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Water samples must be processed as quickly as possible after collection. The equipment most commonly used for sample processing includes sample splitters, filtration units or assemblies, solid-phase extraction systems, and chambers in which samples are processed and treated with chemical preservatives.

The collection of surface water generally results in a single composite sample. Once a sample has been composited, the sample is often subdivided (split) into subsamples for analyses. Each whole-water subsample contains suspended and dissolved concentrations of target analytes that are virtually equal to those in every other subsample.

Cone Splitter
The cone splitter is a pour-through splitting device constructed entirely of fluorocarbon polymers. The cone splitter may be used to process samples with particle sizes < 250 um and suspended-sediment concentrations < 10,000 mg/L. Its primary function is to split the sample simultaneously into as many as 10 equal-volume samples. Below the funnel is a short standpipe that directs sample water in a steady stream into a splitting chamber that contains a notched, cone-shaped splitting head with 10 equally spaced exit ports around its base.

Filtration Systems
Filtration separates particulate substances (solid-phase and biological materials) from the solute or aqueous phase of a water sample. For surface water, the most common filtration system consists of a reversible, variable-speed, battery-operated peristaltic pump or a metering pump that forces whole-water sample through tubing into a filter assembly.

Samples for inorganic analyses sre filtered by use of either a disposable capsule-filter assembly or a plate-filter assembly. Use of a disposable capsule-filter eliminates the potential for contamination from a reusable filter assembly (such as a plate filter) and also eliminates time-consuming field-cleaning procedures that are required for a reusable assembly after each sample if filtered.

Filtering whole-water samples isolates suspended solid phase substances from the aqueous phase, thus allowing separate determinations of organic compounds in each phase. Filtering also helps to preserve samples for organic determinations because microorganisms that could degrade compounds in the sample are removed.

All equipment and components used for filtering whole water samples for organic determinations should be made of materials that will not contaminate the samples or sorb analytes and should be suitable for use with organic cleaning solvents. Such materials include stainless steel or aluminum, flourocarbon polymer, glass, and nonporous ceramics (hard-fused microcrystalline alumina).

Processing and Preservation Chambers
Processing and preservation chambers reduce the possibility of random atmospheric contamination during sample splitting, filtration, and presevation. These chambers are required for samples for trace-element determinations. There is no standard design for either fixed or portable chambers; however, to prevent contamination of inorganic samples with metals, the materials used in their construction should be either nonmetallic or completely covered by or embedded in nonmetallic material.

Use of separate chambers for sample processing and sample preservation can be a most convenient approach and is necessary if more than one type of chemical preservation will be used. Separate chambers help prevent cross-contamination.