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Acetylsalicylic acid or as it is more commonly known by the brand name Aspirin has become one of the most important anti-inflammation drugs to date. Salicylic acid was first obtained plants that contained salicylic compounds. These plants include Willow, Wintergreen, Meadowsweet and as well as numerous herbs. The use of salicylic acid containing plants has been documented throughout history in all civilisation of the world. From the time that acetylsalicylic acid had been isolated, purified and the therapeutic effects of the drug was established for the use in relief of pain and fever, further studies have been preformed, and it has been found to be useful for the treatment for the numerous diseases. Spectrometric analysis can be used for the quantitative analysis of aspirin that is contained in a shop or pharmacy bought drugs. It is important for that the amount of aspirin in a product to be right as if the amount of the drug present has an effect on the person who is taking it. A dosage that is too high may have a toxic effect on the individual and can have serious side effects even permanent damage to the person.
If the dosage is too low then the person dose not receives the desired effect and the effect of the drug may be low or not work at all. This is way all pharmaceutical products are regulated and tests carried out on them to check that they have the right active ingredients and the right dose for that packet.
Aspirin is something that can be found in most households either as aspirin tablets or under branded names such as Disprins or Anadin
The history of acetylsalicylic acid though isolated in the 1800's spans back to early civilization of around the world. In ancient Egypt as early as 1500BC, the civilization had used different plants for different medication that could be used. While they were aware for the use of different plants for different remedies, they were unaware of the active ingredient that was obtained from their remedies. Due to this, they created different recipes. One recipe used by the ancient Egyptians was to create an infusion with the use of myrtle leaves to relieve back pain. They were unaware that the leaves they used contain salicylic acid but found that it was an effective remedy. (Rainsford)
In ancient Greece, a man known Hippocrates, known as the father of medicine, had discovered numerous medicines from plants. He recommended the use of the juice of from willow bark for the treatment of eye diseases as well as being used in relief of pain from childbirth. He also determined that the use of dried myrtle leaves could be used to expel rheumatic pain in the womb. In Roman civilization, Aulus Cornelius Celsus in 30 AD recognized the signs associated with inflammation, which included redness, heat, pain and swelling. In one of his manuscripts, De re medica he stated that an extract obtained from boiled vinegar that contained willow leaves could be used for treatment of pain. Another scholar, known as Pliny the Elder wrote about the use popular bark infusions for pain treatment as well as the use of mixture made from vinegar soaked bark for the treatment of gout. He also identified the use of a paste made from willow ash for the removal of corn and callosities. (Rainsford)
The use of salicylic containing plants was not solely used in European counties. It was also used in the Asian and American cultures. In China, the culture used the back of poplar tree as well as shoots from the Salix babyloncia. In America, the natives used the bark of another willow species, Salix purpura as well as wintergreen. These treatments were commonly used throughout the world but there was little in terms of documented materials until the Reverend Edward Stone wrote about the antipyretic properties of salicylate in a report to the president of the Royal Society of London for the Improvement of Natural Knowledge and as such was the first clinical trail of a salicylate containing preparation, which last over 5 years. It was preformed as a replace for quinine which was commonly used as treatment of fever from malaria. (Schrör)
However there was little research perform on the salicylate compounds until wasn't until 1828 when a German pharmacist named Bucher created a yellow mash that contained a bitter taste he obtained from boiled willow bark. He called this salicin after the Latin name for willow. In 1830, Henri Leroux was able obtain a crystalline form of salicin and proved that the substance was the active ingredient. (Schrör)
In 1832, a French chemist, called Charles Gergardt preformed experiments with salicin and discovered salicylic acid. It was found that it was very good in curing pain, however the problem associated with it was it affected the stomach of its users. People that used this medicine in high doses suffered bleeding and damage to their digestive tracts. By 1853, Gerhardt had neutralized salicylic acid by buffering it with sodium salicylate and acetyl chloride, and created acetylsalicylic acid.(Rainsford) In 1899, a German chemist and employee at Bayer, Germany, Felix Hoffman wanted to figure out a way to synthesize the acid to work better on the stomach. The medicinal salicylic acid was working for the pain, but he needed to find a way to make the acid less irritating to the stomach. In 1887, Hoffman dedicated his time working with the salicylic acid. He understood that the medicine was irritating because it was an acid but he wanted to find a way to make it safe for the stomach lining. Studying the works of Charles Gergardt, Hoffman put the compound through a series of chemical reactions. One of the acidic parts was covered up with an acetyl group. This converted salicylic acid to acetylsalicylic acid. However, Hoffman then came upon another obstacle. He needed to prove that this new form of medication was improved to work better within the body. (Schrör) This was a challenge that he faced with his employees. They did not think that it had been tested thoroughly enough. He later went to Herr Dreser, his superior at Bayer, to show him the new effectiveness of aspirin. Nevertheless, he was discouraged because Dreser and other chemists felt that any good drug must be able to conduct electricity. Because acetylsalicylic acid failed the electrical conductivity test, it was rejected. Instead, Dresser wanted Hoffman to continue his work on heroin, which was another promising new painkiller.(Schrör) A Jewish chemist named Arthur Eichengrun, was convinced and felt that the newly formed salicylic acid was capable of its new responsibilities Hoffman then gave the aspirin to Eichengrun, who secretly gave the powder (it was sold in powder form until 1915) to his cousin who was a dentist. Then other dentists and physicians soon wanted the drug too. The pain-killing effectiveness of the drug was confirmed; thereby opening the eyes of the directors of Bayer. Seeing clear and convincing clinical evidence from physicians and dentists, Bayer started producing the drug. In 1899, Bayer began selling "Aspirin" and registered it as a trademark. In 1971, John Vane discovered the basis as to why aspirin suppresses pain. He acknowledged that aspirin works by restraining the production of prostaglandins. (Rainsford)
1.2 The structure of acetylsalicylic acid
Acetylsalicylic acid is the main ingredient in aspirin. It is responsible for the antipyretic and analgesic effects. Is a weak acid with the formula C9H8O4 and it is made up of a benzene ring with a CO2H and an O double bond O and a CH3 attached to it. It has a molecular weight of 180.2g.(Advameg, Inc) It comes in the form of a white crystalline powder. It is soluble in water but it takes a lot to dissolve it. Whereas it takes a lot less to dissolve the acetylsalicylic acid in chloroform and diethyl ether, so it is more soluble in these chemicals. It is less soluble in anhydrous diethyl ether.
Figure 1: Structure of acetylsalicylic acid (Gaur et al)
1.3 The therapeutic effects of Aspirin
With every drug, there are therapeutic effects and adverse/side effects. These effects are caused by the main compound in the drug in this case aspirins main ingredient is acetylsalicylic acid. Acetylsalicylic acid is also a pro drug this means that when the drug is taken into the body it is transformed in the body into the active formation of the drug salicylate. These salicylates are anti-inflammatory. Acetylsalicylic acid breakdowns in salicylic acid about 20 minutes after it enters the bloodstream. Acetylsalicylic acid can be used to treat a number of aliments. It can be used to treat a headache, which occurs, by the production of the chemical messenger known as prostaglandin. COX-2 enzyme is the chemical messenger associated with pain. Acetylsalicylic acid binds to a binding site on the COX-2 enzyme to prevent its production. It is the same procedure that occur when acetylsalicylic acid is used to treat pain as prostaglandin do not move from the cells. It is used for the prevention of heart attacks and strokes by the inhibition of the cyclooxygenase enzyme which is responsible for the synthesis of eicosanoids. Aspirin also prevents the formation of thromboxane A2, a substance that induces platelet aggregation. As platelets are unable to generate new cyclooxygenase due to being aspirin inhibiting the enzyme, the effect last the length of the lifetime of the cell which is 10 days. (Fuster et al)
1.4 History of Acetylsalicylic acid analysis
The analysis of acetylsalicylic acid can be done in many different way but the main areas are chromatography, spectrometry and electrochemistry and titration techniques
Most of the analysis of acetylsalicylic acid can be done in two way analysing the tablets themselves or analysis them in different matrixes such as blood plasma and urine. (Schrör) The main reason for the analysis of acetylsalicylic acid was to isolate the antipyretic constituent of acetylsalicylic acid. Another side to the analysis of acetylsalicylic acid is the pharmacokinetic side, in how the acetylsalicylic acid could be used for treating other dieses. One was to see if the acetylsalicylic acid could be manipulated into being a more beneficial and powerful drug and to see if it had any other properties other than its existing antipyretic property. Acetylsalicylic acid was also analyzed to change some of the ingredient to reduce side effects to the user. It was these different tests over the late 19th century that lead to the discovery that it could be used as an analgesic and antirheumatic drugs. In the 20th century, it was also this testing that lead to a safe dosage being established for acetylsalicylic acid and is now how we see it packaged today. It was also during this time it was discovered that acetylsalicylic acid could help people who had suffered for heart complaints or heart attacks.(Rainsford)
By today's standards these test are very important, as these drugs that contain acetylsalicylic acid are almost in every house and hospital in the world, pharmaceutical companies invest billions a year into these testing to ensure that the product they produce are not only the right dosage but in the right form they are indented form. In these modern times there is more counterfeit drugs in the world now than any other time in history, the raw materials now have to be check as they enter the production line as they may be not be what is required or a poor quality drug or that they have been swapped for counterfeited drugs. Therefore, that is why a lot of time, energy, and money have gone into fine-tuning these and into perfecting the different techniques for the analyzing Acetylsalicylic acid. (Schrör)
1.5 UV-Visual Spectrometry
UV-Vis spectrometry works under two different sources of light, one for the visible region which is a tungsten filament lamp and one for ultraviolet region which is a hydrogen/deuterium discharge lamp. The UV/VIS is based on a monochroamator this is used to select a single wavelength from all the wavelengths from the source and most monochroamtors are based on diffraction grating and reflection grating.
Diffraction instrumentation allows the structure of a compound at the atomic level to be understood. The absorption of UV or Vis radiation corresponds to the excitation of outer electrons in the molecule.
Samples and reference.
Almost all of the samples used for UV/VIS are in liquid form; solid samples can be made into liquid samples by gringing and crushing the sample and weighing it to this a know solvent which is approite is added to the now powdered sample which turns the solid into a liquid. the liquid samples are placed in a 1cm pathlenght cell. These cells must be transparent to allow the light source to pass through. These cells are called cuvettes and they can be removed from the instrument. Different materials are used for these cells depending on which region that is being used. For the UV region a quartz cell is used this allow the light source to pass through while for the visible region a plastic cuvette may be used. The most common cell has a pathlength of 1 cm, although cells with shorter (1 mm) and longer pathlength (10 cm) are available. Cells with a longer pathlength are useful for the analysis of very dilute solutions or for gaseous samples. The highest quality cells are constructed in a rectangular shape, allowing the radiation to strike the cell at a 90° angle, where losses to reflection are minimal. These cells, which are usually available in matched pairs having identical optical properties thus allowing for a one to contain a blank while the second can contains the sample.
These cells/cuvettes must be polished, clean and when the sample is poured in, it must be free from bubbles. For the reference cell, it is usually filled with a solvent. Typically, radiation of a specific intensity is passed through a liquid sample, often held in a quartz cuvette. When the radiation emerges on the other side of the cuvette, it is reduced in intensity owing to losses from a) reflection off the cuvette windows, b) scattering and c) absorption by the sample itself. Often, a reference solution, which has no analyte, is also analyzed to account for the losses due to reflection and scattering; thereby the intensity attenuation due to absorption alone can be worked out by simple subtraction.
The optical chopper is a rotating segmented mirror which controls the radiation's path, alternating it between the sample, the blank, and a shutter. The signal processor uses the chopper at known speed of rotation to resolve the signal reaching the detector to determine the transmission of the blank (P0) and the sample (PT).
This can be controlled by the means of adjustable slits at the entrance and exit of the monochromator that ranges between 0.2 nm and 3.0 nm.
The used for UV is a photomultiplier tube; photomultiplier tubes are monochannel detectors and are still very popular. They consist of a photosensitive surface and a series of electrodes (dynodes), where there is an increased potential compared to the one before. When a photon strikes the photosensitive surface, a primary electron is emitted and accelerates towards the first dynode. This electron impacts the dynode and causes the release of a number of secondary electrons, which hit the next electrode and so on, until the signal is amplified many times over. Thus, this allows extremely small signals to be detected. (Kellner et al)
The readout is usually displayed on a computer but can be displayed on a chart or meter. The readout will be illustrated in absorbance units in some applications it may be shown as percentage transmittance.
The PC that collects the data converts it from transmission to absorbance and displays the spectrum. The PC can often carry out baseline subtraction and smoothing and filtering tasks as well as qualitative and quantitative analysis. It may have other capabilities, such as the ability to compare a spectrum to those in a spectral library and to carry out peak purity checks.
In organic molecules, this absorption is restricted to certain functional group that contains electrons. Of low excitation energy. Aromatic molecules, for example, mostly absorb UV in the 200-300 nm regions. An absorption spectrum is usually a plot of absorbance versus wavelength and is normally continuous and broad with little fine structure. The broad spectrum is due to the fact that the higher energy radiation involved means that vibration and rotational transitions co-occur as well as electronic transitions; all of these are superimposed on each other resulting in broad bands rather than sharp peaks. In UV-Vis absorption spectrometry, concentration of the species is related to absorbance by the Beer Lambert Law where A, absorbance at a particular wavelength, Îµ is an extinction coefficient at a particular wavelength (Î»), c is concentration and l is the path length. During most experiments, Îµ and l remain constant, so absorbance is proportional to concentration, a relationship that is exploited for quantitative analysis. (Kellner et al)
1.6 Infra-Red spectrometry
Infrared (IR) is a vibrational spectroscopy technique. It are extremely useful for providing structural information about molecules in terms of their functional groups, the orientation of those groups and information on isomers. It can be used to examine most kinds of sample and is a nondestructive method of analysis. It can also be used to provide quantitative information. The IR region, covers the range 4000-400 cm-1 (2500-25,000 nm)however in most cases analysis in done between 4000 - 700 cm1 the instrument produces spectra based on the vibrational transitions within a molecule and use the same region of the electromagnetic spectrum. They differ in how observation and measurement are achieved, since IR is an absorption (transmission) method. Many molecules absorb IR radiation, which corresponds to the vibrational and rotational transitions of the molecules. For this absorption to occur, there must be a change in polarity of the molecule. IR radiation is too low in energy to excite electronic transitions. There are a number of vibrations and rotations that the molecule can undergo which all result in absorption of IR radiation. An IR spectrum is a plot of transmittance versus wavelength. It is normally a complex series of sharp peaks corresponding to the vibrations of structural groups within the molecule. a ratio method is often used where a peak that is apart from those being used for quantitative measurement is chosen and is employed as an internal standard. This strategy serves to minimise relative errors, such as those due to differences in sample size. However, under controlled experimental conditions, IR can comply with the Beer-Lambert Law directly for quantitative measurements. Conventional IR spectrometers are known as dispersive instruments but have now been largely replaced by Fourier Transform infrared (FTIR) spectrometers. (Clear, 2007)
Fourier Transform infrared (FTIR) spectrometers.
The heat sources used in IR, such as the Nernst glower, the Globar. Most IR instruments an Michelson interferometer, where the spectral encoding takes place, The Michelson interferometer is a multiplex system with a simple design - a fixed mirror, a moving mirror and an optical beam splitter. The source radiation hits the beam splitter from where some of the light is reflected to the moving mirror and some is transmitted to the fixed mirror. The mirrors reflect the light back to the beam splitter, some of which recombines and goes on to the detector. The key point of the moving mirror is to generate a difference in the optical paths of the two paths of light separated by the beam splitter; consequently, one is slightly out of phase from the other since it travels a slightly different distance. The recombined light produces an interference spectrum of all the wavelengths in the beam before passing through the sample. Therefore the sample sees all the wavelengths simultaneously and the interference pattern changes with time as the mirror is continuously scanned at a linear velocity. The result of the sample absorbing radiation is a spectrum in the time domain called an interferogram. Fourier transformation (FT) converts this very complex signal to the frequency domain.
The advantages of FTIR is that there is a greater signal-to-noise ratio, speed and simultaneous measurement of all wavelengths.
Infrared spectroscopy is routinely used for the analysis of samples in the gas,
liquid, and solid states. For liquid samples they can be placed in-between two NaCl plates (windows). For soild samples there are two methods of preparing the samples 1) this done by mixing the soild sample with paraffin to form a null this is then placed in the NaCl plates.
2) another method of preparing a solid sample is to weigh the solid then grind it in a mortar and pestle until it's a fine powder and then adding KBr. The reason KBr is used is because it dosent absorbe in the IR region
Gases are analyzed using a cell with a pathlength of approximately 10 cm. Liquid samples are analyzed in one of two ways. For nonvolatile liquids a suitable sample can be prepared by placing a drop of the liquid between two NaCl plates, forming a thin film that typically is less than 0.01 mm thick. Volatile liquids must be placed in a sealed cell to prevent their evaporation.
In a Fourier transform, infrared spectrometer, includes only a single optical path, it is necessary to collect a separate spectrum to compensate for the absorbance of atmospheric CO2 and H2O vapor. This is done by collecting a background spectrum without the sample and storing the result in the instrument's computer memory. The background spectrum is removed from the sample's spectrum by creating a ratio between the two signals. In comparison to other IR instruments, an FT-IR provides for rapid data acquisition, allowing an enhancement in signal-to noise ratio through signal averaging.
The most common detectors in IR are thermal, i.e. thermocouples, thermistors and bolometers. A thermocouple is based on the use of two different conductors connected by a junction. When a temperature difference is experienced at the junction, a potential difference can be measured. A series of thermocouples together is called a thermopile. Thermistors and bolometers are based on a change in resistance with temperature. They have a faster response time than thermocouples.
With an FT instrument, the main function of the PC is to carry out the Fourier Transformation of the interferogram, i.e. conversion of the information from the time domain to the frequency domain . However, the PC also carries out both qualitative and quantitative analysis. Library searching, spectral matching, chemometrics and other software are readily available. IR measurements can deviate from the Beer-Lambert Law and thus allowing the instrument to be used as a quantitative technique (Clear, 2007)
1.7 Colorimeter spectrometry in aspirin analysis
The source of light is a tungsten filament lamp is used, this lamp produces radiation at all wavelength across the visible region.
Wavelength selector in Colorimeter is a filter wavelength selector that is achieved by means of different filter, which allows transmitted light across a limited range or band of wavelengths. A typical filter colorimeter has six to eight colour filters however some modern colorimeter use a monochromotor which allows the selection of individual wavelengths across the visible region.
For samples to be analysed it must absorb light from the visible region. In other words, the sample must be pre coloured before it can be tested. All samples must be solution and placed into a glass or plastic cuvette or cell with a fixed pathlengh of 1cm. for calibration purposes a blank is used, the blank should contain everything in solution expect for the absorbing species, the blank also allows for the calibration of the Colorimeter at 100% transmittance and zero absorbance.
A choice of two detectors can be used a phototube and photomultiplier tube They consist of a photosensitive surface and a series of electrodes (dynodes), where there is an increased potential compared to the one before. When a photon strikes the photosensitive surface, a primary electron is emitted and accelerates towards the first dynode. This electron impacts the dynode and causes the release of a number of secondary electrons, which hit the next electrode and so on, until the signal is amplified many times over. Thus, this allows extremely small signals to be detected. (Clear, 2007)
Typically, a meter which is calibrated in both % transmittance and absorbance values is used. Absorbance values are directly proportional to the concentration provided that it has followed Beer's law.
Transmittance (T) = Light transmitted (l) = Absorbance = Log (1/T) = abc
Incident light (l0)
"a" is a constant --the ability of a given molecule to absorb a particular wavelength of light
"b" is the path length--the longer the path, the less light gets through.
"c" is the concentration--the more molecules in the solution, the more light is absorbed. (Thermo scientific)
1.8 Conductimetry spectrometry in aspirin analysis
The quantification determination of a reagent is based on the consumption of the reagent in question by another, until there is a chemical equivalence is obtained thus resulting in a change in conductive properties of the sample as in solution, different ions have different capabilities of conducting electrons . The titration endpoint is the point obtained by the intersection of two straight lines fitted to the linear part of the titration curve recorded over the titration process.
This method has the advantage of a titration curve being constructed on the basis of a few data points. The method is extensive used in the analysis of acid base titrations. However for well defined titrations end point the method should be used by a titration of strong acid to strong base and weak acid to weak base. (Kellner et al)
Titration of a strong acid by strong base
Since HCl is fully dissociates the cell has a high equivalent point before the end point conductivity is used as H+ ions are replaced by less conducting Na ions. After the equivalent, point the conduction increases with increasing convention of Na+ and particularly OH-
Titration of weak acid by a weak base
Before the equivalence point activity increases as non-ionic CH2CO2H is converted to CH3CO2NH4 after the equivalence point conductivity remains the same as it is unaffected by undissociated a NaOH.
The technique requires that the titrant should be 10 times concentrated to in order to keep the volume change small as large changes in volume can affect this method of analysis. (Kellner et al)