PRINCIPLE, INSTRUMENTATION AND APPLICATIONS OF GC - MS

1. GC-MS
PRESENTED BY
MR K V NANDA KUMAR
ASSOCIATE PROFESSOR
KRISHNA TEJA PHARMACY COLLEGE, TIRUPATHI

2. Gas
Chromatography-
Mass
Spectroscopy
Gas chromatography-mass spectroscopy (GC-MS) is one of
the so-called hyphenated analytical techniques.
As the name implies, it is two techniques that are
combined to form a single method of analyzing mixtures
of chemicals.
Gas chromatography separates the components of a
mixture and mass spectroscopy characterizes each of the
components individually.
By combining the two techniques, an analytical chemist
can both qualitatively and quantitatively evaluate a
solution containing a few chemicals.

4. Instrumentation
The GC-MS is composed of two major building blocks: the gas chromatograph and the mass spectrometer.
The gas chromatograph utilizes a capillary column whose properties regarding molecule separation depend on the column's
dimensions (length, diameter, film thickness) as well as the phase properties (e.g. 5% phenyl polysiloxane).
The difference in the chemical properties between different molecules in a mixture and their relative affinity for the stationary
phase of the column will promote separation of the molecules as the sample travels the length of the column.
The molecules are retained by the column and then elute (come off) from the column at different times (called the retention
time), and this allows the mass spectrometer downstream to capture, ionize, accelerate, deflect, and detect the ionized
molecules separately.
The mass spectrometer does this by breaking each molecule into ionized fragments and detecting these fragments using their
mass-to-charge ratio.

5. Types of detectors for mass spectrometry
Typical detectors for GC-MS is the quadrupole mass spectrometer.
This consists of four cylindrical parallel rods that use oscillating electrical fields to selectively stabilize or destabilize the path of
charged molecules passing through the field created by the quadrupole.
Charged molecules are selectively passed through the system that has a mass to charge ratio of a certain range.
The change in potential of the rods allows for a wide range of charged molecules to be rapidly swept through the system.
A quadrupole is effectively a mass selective filter and is similar to an ion trap, however, the quadrupole mass analyzer is designed to
allow ions to pass through the system compared to an ion trap that collects the trapped ions.
Another common detector is time of flight (TOF), which uses an electric field to accelerate the ions through an electric field, and then
calculates the time taken to reach the detector.

6. Applications of GC-MS
GC-MS has a broad range of applications covering many scientific disciplines.
GC-MS is commonly used in environmental science subjects to quantify the levels of organic
contaminants.
Specifically, it has been to distinguish the varying types of hydrocarbons in a sample for
monitoring and bioremediation purposes.
GC-MS has been used for forensic toxicology and criminal investigations as well as for law
enforcement for drug detection.

7. THANK YOU