Monday, January 27, 2020

Application of Gas Chromatography in Pharmaceutical Analysis

Application of Gas Chromatography in Pharmaceutical Analysis Chromatography is a physical method of separation in which components to be separated are distributed between two phases, one of which is stationary phase while the other mobile phase move in a definite direction. The stationary phase may be a solid or a liquid supported on a solid or a gel. The mobile phase may be gaseous or liquid. The basis for gas chromatography separation is the distribution of a sample between two phases. one of these phases is a stationary bed of large surface area, and the other phase is a gas which percolates through the stationary bed. The physical state of the mobile phase distinguishes the fundamental type of a chromatographic separation. Liquid chromatography (LC), gas chromatography (GC) and super critical fluid chromatography (SFC) all named for the state of their respective mobile phases. The first person to chromatography was Tswett (1872-1919) the Russian chemist. He used chromatography from the Greek for colour chroma and write- graphein to describe his work on the separation of coloured plant pigments. Until 1930s chromatography in the form of thin-layer and ion-exchange chromatography became a regularly used technique. In 1940 development of partition chromatography and paper chromatography followed by the first disclosure of effective gas chromatography (GC) by Martin and his co-worker James in 1953. GC is a technique for separating volatile substances by percolating a gas stream over a stationary phase. It is a technique that revolutionized analytical chemistry. GC has been applied successfully to numerous compounds in variety of fields. Headspace GC has been used since the 1980s, but only recently has it become part of mainstream of pharmaceutical analysis. In this essay GC technical aspect and its application for pharmaceutical quantitative analysis has been explained. Moreover, the comparative advantage over other techniques and the disadvantage of using GC has been also discussed and reached on some conclusion. 2. Gas Chromatography 2.1 Technical Aspect In GC the components to be separated are carried through the column by an inert gas. Here the mobile phase is a gas, often nitrogen, but sometimes helium, hydrogen or occasionally another gas. It is called the carrier gas. GC is equipped with standard oven for temperature programming, split/split less injection ports and flame ionization detector. The sample mixture is partitioned between the carrier gas and a non volatile solvent (stationary phase ) supported on an inert size-graded solid. The solvent selectively retards the sample components, according to their distribution coefficient, until they form separate bands in the carrier gas. These component bands leave the column in the gas stream and are recorded as a function of time by a detector. This elution technique has the following advantages : The column is continuously regenerated by the inert gas phase. Usually the sample components are completely separated and mixed only with an inert gas making collection and quantitative determinations easy. The analysis time is very short. In general GC is a powerful and widely used technique for the separation, identification and quantitation of components in a mixture. In this technique a sample is converted to the vapor state and a flowing stream of carrier gas sweeps the sample into a thermally -controlled column. In GC the column is usually packed with solid particles that coated with a non-volatile solvent. Retention time is defined from injection of the sample to time a specific sample component is detected. After exiting the column the separated components are detected and a detector response is recorded. Polarity and boiling points of the components are also vital properties in GC separation. While polarity is the major factor governing separation; the boiling points of components of the sample also play a significant role in determining the retention time. Components with higher volatility have lower boiling point. 2.2 Advantages of GC 2.2.1. Speed The entire analysis is completed less than half an hours. The use of gas as the moving phase has the advantage of rapid equilibrium between the moving and stationary phases and allows high carrier gas velocities to be employed. Separations requiring only seconds have been reported, however, analysis time of minutes duration is more common in GC. Preparative scale separations, or resolution of wide-boiling complex samples may require hours. 2.2.2. Resolution The separation of some compounds such as methyl esters of stearic, oleic and linoleic acids by other techniques is extremely difficult or impossible. The boiling point differences are negligible in that the compounds vary only in degree of unsaturation. By using selective solvents, however, GC can provide resolution impossible by distillation or other techniques. 2.2.3. Qualitative Analysis The retention time in GC is that time from injection to peak maxima. This property is characteristic of the sample and the liquid phase at a given temperature. With proper flow and temperature control, it can be reproduced to within 1% and used to identify each peak. Several compounds has only one retention time. This retention time is not influenced by the presence of other components. 2.2.4. Quantitative Analysis The area peak produced for each on chromatogram is proportional to concentration of the peak in GC analysis. This can be used to determine the exact concentration of each component. Accuracy attainable with GC depends upon, detector, integration method and sample concentration. 2.2.5. Sensitivity A major reason for the extensive analytical application of GC is the sensitivity available. The simplest forms of thermal conductivity cells can determine down to 0.1 %.The flame detector easily sees parts per million, and the specific electron capture and phosphorus detectors can measure parts per billion. An advantage of this extreme sensitivity is the small size sample or micro liters of sample are sufficient for complete analysis. This is indeed trace analysis is also easily achieved. It is simple to operate and understand. Interpretation of the data obtained is also rapid and straight forward. The cost of GC is very low compared to the data obtained. 3. Application of GC in Pharmaceutical Analysis The major success of the application of GC in pharmaceutical quantitative analysis is firstly due to the very high efficiencies of separation power, secondly to the extreme sensitivity of the detection of even very small amounts of separated species and finally to the precision and accuracy of the data from quantitative analyses of very complex mixtures. GC analyses are also easy to automate from sample introduction to separation. Because of the above main advantages and its short analysis time and reliable results GC is used as quality control purposes in the pharmaceutical industry. In fact pharmaceutical analysis generally involves two steps; separation of the compound of interest and quantitation of the compounds. The better the separation the easier the quantitation. GC detectors have different responses to each compound. In order to determine quantitative amounts of various compounds in a separation the detector must be calibrated using standards. Standard solutions of sample a re injected and the detector response recorded. Comparison of the standard and sample retention times allows qualitative analysis of the sample. Comparison of the peak area of the standards with that of the sample allows quantitation of analyte. Due to this fact, GC is widely used as a routine analytical technique in pharmaceutical quantitative analysis mostly used in for the determination of organic volatile impurities and nicotine level during drugs formulation. 3.1. Determination of Organic Volatile Impurities by GC Organic Volatile impurities are residual solvents that are used in and are produced during the synthesis of drug substances, or in excipients used in the production of drug formulations. Many of these residual solvents generally cannot be completely removed by standard manufacturing processes or techniques and are left behind, preferably at low levels. Organic solvents such as acetone, ethyl acetate, isopropyl alcohol, methanol, tetrahydrofuran and toluene frequently used in pharmaceutical industry for the manufacturing of Active Pharmaceutical ingredients therefore ,in manufacturing drug substances and from one or more steps of the synthetic process, volatile solvents can be retained in the end products. Most of the time ethanol and acetone are used in the preparation of the polymeric coating of tablets. On other hand isopropyl alcohol is used in the crystallization of the active ingredient while ethyl acetate is a process solvent for the gel forming polymer. Low levels of these org anic solvents are inevitably present in the drug product even after drying process. These organic volatile residuals affect physiochemical properties of a drug, such as particle size, dissolution rate and stability, but also can present a serious potential health hazard. Very often these solvents, referred to as residual solvents, are carried to the pharmaceutical preparation concerned and making their determination very important. Therefore, GC is superior to other techniques for analysis of these residual solvents. It provide good retention and separation at low oven temperatures. Due to the above fact the content of residual organic solvents in pharmaceutical industry is routinely measured by GC technique. 3.2. Determination of Nicotine by GC Because of its rapid and accurate analytical result; GC is used to determine the nicotine level in pharmaceutical drugs formulation. GC applications in combination with other techniques are also vital in pharmaceutical industries for isolation and characterization of volatile compounds.Currently the use of GC in pharmaceutical quantitative analysis is very usual and include the analysis of samples of active pharmaceutical ingredients and their intermediates as well as in- process testing for residual solvents to optimize the drying process. 4. Discussion and Conclusion 4.1. Discussion The disadvantage of GC are that the components of the sample must be volatile at temperature at which they will not decompose. As there are more involatile materials than there are volatile, and volatility immediately places a serious limitation on the field of application. In addition to these GC is also strongly retained components travel very slowly, or in some cases do not move at all. However, this difficulty can be overcome by using temperature programming of the column to decrease elution time. Temperature programming is the increase of temperature during an analysis to provide a faster and more adaptable analysis. 4.2. Conclusion Even though, GC has a few limitation in field of application due to its high detector sensitivity and high resolving power it is generally used extensively in pharmaceutical industry both in research and quality control purposes.

Sunday, January 19, 2020

Dr Jekyll and Mr Hyde Essay -- English Literature

Dr Jekyll and Mr Hyde This novel is more than just a traditional horror story as it has many hidden and complex meanings and explanations, of what seem and would have normally before this book, been simple events. Stevenson has very strong opinions and some are expressed in the book. A traditional horror story would either be a super natural In this novel Stevenson's characters, Jekyll and Hyde, are stereotypes of people who are 'good' and 'evil'. The good is the friendly doctor (the caring profession) and the evil is the hunched, ugly murderer. These two stereotypes combine to create the average man who has the capacity to be both 'good' and 'evil', and they have both 'good' and 'evil' thoughts and emotions. All people have the same emotions, some good and some bad and, like Hyde, when you follow the evil emotions like hate, jealousy and revenge, you are considered evil. Jekyll and Hyde both have these 'evil' emotions but what makes Jekyll 'good' is that he hides them, Jekyll is driven by reason whereas Hyde is driven by desire, he'll do what he wants when he wants. Londonand Jekyll's Houses The street where Jekyll lives is described as merely an anonymous street in London, whose shop fronts "like rows of smiling women" have a brightness that stands out in contrast to the dingy neighborhood. And yet on this street, two doors from the corner, stands a dreary, Gothic house, which "bore in every feature the marks of prolonged and sordid negligence." As we proceed further in the novel, Jekyll's houses will be seen to have their own connection with the characters prosperous, respectable, as well as threatening, mysterious, and sinister. It is clear by each of its two appearances the respectable; Je... ...public has seen only a veneer of my real self." This is true due mostly to the fact that no one knew Mr. Hyde was a part of Dr. Jekyll. Jekyll constantly emphasizes the greatness of his background. He reminds us of his wealthy family, and great education. But he also states "that man is not truly one, but truly two." Dr. Jekyll needed something, or someone to represent the evil which has built up inside of him. He created this through experiments, which lead to a potion. This potion transformed him anytime he wanted. He was transformed into Mr. Hyde. Evil is just a small portion of men, perhaps that is why Mr. Hyde had a dwarfish appearance. The main point was that the potion took over his life, and Dr. Jekyll finally realizes he is unable to transform back into his goodness. He attempts to commit suicide, as this is his only way of destroying Mr. Hyde.

Saturday, January 11, 2020

Howard Zinn and the Us Constitution

The late Howard Zinn is a much respected historian. His views are known to be bold and nonetheless controversial. In his book, â€Å"A People’s History of the United States,† Zinn touches on topics such as indentured servants, angry civilians, and the United States Constitution. Indentured servants were people of a lower economic class who worked for people of a higher economic background. These servants worked for a given amount of time, usually between five and seven years and either worked for money, food, shelter, or freedom.Indentured servants were originally made up of mostly young white males who were trading their time in prison or their poverty for time working as a servant. The number of indentured servants began to decrease and soon after English colonists looked for other potential people to enslave. The Virginia colony needed labor. They needed to grow corn for subsistence, and needed to grow tobacco for export because they had just learned to grow tobacco. Virginia couldn’t make the Indians work for them like Christopher Columbus had done in the past. The colonists would be outnumbered if they decided to try to take over the Indians even though they were equipped with firearms. The Indians were resourceful, defiant, tough, and practically fearless. The colony needed an alternate choice. African slaves were the answer to Virginia’s labor problem. Blacks had already been imported as slaves to South America and the Caribbean to Spanish and Portuguese colonies.The blacks made enslavement easier because of how hopeless they were. They were robbed of their homeland and culture and in most cases they were separated from their families. Zinn referred to the slavery against the blacks to be the cruelest form of slavery in history. The British were taxing the colonial population to pay for the French war. Many colonists did not agree with the Stamp Act and wanted it repealed.That summer, Ebenezer Macintosh, a shoemaker, led a mob in destroying the house of a rich Boston merchants like Andrew Oliver and Thomas Hutchinson. Rioters smashed up their houses with axes, drank all the wine in the cellars, and looted the houses of the furniture and other objects. English officers reported these acts to be a part of a larger scheme in which the houses of 15 rich people were to be destroyed. The riots against the Stamp Act swept Boston in 1767.It took the Stamp Act crisis to make the leadership aware of its dilemma. After the riots a town meeting was arranged and mainly upper and middle class citizens were allowed to attend. Zinn argues the Founding Fathers, Benjamin Franklin, George Washington, John Adams, Thomas Jefferson, John Jay, James Madison, and Alexander Hamilton, may have had ulterior economic and class preservation motivations that were hidden by the universal language of the constitution document.Zinn also argues that the rich, in order to secure their own interests and economic status, must either control the government directly or control the laws by which government operates. Zinn often refers to the views and writings of historian Charles Beard. Beard studied the economic backgrounds and political ideas of the fifty-five men who gathered in Philadelphia in 1787 to draw up the constitution. In his findings a majority of them were lawyers by profession, most of them were wealthy due to land, slaves, manufacturing, or shipping.Half of them had money loaned out at interest, and that forty out of fifty held government bonds according to the records of the treasury department. Beard also found that most of the makers of the constitution had some direct economic interest in establishing a strong federal government. Beard did not think the constitution as written to benefit the Founding Fathers personally. The problem of democracy in the post- revolutionary society was not however the constitutional limitations on voting.It lay much deeper beyond the constitution in the division of societ y into rich and poor. The constitution then illustrates the complexity of the American system: that it serves the interests of wealthy elite, but also does enough for small owners, for middle-income farmers and mechanics to build a broad base of support. Alexander Hamilton, Secretary of Treasury and one of the Founding Fathers, believed that the government must ally itself with the richest elements of society to make itself strong.

Friday, January 3, 2020

Plato and Rawls Justice in Philosophy - 652 Words

Justice in philosophy is one of the most important political and moral concepts. The word justice comes from the Latin word jus, which means right or law. English Dictionaries defines it as one who typically does what is morally right as well as offering the word â€Å"fair† as a synonym. But philosophers get beyond etymology and what the dictionary definitions are and look deeper into it. For example, the nature of justice is both a moral virtue of character and a quality needed for political society, as well as knowing how it applies to social and ethical decision making. The question to answer is how Plato and Rawls theories were used for philosophical conceptions of justice. These are known to be the greatest theories of ancient Greece. 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