Detection of part per trillion levels of 2,4-d in drinking water


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MATRIX: Drinking water

ANALYTES: 2,4-D (2,4-dichlorophenoxyacetic acid) and related phenoxy acids

LIMIT OF DETECTION: 70 ppt to 5 ppb (for 10 mL sample), 7 ppt to 0.5 ppb (for 100 mL sample)

2,4-D RaPID AssayÒ Kit and Sample Diluent Reagents: 2,4-D control (preparation described below), methanol and ethyl acetate (pesticide grade), hydrochloric acidH (Cl) and distilled or deionized water. Equipment: vacuum filter device, vacuum manifoldS, upelclean ENVIÔ-18 solid phase extraction columns (6 mL, Supelco, Inc.), 10 mL volumetric pipet, pH electrode, glass scintillation vials (for 10 mL sample) or clean 125 mL Erlenmeyer flasks (for 100 msaLm ples), nitrogen gas and evaporating apparatus, glass test tubes.

For 10 mL sample: measure 10 mL of the drinking water to be tested into a glass scintillation vial. Acidify the sample to pH 2 to 2.2 with approximately three drops of 1N HCl. For 100 mL sample: measure 100 mL of the drinking water to be tested into an Erlenmeyer flask. Acidify the sample to pH 2 to 2.2 with approximately ten drops of 6N HCl. For each sample to be analyzed, prepare 15 ml of acididf ideistilled or deionized water ('acid DI H2O') by adding approximately 4 drops of 1NH Cl to 15 mL of DI water.

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

With the vacuum off, add 5 mL of acid DI H2O to the column. Attach a 25 mL or larger reservior to the column with an adapter. Add the acidified drinking water sample to reservior. Turn on the vacuum. Rinse the empty glass sample container with 5 mL of acid 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.

Extract the 2,4-D from the column with 3 x 1 mL of ethyl acetate. Collect the extract in a glass test tube. Evaporate the ethyl acetatee luate to dryness under nitrogen. Avoid placing the nitrogen delivery device directly into theel uate during evaporation. This may result in contamination of the sample.R edissolve the residue in exactly 1 mL of 2,4-D SampDlei luent. Gently swirl or vortex to mix.

Prepare a standard curve according to the directions in the 2,4-D RaPID Assay package insert. Analyze ther edissolved residue as the 'sample'. Calculate the 2,4-D concentration in the original drinking water sample by multiplying the assay result (in ppb) by 0.1 (for 10 mL sample) or 0.01 (for 100 mL sample).

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