This standard specifies a method for the determination of sodium content in lithium by flame atomic absorption spectroscopy (AAS), suitable for the determination of sodium content in the range of 0.0005% to 2.0%. Absorbance measurement of sodium using an air-acetylene oxidation flame by dissolving the sample in a nitric acid medium at a wavelength of 589.6 nm (or 330.2 nm). The standard details the preparation of the required reagents, the calibration of the instrument and the operation steps to ensure the accuracy and reproducibility of the measurement, providing a normative basis for the detection of sodium content in lithium products.