Question

化学本科 仪器分析题目5： 用极谱分析法测定试液中的Pb离子,准确移取50mL试液2份,测得一份试液的极限扩散电流为32

Answer 1

5.极限扩散电流id = Kc; id/c 为常数.设溶液中铅的质量浓度为c mg/ml:

32.5/c = 67.0/(c+0.5*0.3/50)

c = 0.002826 mg/ml = 0.002826 g/L

6.死时间tM = 1.30min

A:校正保留时间tR'(A)= tR(A) - tM = 16.00 - 1.30 = 14.70min

B:校正保留时间tR'(B)= tR(B) - tM = 17.00 - 1.30 = 15.70min

（1）两组分的相对保留值 r(B,A)=tR'(B)/tR'(A) = 15.70/14.70 =1.068

(2)n(有效)=16*(tR'/W)^2; W为峰宽.H= L/n

A：n(有效,A)=16*(tR'/W)^2 = 16*(14.70/1.10)^2 = 2857.4

B:n(有效,B)=16*(tR'/W)^2 = 16*(15.70/1.20)^2 = 2738.8

色谱柱平均有效塔板数n=(2857.4+2738.8)/2 = 2798

色谱柱塔板高度 = 30/2798 = 0.0107 cm

（3）组分的分离度 R=2(tRB-tRA)/(WB+WA) = 2(17.00-16.00)/(1.20+1.10) =0.87;

（4）设达到完全分离时柱长为x cm:

30 :x = 0.87 :1

x= 30/0.87 = 34.5 cm