What would be an optimum wavelength for measuring the absorbance versus concentration of a series of FD&C Blue 1 dye solutions?

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1. What would be an optimum wavelength for measuring the absorbance versus concentration of a series of FD&C Blue 1 dye solutions? Explain your answer. Absorbance measurements are most accurate and sensitive in the range 0.2 - 1.0.

2.Using the information provided in Question 1; predict the absorbance of each solution A-H at the optimum wavelength. Refer to Equation 3 in the Background section. The value of ε is 130,000 M-1 cm-1 .


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Explanation & Answer

uM
1.6
2.3
3
3.7
4.4
5.1
5.8
6.5

Absorbance
0.208
0.299
0.39
0.481
0.572
0.663
0.754
0.845

1
0.9
0.8
0.7

Absorbance

Solution
A
B
C
D
E
F
G
H

0.6
0.5
0.4
0.3
0.2
0.1
0
0

1

2

Absorbance = 0,13 * Concentration

3

4

5

[FD&C blue 1 dye], uM

6

7

8


FD&C blue 1 (Figure 1) is a blue food azoic dye. As can be observed, the absorption spectrum (Figure 2)
presents two different peaks, the most intense at  = 628 nm and the least intense at  = 408 nm.

Figure 1. Chemical structure of the FD&C blue 1 dye

Figure 2. Absorption spectrum of the FD&C blue 1 dye
Even if we could theoretically use any of these for the determination of the concentration of FD&C blue 1 dye,
there are two main reasons for selecting the first peak:
-

On the first hand, absorption measurements are more selective at higher wa...


Anonymous
This is great! Exactly what I wanted.

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