5-Br-PADAP作为铋的指示剂的研究

The Investigation of 2-(5-Bromo-2-Pyridylazo) -5-Diethylami-nophenol (5-Br-PADAP) as Metallochromic Indicator for Bismuth

2-(5-溴-2-吡啶偶氮)-5-二乙氨基苯酚(简称5-Br-PADAP)作为光度显色剂已有报导,但尚未见有用作金属指示剂.我们初步试验发现5-Br-PADAP 作为铋的指示剂最好.在pH1至3,5-Br-PADAP 呈金黄色,与铋络合呈紫红色,用EDTA

2-(5-Bromo-2-Pyridylazo)-5-Diethylaminophenol (5-Br-PADAP) has been usedfor the photometric determination of Zn,Cu,Co (Ⅱ),Fe (Ⅱ),Mu (Ⅱ),Ti(Ⅳ),U(Ⅵ) and Ni,but the properties as a metallochromic indicator in complexome-tric titration have not been thoroughly investigated.Through the determinations of the absorption curves of Bi-5-Br-PADAP com-plex and its apparent stability constants at pH 1 to 2,it was found that thetransition point of the indicator complex is very close to the equivalence pointof the EDTA titration of bismuth.The end point is very sharp,with a colorchange from violet red to golden yellow.The end pointis even better than thatof xylenol orange and pyrocatechol violet.At pH 1 to 1.5 microquantities ofbismuth can be spectrophotometrically titrated as low as 5 μg in 30 mlsolution(?)