The @S06021@ concentration, \(c_{\text{B}}\), of a component B in a system is given by the expression: \[c_{\text{B}}=\frac{n_{\text{B}}}{V}\] where \(n_{\text{B}}\) is the @S06021@ @A00297@ of component B in the system and \(V\) is the volume of the system. The component added to the system may dissociate or react with other components to form a series of derived components and only a fraction of the original component may actually exist in a free form in the system. It is therefore essential to distinguish between the @S06021@ concentration and the @A00298@ of the free form of the component in the system. Sometimes @S06021@ quantities are indicated by a subscript (\(_{\text{o}}\)), e.g. \(n_{\text{o,B}}\), \(c_{\text{o,B}}\). In clinical chemistry, the term @S06021@ concentration is rarely employed. Instead, the name of the component is modified to indicate inclusion of the various derived forms, e.g. mixtures of a defined chemical component and its derivatives may be denoted by the plural form of the name of the pure unchanged substance, or to indicate the sum of components specified in individual quantities the specification 'total' may be employed.