5.0 µg/L. If the concentration is greater than 5.0 µg/L, the sample extract is diluted (volume increased to approximately 150 µL with the reconstitution solution (0.3 percent acetic acid, 24 percent methanol, 35.7 percent distilled water, and 40 percent acetonitrile) and re-analyzed. If the concentration is greater than 10 µg/L, the sample is re-extracted with a 1:10 (sample:distilled water) dilution and re-analyzed for those compounds that were greater than 10 µg/L. Linearity experiments have been conducted showing linear response curves from 0.5 to 10 µg/L.
A reagent-water sample, a surface-water sample collected from Poison Creek in Valley County, Idaho, and a ground-water sample collected from a well in Valley County, Idaho, were used to test the method performance. The surface- and ground-water samples were collected in 45-L carboys and were split into twenty-one 123-mL samples. One set of seven samples was spiked with 0.05 µg/L of each chloroacetanalide metabolite of interest, one set with 0.20 µg/L, and the other set of seven samples was spiked with 2.0 µg/L. In addition, unspiked samples of surface and ground water were extracted and analyzed to determine background concentrations of the pesticides. All subsamples were analyzed in one laboratory (the USGS Organic Geochemistry Research Laboratory in Lawrence, Kansas) using one HPLC/MS system. Each sample set was extracted and analyzed on different days from November 1998 through January 1999, so comparison of different matrices and concentrations included bias from day-to-day variation. Method recoveries from the analyses are listed in tables 9, 10, and 11.
Corrections for background concentrations: Neither surface- nor ground-water samples required correction for background concentrations of metabolites. All unspiked reagent-water samples also had no detections of metabolites.
Method detection limits (MDL's): An MDL is defined as the minimum concentration of a substance that can be identified, measured, and reported with a 99-percent confidence that the compound concentration is greater than zero. MDL's were determined according to procedures outlined by the U.S. Environmental Protection Agency (1992). Seven replicate samples of reagent water spiked with 0.05 µg/L of each of the metabolites of interest and were analyzed to determine MDL's (table 12). Each sample was analyzed on different days during November 1998 through January 1999, so day-to-day variation is included in the results. The MDL was calculated using equation 5.
The estimated mean MDL's ranged from 0.04 to 0.05 µg/L (table 12). According to the U.S. Environmental Protection Agency (1992) procedure, the spiked concentrations should be no more than five times the estimated MDL. The spiked concentrations were within five times the MDL.
Mean recovery: Mean recovery in reagent-, surface-, and ground-water samples was determined by comparing the mean calculated concentration (see "Quantitation" section) from seven replicate samples to the spiked concentration. Mean recoveries were highest in surface water at the 2.0-µg/L concentration (table 10), except for acetochlor ESA in reagent water spiked at 0.05 and 0.20 µg/L and in surface water spiked at 0.05 µg/L and for metoalchlor ESA in reagent water spiked at 2.0 µg/L. Acetochlor OXA and alachlor OXA exhibited the lowest recoveries in reagent water, and acetochlor ESA and metolachlor ESA exhibited the highest recoveries regardless of matrix. The mean recoveries of all compounds spiked at all concentrations in table 9 were combined to calculate the mean recovery for reagent-water samples. The mean recovery in reagent water at all spiked concentrations was 100.7 percent.
Method discussion: A HPLC/MS method for the analysis of ethanesulfonic acids and oxanilic acids of acetochlor, alachlor, and metolachlor was reported by Ferrer and others (1997). The described HPLC system used an 5-µm, 250- x 3.0-mm C-18 column, with a mobile phase consisting of 0.3 percent acetic acid in 24 percent methanol, 36 percent distilled water, and 40 percent acetonitrile solution. With this configuration, peak resolution was not achieved for acetochlor ESA and alachlor ESA, which have the same quantitation ion (table 8). Thus, accurate quantitation of these metabolites was not possible. Chromatographic separation of acetochlor ESA and alachlor ESA was achieved with the same mobile phase by coupling two 5-µm, 250- x 3.0-mm C-18 columns to one (or two, if backpressure permits) 3-µm, 150- x 2.0-mm C-18 column. Figure 2 shows a total ion chromatogram (TIC) of a 0.05-µg/L control reagent-water sample. Figure 3 shows the extracted ion chromatogram for the molecular ion (314 mass-to-charge ratio) of acetochlor ESA and alachlor ESA with near baseline separation. The elution order of the metabolites using the HPLC/MS method differs from that of the HPLC-DAD method because the pH of the respective mobile phases are different. They are different because the HPLC buffer is nonvolatile and not compatible with mass spectrometry.
2,4-dichlorophenoxy acid was used as the internal standard because it is amenable to negative ion electrospray and is readily available as a commercial standard. The use of deuterated surrogate standards is being investigated.
This report presents two methods for routine analysis of six chloracetanalide herbicide metabolites in natural water samples. From the data presented in this report, solid-phase extraction and determination by high-performance liquid chromatography-diode array detection (HPLC-DAD) or high-performance liquid chromatography/mass spectrometry (HPLC/MS) are shown to be sensitive and reliable methods for the determination of low concentrations. Good precision and accuracy were demonstrated for both the HPLC-DAD and HPLC/MS methods in reagent water, surface water, and ground water. Method detection limits for the HPLC-DAD method ranged from 0.09 to 0.17 µg/L. Method detection limits for the HPLC/MS method ranged from 0.04 to 0.05 µg/L. The mean HPLC-DAD recoveries of the chloroacetanilide herbicide metabolites from water samples spiked at 0.25, 0.50, and 2.0 µg/L ranged from 84 to 112 percent, with relative standard deviations of 18 percent or less. The mean HPLC/MS recoveries of the metabolites from water samples spiked at 0.05, 0.20, and 2.0 µg/L ranged from 81 to 125 percent, with relative standard deviations of 20 percent or less. The limit of quantitation (LOQ) for all metabolites using the HPLC-DAD method was 0.20 µg/L, whereas the LOQ using the HPLC/MS method was 0.05 µg/L. Information about the fate and transport of the chloroacetanilide herbicides-acetochlor, alachlor, and metolachlor-in water can be acquired from the analysis of surface-water runoff and ground water from wells. These methods also can be useful for water-quality determinations and analytical verification in toxicological studies.
U.S. Department of the Interior |
U.S. Geological Survey
URL: /pubs/reports/ofr.00-182.html
Page Contact Information: GS-W-KS_info@usgs.gov
Page Last Modified:Wednesday, 17-Sep-2008 13:01:58 CDT
