Molecular andAtomic SpectroscopyCH7020 M203 – Determinationof Aspirin and Caffeine in an Analgesic Preparation by NMRSpectrometry Date of lab work:18.01.
2018 Date of report: 31.01.2018 Joanna ToporowskaK1600416 DATA AND RESULTS Weight of empty flask – 9.1095gMass of s-trioxane – 0.0503 gMass of tablet – 0.4322 gMass of half tablet – 0.
2122 g RMM of aspirin – 180 g/molRMM of caffeine – 194 g/molRMM of s-trioxane – 90 g/mol = = Percentage of asp in tablet = Percentage of asp in tablet = Percentage of caffeine intablet = Percentage of caffeine in tablet = DISCUSSION1. Chemicalshift positions of the methyl groups in aspirin and caffeine. Fig.1.Structure of the aspirin. As it’s seen above,aspirin has one methyl group (Fig.
1 – blue circle) with three equivalenthydrogens that is attached to carbonyl group. As there are no hydrogens in theclose neighbourhood in the spectrum appears uncoupled singlet, at 2.3483. Expectedpeak should be at 2.1 ppm, but it’s slightly higher which could happen becauseof inductive deshielding from the oxygen side (ThermoFisher, 2017).
It can be alsoseen very broad peak at 11.0658 which correspond to hydrogen in carboxyl group(Fig.1. – purple circle), which shifts that singlet towards the left side. Usuallyheight of that signal is very low because it’s very wide, so the area of thatpeak is the same as for the other protons appearing on the spectrum (ThermoFisher, 2017).
There are 4hydrogens that are part of the benzene ring (Fig.1. – red circle) and they giverise to the peaks in range between 7.1262 and 8.1313.
They create the series ofmultiplets. Doublets appear at 8.1075 – 8.1313 ppm and at 7.1262 – 7.1490 ppm.Triplets appear at 7.
3314 – 7.3726 ppm and 7.5987 – 7.6419 ppm. Multiplicity appear due to vicinal 3J and long-range4J coupling of H+ around the ring. H1 and H3 are shifted downfieldbecause of the electron withdrawing (CO2H). H2 and H4 are shiftedupfield because of oxygen in acetoxy group that is electron-donating (ThermoFisher, 2017).
Fig.2.Structure of the caffeine.
In the spectrum ofthe caffeine can be seen 4 singlets due to 4 types of hydrogens that are indifferent environment. The compound has 3 methyl groups. The first one (Fig.2.– red circle) is attached to the nitrogen which is bonded to two carbonylgroups, it gives rise to the signal at 3.9886. The second one (Fig.2.
– blue circle)is attached to nitrogen that is bonded to carbonyl group and one of the carbonsin ring. Signal appears at 3.5989. The last methyl group (Fig.2. – greencircle) is attached to nitrogen that is bonded to carbons that are part of thering. Because of the nitrogen thatare close to all the hydrogens deshielding can be observed. Mostly it can beseen in the third peak because the position of hydrogens is near to a carbonthat is attached to a nitrogen (Shaikh Z.
, 2017). In the spectrum is also 1 hydrogen (Fig.2. – purplecircle) which is attached to the carbon that has in neighbourhood two nitrogen,with one of them is double bonded. For that hydrogen signal rise at 7.2628. 2.Comparison of the results with contents claimed bythe manufacturer.
Information provided by manufacturer, Pfizer Consumer Healthcare (EMC, 2017):Quantitative composition for Anadin Original –tablets:Active Ingredients: Aspirin BP 325mg/tablet Caffeine PhEur 15mg/tablet Results obtainedduring this experiment are very close to the content claimed by manufacturer,which can indicate that experiment was performed correctly. Higher value foraspirin can be result of measuring smaller integrals for main component (Thomson Eberhart S., Hatzis A., Rothchild R., 1986). 3. Factors affecting signal intensity.
– Relaxationtimes, when the spectra become saturated (Saturation Effects) relaxation timesof protons are different and it can affect the strength of the signal (Reich H.J., 2017). The signal intensity depends also on difference between two energylevels. If the energy level is the same as the number of transitions, thenenergy release and absorption will be 0 and it will be nothing to see on thespectrum (Edwards J.C., 2017).- Decoupling– when it’s used then Nuclear Overhauser Effect occurs and can change theintensity of the signals (Reich H.
J., 2017)- Acquisitiontime – increasing this time will maximize the amount of signal (Reich H. J.,2017),- Temperaturecan affect the duplicability of quantitative results. It should be constantduring the acquisition time. It can also affect the relaxation properties (Kumar Bharti S., Roy R., 2012)- Gyromagneticratio, it is a ratio of magnetic moment to its angular momentum.
Itsproportional to signal strength. (Freude D., 2006)- Nuclearspin (Freude D., 2006)- Measurementtime (Freude D., 2006)- Densityof nuclei (Freude D., 2006)- Strengthof external magnetic field, which is proportional to signal intensity (FreudeD.
, 2006) Shimming, which means homogeneity of the magnetic field should beapplied (Kumar Bharti S., Roy R., 2012)- ReceiverGain, can’t be either too high or low. It can cause loos of signal ordistortion (Kumar Bharti S., Roy R.
, 2012)- correcttuning and matching the frequency before the experiments should be done for allsamples as it can affect the signal intensity (Kumar Bharti S., Roy R., 2012)- Signalto noise ratio should be appropriate (Kumar Bharti S., Roy R.
, 2012)- ElectrondensityAll these factors canchange the resolution, affect the peak shape, and cause even loos of signal.Without good resolution, proper peak shape, baseline etc quantitative analysisof the samples can’t be perform. Signal to noiseratio should be appropriate and time domain to provide precise quantitativeresults (Kumar Bharti S., Roy R., 2012). 4. Comparison of NMR with UV and HPLC. UV:- Simpleand rapid, cheaper than HPLC as it doesn’t require expensive solvents (Eag.
Laboratories, 2017), – Non-invasive(Geisler J., 2015)- Canreveal potential sample contaminants (Geisler J., 2015)- Canbe used to determine the metal ions- Highersensitivity and detection limit than NMR (Clark B.J., Frost T.
, RussellM.A., 1993)- Doesn’tgive enough information about the structure of the compound, thus it can’t beidentified completely (Clark B.
J., Frost T., RussellM.A., 1993)- Shorttime of analysis and small amount of sample required for experiment (Eag.
Laboratories, 2017)- Lowselectivity and sensitivity, it can be inadequate at low concentrations (GeislerJ., 2015)- Widelyused for quantitative analysis (Clark B.J., Frost T., RussellM.
A., 1993)- Othercomponents in the sample can cause the interferences (Eag.Laboratories, 2017)- Itdoesn’t work with compounds that don’t absorb light at that region (Geisler J.
,2015)- Oneof the disadvantages of that method are sample conditions, that can influencethe absorption. Such as pH, temperature or impurities (Geisler J., 2015) HPLC:- Separationis rapid and can be repeated, also very efficient. Can be completed in 10-30min with very high resolution and accuracy (Smith C., 2017)- Preparationof standard solutions required (Dong M.W.
, 2013)- Complexmixtures can be analysed using this method, it can be used to analysesubstances from small ions and organic molecules to big biomolecules andpolymers (Dong M.W., 2013)- Columncan be used many times (Smith C.,2017)- Lowsensitivity for some of the compounds (Smith C., 2017)- Canseparate mixtures and give the pure compounds (Dong M.W., 2013)- Betterabsorptivity onto stationary and mobile phase than UV (Dong M.
W., 2013)- Nodilution errors compare to UV (Smith C.,2017)- Canbe expensive as it requires a lot of different organic solvents (Smith C., 2017)- Canbe used in qualitativeand quantitative analysis (Dong M.W.
, 2013)NMR:- Expensivemethod (Banwell C. N., 1994)- Samplescan’t contain any impurities before analysis (Emwas A.H., 2015)- Veryhigh reproducibility (Emwas A.H.
, 2015)- Candistinguish even close related compounds better than UV or HPLC and thanks tothat specificity can be used to advantage in validation of methods for examplein chromatographic techniques (Holzgrabe U.,, Wawer I.,, DiehlB., 2008)- Themost suitable method to determine the structure of the compound (Banwell C. N.
,1994)- Solidsamples, gas samples or tissues can be analysed by this technique, not justliquid (Emwas A.H., 2015)- Purityof the compound can’t be determined but it can be by use of HPLC (KomoroskiE.M.
, Komoroski R. A., 2000)- Non-destructivemethod compared to HPLC (Emwas A.H., 2015)- Requiressmall sample volume (Komoroski E.
M., Komoroski R. A.
, 2000)- Littleor no sample pre-treatment (Komoroski E.M., Komoroski R. A., 2000)- Canbe used to analyse the chemical and physical properties of the compounds, suchas electron density etc (Emwas A.H., 2015)- Inquantitative NMR the main parameter that has an influence on signal is the typeof the solvent (Wawer I., Diehl B.
, 2017) NMRlimitations:- Quitebroad resonance that normally appears (Banwell C. N., 1994)- Highdetection limit that result in difficulties with trace detection (KomoroskiE.M., Komoroski R. A., 2000).- Canbecome complicated once the molecules will get bigger (Holzgrabe U.
, WawerI., DiehlB., 2008)- Samplescan’t contain any impurities before analysis (Holzgrabe U., WawerI., DiehlB., 2008)- Lowsensitivity, but it’s possible to improve it by increasing field strength ordynamic nuclear polarization (Emwas A.
H., 2015). Result of that it’s limitationin quantitative applications (Holzgrabe U.
, WawerI., DiehlB., 2008)- InNMR spectroscopy is just few parameters that can be changed to improve theseparation. In HPLC are many of them that can be optimized to achieve the bestseparation, such as packing material in the column, particle size, modificationof the stationary phase etc. Also, composition of mobile phase can be various,many options are possible to achieve the best results (Wawer I., Diehl B., 2017). REFERENCESEdwards J.
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