NAMESEGOKGO STUDENT NUMBER GROUP/DAY : LORRAINE KESEGO : 201002660 : TUESDAY WEEK : THIRD DATE : 12/MARCH/2013 TITLE: THE SIMULTANEOUS DETERMINATION OF CAFFEINE AND ACETYLSALICYLIC ACID IN AN ANALGESIC BY ULTRAVIOLET SPECTROPHOTOMETRY a 300-∝m solarization resistant optical fiber. UV-vis Spectrophotometer Systems utilize the optical bench of Ocean Optic’s second-generation miniature fiber optic spectrometer. a miniature deuterium tungsten light source with integrated cuvette holder. where a is a proportionality constant called absorptivity and b is the path length of the light beam through the absorbing medium. concentration) with standard solutions. with the units of L cm-1 mol-1. Absorption spectrometry involves measuring the fraction of light of a given wavelength that passes through a sample. The light transmitted through the sample is . When a monochromatic light beam passes through a layer of solution with a thickness. Thus. When an atom or molecule absorbs energy. the power of the beam is attenuated from Po to P. When the c is expressed in M (moles per liter). The absorbance A of a solution is defined by the equation: A = log (P / Po) = abc. The light source supplies light to the sample. as the consequence of interactions between the photons and absorbing particles. by mounting it onto an A/D converter and turning the system into a PC plug-in spectrometer. Many molecules absorb ultraviolet or visible light. and b in cm. You will first determine the molar absorptivity ε of each component by constructing a calibration curve (absorbance vs. The UV-vis consists of four basic elements: the PC2000 UV-vis PC Plug-in Fiber Optic Spectrometer (200-850 nm). Then by measuring absorbance of the tablet solution at maximum absorption wavelength of both components. and OOIChem operating software. you will determine the amount of caffeine and acetylsalicylic acid in an analgesic tablet by UV spectrophotometry.AIM To figure out the amount concentration of caffeine and acetylsalicylic acid in an analgesic tablet by ultraviolet spectrophotometry. A = εbc In this experiment. electrons are promoted from their ground state to an excited state. absorptivity and concentration of an absorbing species. This is Beer’s law. you will be able to figure out the amount of each component in the tablet. there are two components caffeine and acetylsalicylic acid) in the analgesic tablet. a is called the molar absorptivity and is given the special symbol ε. the S2000. INTRODUCTION In this experiment. the software performs basic acquisition and display functions on your data. Finally. The A/D converter.collected and sent to the spectrometer via the fiber. The spectrometer measures the amount of light at each wavelength in the sampled spectrum. PRELABORATORY ASSIGNMENT . on which the spectrometer is mounted. transforms the analog data from the spectrometer into digital information that is passed to a computer. 0. The UV-Vis spectrophotometer was the adjusted by setting the initial wavelength as 220nm and final as 320nm.35.0-ml of the sample solution was added to each 50-ml volumetric flasks then filled to the mark by methanol. The two curvets were used and the other had methanol and another was used to measure the blank. 0.117g of caffeine and 0. The same procedure was also followed to prepare five standards of acetylsalicylic and the volumetric flasks were labeled. 1.25.EXPERIMENTAL SECTION APPARATUS REAGENTS 2* 1-cm curvets 1-ml pipette 2-ml pipette Scanning UV-Vis spectrophotometer 14* 50ml volumetric flasks 3* 250ml volumetric flasks Methanol Caffeine Acetylsalicylic acid Analgesic tablet a) REAGENT AND APPARATUS b) PROCEDURE 0. . The baseline absorbance was set to zero and the other curvets were used to measure different standards of caffeine and acetylsalicylic acid and also the sample. 0.55 and 0.12g of acetylsalicylic were weighed and dissolved into methanol. 0. five different standards of 0. From the caffeine solution. The pipettes were used to deliver 0. The solution was then transferred into a 100-ml volumetric flask then filled to the mark by methanol.35-ml of caffeine and acetylsalicylic acid in a 50-ml volumetric flask filled to the mark by methanol. The solutions were then transferred into labeled 250-ml volumetric flasks then filled to the mark with methanol.25-ml and 0.45.65 ml were prepared in labeled 50-ml volumetric flasks and they were filled to the mark by methanol.045g of analgesic tablet was weighed and dissolved with methanol. 686 0.68 0.1174g/194.584 MIXTUR 0.002481M Concentration of Caffeine= 2.15 g.646 0.0006046moles [Caffeine]= 0.587 -0.151 .002751M Concentration of acetylsalicylic acid = 2.17g/mol Moles of Caffeine= 0.7*10-5 M of caffeine The table for the % absorbance against concentration of acetylsalicylic acid which was 225nm ACETYSALICYLIC ACID CONC × 10-5 ABS FACTOR CORRECTE D STD1 1. mass of Caffeine measured= 0.16 0.15g/mol Moles of Caffeine= 0.164 STD4 2.159 STD3 2. [Acetylsalicylic acid] = (2.522 0.64 0.502*10-4 M The table for the % absorbance against concentration of caffeine which was 270nm CAFFEINE -5 CONC × 10 ABS FACTOR CORRECTE D STD1 1.663 E The graph shows that the sample had 0.mol-1 = 0.522 0.1239g/180.738 3.418*10-3 M For the standards.418*10-3 M*50ml)/250ml = 4.19g.RESULTS AND ANALYSIS OF DATA From the stock solution.522 0.mol-1 = 0.12 0.587 0.522 SAMPLE 0.0006878moles/250*10-3L = 0.239 STD5 3. mass of acetylsalicylic acid measured is 0.43 3.0006046moles/250*10-3L = 0.1239g & molar mass is 180.0006878moles [Acetylsalicylic acid]= 0.419 3.836*10-4 M From the stock solution.327 STD2 1.89 3.522 0.914 3.282 BLANK 0 0.35 3. [caffeine] = (2.168 STD3 2.124 STD2 1.804 0.681 0.522 0.1174g & molar mass is 194.751*10-3 M For the standards.751*10-3 M*50ml)/250ml = 5.761 0.25 0.587 0. 6 0.04*10-5 M of acetylsalicylic GRAPHS.9 0.587 3.437 3.53 R² = 0.4 0.1 0 0 0. a) THE GRAPH OF ABSORBANCE AGAINST CONCENTRATION OF CAFFEINE TO DETERMINE THE CONCENTRATION OF THE SAMPLE 0.914 3.97 3.5 1 1.09x + 0.5 %Absorbance 0.738 3.587 3.8 f(x) = 0. 2.5 .51 0 3.98 0.587 0.7 0.5 3 3.587 3.5 2 Concentration/ 10-5 M b) 2.151 0.STD4 STD5 BLANK SAMPLE MIXTUR E The graph acid.2 0.327 shows that the sample had around 0.3 0. . some of the solution was lost through a pipette making the solution to be less than the required amount and also during the dilution of both the stock solutions and the standards especially for acetylsalicylic acid because the solvent which is methanol was poured beyond the mark. CONCLUSION The analgesic tablet had 0.7*10-5 M of caffeine at the wavelength of 270nm and 0.THE GRAPH OF % ABSORBANCE AGAINST CONCENTRATION OF ACETYSALICYLIC ACID TO DETERMINE THE CONCENTRATION OF SAMPLE 4 3.59 3.1673 which far from 1.9 3.9777 which is close to 1 whereas the values for acetylsalicylic acid were not at all précised because the r-squared value was 0.06x + 3.5 1 1.1 0 0.5 3. The values obtained for concentration and % absorbance of caffeine seem to be précised because of the r-squared value which was 0.004*10-5 M of acetylsalicylic acid at the wavelength of 225nm.7*10-5 M of caffeine at the wavelength of 270nm and 0.5 2 2. This might have been caused by random error because when making standard solutions.004*10-5 M of acetylsalicylic acid at the wavelength of 225nm.6 % Absorbance 3.17 3.7 R² = 0.5 3 3.2 3.4 3.3 3.5 4 Concentration/10-5 M DISCUSSION The results obtained shows that there is 0.8 f(x) = 0. 108 (1968) 568-571. Turkish J. Quantitative analysis of pharmaceutical preparations containing analgesic and antipyretic agents. 2. Simultaneous determination of active ingredients in binary mixtures containing caffeine using liquid chromatographic and spectrophotometric methods.. .REFERENCES 1. 2 (2004)115-138. Pfandl A..
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