The fluorescence of a series of acidic solutions of quinine was each determined
ID: 913751 • Letter: T
Question
The fluorescence of a series of acidic solutions of quinine was each determined five times; the results are given below: Calculate the confidence limits for the concentration of a solution with a fluorescence intensity of 90 counts-s^-1. A solution of unknown quinine concentration gave a fluorescence signal of 155 counts-s^-1. A 5 mL aliquot of solution was pipetted into a 10 mL volumetric flask, which as then filled with the appropriate solvent to the mark. The fluorescence intensity of the diluted solution was measured to be 52 counts-s^-1. What is the concentration of quinine in the original sample? Still related to (b). Is the relationship between fluorescence intensity and quinine concentration linear at the concentration of the unknown? Justify your answer.Explanation / Answer
a) I dont know this one. I will try it. Please give some comment so if I get answer I can reply
b)
Conc (mg/ml)
0
10
20
30
40
50
Fluorescence intensity (counts/s)
4
22
44
60
75
104
3
20
46
63
81
109
4
21
45
60
79
107
5
22
44
63
78
101
4
21
44
63
77
105
Average
4
21.2
44.6
61.8
78
105.2
So if we plot average fluorescence intensity as a function of conc we get a straight line with relation
y (intensity) = 1.9817 * x (conc) + 2.9238
So in the conc range the relation is linear. Using the trend line relation
y = 1.9817 * x + 2.9238
52 = 1.9817 * x + 2.9238
So
X = 24.7647 mg/ml
5 ml quinine solution is diluted to 10 ml. So the original quinine conc is
= 24.7647 * 2
= 49.52939 mg/ml
c) Relationship between fluorescence intensity and quinione concentration of the unknown solution is not linear, as after diluting 5 ml solution to 10 ml the intensity should have reduced from 155 counts/s to half i.e. 77.5 counts/s, however the intensity of the diluted solution is 52 counts/s.
Conc (mg/ml)
0
10
20
30
40
50
Fluorescence intensity (counts/s)
4
22
44
60
75
104
3
20
46
63
81
109
4
21
45
60
79
107
5
22
44
63
78
101
4
21
44
63
77
105
Average
4
21.2
44.6
61.8
78
105.2