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自提出以氟化物(包括钠、钾、铵盐)置换EDTA-铝(Ⅲ)络合物中EDTA后,使络合滴定测定铝的选择性大为改善。然而氟化物也能与钛(Ⅳ)、锡(Ⅳ,Ⅱ)EDTA络合物中的金属离子形成更稳定的络合物因而释放出EDTA干扰测定。文献[2]提出以六偏磷酸钠代替氟化物,仍不能消除钛(Ⅳ)、锡(Ⅳ,Ⅱ)干扰。近年来,曾采用苦杏仁酸作钛(Ⅳ)的掩蔽剂,取得良好效果,但锡(Ⅳ,Ⅱ)仍有干扰。消除锡干扰,通常采用氯化铵焙烧锡矿石或滴定前以溴氢酸挥发等方法除锡的繁琐手续。我们注意到铝、硅、锡的氟络合物不稳定常数的差别,提出利用不能置换CyDTA-锡络合物中的CyDTA的氟硅酸钠作为释放剂。试验表明,如采用EDTA作络合剂,
Since the replacement of EDTA in the complex of EDTA-aluminum (III) with fluoride (including sodium, potassium and ammonium salts), the selectivity of complexometric titration of aluminum has been greatly improved. However, fluoride also forms a more stable complex with the metal ions in the titanium (IV) and tin (IV, II) EDTA complexes, thereby releasing the EDTA interference assay. Literature [2] proposed to sodium hexametaphosphate instead of fluoride, still can not eliminate the titanium (Ⅳ), tin (Ⅳ, Ⅱ) interference. In recent years, mandelic acid has been used as masking agent for titanium (Ⅳ), and achieved good results, but tin (Ⅳ, Ⅱ) still has interference. Elimination of tin interference, usually using ammonium chloride roasting tin ore or titration before brominated hydrogen acid volatilization and other methods of tedious procedures. We note the difference in the instability constants of fluoro complexes of aluminum, silicon, and tin, and propose the use of sodium fluorosilicate that can not displace CyDTA in the CyDTA-tin complex as a releasing agent. Experiments show that, if using EDTA as complexing agent,