Sodium salts are very soluble, and sodium leached from soil and rocks tends to remain in solution. Water with a high ratio of sodium to calcium is deleterious to soil structure.

Sodium is not particularly significant in potable water except for those persons having an abnormal sodium metabolism, but water supplies in some areas contain sufficient sodium to be a factor in the planning of sodium-free diets.

The use of sodium salts is common in industry; therefore, many industrial wastewaters contain significant quantities of sodium. For high-pressure boiler feed-water even trace amounts of sodium are of concern.

1.1 This test method covers the determination of low amounts of sodium in waters having low solids content. The applicable range of this test method is from 0.20 to 3.0 mg/L when using the 589.6-nm resonance line. This range may be extended upward by dilution of an appropriate aliquot of sample or by use of the less-sensitive 330.2-nm resonance line (see Test Method D 3561). Many workers have found that this test method is reliable for sodium levels to 0.005 mg/L, but use of this test method at this low level is dependent on the configuration of the aspirator and nebulizer system available in the atomic absorption spectrophotometer as well as the experience and skill of the analyst. The precision and bias data presented are insufficient to justify use of this test method in the 0.005 to 0.20-mg/L range.

1.2 This test method has been used successfully with spiked reagent water. It is the analyst's responsibility to assure the validity of the test method to other low dissolved solids matrices.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.