Table of Contents
Operating parameters and Caffeine Stock, Substock, and External Standard Solutions 1
Regression Method 4
Single Point Approach 7
Summary of Results and Unknown Identification 11
Qualitative UV Spectrum 13
Discussion 14
References – 16
Table of figures
Figure 1 Representing the preparation of external calibration standard solutions from caffeine stock solution 3
Figure 2- Representing the dilution scheme of unknown power drink sample 4
Figure 3 Chemical structure of Caffeine(2) 13
DETERMINATION OF CAFFEINE IN SPORTS DRINKS USING UV SPECTROPHOTOMETERY
Operating parameters and Caffeine Stock, Substock, and External Standard Solutions.
1. UV spectrometer instrumental settings is shown below-
Instrument
Cary 300
Instrument version no.
9.00
Wavelength (nm)
273.01
Ordinate mode
Abs
SBW (nm)
1.5
Ave time (sec)
0.100
Beam mode
Double auto select
Beam interchange
Normal
Replicates
1
Standard / Sample averaging
Off
Weight and Volume corrections
Off
Fit type
Linear
Min R2
0.95000
Concentration units mg/L 2. Unknown ED # 53
Mass of pure Caffeine = 0.02121g 0.00001g
Size of volumetric flask = 200.0ml 0.1ml
Actual concentration of caffeine stock solution (in ppm) = = 106.05mg/L 106.1mg/L
3. Actual concentration of Caffeine for each external calibration standard solution,
For standard # 5,
Using the equation C1V1 = C2V2
Where C1 = actual concentration of caffeine stock solution C2 = actual concentration of standard solution 5 V1 = volume of stock solution pipette to standard solution 5 V2 = volume of flask containing standard solution 5
So, C2 = C2 = 19.089 19.09mg/L
Table 1 – Showing the concentration in ppm and corresponding absorbance value of each external calibration standard solution.
Standard #
Volume pipette (in ml)
Actual concentration (in ppm)
Absorbance value
1.
0.500
2.121
0.0601
2.
1.500
6.363
0.3172
3.
2.500
10.61
0.4760
4.
3.500
14.85
0.6917
5.
4.500
19.09
0.9029
Sample #
Volume pipette from unknown (in ml)
Wavelength (in nm)
Absorbance value
1.
0.500
273.01
0.4656
2.
0.500
273.01
0.4688
3.
0.500
273.01
0.4703
4. Diagram representing the procedure involved in the preparation of caffeine stock solution and external calibration standard solutions. Weight of pure Caffeine = 0.02121g 0.00001g
Figure 1 Representing the preparation of external calibration standard solutions from caffeine stock solution
5. Diagram representing the preparation of unknown powder drink sample
Figure 2- Representing the dilution scheme of unknown power drink sample
Regression Method
6. From linear regression output obtained from the UV spectrophotometer,
The line of equation, Abs = 0.04856 C – 0.02541
And correlation coefficient = 0.99615
7. Caffeine concentration in the diluted unknown sample for each replicate using the regression equation,
In unknown sample # 1,
Absorbance = 0.4656
Line of equation, Abs = 0.04856 C – 0.02541
Putting value of absorbance in line of equation,
0.4656 = 0.04856 C – 0.02541 C = 10.1114 10.11ppm
Similarly for the other two unknown sample as shown in the table below-
Table 2-Showing the calculated results for each diluted replicate of unknown sample.
Unknown replicate sample #
Absorbance
Actual concentration of caffeine in diluted unk. Sample (in ppm)
Mass of caffeine in original 710ml bottle in each replicate sample (in mg)
1.
0.4656
10.11
359.0
2.
0.4688
10.18
361.3
3.
0.4703
