为了解决湿法磷酸生产中高含量SO₃的测定，对硫酸钡浊度测定法的反应条件进行了改进，并自行设计制造了自动化的分析系统。测定时样品由蠕动泵（P）推入酸化盘管（AC）中进行酸化和稀释，由定量环（Sv）取样25 μL，注入反应系统。在第一反应盘管（RC₁）中，SO₃与第一混合试剂中的BaCl₂溶液反应生成BaSO₄悬浊液，该溶液中的聚乙二醇-4000（PEG-4000）和乙醇通过协同作用避免了BaSO₄颗粒的团聚，降低粒子间的相互作用，使BaSO₄的生成减少，降低了测定的灵敏度，提高了稳定性。在第二反应盘管（RC₂）中，BaSO₄与第二混合试剂中的NH₃·H₂O/乙二胺四乙酸二钠（Na₂EDTA）溶液发生络合反应同时被Na₂EDTA包裹，进一步降低其灵敏度。最后反应溶液进入流通式光度检测器，在680.0 nm波长处测试BaSO₄悬浊液的吸光度。经优化试验条件，上述第一混合试剂中3种组分的质量分数或体积分数为：BaCl₂ 4%，PEG-4000 3%和乙醇2%；第二混合试剂中Na₂EDTA的质量分数为6%，NH₃·H₂O的体积分数为6%。对实际按本方法及重量法分析进行测定，两种方法所得结果的相对偏差在±2%以内，且不受共存的高含量PO₄^3-和F^-的干扰。

For determination of SO₃ in high content in production of phosphoric acid by wet process, a self-designed automatic analyzer system was fabricated and modification of reaction condition for turbidimetric determination of BaSO₄ suspension was made. In the determination by the automatic analyzer, the sample was pumped into the AC coil where the sample was acidified and diluted. 25 μL of the sample was taken by a volumetric vessel and injected into the reaction system of RC₁ and RC₂. In reaction coil RC₁, SO₃ in the sample was reacted with BaCl₂ in mixed reagents solution Ⅰ to form BaSO₄ suspension; and through co-reaction of 2 other reagents in the mixed reagents solution Ⅰ, i.e. PEG-4000 and ethanol, coagulation of BaSO₄ particles was avoided and interaction among particles were reduced, leading to less formation of BaSO₄ and lowering the sensitivity of determination and raising of stability. The reaction mixture was then passed through the reaction coil RC₂ where complexation reaction was occured between the BaSO₄ and Na₂EDTA present in mixed reagent solution Ⅱ, and BaSO₄ was simultaneously wrapped up by Na₂EDTA, thus leading to further lowering of sensitivity. Finally, the reaction solution was passed to the flowing cell of the spectrophotometer, and the absorbance of the BaSO₄ suspension was measured at the wavelength of 680.0 nm. By the optimizing test, the mass fraction or volumic fraction of the reagents found were as follows:in mixed reagent solution Ⅰ, BaCl₂ 4%, PEG-4000 3% and ethanol 2%; in mixed reagents solution Ⅱ, Na₂EDTA 6%, aq. ammonia 6%. Five substantial samples were analyzed by the proposed method and checked by the gravimetric method, the results obtained by the 2 methods were checked quite well, giving relative deviations within ±2%. Interferences of macro amounts of coexisting PO₄^3- and F^- were eliminated by controlling the acidity at pH 2.