Gas chromatography-atomic absorption spectroscopy (GC-AAS) is an analytical technique used to separate and quantify elemental components in a sample. It combines gas chromatography, which separates compounds, with atomic absorption spectroscopy, which measures elemental concentrations. Key components of a GC-AAS system include a gas chromatograph unit with a carrier gas, injection port, column, and detector; an atomic absorption spectrometer with a light source, atomizer, monochromator, and detector; and an interface connecting the two instruments. GC-AAS is applied to quantify metals in various samples like industrial waste, alloys, foods, and more.

1. HYGIA INSTITUTE OF PHARMACEUTICAL EDUCATION AND RESEARCH
Ghaila Road, Gazipur Balram Rd, near IIM Road, Prabandh Nagar, Lucknow, Uttar Pradesh 226020

2. Contents
 Introduction of Gc-AAS
Instumentation of Gc-AAS
1) Flow Regulator
2) Injection Devices
3) Column
4) Light Source
5) Atomizer
6) Monochromator
7) Detector
Application of Gc-AAS

3. GC – AAS (Gas Chromatography And Atomic
Absorption Spectroscopy)
Gas Chromatography (GC) - is technique which is used to the analysis of small, relatively volatile
molecules. It can be used both to identify and quantify substances. In general, for measurements a
sample or solution of the pure material and these are often obtained from specialist suppliers.
AAS quantitatively measures the concentrations of elements present in a liquid sample. It utilizes the
principle that elements in the gas phase absorb light at very specific wavelengths which gives the
technique excellent specificity and detection limits.
The sample may be an aqueous or organic solution; indeed, it may even be solid provided it can be
dissolved successfully. The liquid is drawn into a flame where it is ionised in the gas phase. Light of
a specific wavelength appropriate to the element being analysed is shone through the flame, the
absorption is proportional to the concentration of the element. Quantification is achieved by
preparing standards of the element.

4. INSTRUMENTATION
The instrument used in GC - AAS are :
 GC unit
 Light source
 Atomizer
 Monochromators
 Detector
 Amplifier
 Read out device

5. Diagram - GC unit
Diagram - Atomic Absorption Spectroscopy
Gas Chromatography + Atomic Absorption Spectroscopy = GC-AAS

6. Diagram – GC - AAS

7. 1. GC unit
GAS CHROMATOGRAPHY
 Inert carrier gas
 Flow regulators & Flow Meters
 Injection devices
 Columns
 Detectors
 CARRIER GAS
Inertness
Suitable for the detector
High purity
Easily available
Cheap
Should not cause the risk of fire
Should give best column performance
It should be
Hydrogen, Helium and Nitrogen are inert gas taken in GC because it has high thermal conductivity,
inexpensive and inflammable
Diagram - GC unit

8.  Flow regulators & Flow meters
Deliver the gas with uniform pressure/flow rate - Rota meter & Soap bubble flow meter
Rota meter - Placed before column inlet it has a glass tube with a float held on to a spring. the level of the
float is determined by the flow rate of carrier gas
Soap Bubble Meter - Similar to Rota meter & instead of a float, soap bubble formed indicates the flow rate.

9.  Injection Devices
The injection port consists of a septum through which a syringe needle is inserted to inject the
sample.
The sample is injected into a stream of inert gas usually at an elevated temperature by a micro
syringe.
The vaporized sample is carried into a column packed with the stationary phase.
To ensure rapid & complete solute volatilization temp of injector → 30-50 degree Celsius >column
temp
The injection port Is a hollow, heated, glass-lined cylinder.
The injector is heated so that all components in the sample will be vaporized.
If the temperature is too low, separation is poor and broad spectral peaks should result or no peak
develops at all.
If the injection temperature is too high, the specimen may decompose or change its structure.
The temperature of the sample port is usually about 50°C higher than the boiling point of the least
volatile component of the sample.

10. Injector Types
1. Split/ Split less Injector
2. On-Column Injector
3. High Oven Temperature On-Column Injector
4. Large Volume On-Column Injector
5. Packed Column Injector
6. Purged Packed Injector
7. Programmable Temperature Vaporizing Injector
1. Split mode
1. The split vent is open, part of the sample goes into the column.
2. When analyzing high concentration or neat samples.
3. Yields the sharpest peaks if the split gas is properly mixed.
4. Standard for capillary columns.
Split-less mode
1. The split vent is closed, most of the sample go into the column.
2. When analyzing low concentration or diluted samples.
3. Splitless times of ~ 1 minute are typical.
4. Standard for capillary columns.

12.  Columns
Column is one of the important parts of GC which decides the separation efficiency. Columns are made
up of glass and stainless steel.
Is where the chromatographic separation of the sample occurs.
Several types of columns are available for different chromatographic applications.
The heart of the system.
It is coated with a stationary phase which greatly influences the separation of the compounds.

13.  Light Source
Hollow Cathode Lamps
HCL is the most common radiation source in AAS. It contains a
tungsten anode and a hollow cylindrical cathode made of the
element to be determined. These are sealed in a glass tube filled
with an inert gas (neon, argon). Each element has its own unique
lamp which must be used for that analysis.
Electrode less Discharge Lamp
A small amount of the metal or salt of the element for which the
source is to be used is sealed inside a quartz bulb. This bulb is
placed inside a small, self-contained RF generator or “driver”.
When power is applied to the driver, an RF field is created. The
coupled energy will vaporize and excite the atom inside the bulb
causing them to emit their characteristic spectrum. They are
typically much more intense and, in some cases, more sensitive
than comparable HCL. Hence better precision and lower detection
limits where an analysis is intensity limited. EDL are available for
a wide variety of elements, including Sb, As, Bi, Cd, Cs, Ge, Pb,
Hg, P, K, Rb, Se, Te, Th, Sn and Zn.

14.  Atomizer
Atomization is separation of particles into individual molecules and breaking molecules into atoms. This is done
by exposing the analyte to high temperatures in a flame or graphite furnace Atomizer converts the liquid into
small droplets which are easily vaporized.
Types of Atomizers
I. Flame atomizer
a.) Total consumption burner
Total consumption burner. In this whole sample is atomized into the flame, hence named as total
consumption burner. In this burner, the sample solution, the fuel, and oxidizing gases are passed through
separate passages to meet at the opening of the base of flame. Then the flame breaks the sample in liquid
form into the droplets which are evaporated and burns. Leaving the residue which is reduced to atoms.
Fuel used – H2 /acetylene
b.) Premixed burner
It is most widely used because of uniformity in flame intensity. In this the sample solution, fuel and
oxidant are mixed before they reach the tip. The fine droplets get carried out along with the fuel gas at
outlet, the large drops of sample get collected in chamber and are drained out.

15. Advantages
Non-turbulent
Noiseless
Stable
Disadvantages
Only 5% sample reaches to the flame
Rest 95% is wasted.
II. Non-flame atomizer (Electro thermal atomizer)
Nebulization- Conversion of the liquid sample to a fine spray
Desolvation- Solid atoms are mixed with the gaseous fuel.
Volatilization- Solid atoms are converted to a vapor in the flame.
There are three types of particles that exist in the flame:
1) Atoms
2) Ions
3) Molecules

16. Nebulization: - Before the liquid sample enters the burner, it is converted into droplets this method a formation of small
droplets its called nebulization. Common method of nebulization is by use of gas moving at high velocity, called pneumatic
nebulization.
 Monochromators
Important part in an AA spectrophotometer. It is used to separate out all of the thousands of lines. Without a good
monochromator, detection limits are severely compromised. A monochromator is used to select the specific wavelength of
light which is absorbed by the sample, and to exclude other wavelengths. The selection of the specific light allows the
determination of the selected element in the presence of others.
They are of two types:
Prism monochromator : - Quartz material is used for making prism, as quartz is transparent over entire region. Grating
Monochromator : - It consists of a series of parallel straight lines cut into a plane surface.

17.  Detector
The light selected by the monochromator is directed onto a detector that is typically a photomultiplier tube, whose
function is to convert the light signal into an electrical signal proportional to the light intensity. The processing of
electrical signal is fulfilled by a signal amplifier. The signal could be displayed for readout, or further fed into a data
station for printout by the requested format.
Photomultiplier Tubes
Components
Made of a glass vacuum tube
Photocathode
Several dynodes
One anode

18. APPLICATIONS
Quantitative metal concentrations in solution
Analysis of lead in paint
Monitoring of trace metals in industrial effluent streams
Trace elements in product/raw materials along with ICP-MS
Analysis of additives and purity in steels and other metal alloys Analysis of low-level contaminants