Stability of solutions of nutrient salts during storage

The addition of chemicals, particularly mercuric chloride, to preserve samples of natural water for subsequent analysis is reviewed. It is suggested that faulty calibration techniques contribute to inter- and intra-laboratory variability in the determination of nutrients, and that the instability of stored standard solutions may be an important source of error. The results of collaborative work involving 18 laboratories are discussed in support of a recommended preservative regime for standard solutions.