Detection of alachlor and its sulfonic acid metabolite in water

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MATRIX: Groundwater, surface water and well water

ANALYTES: Alachlor and its major soil metabolite, ethane sulfonic acid (ESA)

LIMIT OF DETECTION:
Alachlor: 5 ppt to 500 ppt (for 10 mL sample) 0.5 ppt to 50 ppt (for 100 mL sample)
ESA: 30 ppt to 3 ppb (for 10 mL sample) 3 ppt to 300 ppt (for 100 mL sample)

MATERIALS:
Alachlor RaPID AssayÒ Kit and Sample Diluent Reagents: methanol and ethyl acetate (pesticide grade) and distilled or deionized water (DI H2O). Equipment: vacuum filter device, vacuum manifold, Supelclean ENVIÔ-18 solid phase extraction columns (3 mL, Supelco, Inc.), 25 mL or larger reservoirs and adapters for solid phase extraction columns, flask, nitrogen gas and evaporating apparatus, glass test tubes.

COLUMN PREPARATION:
Under vacuum, condition the SPE column with 3 mL methanol, followed. 2 x 3 mL ethyl acetate, followed by 3 mL methanol, followed by 3 mL of DI H2O. Adjust vacuum to a flow rate of 5 mL/min for water (10 mm Hg). Do not allow column to dry between methanol and water conditioning or following the water conditioning.

EXTRACTION PROCEDURE:
With the vacuum off, add 2 mL of DI H2O to the column. Attach a 25 mL or larger reservior to the column with an adapter. Add the water sample to reservior. Turn on the vacuum. Rinse the empty sample container with 5 mL of DI H2O and add to the reservoir. Do not let column run dry between sample and rinse. After the rinse has passed through, increase vacuum to 25 mm Hg for 10 minutes or longer to dry the column completely.

SOLVENT EXCHANGE:
Adjust vacuum to 10 mm Hg and extract the alachlor from the column with 3 mL of ethyl acetate. Collect the extract in a glass test tube. Next, extract the ESA metabolite from the column with 3 mL of methanol. Collect the extract in a separate glass test tube. Evaporate the ethyl acetate eluate (alachlor) and methanol eluate (ESA) to dryness under nitrogen. Avoid placing the nitrogen delivery device directly into the eluate during evaporation. This may result in contamination of the sample. Redissolve the residues in exactly 1 mL of Alachlor Sample Diluent. Gently swirl or vortex to mix.

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