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Gas chromatography-mass spectrometry :

Gas chromatography-mass spectrometry

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Gas chromatography-mass spectrometry Prepared & presented by: Shraddha Patel Mpharm 1st SEM (QA) Roll no: 16 Guided by: Dr. Nehal.J.Shah Dharmaj Degree Pharmacy College Dharmaj

What is GC/MS?:

What is GC/MS? Gas chromatography/mass spectrometry (GC/MS) is the synergistic combination of two powerful analytic techniques. The gas chromatography separates the components of a mixture in time The mass spectrometer provides information that aids in the structural identification of each component

GC/ Mass Spectrometry:

GC/ Mass Spectrometry GC equipment can be directly interfaced with rapid-scan Mass Spectrometers The flow rate is usually small enough to feed directly into the ionization chamber of the Mass Spectrometer Packed columns use a jet separator, which removes the carrier gas for the analyte

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Increase momentum of heavier analyte molecules so that 50% or more go into the skimmer Lighter helium molecules are deflected by vacuum and pumped away Use to identify components present in natural and biological systems odor/flavor of foods - pollutants


PRINCIPLE: It is coupled with principle of gas chromatography and mass spectroscopy The chromatography utilizes a capillary column which depends on the column’s dimension (length, diameter, film thickness) as well as the phase properties (e.g. 5% Phenyl polysiloxane ) The it is separated by elution technique Then the elute is bombarded which a series of electrons in the ioization chamber and then detected by quadrupole or ion trap system.

Stationary Phase: :

Stationary Phase: Present as coils wound togather present in oven The stationary phase is made of polysiloxane and the other coupled layer of other material like Mobile phase : The mobile phase is mainly a gas The gas must be inert or should possess specific properties to meet the standerds Generally Nitrogen is employed.

Mass Spectrometer Detectors:

Mass Spectrometer Detectors The most common type of mass spectrometer (MS) associated with a gas chromatograph (GC) is the (1) quadrupole mass spectrometer"Mass Selective Detector" (MSD). (2) Another relatively common detector is the ion trap mass spectrometer. detectors may be encountered such as time of flight (TOF), tandem quadrupoles (MS-MS) or in the case of an ion trap MS n where n indicates the number mass spectrometry stages.

Analysis :

Analysis A mass spectrometer is typically utilized in one of two ways: (1)Full Scan or (2) Selective Ion Monitoring (SIM). The typical GC/MS instrument is capable of performing both functions either individually or concomitantly, depending on the setup of the particular instrument.


Ionization . Electron impact source.( EI source ) It is commonly used source in GC-MS. The gaseous molecules are bombarded by high energy electron beams, usually of 70eV, generated from tungsten filament. An electron that collides with a neutral molecule may impart sufficient energy to remove the electron from the molecule resulting from singly charged ion. Mass range- upto 1000 daltons . It’s a hard method also versatile and provides structure information

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Chemical ionization source( CI source ) The EI source is a “hard source” and may produce too much fragmentation to allow positive identification of the analyte , and no molecular ion may be present. Consecutive ion fragmentation may result in low-mass ions carrying the large share of the total ion intensity, and the more analytically important primary fragments are absent or missing .

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Positive Chemical Ionization The reagent gas interacts with the target molecule, most often with a proton exchange. This produces the species in relatively high amounts. Negative Chemical Ionization The reagent gas decreases the impact of the free electrons on the target analyte . This decreased energy typically leaves the fragment in great supply

The GC/MS Interface:

The GC/MS Interface Transports the effluent from the gas chromatograph to the mass spectrometer Analyte must not condense in the interface Analyte may not decompose before entering the mass spectrometer ion source The gas load entering the ion source must be within pumping capacity of the mass spectrometer Capillary Columns Macrobore and Packed Columns

Capillary Columns:

Capillary Columns Insert exit end of column into ion source Under normal operating conditions, the mass spectrometer can handle the entire effluent of the column Must heat the capillary column to prevent condensation Surface of columns must be inactive

Macrobore and Packed Columns:

Macrobore and Packed Columns Effluent must be reduced before entering ion source Splitting the effluent results in a loss of sensitivity Enrichment devices are used Jet Separators are most common

Jet Separator::

Jet Separator: Two capillary tubes aligned with a small space between them. (1 mm) A vacuum is created between the two tubes using a rotary pump The GC effluent enters the vacuum region, those molecules which continue in the same direction enter the second capillary tube and continue to the ion source

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The carrier gas molecules are more easily diverted from the linear path by collisions The analyte molecules are much larger and carry more momentum The surface of the separator must be inactive and a reasonably even temperature Prone to leaks

Resolution and Mass Accuracy:

Resolution and Mass Accuracy With a modern mass spectrometer, it is possible to measure the mass of an ion to 1ppm with a resolution of 100,000 or better GC/MS scanning conditions are limited to 5-10 ppm mass accuracy and resolution is only between 2,000 and 10,000. These limitations are usually sufficient to allow for only a few reasonable and possible compositions

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Resolution can be increased by restricting the height and the width of the ion beam A compromise must be made between minimizing mass interference and signal intensity for low levels of material Gas chromatograph eliminates most compounds that cause mass interference. Principle cause of peak overlap is the internal mass standard.

Uses for GC/MS:

Uses for GC/MS May separate, analyze and identify unknown mixutres May separate, and analyze known mixtures For sample GC/MS experiments check out: http://www.lehigh.edu/~ingcms/ingcms.html

Applications :

Applications Environmental Monitoring and Cleanup : choice for tracking organic pollutants including many major classes of pesticides Criminal Forensics: analyze the particles from a human body in order to help link a criminal to a crime Law Enforcement: GC-MS is used for detection of illegal narcotics, and may eventually supplant drug-sniffing dogs.also used in forensic toxicology to find drugs and/or poisons in biological specimens of suspects, victims, or the deceased

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Security: , explosive detection systems have become a part of all US airports Food, Beverage and Perfume Analysis: GC-MS is extensively used for the analysis of these compounds which include esters , fatty acids , alcohols , aldehydes , terpenes etc. It is also used to detect and measure contaminants from spoilage or adulteration which may be harmful and which is often controlled by governmental agencies, for example pesticides .

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Astrochemistry : Medicine: The GC-MS is used for determining metabolic activity . Most applications are based on the use of 13 C as the labeling and the measurement of 13 C/ 12 C ratios with an isotope ratio mass spectrometer ( IRMS ); an MS with a detector designed to measure a few select ions and return values as rati


Reference: Braun Robert D., I ntroduction to Instrumental Analysis, chapter no.26, first edition, year2006, pharma book syndicate, page no. 890 – 928 http://en.wikipedia.org/wiki/Gas_chromatography-mass_spectrometry Wilard ,Merritt, Dean , settle.Instrument methods of Analysis, chapter no.18 , seventh edition page no:569

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