(A) Glassware contamination: Thoroughly clean glassware, including baking or solvent rinse.

(B) Reagent contamination: Use high purity reagents.

(C) Extracted interferences: Interference from extracted non-target compounds, with retention times similar to target compounds, can be reduced by performing a cleanup procedure.

(D) Dichlorobenzenes: Extract samples with 2 different column packings to reduce interference from coelution of dichlorobenzes with haloethers.

Each laboratory that uses this method is required to operate a formal quality control program. The minimum requirements of this program consist of an initial demonstration of laboratory capability and an ongoing analysis of spiked samples to evaluate and document data quality. The laboratory must maintain records to document the quality of data that is generated. Ongoing data quality checks are compared with established performance criteria to determine if the results of analyses meet the performance characteristics of the method. When results of sample spikes indicate atypical method performance, a quality control check standard must be analyzed to confirm that the measurements were performed in an in-control mode of operation.

Grab samples must be collected in glass containers. [Note: Do NOT pre-rinse bottles]. Composite samples should be collected in refrigerated glass containers in accordance with the requirements of the program. Automatic sampling equipment must be as free as possible of Tygon tubing and other potential sources of contamination.

All samples must be iced or refrigerated at 4^oC from the time of collection until extraction. Fill the sample bottles and, if residual chlorine is present, add 80 mg of sodium thiosulfate per liter of sample and mix well. EPA Methods 330.4 and 330.5 may be used for measurement of residual chlorine. Field test kits are available for this purpose.

Extract w/in 7 days; Analyze extracts w/in 40 days.