Lab 6 Fluorescence Determination of Quinine CHM3120L November 4 2021 Introduction Quinine is a widely used compound in flavoring substances such as tonic water It is found in the bark of the cinchona tree and was originally developed as a medicine to fight against malaria The structure of quinine includes phosphors which gives it the ability to re emit absorbed energy as fluorescent light For this reason the concentrations of quinine in tonic water and in Cinchona bark can be determined utilizing fluorescence spectroscopy 1 In order to measure quinine concentrations one can utilize its unique physical property of molecular fluorescence which is the emission of light by molecules upon excitation with a light of shorter wavelength or high energy The molecule that absorbs energy is originally in the ground state then gets excitation by the absorption of radiation and then goes to the ground state again The radiation emitted from this change in states appears at a long wavelength in the observed fluorescence These measurements are highly selective meaning that it is very specific to the molecule which results in minimal interference from other molecules present in the solution Along with this fluorescence is a very sensitive method suggesting that it can measure very low concentrations of a substance Compared to absorption measurements fluorescence detects smaller changes because it measures light intensity against a dark background rather than a high background on absorption 2 The method of standard addition is utilized by adding small known amounts to the sample being analyzed The emission spectrum is recorded to find the intensity after each addition By adding small known concentrations of quinine in several samples of known concentrations of a stock solution of quinine sulfate a plot of fluorescent intensity against amount of quinine in the standard addition can be created in order to determine the unknown concentration at a specific fluorescence emission This method is used in this experiment in order to determine the concentration of quinine in various tonic water samples and in a sample of quinine extracted from cinchona bark Experimental Part1 100 L of 1 0 M sulfuric acid 1 00 mL of tonic water 1 Canada Dry and 1 00 mL of DI water were added and mixed in a clean cuvette using a micropipette The cuvette was placed into the fluorescence spectrometer and 5 readings of the background intensity were recorded at a wavelength of 771 281 nm The mean and standard deviation of these 5 values was calculated Then the cuvette was spiked with eight 50 L spikes of a 0 4 mM quinine sulfate stock solution The intensity was recorded 5 times at 440 nm for the solution along with each spike and the average and standard deviation were calculated for each spike of quinine sulfate These values were inserted into a standard addition plot with a linear regression line in order to calculate the intersection at the abscissa The same procedure was repeated for Tonic Water samples 2 3 and 4 Schweppes Publix and Seagram respectively The only different step for these samples was recording the net intensity as it was done at different wavelengths These values were recorded at 718 036 nm for Tonic 2 800 297 nm for Tonic 3 and 694 517 nm for Tonic 4 Part 2 0 2006 g of powdered Cinchona bark was precisely weighed and added to 100 mL of water which was set to gently boil for 30 minutes Then this solution was left to sit for a bout 15 minutes to cool down and allow the solids to settle onto the bottom A 1 mL aliquot of this solution along with 100 L of 1 0 M sulfuric acid and 1 00 mL of DI water were added and mixed in a clean cuvette using a micropipette The cuvette was placed in a fluorescence spectrometer and the background was recorded at 726 67 nm Then the intensity of the sample was recorded 5 times along with the intensity after eight 50 L spikes of quinine sulfate solution was added at 440 nm The spectrometer was set at 10 scans to average 5 msec data upate rate and an integration time of 100 ms The mean and standard deviation were calculated and the intensity and concentrations of quinine were plotted in a graph The concentration of quinine was found using the linear regression equation and then converted to wight percent Results Part 1 M quinine added mean stdev 0 1 86E 05 3 64E 05 5 33E 05 6 96E 05 8 51E 05 0 0001 0 00011 0 00013 2552 58 2552 08 2562 75 2564 05 2563 79 2559 05 2960 13 3049 21 3150 26 3226 38 2858 73 2323 54 2979 53 3066 52 3129 16 3238 39 2894 71 2357 12 2985 7 3053 44 3133 48 3230 96 2908 1 2344 45 2974 75 3052 01 3131 55 3222 51 2897 74 2353 1 2975 24 3070 74 3153 47 3227 16 2900 22 2355 6 2346 762 2975 07 3058 38 3139 58 3229 08 2891 9 13 876016 6 15628541 8 05282124 19 1957873 9 43694071 9 59295 11 3717 6 00732 1985 43 1984 02 1985 95 1987 59 1985 89 1985 78 1 27839 Table 1 Measurement of mean and standard deviation for the net intensity readings for Tonic 1 Canada Dry sample 2770 89 2754 8 2762 83 2752 2752 9 2758 684 Figure 1 Standard Addition plot of quinine concentration in molarity vs intensity in Tonic 1 Canada Dry Table 2 Measurement of mean and standard deviation for the net intensity readings for Tonic 2 Schweppes sample 0 50 100 150 200 250 300 350 400 0 1 86E 05 3 64E 05 5 33E 05 6 96E 05 8 51E 05 0 0001 0 00011 0 00013 2144 56 2536 66 2147 06 2530 57 2152 25 2535 69 2139 91 2527 45 2147 4 2527 47 3063 558 2146 24 4 50081 4 40644074 3 76011303 6 68174902 6 77533911 12 3382868 2841 02 2843 67 2847 79 2850 6 2833 31 3084 22 3056 62 3055 12 3065 85 3055 98 2470 8 2463 85 2461 77 2461 7 2465 73 3021 08 3005 22 3008 22 3018 3016 67 2843 278 3013 838 2531 568 2464 77 3157 67 3272 2 3286 75 3158 99 3280 89 3286 17 3163 09 3282 58 3272 04 3151 22 3272 47 3286 89 3158 01 3262 53 3275 34 3157 8 3274 13 3281 44 4 2649 8 03338 7 17359 L of quinine added M quinine added Mean stdev Figure 2 Standard Addition plot of quinine concentration in molarity vs intensity in Tonic 2 Schweppes Table 3 Measurement of mean and standard deviation for the net intensity readings of Tonic 3 Publix 0 00 50 00 100 00 150 00 200 00 250 00 300 00 350 00 400 00 0 1 86047E 05 3 64E 05 5 33E 05 6 96E 05 8 51E 05 0 0001 0 000114 0 000128 1654 34 1691 82 1657 94 1701 3 1657 15 1672 51 22 24918 2153 89 2161 …