硫酸盐的测定都需转化成BaSO₄的形式来测定，而硫酸钡比铬酸钡沉淀稳定，因此，在含有硫酸盐的试液中加入铬酸钡，则硫酸盐可定量取代出铬酸根，生成更稳定的硫酸钡，由光度法定量测出铬酸根的量，便可计算出硫酸根的量。

The determination of sulphate is always by means of converting the sulphate into BaSO₄.The barium sulphate is more stable than barium chromate.So when we add barium chromate to the sulphate solution,the chromate can be replaced by sulphate,forming barium sulphate,which is more stable,the quantity of the chromate that is determined by spectropho tometry can be used to calculate the quantity of the sulphate.