Atomic-absorption spectrophotometry was used to determine trace levels of metal ions in aqueous solution in order to investigate the effect of pH upon their stability, solubility and ease of adsorption during storage. It was found that of the thirteen metal ions investigated, namely those of gold, barium, bismuth, cadmium, indium, lithium, palladium, platinum, rhodium, ruthenium, antimony, tin and thallium, with the exception of lithium, none is stable over the pH range from 1 to 11, and that to ensure the stability of solutions containing these ions it is necessary to acidify them to pH 1 with hydrochloric acid immediately after sampling.