INTRODUCTION

Consumer Products Services (BD) Ltd.
S Central Store Area,
Karnaphuli Export Processing Zone (KEPZ)
North Patenga, CHITTAGONG
Telephone: +880 31 250 2241-2
Fax Number: +880 31 250 2242
Located in the Karnaphuli Export Processing Zone (KEPZ) in Chittagong, Bangladesh.

The new lab is the first of its kind in Chittagong, and offers a suite of comprehensive softlines testing, inspection and assessment services for apparel exporters in the Chittagong region and surrounding areas.

Due to short time it was not possible for us to see all the equipment.

ATOMIC ABSORPTION SPECTROSCOPY

Atomic absorption spectroscopy (AAS) is a spectroanalytical procedure for the quantitative determination of chemical elements using the absorption of optical radiation (light) by free atoms in the gaseous state.

Introduction :
 Atomic Absorption Spectroscopy (AAS) is a quantitative method of analysis
that is applicable to many metals and a few non-metals.
 Almost every metallic element can be determined quantitatively by using the
spectral absorption characteristics of atoms.
 It is a very common technique for detecting and measuring concentration of
metals in the samples.
 It can analyze over 62 elements.
 Only a drop of sample needed
 The metals need not be removed from other
 components (AA is a highly selective technique)
 Sensitive in the ppm range (even ppb with the right equipment)

WORKING PRINCIPLE OF ATOMIC ABSORPTION SPECTROSCOPY.

• The metal vapor absorbs energy from an external light source, and electrons jump from the
ground to the excited states
• The ratio of the transmitted to incident light energy is directly proportional to the
concentration of metal atoms present
• A calibration curve can thus be constructed [Concentration (ppm) vs. Absorbance
• The sample is made up, typically in water
• A flame is created, usually using ethyne & oxygen (fuel)
• The flame gases flowing into the burner create a suction that pulls the liquid into the small
tube from the sample container. This liquid is transferred to the flame where the sample is
atomized [mixing the sample with air to create fine droplets]. The metal atoms then absorb
light from the source (cathode lamp).
• The light passes through a monochromater (a device used to select a particular wavelength
of light for observation)
• The intensity of the light is fairly low, so a photomultiplier tube (PMT) is used to boost the
signal intensity
• A detector (a special type of transducer) is used to generate voltage from the impingement
of electrons generated by the photomultiplier tube
• The light passes through a monochromater (a device used to select a particular wavelength
of light for observation)
• The intensity of the light is fairly low, so a photomultiplier tube (PMT) is used to boost the
signal intensity
• A detector (a special type of transducer) is used to generate voltage from the impingement
of electrons generated by the photomultiplier tube

Instrumentation

In order to analyze a sample for its atomiccon stituents, it has to be atomized. The atomizers most
commonly used nowadays are flames and electrothermal ( graphite tube) atomizers. The atoms
should then be irradiated by optical radiation, and the radiation source could be an element- specific line radiation source or a continuum radiation source. The radiation then passes through a monochromator in order to separate the elementspecific radiation from any other radiation emittedby the radiation source, which is finally measured by a detector.

Atomizers

The atomizers most commonly used now a days are (spectroscopic) flames and electrothermal (graphite tube) atomizers. Other atomizers, such as glow-discharge atomization, hydride atomization, or cold-vapor atomization might be used for special purposes.

Flame atomizers

The oldest and most commonly used atomizers in AAS are flames, principally the air acetylene flame with a temperature of about 2300 °C and the nitrous oxide system (N 2 O)-acetylene flame with a temperature of about 2700 °C. The latter flame, in addition, offers a more reducing environment, being ideally suited for analytes with high affinity to oxygen. A laboratory flame photometer that uses a propane operated flame atomizer Liquid or dissolved samples are typically used with flame atomizers. The sample solution is aspirated by a pneumatic analytical nebulizer , transformed into an aerosol , which is introduced into a spray chamber, where it is mixed with the flame gases and conditioned in a way that only the finest aerosol droplets (< 10 μm) enter the flame.

The processes in a flame include the
following stages:
Desolvation (drying) – the solvent is evaporated and the dry sample nanoparticles
remain;
Vaporization (transfer to the gaseous phase) – the solid particles are converted into gaseous
molecules;
Atomization – the molecules are dissociated into free atoms;
Ionization – depending on the ionization potential of the analyte atoms and the energy available
in a particular flame, atoms might be in part converted to gaseous ions.
Each of these stages includes the risk of interference in case the degree of phase transfer is
different for the analyte in the calibration standard and in the sample. Ionization is generally
undesirable, as it
reduces the number of atoms that are available for measurement, i.e., the sensitivity.In flame AAS
a steady-state signal is generated during the time period when the sample is aspirated. This
technique is typically used for determinations in the mg L −1 range, and may be extended down
to a few μg L −1 for some elements.

Electrothermal atomizers

Graphite tube
Electrothermal AAS (ET AAS) using graphite tube atomizers was pioneered by Boris V. L’vov
at the Saint Petersburg Polytechnical Institute , Russia,[4] since the late 1950s, and investigated
in parallel by Hans Massmann at the Institute of Spectrochemistry and Applied Spectroscopy
(ISAS) in Dortmund, Germany. [5] Although a wide variety of graphite tube designs have been
used over the years, the dimensions nowadays are typically 20–25 mm in length and 5–6 mm
inner diameter. With this technique liquid/ dissolved, solid and gaseous samples may be analyzed
directly.
The graphite tubes are heated via their ohmic resistance using a low-voltage high-current power
supply; the temperature in the individual stages can
be controlled very closely, and temperature ramps between the individual
stages facilitate separation of sample components. Tubes may be heated
transversely or longitudinally, where the former ones have the advantage of a more homogeneous
temperature distribution over their length.

LIGHT SOURCES

Hollow cathode lamps (HCL) are the most common radiation source in LS AAS. Inside the sealed lamp, filled with argon or neon gas at low pressure, is a cylindrical metal cathode containing the element of interest and an anode. A high voltage is applied across the anode and cathode, resulting in an ionization of the fill gas. The gas ions are accelerated towards the cathode and, upon impact on the cathode, sputter cathode material that is excited in the glow discharge to emit the radiation of the sputtered material, i.e., the element of interest.

Electrodeless discharge lamps
Electrodeless discharge lamps (EDL) contain a small quantity of the analyte as a metal or a salt
in a quartz bulb together with an inert gas, typically argon, at low pressure. The bulb is inserted into a coil that is generating an electromagnetic radio frequency field, resulting in a low-pressure inductively coupled discharge in the lamp.
Deuterium lamps
Deuterium HCL or even hydrogen HCL and deuterium discharge lamps are used in LS AAS for background correction purposes. The radiation intensity emitted by these lamps decreases significantly with increasing wavelength, so that they can be only used in the wavelength range between 190 and about 320 nm. Xenon lamp as a continuous radiation source

APPLICATIONS OF ATOMIC ABSORPTION SPECTROSCOPY

Atomic absorption spectrometry has many uses in different areas of chemistry such as:
Clinical analysis: Analyzing metals in biological fluids and tissues such as whole blood, plasma,
urine, saliva, brain tissue, liver, muscle tissue, semen.
Pharmaceuticals: In some pharmaceutical manufacturing processes, minute quantities of a
catalyst that remain in the final drug productWater analysis: Analyzing water for its metal
content.

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