该方法基于称量试样，在水中溶解，加入草酸铵溶液、磷酸氢二铵溶液和氢氧化铵溶液，静置至少8小时，通过滤纸过滤出沉淀物，将带有沉淀物的滤纸转移到准备好的坩埚中，在气体燃烧器上燃烧，在熔炉中焚烧残渣，在干燥器中冷却，然后重新称重。

The method is based on weighing a test portion, dissolution in water, addition of ammonium oxalate solution, diammonium hydrogen phosphate solution and ammonium hydroxide solution, allowing to stand for at least 8 h, filtering out the precipitate through filter paper, transfer of the filter paper with precipitate to a prepared crucible, burning it over a gas burner, incineration of the residue in a furnace, cooling in a desiccator, and reweighing.