# Solutions mgl absorbance at max 1 absorbance at max 2

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Solutions mg/L Absorbance at max, 1 Absorbance at max, 2 C1 3.186 0.08417 0.1232 C2 7.434 0.1850 0.3626 C3 10.62 0.2603 0.5128 Sample calculation, mg/L Benzoic acid: C-1: 150 L μ ( 1 × 10 6 L 1 μL ) ( 0.2124 g 1 L )( 1000 mg 1 g )( 1 0.010 L ) = 3.186 mg L
Figure 3. Plot of Caffeine concentration versus absorbances at max, 1 and max, 2 to determine the calibration curves based on Table 2 data. 10 15 20 25 30 35 40 0 0.1 0.2 0.3 0.4 0.5 0.6 f(x) = 0.02 x − 0.13 R² = 1 f(x) = 0.01 x − 0.03 R² = 1 Linear () Linear () mg/L Absorbance Figure 4. Spectra of solutions U1 and U2 (unknowns) prepared from the soft drink and the standards.
210 220 230 240 250 260 270 280 290 300 310 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 U2 U1 Wavelength (nm) Absorbance Table 3. Raw data for the simultaneous equation solution. Absorbances of U1 and U2 are read from Figure 4 at the specified wavelengths max, 1 , and max, 2 . Slopes are given in previous figures (calculated by Excel). at max, 1 at max, 2 Benzoic acid slopes 0.1004 0.0056 Caffeine slopes 0.0244 0.0484 Absorbance of U1 0.579736 0.331849 Absorbance of U2 0.802348 0.326103 Simultaneous equation sample calculation for U1: (0.1004x + 0.0244y = 0.5797)x(0.0484) (0.0056x + 0.0484y = 0.3318)x(-0.0244) 4.86 × 10 -3 x + 1.18 × 10 -3 y = 0.0281 -1.37 ×10 -4 x – 1.18 × 10 -3 y = -0.00810 0.00472x + 0y = 0.0200 x = 0.0200 0.00472 = 4.24
5.56×10 -3 (4.24) + 0.0484y = 0.331849 y = 6.37 Table 4. Results of Benzoic acid and Caffeine obtained from the simultaneous equation method after using the correct dilution factors . Benzoic acid Caffeine U1: mg/L drink solution 206.5 316.5 U2: mg/L Found 128.6 238.0 U2: mg/L Expected 129.4 212.4 % Recovery of U2 99.38% 112.05% Sample calculation for Benzoic acid in drink solution: 4.13 mg L Benzoic Acid
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