MS and Time of Flight

Chapter 16

Downloaded by UNIV ILLINOIS URBANA on June 3, 2013 | http://pubs.acs.org Publication Date: May 20, 2003 | doi: 10.1021/bk-2003-0850.ch016

Interlaboratory Comparison and Validation of Methods for Chloroacetanilide and Chloroacetamide Soil Degradates in Environmental Waters 1

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John D. Vargo , Edward A. Lee , and John D. Fuhrman 1

Hygienic Laboratory, University of Iowa, Iowa City, IA 52242 U.S. Geological Survey, 4821 Quail Crest Place, Lawrence, KS 66049 Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, MO 63167 2

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This paper describes a corroborative evaluation of three different analytical methods for the analysis of soil degradates of chloroacetanilide and chloroacetamide herbicides in environmental waters. Independent methodologies were developed at the University of Iowa Hygienic Laboratory (IHL), U . S. Geological Survey Laboratory (USGS) (Lawrence, KS.) and at Monsanto Company (MON) with the goal of quantitating the common soil degradates at concentrations below 0.1 μg/L. Liquid chromatography / mass spectrometry (LC/MS) is the fundamental basis of these methods which use differing approaches at concentration and MS detection. All methods quantified the ethanesulfonic acids (ESA) and oxanilic acids (OXA) of acetochlor (Ac), alachlor (Al), dimethenamid (Di) and metolachlor (Me). Correlation of results between laboratories was excellent. At residue levels >0.05 μg/L and using relative standard deviation (RSD) as an indicator of variability, the average RSD across labs for all surface water samples was 9.3% for the eight primary degradates. Overall, the average recovery from the laboratory fortified samples was nearly identical between laboratories.

© 2003 American Chemical Society

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In Liquid Chromatography/Mass Spectrometry, MS/MS and Time of Flight MS; Ferrer, I., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

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Introduction Chloroacetanilides are soil-applied herbicides used for pre- and early postemergence control of grasses and broadleaf weeds in a variety of crops. The major chloroacetanilides, acetochlor, alachlor and metolachlor are used extensively worldwide. The major soil metabolites of these materials are occasionally found in surface water and ground water but usually at very low concentrations. There now exist a variety of highly sensitive analytical methods to determine residues of these compounds in environmental waters. Three laboratories participated in a study designed to evaluate potential sources of interlaboratory variation in the analysis of chloracetanilide herbicide soil metabolites. The participating laboratories included, Iowa Hygienic Laboratory, Iowa City, Iowa, United States Geological Survey, Lawrence, Kansas and Monsanto Company, Saint Louis, Missouri. Each laboratory had developed in-house analytical methodology based on LC/MS. While the LC/MS fundamentals are similar between laboratories, each lab took a unique and different approach to quantitation. The three participating laboratories used different extraction procedures and all used different LC/MS instrumentation. The Iowa Hygienic Lab used Envi-CARB SPE to concentrate the water samples with quantitation using a Micromass Quattro tandem quadrupole system. The USGS used Qg SPE to concentrate water samples and a Hewlett-Packard single quadrupole system for quantitation. Monsanto directly injected the water samples into an HPLC system with quantitation using a PE Sciex API-3000 tandem quadrupole system. A l l three LC/MS systems used pneumatically assisted electrospray interfaces. Each method targeted a unique spectrum of soil dégradâtes and / or parent herbicide for detection and quantitation. Actual field samples were collected for use in this study. Some samples were laboratory fortified to ensure measurable residues were present for analysis. All methods quantified the ethanesulfonic acids (ESA) and oxanilic acids (OXA) of acetochlor (Ac), alachlor (Al), dimethenamid (Di) and metolachlor (Me) which will be the primary focus of this paper and be referred to as "common dégradâtes". Both USGS and MON quantified additional dégradâtes, some common between both methods. The common analytes included; propachlor (Pr) ESA and OXA, alachlor sulfinylacetic acid (SAA) and acetochlor SAA. Analytes unique to USGS included flufenacet ESA and OXA. Analytes unique to the Monsanto method included propachlor SAA and alachlor s-oxanilic acid (s-OXA). The IHL included parent herbicides in their methodology. A number of papers have been published in recent years regarding the analysis of chloroacetanilide herbicide dégradâtes in environmental waters (1-5). Structures are shown generically in Figure 1 and detailed in Table I.


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Rs R R

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CHU

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Acetanilide

Acetamide

Figure 1: Generic Degradate Structures

Table I. Reference Compounds Abbrev -iation

CAS Registry No. (acetanilide) AcOX 194992-44-4 AcESA 187022-11-3 AcSAA NA AlOX 140939-14-6 A1ESA 140939-15-7 AlsOX 140939-17-9 A1SAA 140939-16-8 HOX NA F1ESA NA MeOX 152019-73-3 MeESA 171118-09-5 PrOX 70628-36-3 123732-85-4 PrESA PrSAA 12373286-2 (acetamide) DiOX NA DiESA 205939-58-8

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Et Et Et Et Et Et Et H H Et Et H H H

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CH OCH CH Œ OCH CH CH OCH CH CH OCH CH OCH H CH OCH CH(CH ) CH(CH ) CH(CH )CH OCH CH(CH )CH OCH CH(CH ) CH(CH ) CH(CH )

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CH(CH )CH OCH CH(CH )CH OCH

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COC0 H COCH S0 H COCH SOCH C0 H COC0 H COCH S0 H COC0 H COCH SOCH C0 H COC0 H COCH S0 H COC0 H COCH S0 H COC0 H COCH S0 H COCH SOCH C0 H 2

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Methods


Samples: Selection / Preparation / Storage Each laboratory provided samples for the round robin analysis. These were intended to be representative surface and ground water samples from the corngrowing region of the Midwest. IHL provided two surface water samples, one from the English River and the other from Coralville Lake, both in Iowa. Samples were provided to all the laboratories as field controls and laboratory fortified field controls. The English River sample was fortified at 3.33 μg/L for all IHL analytes. The Coralville Lake sample was fortified at 1.0 μg/L for all IHL analytes except AcESA, which was spiked at 12.72 μg/L. The USGS lab provided surface water samples from Clinton Lake, in Kansas. Three samples were distributed among the participating labs, a field control and laboratory fortified field controls spiked at two concentration levels. The fortified samples were spiked at 0.50 and 2.50 μg/L, respectively, for all USGS analytes. MON provided samples collected from surface water sources in Illinois. Included were a finished (drinking) water sample from the Kankakee River in Kankakee and a raw surface water sample from the Silver Lake reservoir in Highland. These samples had low level detections of most of the common dégradâtes as determined by prior analysis in a separate monitoring study. These samples were provided, as field controls only, no fortifications were made as many of the analytes were already known to be present. Samples were shipped to the participating labs within one day of preparation. Samples were shipped under chilled conditions (ice packs) and stored at 1 week), it is recommended that the samples be stored at freezer temperatures. The samples were analyzed using a Micromass Quattro LC/MS/MS (tandem quadrupole) system with an electrospray interface. The ESA and O X A dégradâtes were monitored as negative ions while the parent herbicides were monitored as positive ions. All separations were performed using a Zorbax SB C column (3.0 χ 150 mm, dp = 5 μπι) with a mobile phase flow rate of 0.6 mL/min. A mobile phase gradient using acetonitrile (0.15% in acetic acid) and water (0.15% in acetic acid) was used with a linear gradient ramp from 20-100% ACN over 10 minutes. A column temperature of 30°C was used. The injection volume was 50 μL· Unique precursor ion/product ion pairs were monitored in the multiple reaction monitoring mode (MRM) for each analyte. The precursor ions were the protonated molecular ions (positive ion monitoring) or the deprotonated molecular ions (negative ion monitoring). Data acquisition conditions are presented in Table II. 8


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Table II. Data Acquisition Conditions for Micromass Quattro LC/MS/MS Scan Precursor Product Func. Analyte Ion Ion 1 Acetochlor OXA 145.90 264.00 1 Alachlor OXA 159.90 264.00 1 Dimethenamid OXA 197.90 270.00 1 Metolachlor OXA 205.95 278.00 1 Acetochlor ESA 161.90 314.10 1 Alachlor ESA 159.90 314.10 1 Dimethenamid ESA 120.90 320.00 1 Metolachlor ESA 120.90 328.10 2 Acetochlor 223.90 270.10 2 Alachlor 23800 270.10 2 243.95 Dimethenamid 276.10 2 Metolachlor 252.00 284.15 ESA/OXA metabolites monitored as negative ions. Parent herbicides monitored as positive ions. CE = collision energy Function 1: Start time: 2.0 min, End time: 7 0 mm Function 2: Start time: 7.0 min, End time: 11.0 min

Dwell (sec) 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.15 0.15 0.15 0.15

Cone (V) 20 20 20 20 40 40 40 40 20 20 20 20

CE (V) 12 12 12 12 23 23 23 23 10 15 15 16

Experimental - Monsanto The Monsanto method used direct aqueous injection of the water sample. The samples were transferred directly to 2 mL autosampler vials for analysis. No preconcentration, sample cleanup or filtration was necessary prior to analysis. The samples were analyzed using a PE Sciex API-3000 LC/MS/MS (tandem quadrupole) system with a TurboIonSpray interface. All degradate analytes were monitored as negative ions. The dégradâtes were chromatographed on a Zorbax StableBond C column, 50 mm χ 4.6 mm χ 3.5 μ, in combination with a Zorbax StableBond C guard column, 12.5 mm χ 4.6 mm χ 5 μ. The liquid chromatograph was a Hewlett Packard 1100 system, including a binary pump, degasser, column heater and autosampler. The column was maintained at 70°C to minimize chromatographic separation of the rotational isomers. A solvent gradient was used comprising a mixture of mobile phase A: 95:5 water: methanol (with 0.2% acetic acid) and mobile phase B: 50:50 acetonitrile: methanol (with 0.2% acetic acid). Initial conditions were 95:5 A:B, to 50:50 A:B at 3 minutes, to 30:70 A:B at 6.5 minutes and hold to 7.5 minutes. Re-equilibration to 95:5 8

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279 required an additional 2.5 minutes. The flow rate was 700 μΐ. / minute and the column effluent was split approximately 14:1 at the ion source (-50 μΐ. / minute of flow to the ion source). The API-3000 was coupled to the HP1100 L C system through a TurboIonSpray source. A Valco, Model EHMA, electrically actuated


Table III. Data Acquisition Conditions for Sciex API-3000 LC/MS/MS Scan Precurser Product Dwell Func. Analyte Ion Ion (sec) 1 Propachlor OXA 0.10 206.0 134.0 1 Propachlor SAA 134.0 0.10 282.0 1 Propachlor ESA 121.0 0.10 256.0 2 148.0 Alachlor s-OXA 0.05 220.0 2 Dimethenamid ESA 0.05 320.0 121.0 2 Dimethenamid OXA 198.0 270.0 0.05 2 Alachlor SAA 160.0 0.05 340.0 2 Acetochlor SAA 146.0 0.05 340.0 2 Alachlor OXA 160.0 0.05 264.0 2 Acetochlor OXA 146.0 0.05 264.0 2 Alachlor ESA 176.0 0.10 314.0 2 Acetochlor ESA 162.0 0.10 314.0 2 Metolachlor ESA 121.0 328.0 0.05 2 Metolachlor OXA 206.0 0.05 278.0 DP = declustering potential CE = collision energy All metabolites monitored as negative ions. Function 1: Start time: 3.5 min, End time: 4.5 min Function 2: Start time: 4.5 min, End time: 6.5 min

DP (V) -25 -30 -20 -16 -32 -25 -11 -11 -21 -21 -36 -36 -36 -21

CE (V) -30 -30 -26 -16 -31 -16 -30 -30 -16 -16 -34 -34 -30 -16

6 port switching valve was used to divert the column flow from the ion source prior to and following elution of the analytes of interest. The injection volume was 100 μ ί . The total run time was 10 minutes. Specific precursor ion/product ion pairs were monitored in the M R M mode for each analyte. Data acquisition conditions are presented in Table III.

Experimental - USGS A Waters Qg Sep-Pak (500 mg) is conditioned by sequentially passing 3 mL methanol, 3 mL ethyl acetate, 3 mL methanol, and 3 mL distilled water through each column at a flow rate of 20 mL/min by positive pressure. The


280 filtered water sample, 123 mL, is then passed through the preconditioned SepPak. The Sep-Pak is rinsed with 3.2 mL of ethyl acetate to remove interfering compounds. The adsorbed chloroacetanilide dégradâtes are eluted from the SepPak with 3.5 mL of methanol. The solution is spiked with an internal standard (2,4-dichlorophenoxyacetic acid), evaporated under nitrogen at 50°C, and reconstituted with 125JLLL of 50:50 mobile phase. The sample is transferred to an autosampler vial and stored at

MS and Time of Flight

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