It's about gc meter of analytical chemistry, Exercises of Analytical Chemistry

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CEC ASSIGNMENT

ANALYTICAL CHEMISTRY

TOPIC : GC APPLICATION IN

PHARMA INDUSTRY

NAME : HIRAL CHUDASAMA 19SC BSC CHEMISTRY SEM VI

INTRODUCTION

► Gas Chromatography (GC) is an analytical technique used to sperate the chemical components of a sample mixture and then detect them to determine their presence or absence and/or how much is present. These chemical components are usually organic molecules or gases. ► Gas chromatography (GC) is an analytical technique used to separate the chemical components of a sample mixture and then detect them to determine their presence or absence and/or how much is present. These chemical components are usually organic molecules or gases ► Gas chromatographs are frequently hyphenated to mass spectrometers (GC-MS) to enable the identification of the chemical components.

INSTRUMENTATION

► For having a hold on how does chromatography works, we need to be aware of the individual components of a GC chromatogram or GC Chromatograph. ► The main components are: ❑ Mobile phase ► In gas chromatography, usually, three types of gases are employed namely –

1. Carrier gas – This is needed for the transfer of the injected sample to the separation column. They are also responsible for the subsequent transfer of separated components to the detector. Common examples: Nitrogen, helium, or hydrogen
2. Fuel gas – They support the flame in Flame ionization detector (FID) detector such as Hydrogen.
3. Zero air – These are the purified air that plays the role of oxidant to support the combustion of flame in the detector. Before being led to the gas chromatographic system, the above three are intermixed in the desired proportion.

❑ Sample injector^ : ► The injector is a heated block where the sample is injected. Through the carrier gas stream, the sample is spontaneously vaporized and led to the column. ► With the help of a gas-tight syringe, the liquid sample mixtures are injected whereas, with the help of automated injection valves, the gaseous mixtures are injected. ❑ Column^ : ► This is filled with the stationary phase or its walls are covered with a liquid adsorbent. This is done for selective absorbance and retention of the sample components. ► Commonly used: Packed columns and Capillary columns (More popular) ❑ Component of a Column – Oven^ : ► The column is enclosed by a column oven which is responsible for maintaining a constant temperature during isothermal operation. This temperature when temperature programming is needed can be increased in a controlled way for acquiring effective separation of mixture components possessing different volatilities. .

WORKING

► As the name implies, GC uses a carrier gas in the separation, this plays the part of the mobile phase. The carrier gas transports the sample molecules through the GC system, ideally without reacting with the sample or damaging the instrument components. ► The sample is first introduced into the gas chromatograph (GC), either with a syringe or transferred from an autosampler that may also extract the chemical components from solid or liquid sample matrices. The sample is injected into the GC inlet through a septum which enables the injection of the sample mixture without losing the mobile phase. ► Connected to the inlet is the analytical column , a long (10 – 150 m), narrow (0.1 – 0.53 mm internal diameter) fused silica or metal tube which contains the stationary phase coated on the inside walls. ► The analytical column is held in the column oven which is heated during the analysis to elute the less volatile components. ► The outlet of the column is inserted into the detector which responds to the chemical components eluting from the column to produce a signal. ► The signal is recorded by the acquisition software on a computer to produce a chromatogram.

► (^) After injection into the GC inlet, the chemical components of the sample mixture are first vaporized, if they aren’t already in the gas phase. For low concentration samples the whole vapour cloud is transferred into the analytical column by the carrier gas in what is known as splitless mode. For high concentration samples only a portion of the sample is transferred to the analytical column in split mode, the remainder is flushed from the system through the split line to prevent overloading of the analytical column. ► (^) Once in the analytical column, the sample components are separated by their different interactions with the stationary phase. Therefore, when selecting the type of column to use, the volatility and functional groups of the analytes should be considered to match them to the stationary phase. Liquid stationary phases mainly fall into two types: polyethylene glycol (PEG) or polydimethylsiloxane (PDMS) based, the latter with varying percentages of dimethyl, diphenyl or mid-polar functional groups, for example cyanopropyl phenyl. Like separates like, therefore non-polar columns with dimethyl or a low percentage of diphenyl are good for separating non-polar analytes. ► (^) Those molecules capable of π-π interactions can be separated on stationary phases containing phenyl groups. Those capable of hydrogen bonding, for example acids and alcohols, are best separated with PEG columns, unless they have undergone derivatization to make them less polar. ► (^) The final step is the detection of the analyte molecules when they elute from the column. There are many types of GC detectors, for example: those that respond to C-H bonds like the flame ionization detector (FID); those that respond to specific elements for example sulfur, nitrogen or phosphorus; and those that respond to specific properties of the molecule, like the ability to capture an electron, as is used with the electron capture detector (ECD).

2. Residual Solvent Analysis : ► Residual solvent analysis in pharmaceuticals refers to the analysis of organic volatile impurities that are formed as by-product during the synthesis of drug products or during the packing and storage. According to GLP norms it is mandatory for drug manufacturers to ensure that these residues are removed, or are present only in limited concentrations in the products. Gas chromatography is widely being used for the residual solvent analysis. The detectors mainly used for the detection of these volatiles are flame ionization detector (FID) or Mass spectrometry (MS). Most popular sample introduction technique is by using static Headspace sampler/dynamic headspace analyser, solid-phase microextraction, and direct injection of solution containing bulk drug substance or drug product into the gas chromatograph.

3. Analysis of Drugs of Abuse : ► GCMS Coupled with Headspace makes a good analytical tool for the analysis of drugs of abuse. Analysis of Amphetamines and its metabolites in urine, Nicotine content in pharmaceutical drugs is an example for this type of analysis. GCMS coupled with chemical ionization and conventional headspace will give better sensitivity of about 20 times in SIM mode. GC MS produces a constant ionization making it easier for the comparison of identified compounds with the library data

4. Clinical Toxicology : ► Molecular ion formation, availability of increased range of compounds that can be analysed using GC, its high sensitivity and faster analysis makes it useful in the field of clinical toxicology. Usually Supersonic GCMS finds application in clinical toxicology. This is also used for the confirmation and also rejection of LCMS analysis reports in certain cases. Toxins and venoms are usually identified and quantified using this method. 5. Functional Group Identification : ⮚ There are different ways of identification of functional groups in pharmaceutical compounds using GC coupled with IR and UV as detectors. Before the invention of FTIR instruments (which are fast), GC-IR was used for the identification of functional group. In this case sample injected into GC after separation using column gets deposited on to a salt window in the IR instrument giving IR absorption of the functional groups present in the. Like GC-MS, this is a separation technique followed by identification, using infrared spectroscopy.