[Determination of lithium in the oil field water by flame atomic absorption spectrometry]

Flame atomic absorption spectrometry was applied to the determination of micro amount of lithium in the oil field water of certain area. In order to determine which method is more appropriate for the determination of lithium content in the oil field water, standard curve method and standard addition method were compared. The effects of dilution, coexistent ions, and deionizers on the determination were studied. For the determination of lithium content in the same diluted oil field water samples, there exist obvious differences between the results obtained from standard addition method and standard curve method. Standard addition method gives results with a larger error, whereas standard curve method gives more accurate results. It is difficult to eliminate the interferences when the standard addition method is used. The standard curve method is found to be more suitable for the determination of micro amount of lithium in the oil field water for its accuracy, simplicity, and feasibility. When the standard curve method is used, both the determined lithium concentration and the recovery change with the dilution extent of the oil field water. In order to get an accurate result, the oil field water sample should be diluted to 1/200 or less. In this case, the recovery by standard addition method ranges from 94.3% to 96.9%. When sodium phosphate or sodium chloride is used as the deionizer, the recovery by standard addition method ranges from 94.6% to 98.6%, or from 94.2% to 96.3%. In the determination of lithium content in oil field water, there are larger experimental errors without the addition of any deionizer. When the concentration of coexistent ions is within an allowed range, the addition of sodium phosphate as a deionizer can eliminate the interferences of the coexistent ions with the determination of the lithium content. If sodium chloride is used as a deionizer, a more accurate result can be obtained when the sodium content in the samples is near the sodium content in the standard solutions. In general, under suitable experimental conditions, sodium chloride can be used as the deionizer for the determination of lithium content in the oil field water.