This part of the standard specifies the determination method of sulfate content in lithium carbonic acid, lithium hydroxide monohydrate and lithium chloride. It is suitable for the determination range of 0.0050% to 0.80% sulfate. The method is to treat the sample in muriatic acid medium, so that barium ions react with sulfate to form insoluble barium sulfate, and form a suspension within a certain time. Absorbance of barium sulfate suspension is determined by using spectrophotometer measurement at 420 nm wavelength. The reagents used include muriatic acid, ammonia water, glycerol, barium chloride solution and p-nitrophenol indicator, etc. The standard solution is used for calibrating and measurement to ensure the accuracy of the test.