Atomic absorption spectroscopy is the study of the absorption of radiation by atoms. As an analytical process, it involves the conversion of compounds to atoms, and the absorption of energy by these atoms. A flame burning in air is the conventional means for converting the solution to be analysed into atomic vapour. The number of free atoms produced in the flame is reduced if chemical bonds between the analyte and its matrix fail to break readily at the flame temperature, i.e., chemical interference takes place under some conditions. Chemical interference is a common occurence in the determination of calcium, magnesium and strontium in low-temperature flames (below about 3000 K). As a general rule, the anions most likely to cause chemical interference are stable oxyanions. Studies have been made in this work of the interference of fluoride, molybdate, phosphate, sulphate and tungstate ions in the determination of the alkaline earth elements, chromium, molybdenum and nickel, using an air-acetylene flame. Only in the case of calcium and strontium determinations were large interferences encountered. The magnitude of the interference was greatest with tungstate and phosphate, and least with fluoride. Interferences in the determination of gallium and indium, which had not previously been studied in detail, were investigated. Twenty-eight cations, ten anions, three complexing agents and four acids were tested for potential interference. Several interferences were found (calcium, strontium, borate and phosphoric acid with gallium, and iron (III), zinc, bromide and hydrochloric acid with indium), but none of the effects was as marked as the interferences with alkaline earths. The inhibition by phosphate of the calcium signal is well known in both flame emission and atomic absorption. The variation of the magnitude of the interference with concentration of both calcium and phosphate was studied, and conditions are indicated under which phosphate might be determined quantitatively by means of the interference effect. A similar study was made for the tungstate ion. (Sulphate and molybdate at low concentrations do not interfere significantly with calcium absorption in the air-acetylene flame.). In attempts to identify and/or separate the species responsible for chemical interference effects, the flame emission spectra were recorded when solutions containing calcium and phosphoric acid and a mixture of the two were aspirated into the flame. No new peaks or bands could be found which might be ascribed to electronic transitions of a new stable species containing both calcium and phosphate. However, the peaks and bands arising from the calcium and phosphate mixture wore reduced in intensity. This indicates that the calcium is combined in one or more molecular species containing the calcium and the phosphate. Similar depression of emission peaks and bands was found with strontium and phosphate mixtures. Solid material, entrained in the flame gases when solutions were aspirated, was collected from a region just above the top of the flame, and infra-red and X-ray diffraction studies were made to identify the solid collected. Where calcium-containing solutions were aspirated, the solid products varied according to the nature and concentrations of various anions present in the solution. Calcium carbonate was the sole identifiable product when nitrate ions were present. The presence of both phosphate and chloride led to the formation of both chlorapatite, 3 Ca₃(PO₄)₂, CaCl₂ and ∝- calcium orthophosphate under some conditions; phosphate alone led to a solid which may be secondary calcium orthophosphate, CaHPO₄. Similar compounds were found with strontium and magnesium, although these did not correspond to any for which X-ray and infra-red data are recorded in the literature. The exact composition of the solid products of the flame reactions therefore varies with the nature and concentration of the anions, and is probably also sensitive to parameters such as the fuel-air ratio in the flame, and to changes in the location of the point of collection of the solids.