ppt AES

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ATOMIC EMISSION SPECTROSCOPY G . Parimala P,ceutical analysis & QA, Raghu college of pharmacy,vizag .

Introduction: :

Introduction: Interaction of electromagnetic radiation with atoms is called as emission spectroscopy. Def: if the initial excitation of the atoms or ions is caused by a process other than absorption of UV-VISIBLE radiation and if the emitted radiation is monitored , the analytical technique is called as atomic emission spectroscopy(AES). AES has long been the standard method for metal analysis.

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AES is divided categories according to the source of energy that causes the initial excitation. In AES the cell is required to atomize or ionize the sample to excite the atoms or ions and to retain the sample for sufficient time to obtain the analytical measurement. Flame emission spectroscopy(FES) Uses Flame As the cell. the from flame provides the energy i.e. required for excitation. Other sources of AES are plasma, electricity, and some non flammable sources.

Principle :

Principle Atoms in the sample absorb electromagnetic radiation from the source or excitation source then undergoes transition from ground to excited state , the excited state in which they are unstable , they return to the ground state by emitting radiation at particular wavelength. The λmax at which the intensity of atom is measured is termed as qualitative analysis. Contd …

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Reproducible , representative amount of sample is introduced into atomization and excitation of sample , the atoms undergoes atomization and excitation and gets exited and returns to ground state by emitting radiation. Provides information about the qualitative and quantitative analysis. Contd …

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Wide variety of atoms – are used as excitation sources Electrical discharges. Laser microprobe. Plasma source  microwave plasma. Inductively coupled plasma. Direct current plasma. Arc source. Spark source. Applications : This is employed for the analysis of alloy to ores & organic materials to atmospheric dusts.

Instrumentation: :

Instrumentation: 2 types of instruments are used Spectrometer(if detector is employed). Spectrograph(if photographic flame or plate is employed) Components: Sources. Sample introduction system. Wave length selector. Slits. Detector or photographic plate.

Instrumentation::

Instrumentation:

1. SOURCE:

1. SOURCE It is a atomization or excitation source. Ideal characteristics of atomization & excitation: 1. It should convert sample solution to vapour of analyte . It should convert vapour of analyte to atoms. It should provide energy to electrons to undergo excitation from ground state to excited state. It should provide reproducibility from sample to sample. It should provide sufficient light intensity so as to detect lines. It must be capable to excite all the elements of interest.

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Before selecting a source the below considerations must be taken: Vapour pressure of the elements. Concentration of the sample to be determined. Physical state of the sample. Solid samples  arc source-more sensitive. spark source-more stable. Gaseous & liquid samples  plasma source. contd …

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ARC: Electric arc is a device in which electrical discharge takes place. In arc and spark source excitation and atomization occurs in gap between pair of electrodes. Arc is a device in which discharge takes place between the 2 points , separated by a gas. (2 points are known as electrodes i.e. anode & cathode) Cathode: electrode from which current originates . Anode: electrode to which current gets. Arc & spark sources are employed in the elementary analysis of metals and metalloids .

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72 elements in the periodic table are determined by arc source. Types of arc sources: DC arc AC arc AC spark Laser microprobe Gas discharge tube contd …

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1. DC arc sources: It is more sensitive compared to various arc sources. It is most suitable for analysis of solid sample. It uses a DC potential i.e. between 10 & 50 V to cause an electrical discharge that corresponds to a current of between 1 & 35Aº to flow between the counter & same electrode. The temperature generated by the electrical discharge is about 4000⁰c at the anode & about 3200⁰c at the cathode . Between the electrodes the temperature is at 4000-7000⁰c range. The sample electrode can be either a cathode or an anode , but generally it is anode.

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Disadvantages: Production of gaseous cyanogens which has broad band radiation b/w 360-420nm. Gaseous cyanogen is formed by carbon of the electrode & N of the air. It can be minimized by blanketing the gap of electrode & tip of electrode with argon or mixture of argon(70-80%) & oxygen(20-30%).

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2. AC arc (alternating-current arc): An AC arc is similar to a DC arc except the discharge b/w electrodes is not continuous. The cathode and anode alternate after each half cycle of the applied AC potential. Typically the potential supply operates at 60Hz which result in polarity reversal of electrodes at a rate of 120 times each sec. During the discharge in each half-cycle the current is continuous as in DC arc. The use of a potential b/w 2000 & 3000 v usually results current b/w 1 & 5A. Start and stop flow of current. Copper electrodes as well as graphite electrode can be used as an AC arc. It shows reproducible results.

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3. AC spark: Not much sensitive when compared to DC arc but produce high degree of reproducibility &stability. Electrodes are made up of steel & graphite. Concentrations more than 0.01% are determined by this source , in case of solids. But for liquids 1µg/ml . powders are compressed into pellets and introduce into point electrode. the spark is active for periods between 10-100µs & typically discharges at a rate of 120-180 times each sec. the time required to obtain a spectrum with a spark about 10 sec.

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4. Laser microprobe: Laser microprobe

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it utilizes the microscope to pass the beam of light on to the surface of sample . Laser light diameter which falls on surface of the sample IS 10-50µm. point electrodes are placed at a distance of 25µm above the surface of the sample. Electrodes are used to control the location of electric field during the discharge. 5.Gas discharge tube: Used for the analysis of sample. Not widely used because of handling problems of gas & difficulty in maintaining pressurized conditions .

2.SAMPLE INTRODUCTION SYSTEM:

2. SAMPLE INTRODUCTION SYSTEM Various forms of electrodes are used and prepared from graphite carbon because graphite is conductive & doesn’t spectrally interfere with elemental analysis. Elements to be analysed are also be used to prepare electrodes. Electrodes are cylindrical in shape. Length-38mm Diameter-6.2mm Electrical discharge takes place at counter electrodes.

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S ample introduction devices

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Sample electrodes: Pointed electrode. Rotating disc electrode. Rotating platform electrode. Pointed electrode: Sample solution is poured at a point. Sample electrode may be graphite cup electrode. Solid samples are poured in a cup formed by drilling. Pour cup electrode is used for solutions

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cup 3mm pointer electrode

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Rotating disc electrode: Diameter is 1.3mm which is mounted on axle and dipped in sample solution. Counter electrode is placed at top of the disc. Disc and electrode rotates at 5-30 resolutions/min . disc axle sample soln

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Rotating platform electrode: Sample solution is placed on platform. For gaseous samples,plasma source is required. rotating platform

3. WAVE LENGTH SELECTOR:

3. WAVE LENGTH SELECTOR These are of two types: Prisms(UV radiation). Grating monochromators . a ) prisms are made up of quartz or fused silica. b ) grating monochromators are used in sophisticated instruments. Detection of lines are simple. “ echelle monochromators ” employs both prisms & grating monochromators . Contd …

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SLITS These are made up of parallel metal strips adjusted manually & independently. Entrance slit checks out radiation and allows the radiation only from source. Exit slit allows only the required wavelength radiation to reach the detector. Slits are 1cm length & 0.1cm wide .

4. DETECTORS :

4. DETECTORS There are three basic types of detector systems: These are  photomultiplier tubes (PMTs),  photodiode arrays (PDAs), and  charge coupled devices (CCDs).

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Most of the instruments use photoelectric means of detection in the form of photomultiplier tubes (PMTs), or with photodiode arrays respectively . In addition to this, in some cases photoplates are also used for detection purposes in AES. A number of modern instruments have now switched to solid state Array detectors that use charge coupled devices (CCDs) or charge injection devices (CIDs).

5. PROCESSING AND READOUT DEVICE:

5. PROCESSING AND READOUT DEVICE Whether the detection of the analyte signal is done sequentially or simultaneously, a large amount of data needs to be handled in terms of the positions of the spectral lines and their intensities. Therefore the processing of the data needs good computers along with multichannel analog to digital converter to acquire and save the detected signals for further processing . The results of the determinations are printed out by a dedicated printer . The dispersion and detection devices are typically combined with other essential components in different configurations to create different types of instruments.

Applications::

Applications : Agricultural science : Analysis of agricultural products and foods besides soil analysis. Health sciences : Determination of Al in blood, Cu in brain tissue, Se in liver , Na in breast milk. Direct determination of Ca, Fe, Cu, Mg, Na and K in serum samples. Geological sciences : Presence of lanthanides and other elements in rock samples. Forensic Sciences : Crime scene soil analysis .

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Metallurgy : Analysis of trace elements in stainless steel. Environmental Science : Waste water analysis, determination of pollutant metals in variety of matrices. Industry : Presence of metals like Cu, Fe, Ni, and Si in lubricating oils or gasoline at tracer concentration. Traces of metals like Ca, Cu, Fe, Mn , Mg, P, K and Zn in beer or wine; determination of trace elements in polymers , evaluation of catalysts, and so on.

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Thank you