NAME SEGOKGO
STUDENT NUMBER
GROUP/DA GROUP/ DAY Y
: LORRAINE KESEGO
: 201002660
: TUESDAY TUESDAY
WEEK
: THIRD
DATE DATE
: 12/MARCH/2013 12/MARCH /2013
TITLE: THE SIMULTANEOUS DETERMINATION OF CAFFEINE AND ACETYLSALICYLIC ACID IN AN ANALGESIC BY ULTRAVIOLET SPECTROPHOTOMETRY
AIM To fgure out the amount concentration o caeine and acetylsalicylic acid in an analgesic tablet by ultraviolet spectrophotometry. INTRODUCTION In this experiment, you will determine the amount o caeine and acetylsalicylic acid in an analgesic tablet by UV spectrophotometry. any molecules absorb ultraviolet or visible light. !hen an atom or molecule absorbs energy, electrons are promoted rom their ground state to an excited state. "bsorption spectrometry involves measuring the raction o light o a given wavelength that passes through a sample. !hen a monochromatic light beam passes through a layer o solution with a thic#ness, absorptivity and concentration o an absorbing species, as the conse$uence o interactions between the photons and absorbing particles, the power o the beam is attenuated rom %o to %. The absorbance " o a solution is defned by the e$uation& A = !" #P / P!$ = %&'(
This is B))*+, %-, where % is a proportionality constant called absorptivity and & is the path length o the light beam through the absorbing medium. !hen the ' is expressed in 'moles per liter(, and b in cm, % is called the molar absorptivity and is given the special symbol ., with the units o ) cm*+ mol*+. Thus, A = .&'
In this experiment, there are two components caeine and acetylsalicylic acid( in the analgesic tablet. ou will irst determine the molar absorptivity o each component by constructing a calibration curve 'absorbance vs. concentration( with standard solutions. Then by measuring absorbance o the tablet solution at maximum absorption wavelength o both components, you will be able to fgure out the amount o each component in the tablet. UV*vis pectrophotometer ystems utili/e the optical bench o 0cean 0ptic1s second*generation miniature fber optic spectrometer, the 2333, by mounting it onto an "45 converter and turning the system into a %6 plug*in spectrometer. The UV*vis consists o our basic elements& the %62333 UV*vis %6 %lug*in 7iber 0ptic pectrometer '233*893 nm(, a miniature deuterium tungsten light source with integrated cuvette holder, a :33*;m solari/ation resistant optical fber, and 00I6hem operating sotware. The light source supplies light to the sample. The light transmitted through the sample is
collected and sent to the spectrometer via the fber. The spectrometer measures the amount o light at each wavelength in the sampled spectrum. The "45 converter, on which the spectrometer is mounted, transorms the analog data rom the spectrometer into digital inormation that is passed to a computer. 7inally, the sotware perorms basic ac$uisition and display unctions on your data. PRELABORATORY ASSIGNMENT
EPERIMENTAL SECTION APPARATUS
REAGENTS
2< +*cm curvets +*ml pipette 2*ml pipette canning UV*Vis spectrophotometer +=< 93ml volumetric >as#s :< 293ml volumetric >as#s
ethanol 6aeine "cetylsalicylic acid "nalgesic tablet
%$ REAGENT AND APPARATUS
&$ PROCEDURE
3.++?g o caeine and 3.+2g o acetylsalicylic were weighed and dissolved into methanol. The solutions were then transerred into labeled 293*ml volumetric >as#s then flled to the mar# with methanol. 7rom the caeine solution, fve dierent standards o 3.29, 3.:9, 3.=9, 3.99 and 3.@9 ml were prepared in labeled 93*ml volumetric >as#s and they were flled to the mar# by methanol. The same procedure was also ollowed to prepare fve standards o acetylsalicylic and the volumetric >as#s were labeled. The pipettes were used to deliver 3.29*ml and 3.:9*ml o caeine and acetylsalicylic acid in a 93*ml volumetric >as# flled to the mar# by methanol. 3.3=9g o analgesic tablet was weighed and dissolved with methanol. The solution was then transerred into a +33*ml volumetric >as# then flled to the mar# by methanol. +.3*ml o the sample solution was added to each 93*ml volumetric >as#s then flled to the mar# by methanol. The UV*Vis spectrophotometer was the adAusted by setting the initial wavelength as 223nm and fnal as :23nm. The two curvets were used and the other had methanol and another was used to measure the blan#. The baseline absorbance was set to /ero and the other curvets were used to measure dierent standards o caeine and acetylsalicylic acid and also the sample.
RESULTS AND ANALYSIS OF DATA 7rom the stoc# solutionB mass o 6aeine measuredC 3.++?=g D molar mass is +E=.+?g4mol oles o 6aeineC 3.++?=g4+E=.+Eg.mol *+ C 3.333@3=@moles F6aeineGC 3.333@3=@moles4293<+3 *:) C 3.332=8+ 6oncentration o 6aeineC 2110 43 M 7or the standardsB FcaeineG C '2.=+8<+3*: <93ml(4293ml C 36104 M 7rom the stoc# solutionB mass o acetylsalicylic acid measured is 3.+2:Eg D molar mass is +83.+9g4mol oles o 6aeineC 3.+2:Eg4+83.+9 g.mol *+ C 3.333@8?8moles F"cetylsalicylic acidGC 3.333@8?8moles4293<+3 *:) C 3.332?9+ 6oncentration o acetylsalicylic acid C 25110 43 M 7or the standardsB F"cetylsalicylic acidG C '2.?9+<+3*: <93ml(4293ml C 0210 4 M The table for the % absorbance against concentration of caeine which was 270nm CAFFEINE 4 CONC 7 10 ABS FACTOR CORRECTE D T5+ +.29 3.@=@ 3.922 3.+2= T52 +.@8 3.@8+ 3.922 3.+9E T5: 2.+@ 3.@8@ 3.922 3.+@= T5= 2.@= 3.?@+ 3.922 3.2:E T59 :.+2 3.83= 3.922 3.282 BLANK 022 3 SAMPLE 0 MITUR 0663 E The graph shows that the sample had 05104 M o caeine The table for the % absorbance against concentration of acetylsalicylic acid which was 225nm ACETYSALICYLIC ACID CONC 7 104 ABS FACTOR CORRECTE D T5+ +.:9 :.E+= :.98? 3.:2? T52 +.8E :.=+E :.98? *3.+@8 T5: 2.=: :.?:8 :.98? 3.+9+
T5= 2.E? :.?:8 :.98? 3.+9+ T59 :.9+ :.E+= :.98? 3.:2? BLANK 35 3 SAMPLE 35 MITUR 335 E The graph shows that the sample had around 00104 M o acetylsalicylic acid.
H"%JB a(
THE GRAPH OF ABSORBANCE AGAINST CONCENTRATION OF CAFFEINE TO DETERMINE THE CONCENTRATION OF THE SAMPLE 3.E 3.8 f'x( C 3.3Ex K 3.9: IL C 3.E8
3.? 3.@ 3.9 ;A&,!*&%8') 3.=
3.: 3.2 3.+ 3 3
3.9
+
+.9
2
C!8')89*%9:!8/ 1046 M
b(
2.9
:
:.9
THE GRAPH OF ; ABSORBANCE AGAINST CONCENTRATION OF ACETYSALICYLIC ACID TO DETERMINE THE CONCENTRATION OF SAMPLE = :.E :.8
f'x( C 3.3@x K :.9E :.? IL C 3.+? :.@ ; A&,!*&%8') :.9
:.= :.: :.2 :.+ 3
3.9
+
+.9
2
2.9
:
:.9
=
C!8')89*%9:!8/1046 M
DISCUSSION
The results obtained shows that there is 3.?<+3*9 o caeine at the wavelength o 2?3nm and 3.33=<+3*9 o acetylsalicylic acid at the wavelength o 229nm. The values obtained or concentration and M absorbance o caeine seem to be prNcised because o the r*s$uared value which was 3.E??? which is close to + whereas the values or acetylsalicylic acid were not at all prNcised because the r*s$uared value was 3.+@?: which ar rom +. This might have been caused by random error because when ma#ing standard solutions, some o the solution was lost through a pipette ma#ing the solution to be less than the re$uired amount and also during the dilution o both the stoc# solutions and the standards especially or acetylsalicylic acid because the solvent which is methanol was poured beyond the mar#.
CONCLUSION
The analgesic tablet had 3.?<+3*9 o caeine at the wavelength o 2?3nm and 3.33=<+3*9 o acetylsalicylic acid at the wavelength o 229nm.
REFERENCES
+. %andl "., Quantitative analysis of pharmaceutical preparations containing analgesic and antipyretic agents, +38 '+E@8( 9@8*9?+. 2. Tur#ish O., Simultaneous determination of active ingredients in binary mitures containing caeine using li!uid chromatographic and spectrophotometric methods" 2 '233=(++9*+:8.
