A Solphadine tablet was analysed by HPLC in order to determine the quantity of c
ID: 871093 • Letter: A
Question
A Solphadine tablet was analysed by HPLC in order to determine the quantity of caffeine. One tablet (0.3478g) was dissolved in water and made up to 200 mL. Caffeine standards were prepared from a stock solution of 100mg/ 100mL of caffeine. 10, 20, 30, 40, and 50 mL aliquots were taken and made up to a final volume of 100 mL in water. The standards and tablet sample were injected into the HPLC using a 20?L injection loop. The separation was achieved using a 15cm 4.6mm id ODS stationary phase with 60:40 H2O:CH3OH as the mobile phase. Detection was by uv absorption at 265nm. .
Table 1 gives the peak areas obtained for each solution
Caffeine
Conc (mg/100mL)
Std1
Std2
Std3
Std4
Std5
tablet
Caffeine peak area
990
1900
2894
3818
4584
2742
Plot a suitable graph and determine the caffeine content of the tablets on in mg
Calculate the % caffeine in the tablet.
Caffeine
Conc (mg/100mL)
Std1
Std2
Std3
Std4
Std5
tablet
Caffeine peak area
990
1900
2894
3818
4584
2742
Explanation / Answer
Caffeine standards:
100mg/100mL x aliquot mL / 100mL = conc. in standard (see table)
Caffeine
Conc (mg/100mL)
Std1
10
Std2
20
Std3
30
Std4
40
Std5
50
tablet
Caffeine peak area
990
1900
2894
3818
4584
2742
Calibration curve:
10
20
30
40
50
990
1900
2894
3818
4584
slope =
91.06
intercept=
105.4
Area = 91.06c +105.4
Tablet sample concentration:
2742 = 91.06c +105.4
C = (2742-105.4)/91.06 = 28.93 mg/100mL
Mass of caffeine = 28.93 mg/100mL x 200mL = 57.86 mg
Contration in tablet C= 100 x 57.86 mg/ 347.8mg = 16.63 %
Caffeine
Conc (mg/100mL)
Std1
10
Std2
20
Std3
30
Std4
40
Std5
50
tablet
Caffeine peak area
990
1900
2894
3818
4584
2742
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