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Free «Chromatography» Essay Sample


British pharmacopoeia (BP) is the only source of pharmaceutical standards in Britain. This is a leading collection of standards in the UK pharmaceutical substances and medicinal products. By publicly setting the quality of medicine, BP makes an important contribution to British public health through its commission secretariat of medicine and healthcare product regulatory agency. The BP remains a key reference for organisations and individuals working with pharmaceutical research and development, testing and manufacturing in the world.

Q1. British pharmacopeia monograph specification for methimazole in Carbimazole

Published reports and standards on pharmaceuticals are legally enforceable standards for all medicinal products and their constituents. Pharmacopoeia is an important statutory organ in the control of medicine. This body compliments and assists in licencing, and inspection process in medicine and HealthCare product Regulatory Agency in UK. The standards set are compliance requirements that provide means for independent judgement in quality of articles and also applied throughout the product shelf life. They apply throughout the products supply line, that is, suppliers, inspectors, purchasers, medicine regulators, and independent control laboratories (General Medical Council 2000, p. 78-86).

Administration and Dosage of Carbimazole

The initial dose of a tablet coated with FELIMAZOLE contains 2.5 mg administered twice a day. After 3 weeks of cure, the dose is titrated to effect the established on a person’s serum total T4 levels and medical response. Dose adjustments are made in increments of 2.5 mg. The maximum dosage is 20.0 mg on a daily basis, not exceeding 10.0 mg as a single treatment. Thereafter, blood work is monitored quarterly and the dosage adjusted accordingly.

Q.2 Biological Activity of Carbimazole

Carbimazole is a pro-drug, after the absorption is converted to the active form, methimazole which prevents thyroid peroxidase enzyme from iodising and coupling the tyrosine residues on Thyroglobulin. The pro-drug, thus, reduces the production of thyroid hormones T4 and T3. Carbimazole is used judiciously in pregnancy as it goes across the placenta and it is rarely related with congenital defects. However, it predictably causes fatal hydrothyroidism in small dosage. Carbimazole is, thus, used to control maternal hyperthyroidism and breast feeding is never contraindicated (Das, Mugesh & Govindasamy 2010).

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Q.3 Conversion of Carbimazole to Methimazole

Carbimazole belongs to the family of mercaptoimidazoles and as a pro drug of methimazole that depresses the thyroid function after an inhibiting the thyroid peroxidase that is required to synthesize the thyroid hormones. Currently the treatment option in the United Kingdom for pets (cats) with hyperthyroidism is radioactive iodine therapy which has a limited existence. Surgery is not recommended as the best option for high risk patient who have incurrent diseases (British Pharmacopoeia Commission 2009).

Thioamide is a functional group with the general structure R-CS-NR'R, (where R, R', and R, are organic groups). They are comparable to amides but they reveal greater multiple bonding characters along the C-N bond, resulting in a higher rotational barrier. One of the well-recognised thioamides is thioacetamide used as a source of the sulfide ion and it is a building block in the structure of heterocyclic chemistry.

Q.4 Iodine as a TLC (thin layer chromatography) visualisation reagent

Thin layer chromatography is a method of analysing mixtures by separating compounds in a mixture. TLC enables to determine the number of components a mixture has, and the percentage of purity in a compound. It can also be used to monitor the progress of a reaction by observing the disappearance of a reactant or the appearance of a product. TLC takes little time for analysis (about 5-10 minutes) and is also one of the most sensitive techniques for analysing microgram quantities.

Why iodine?

Iodine is a dark grey, non-metallic, lustrous solid element. It is the most electropositive and the least reactive halogen but it still forms compounds with various elements. The halogen sublimes upon heating to give a purple vapour. Iodine is slightly soluble in water and dissolves in some solvents such as carbon tetrachloride. For this reason iodine vapour is used in detection of an organic compound in a mixture of substance.

It is quite simple to visualize coloured compounds, the spot can be clearly observed after the development. Because most of the compounds used are colourless, visualisation method is needed.  To achieve this, a silica gel is impregnated with a fluorescent material that glows under ultraviolet rays. A spot interferes with the fluorescence process and appears as a dark spot on the background of the glow.  The other method of visualisation is accomplished by the plate in an iodine vapour for a short while.

Iodine vapour is a universal detector and exemplary applies to all types of substances like amino acids, alkaloids, lipids, and psychoactive substances. Many organic compounds form a dark coloured complex compound with iodine. Organic compounds are those members of a larger class of solid, liquid, or gaseous chemical compounds that contain a carbon atom in their molecular structure. However, some of the carbon containing compounds like oxides of carbon, carbonates, carbides, cyanides as well as allotropes of carbon such as diamond and graphite are considered inorganic. To achieve some desired levels of accuracy, it is often advisable to use at least two visualisation techniques when a compound fails to show up with one method. 

Q.5 Why compounds show up darker spots when viewed under ultra violet light in TLC

Due to the colourless nature of most compounds, visualisation methods enables recording of observable changes. When the TLC plate is illuminated with ultra violet light, a dark spot interferes with the fluorescence which is outlined with a pencil mark to determine its location. It is important to detect compounds in a chromatogram without actually causing any chemical change in them. In this case, substances that contain conjugated double or triple bond when observed under ultra-violet light are practically recommended. The layer containing a fluorescent indicator that emits radiations with shorter wavelength the zone that absorbs substance appears as a dark spot with a bluish or yellowish emitting background.  Such substances absorb radiations and then emit them in the visible region of the spectrum so that they appear as a bright luminous zone differentiated by colour.

Q.6 BP specification for Chloroxylenol in disinfectant solution

Chloroxylenol is an antimicrobial chemical compound that is used in control of algae, fungi and bacteria in impulsive, adhesives wash tanks and paints. It is used commonly in antibacterial soaps and household antiseptics like Dettol cream, and liquid and medicated Vaseline. Chloroxylenol is harmless to human and other mammals but is practically harmful to birds, moderately toxic to invertebrates living in freshwaters, and highly toxic to fish.  However, it produces a mild skin irritation and may be allergic to some people.

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The IUPAC name of Chroloxylenol is 4-chloro-3, 5-dimethylphenol. The substance has a good chemical stability and does not lose its activity in normal storage conditions. Its solubility in water is 0.03wt% and highly soluble in organic solvents like ether and alcohols. The British pharmacopoeia recommended the chemical as a disinfectant in 1944 (British Phamacopoeia, publication: Drugs Under Experimental and Clinical Research, vol.29 Pg 100).

Q.7 Principles behind head space analysis

Headspace injection is characterized by a simple and easy handling method of complicated solid and solution matrix. Headspace analysis, however, is not recommended for high molecular weight substances like non-volatile compounds. A derivation headspace technique was studied for short chain lipids. The developed technique simplified the old conventional derivatization procedures and integrated the sample preparation and GC/MS analysis into one step. The thermostatting solvent, temperature, time, and matrix effects were investigated. Low calorie lipids and some agricultural samples are analyzed.

Since the inception of the SPME-Headspace, various applications such as food, pharmaceutical, and environmental samples have been studied. In SPME-Headspace, a solid sample is set into a headspace vial and then sealed. The vial is heated to raise the temperatures which in turn increase the vapor pressure of the target compounds from the sample. Chemical equilibrium is allowed to be established between the solid sample and the vapour headspace. A SPME fiber is inserted into the headspace without contacting the sample (Carr 1978). The fiber coating absorbs vapour of analyses from the headspace.

Q.8 Advantages of HPLC assay over the UV spectroscopic technique

HPLC (high performance liquid chromatography) is a process of separating already dissolved substances in a solution. Assay involves analysing the results of the process. It involves an injector column and a pump where the solution moves through. There are different methods in existence for results analysis depending on the detector used in the analysis (Hong & Altorfer 2001).

Ultra-violet spectroscopic technique involves an application of ultraviolet light to detect and analyse compounds dissolved in a solution. Ultraviolet light manifest itself in various wavelengths though unseen by the human eye (Roy et al. 2001). This method of detection utilises a fixed wavelength of 254nm, which is the standard wavelength measurement in addition to variable wavelength. The UV rays are channeled through a device that makes the light visible for the purpose of identification.

The advantage of HPLC assay method over UV spectroscopic technique is in the areas of accuracy. The results obtained through HPLC are more accurate than any other method of this type. Specificity is another benefit that comes along with HPLC and is more cost effective, simpler, and fewer inferences are obtained. In addition, the HPLC method is highly recommended for its applicability to chemical analysers as it does not require separate measurement for the components (Carr 1978).

Q.9 BP specification for impurities

The BP adopted a number of committees for Medicinal Products for Human to set guidelines relating to impurities in active ingredients of pharmaceuticals. The guidelines do not relate biotechnological and biological APIs and other finished products. The guidelines relating to impurities are set on the manufacturing process or possibly present in new substances of medicinal value formerly excluded from existing active substances. However, most of these principles in the guideline are also applicable to the already existing active substances and derived products.

The British pharmacopoeia states that organic impurities present active substances at a level that is above 0.15% and must be qualified and identified at a level above 0.1%. This is done unless the daily dosage of the active substance exceeds 2g and in this case, the qualification threshold and identification is 0.05% (Adamovics 1997). Generally, the impurities specifications in an existing API product are acceptable if one of these criteria is met:

1) The impurities level is below ICH  threshold of qualification

2) The limits of impurities match with those of a transparent official monograph

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3) Any new product should not contain impurities that exceed those in the market.

Nb, a transparent monograph is one that lists the controlled impurities by name, chemical formula and their organic structure where applicable. A statement that “no individual impurity is greater than 0.5%” means that none of the impurities specified in the monograph exceeds 0.5%.

The experts play a major role in drawing the attention to the fact that they revise the monographs in order to keep the limits of impurities in line with the quality measure of the European markets. By doing so, the problem of unreasonable high content of unidentified impurities will be solved to great extent. The guidelines state that for any well characterised compounds, the levels set for new impurities take into account the structural relationship to the already existing impurities (Boutli & Mourellou 2003, p. 101-105).

Q.10 BP specification for impurities in Diclofenac

Diclofenac impurity is a known impurity formed in Diclofenac sodium ampoules. Its formation depends on the initial pH of the preparation and the sterilization conditions. This is commonly referred to as a method related impurity and, thus, the British pharmacopoeia established standard methods for preparation of medicinal products that maintain the impurity level to acceptable limits (Roy et al. 2001).

Production methods selection depends upon the stability of production method. For Diclofenac sodium injection, the aseptic filtration process has been recommended as the best autoclave that produces impurities. Identification of impurities is very important in synthesis of drug substances and manufacture of dosage forms. It provides crucial data in regards to toxicity, safety and limits of detection and quantitation of several organic impurities.

Q.11 Suitability test is used to ensure that the drug substance is separated from its related substances

The purpose of purity testing is to ensure the need for qualification and identification of organic impurities that may occur in drug substances and drug products. Impurities may originate from manufacturing, synthesis or storage. Through application of purity testing, the impure profile of a drug, whether identified or unidentified in the drug, is identified.

According to Snyder et al. (1997) the release of drug products, the quality of drug substance with respect to impurities is controlled to demonstrate compliance with specifications. Different batches of the same drug prepared in the same way could be expected to contain the same level of impurities (Dasgupta 2012).  However, the relative concentration of impurities may show large variations due to such factors as the nature of the original materials.

Q.12 Factors to consider in testing the robustness of this method

Robustness testing is an important approach applied to develop a new method and establish its performance. The methods that stand the test of time must be robust enough to work in a laboratory environment and deliver the expected requirements in method. The factors to consider for robustness in the method are accuracy, sensitivity, and appropriateness. Tests for robustness are getting increased attention due to the increase in the recognised value in development and validation of methods (Snyder & Dolan 2006).

Q.13 Acidic drug analysis in ion suppression mode

Ion suppression is an analysis of tetracyclines in food substances. The conventional analysis consists of liquid extracts followed by a step of clean-up using solid phase extraction technique. Analysis of mass spectrometric and liquid chromatography detection is, thus, enabled. Various extraction strategies and clean-up are tested in the present work and the effectiveness evaluated in decrease of the ion suppression signals. For instance, treatment methods were tested with five samples of different feeds. The effectiveness of those methods was evaluated in terms of their decrease in ion suppression effect. However, there is also a decrease in variability of ion suppression between their samples (Steinheimer-Froschauer 2011).

Due to the introduction of mass spectronomy in clinical laboratories, specialty has been provided because of its ability to monitor selected ionic masses. It is also sensitive due to the enhanced signal to noise ratio and also fast as it helps to avoid the need for intensive sample clean-up and long time for analysis. However, MS has problems related to interference specifically due to ion suppression effect. 

Whenever there’s mass spectrometric assays development, ion suppression studies should be performed with expected physiologic concentration of the analysis under investigation.

Q.14 Gradient pump and specification

The gradient pump was designed and fabricated by Younglin Gradient as a pump of high performance liquid chromatogram with the exact and precise solvent delivery. It has very diverse functions and excellent performance. The pump is controlled by a microprocessor and involves a gradient program of different curves which are executed using a gradient pump. The pump is connected to 3 instruments or by the use of a solenoid valve. The Gradient pump has a frequency output function that connects it to similar products of other company which are operated by frequency inputs from other instruments (British Pharmacopoeia Commission 2008).

The Gradient Pump is a precisely small quantity pump with ability to indicate constant pressure operation, cumulative liquid delivery, related viscosity, and the elapsed time. It also controls input and output program execution with involved event program and RS232C communication. The pump used for liquid chromatograph requires an excellent precision and accuracy on flow rate and flow rate reproducibility in order to produce reliable data and characteristics to detect limits (Snyder & Dolan 2006).

The gradient pump was designed so that the integrated flow rate realise low pulse operations using a specially designed cam. However, pulse incapable of being neglected is actually caused due to compression of mobile phase proportion to elasticity of high pressure seals. Therefore, the Gradient Pump is controlled in real time to depress the occurrence of pulse proportion to pressure (Huber 1978).

The Gradient curve

The pump can edit 10 gradient programs of 10 lines for gradient analysis (Snyder et al. 2009). The curves which shapes are obtained through an exponential equation may be selected for input in each line. The gradients curves may be applied for, both, flow rate and gradient. 


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