问题 问答题

简述用双波长光度法测定干扰严重两混合物的原理。

答案

参考答案:设有A、B两组分,其中A为待测组分,B为干扰组分,为了消除干扰组分的吸收。一般采用作图法以确定干扰组分的等吸收波长。规定测定波长为λ2;参比波长为λ1。应当遵循的原则是:使干扰组分在λ1处的吸光度等于它在λ2处的吸光度;使待测组分在λ1处的吸光度与它在λ2处的吸光度差值比较大。在选择波长时,一般以持测组分的最大吸收波长为测定波长λ2
根据吸光度的加和原则,混合物在λ1和λ2处的吸光度分别为
Aλ1=Aλ1(A) +Aλ1(B)
Aλ2=Aλ2(A) +Aλ2(B)
双波长分光光度法的测量值为;
△A=Aλ2-Aλ1
也就是:△A=Aλ2 (A) +Aλ2(B)-(Aλ1(A)+Aλ1(B))
由于Aλ1(B)=Aλ2(B)
所以△A=Aλ2 (A) -Aλ1A)=(ελ2(A)λ1 (A) )*b*C
可见双波长分光光度法的测量信号与干扰组分无关,与待测组分浓度成正比。

单项选择题

Low levels of literacy and numeracy have a damaging impact on almost every aspect of adults, according to a survey published yesterday, which offers (1) of a developing underclass. Tests and (2) with hundreds of people born in a week in 1958 graphically illustrated the (3) of educational underachievement. The effects can be seen in unemployment, family (4) , low incomes, depression and social inactivity.

Those who left school at 16 with poor basic skills had been employed for up to four years less than good readers (5) they reached 37. Professor John Bynner, of City University, who carried the research, said that today’s (6) teenagers would even encounter greater problems because the supply of (7) jobs had shrunk.

Almost one fifth of the 1,700 people interviewed for yesterday’s report had poor literacy and almost half (8) with innumeracy, a proportion (9) other surveys for the Basic Skills Agency. Some could not read a child’s book, and most found difficult (10) written instruction.

Poor readers were twice as likely to be a low wage and four times likely to live in a household where partners worked. Women in this (11) were five times as likely to be (12) depressed, (13) both tended to feel they had no control over their lives, and to trust others (14) .

Those who had low literacy and numeracy were seldom (15) in any community organization and less likely than others to (16) in a general election. There had been no (17) in the literary level of (18) reporting problems.

Alan Wells, the agency’s director, said: “ The results emphasize the dangers of developing an underclass people, who were out of work, (19) depressed and often labeled themselves as (20) . There is a circle of marginalization, with the dice against these people and their families.”

14()

A.more

B.much

C.less

D.little

问答题 简答题