Trace element

A trace element is present in only a small amount. The amount depends on context.

 In analytical chemistry, it is an element in a sample that has an average concentration of less than 100 parts per million (ppm) measured in atomic count, or less than 100 micrograms per gram. 

 In biochemistry, it is one that is needed in minute quantities for the proper growth, development, and physiology of the organism.H.J.M. Bowen 1976. Trace elements in biochemistry. 2nd ed, Academic Press. In biochemistry, a trace element is also referred to as a micronutrient. See Cofactor.

In geology, its concentration is less than 1000 ppm or 0.1% of a rock's composition. The term is used mainly in igneous petrology.

 References 

Category:Biochemistry
Category:Geology