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2.0
CHEMICAL COMPATIBILITY OF EQUIPMENT AND THE WATER SAMPLE

By D.B. Radtke and F.D. Wilde

The materials used to construct equipment can directly affect sample chemistry (table 2-1). Equipment designed for water-quality work commonly is constructed of a combination of materials, the most inert being used for components that will contact the sample. Nonsample-wetted components also can be a source of sample contamination, and field personnel must use techniques to minimize potential contamination, implement quality-assurance procedures, and quantify potential effects by using quality-control sample analysis.

When planning equipment use, consider having several sets of precleaned equipment available. A clean set of equipment for each sampling site prevents cross contamination between sites, eliminates the need for time-consuming equipment cleaning in the field, and serves as backup should equipment break or become greatly contaminated.

Materials used in equipment can include plastics, glass, and metals. Chemical reactivity varies widely within the same group of materials, depending on the chemical composition, the physical configuration, and the manufacturing process. Thus, regarding reactivity with water and most other chemical substances, plastics such as fluorocarbon polymers are less reactive than plastics such as polyethylene, and 316-type stainless steel (SS 316) is less reactive than brass, iron, or galvanized steel. For plastics and metals in general:

arrow The softer or more flexible forms of any plastic or metal are more reactive than the rigid forms.
arrow The more polished the surface, the less reactive the material tends to be.

table 2-1


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Last Modified: Wednesday, 02-Jan-2013 18:26:04 EST