INTRODUCTION:

Inductively coupled plasma/optical emission spectroscopy (ICP/OES) is a powerful tool for the determination of metals in a variety of different sample matrices. With this technique, liquid samples are injected into a radiofrequency (RF)-induced argon plasma using one of a variety of nebulizers or sample introduction techniques⁽¹⁾. The sample mist reaching the plasma is quickly dried, vaporized, and energized through collisional excitation at high temperature. The atomic emission emanating from the plasma is viewed, collected with a lens or mirror, and imaged onto the entrance slit of a wavelength selection device. Single element measurements can be performed cost effectively with a simple monochromator/ photomultiplier tube (PMT) combination, and simultaneous multielement determinations are performed for up to 70 elements with the combination of a polychromator and an array detector.⁽²⁾ The analytical performance of such systems is competitive with most other inorganic analysis techniques, especially with regards to sample throughput and sensitivity.

Principle:

The principle used in the inductively coupled Plasma Optical Emission Spectroscopy is When plasma energy is given to an analysis sample from outside, the component elements (atoms) are excited.⁽³⁾ When the excited atoms return to low energy position, emission rays (spectrum rays) are released and the emission rays that correspond to the photon wavelength are measured. The element type is determined based on the position of the photon rays, and the content of each element is determined based on the rays intensity⁽⁴⁾. To generate plasma, first, argon gas is supplied to torch coil, and high frequency electric current is applied to the work coil at the tip of the torch tube. Using the electromagnetic field created in the torch tube by the high frequency current, argon gas is ionized and plasma is generated. This plasma has high electron density and temperature (10000K) and this energy is used in the excitation-emission of the sample. Solution samples are introduced into the plasma in an atomized state through the narrow tube in the center of the torch tube⁽⁵⁾.

Inductively Coupled Plasma Characteristics:

The main analytical advantages of the ICP over other excitation sources originate from its capability for efficient and reproducible vaporization, atomization, excitation, and ionization for a wide range of elements in various sample matrices. This is mainly due to the high temperature, 6000–7000 K, in the observation zones of the ICP.⁽⁵⁾This temperature is much higher than the maximum temperature of furnaces (3300 K). The high temperature of the ICP also makes it capable of exciting refractory elements, and renders it less prone to matrix interferences. Other electrical-discharge-based sources, such as alternating current and direct current arcs and sparks, and the MIP, also have high temperatures for excitation and ionization, but the ICP is typically less noisy and better able to handle liquid samples. In addition, the ICP is an electrode less source, so there is no contamination from the impurities present in an electrode material the following is a list of some beneficial characteristics of the ICP source.

· high temperature (7000–8000 K)

· high electron density (1014–1016cm3)

· Appreciable degree of ionization for many elements simultaneous multi element capability (over 70 elements including P and S)

· Low background emission, and relatively low chemical interference

· High stability leading to excellent accuracy and precision

· Excellent detection limits for most elements (0.1 –100 ng mL1)

· Wide linear dynamic range (LDR) (four to six orders of magnitude)

· Cost-effective analyses.

Instrumentation:

In inductively coupled plasma-optical emission spectrometry, the sample is usually transported into the instrument as a stream of liquid sample. Inside the instrument, the liquid is converted into an aerosol through a process known as nebulisation.⁽¹⁾ The sample aerosol is then transported to the plasma where it is desolvated, vaporized, atomized, and excited and/or ionized by the plasma. The excited atoms and ions emit their characteristic radiation which is collected by a device that sorts the radiation by wavelength.⁽²⁾ The radiation is detected and turned into electronic signals that are converted into concentration information for the analyst. A representation of the layout of a typical ICP-OES instrument is shown in Figure No 1.

Figure No 1: Shows the major components and layout of a typical ICP-OES instrument.

Sample introduction

(1) Nebulizers:

Nebulizers are devices that convert a liquid into an aerosol that can be transported to the plasma. The nebulization process is one of the critical steps in ICP-OES. The ideal sample introduction system would be one that delivers all of the sample to the plasma in a form that the plasma could reproducibly desolvate, vaporize, atomize and ionize, and excite. Because only small droplets are useful in the ICP, the ability to produce small droplets for a wide variety of samples largely determines the utility of a nebulizer for ICP-OES.⁽³⁾

Many forces can be used to break up a liquid into an aerosol; however, only two have been used successfully with an ICP, pneumatic forces and ultrasonic mechanical forces .

Pneumatic nebulizer:

Ex:Babington nebulizer

Babington nebulizer:

The Babington nebulizer, shown in Figure No: 2 works by allowing the liquid to flow over a smooth surface with a small hole in it. High-speed argon gas emanating from the hole shears the sheet of liquid into small drops.

Figure No.2: Shows Babington nebulizer

This nebulizer is susceptible to clogging and can be used for the viscous liquids.

Ultrasonic nebulizer

In ultrasonic nebulisation, liquid sample is pumped onto an oscillating piezoelectric transducer. The oscillations break the sample into a fine aerosol, so aerosol formation is independent of nebulizer gas flow.

More sample will reach the ICP, providing detection limits which are usually 10 times lower than pneumatic nebulization. The higher efficiency of the ultrasonic nebulizer increases the water load to the ICP, so a desolvation unit is added after the nebulizer. The cooling portion of the desolvation unit has been replaced, in some commercially available systems, with a Peltier cooling device. However, the ultrasonic nebulizer is still susceptible to matrix effects, high solids loading and is not HF resistant.⁽⁴⁾

Pumps:

Figure No.4: Peristaltic pump used for ICP-OES.

Babington and Ultrasonic nebulizer require the solution to be pumped into the nebulizer, where as some of the nebulizers like concentric and cross-flow nebulizers can naturally draw the solution into the nebulizer by a process known as aspiration, a pumped flow is useful for these nebulizers also. With a pumped solution, the flow rate of the solution into the nebulizer is fixed and is not dependent on solution parameters such as viscosity and surface tension. The controlled flow rate of liquid also allows for more rapid washout of the nebulizer and spray chamber. Peristaltic pumps, such as the one shown in Figure 4, are almost exclusively the pumps of choice for ICP-OES applications. These pumps utilize a series of rollers that push the sample solution through the tubing using a process known as peristalsis. The pump itself does not come in contact with the solution, only with the tubing that carries the solution from the sample vessel to the nebulizer.⁽^3,5)The special tubing used with a peristaltic pump must be compatible with the sample that is passing through it. Most types of peristaltic pump tubing are compatible with weakly acidified aqueous media. Pumping strongly acidic solutions or organic solvents, however, usually requires the use of tubing made of specific materials.

Spray chambers:

Once the sample aerosol is created by the nebulizer, it must be transported to the torch so it can be injected into the plasma. Because only very small droplets in the aerosol are suitable for injection into the plasma, a spray chamber is placed between the nebulizer and the torch. Some typical ICP spray chamber designs are shown in Figure no.5. The primary function of the spray chamber is to remove large droplets from the aerosol. A secondary purpose of the spray chamber is to smooth out pulses that occur during nebulisation.In general, spray chambers for the ICP are designed to allow droplets with diameters of about 10 m or smaller to pass to the plasma. With typical nebulizers, this droplet range constitutes about 1 - 5% of the sample that is introduced to the nebulizer. The remaining 95 - 99% of the sample is drained into a waste container. The material from which a spray chamber is constructed can be an important characteristic of a spray chamber. Spray chambers made from corrosion-resistant materials allow to introduce samples containing hydrofluoric acid which could damage glass spray chambers.⁽⁶⁾

Figure No.5. Typical spray chamber used with ICP-OES.- Scott double pass type

Drains: The drain carries excess sample from the spray chamber to a waste container can have an impact on the performance of the ICP instrument. Besides carrying away excess sample, the drain system provides the backpressure necessary to force the sample aerosol-carrying nebulizer gas flow through the torch’s injector tube and into the plasma discharge. If the drain system does not drain evenly or if it allows bubbles to pass through it, the injection of sample into the plasma may be disrupted and noisy emission signals can result.

Drains for ICP-OES sample introduction systems come in many forms----loops, blocks, U-tubes, or even tubing connected to a peristaltic pump. For proper performance, it is important to keep the liquid level within the drain system at the recommended position. Also, when introducing organic-based samples into the ICP, it may be necessary to use drain tubing designated for use with organic solvents.⁽⁶⁾

3.2 .production of emission:

Torches: As shown schematically in Figure no.6, the torches contain three concentric tubes for argon flow and aerosol injection. The spacing between the two outer tubes is kept narrow so that the gas introduced between them emerges at high velocity. This outside chamber is also designed to make the gas spiral tangentially around the chamber as it proceeds upward. One of the functions of this gas is to keep the quartz walls of the torch cool and thus this gas flow was originally called the coolant flow or plasma flow but is now called the "outer" gas flow. For argon ICPs, the outer gas flow is usually about 7 - 15 litres per minute. The chamber between the outer flow and the inner flow sends gas directly under the plasma toroid. This flow keeps the plasma discharge away from the intermediate and injector tubes and makes sample aerosol introduction into the plasma easier. In normal operation of the torch, this flow, formerly called the auxiliary flow but now the intermediate gas flow, is about 1.0 L/min. The intermediate flow is usually introduced to reduce carbon formation on the tip of the injector tube when organic samples are being analyzed.

Figure No. 6. Schematic of a torch used for ICP-OES.

At present, the most popular torches are of the demountable type such as the one shown in Figure No.8. These torches can be taken apart so that the tubes can be modified or replaced without replacing the entire torch. The main advantages of the demountable torch lie in the lower torch replacement costs and the ability to use a variety of injector tubes. Such injectors include corrosion-resistant ceramic injectors, narrow-bore injectors for analyses involving organic solvents, and wide-bore injectors for introducing samples with high dissolved solids contents.⁽⁹⁾

Figure No.7. One-piece ICP torch.

Figure No.8. Demountable ICP Torch. A - expanded view, B - assembled view.

Radio Frequency Generators: The radio frequency (RF) generator is the device that provides the power for the generation and sustainment of the plasma discharge. This power ranging from about 700 to 1500 watts, is transferred to the plasma gas through a load coil surrounding the top of the torch. The load coil, which acts as an antenna to transfer the RF power to the plasma, is usually made from copper tubing and is cooled by water or gas during operation.

Most RF generators used for ICP-OES operate at a frequency between 27 and 56 MHz. The specific frequency used for an ICP-OES instrument is partially determined by those frequencies that the U. S. Federal Communications Commission (FCC) and similar agencies worldwide have designated for scientific and industrial use. Earlier most of the ICP generators were operated at 27.12 MHz. However, an increasing number of instruments now operate at 40.68 MHz because of improvements in coupling efficiency and reductions in background emission intensity realized at this frequency. Frequencies greater than 40 MHz also have been used but have not been as successful commercially.

There are two general types of RF generators used in ICP instruments. Crystal-controlled generators use a piezoelectric quartz crystal to produce an RF oscillating signal that is amplified by the generator.

3.3 .Collection and detection of emission

Transfer Optics:

The emission radiation from the region of the plasma known as the normal analytical zone (NAZ) is sampled for the spectrometric measurement. The analytical zone was observed from the side of the plasma operating in a vertical orientation as shown.

Figure No.9.Side-on ICP Viewing.

Figure No.10. End-on ICP Viewing

This classical approach to ICP spectroscopy is referred to as a radial or side-on viewing of the plasma. Whatever the ICP viewing, the radiation is usually collected by a focusing optic such as a convex lens or a concave mirror. This optic then focuses the image of the plasma onto the entrance slit of the wavelength dispersing device or spectrometer.⁽¹⁰⁾

Wavelength Dispersive Devices: The next step in ICP-OES is the differentiation of the emission radiation from one element from the radiation emitted by other elements and molecules. The physical dispersion of the different wavelengths is done by

· Diffraction gratings

· Prisms

· Filters

A reflection diffraction grating is simply a mirror with closely spaced lines ruled or etched into its surface. Most gratings used in ICP-OES instruments have a line, or groove, density from 600 to 4200 lines per millimetre. When light strikes such a grating, it is diffracted at an angle that is dependent on the wavelength of the light and the line density of the grating. In general, the longer the wavelength and the higher the line density, the higher the angle of diffraction will be. Figure 11 shows schematically the paths that light rays of two different wavelengths would take when diffracted from a grating. ^{(11, 12)}

To separate polychromatic light the grating is incorporated in an optical instrument called a spectrometer. The function of the spectrometer is to form the light into a well-defined beam, disperse it according to wavelength with a grating, and focus the dispersed light onto an exit plane or circle. In other words, the spectrometer receives white light or polychromatic radiation and disperses it into monochromatic radiation. One or more exit slits on the exit plane or circle are then used to allow certain wavelengths to pass to the detector while blocking out other wavelengths. ⁽¹³⁾

Figure No.11. shows Diffraction grating separating two wavelengths of light.

The monochromatic radiation which is diffracted from the grating is composed primarily of wavelengths representative of the light emitted by a particular elemental or molecular species in the ICP.

Poly chromators:

Figure No.12. Paschen-Runge mounts used in a Rowland circle polychromator.

With polychromators, each emission line can be observed during the entire sample introduction period, and theoretically more samples can be analyzed in a shorter period of time. The same amount of time is required to determine five elements as it does thirty. Thus, polychromators have a high sample throughput rate. Most polychromators are programmed for 20 to 30 spectral lines.⁽¹⁴⁾

Since the spectral line array for polychromators is fixed, spectral interference corrections may be applied to the analyte only if a spectral line for the element that is doing the interfering is included on the array.

Monochromators:

The most important advantage of monochromator-based systems is their spectral flexibility. By this we mean the ability to access, at any time, any wavelength within the range of the monochromator. Clearly, the spectral flexibility of a monochromator-based ICP-OES instrument allows for the determination of any element whose emission can be measured by the technique. Because of their scanning capability, monochromator-based instruments are much better suited for application of the complex background correction techniques often necessary for ICP-OES. Scanning the region around the analyte line or simultaneously measuring the immediate vicinity of the line assists in validating the analytical result. Monochromators require large amounts of sample and have a lower sample throughput than polychromator systems.⁽¹⁵⁾

Detectors:

Once the proper emission line has been isolated by the spectrometer, the detector and its associated electronics are used to measure the intensity of the emission line.

Most commonly used detectors are⁽¹⁶⁾

Ø Photo multiplier tube

Ø Array detectors

Ø Photodiode array

Ø Charge-injection device (CID)

Ø Charge-coupled device (CCD)

Photo multiplier tube:

The PMT is a vacuum tube that contains a photosensitive material, called the photocathode that ejects electrons when it is struck by light. These ejected electrons are accelerated towards a dynode which ejects two to five secondary electrons for every one electron which strikes its surface. The secondary electrons strike another dynode, ejecting more electrons which strike yet another dynode, causing a multiplicative effect along the way. Typical PMTs contain 9 to 16 dynode stages. The final step is the collection of the secondary electrons from the last dynode by the anode. As many as 106 secondary electrons may be collected as the result of a single photon striking the photocathode of a nine-dynode PMT. The electrical current measured at the anode is then used as a relative measure of the intensity of the radiation reaching the PMT⁽¹⁷⁾.

Figure No.14 shows schematically how a PMT amplifies the signal produced by a photon striking a photocathode.

The major advantages of the PMT over other detection devices are that it can be used to measure light over a relatively wide wavelength range, it can amplify very weak emission levels, and its range of response can be extended to over nine orders of magnitude in light intensity. Photocathode, dynode and anode layout of a photomultiplier tube. Diffraction grating, there is another optical component, the prism, which disperses polychromatic radiation into its characteristic wavelengths. In fact, the instrument used by Kirchhoff and Bunsen in the early 1860’s to detect the four new elements, Cs, Rb, Tl, and In, incorporated a prism to disperse the polychromatic radiation from the Bunsen flame into monochromatic radiation.

In recent years, it has been shown that certain advantages may be obtained by combining the characteristics of two dispersing systems such as a diffraction grating and a prism or two diffraction gratings.

Figure No 15. An echelle optical mount.

The two optical components are positioned perpendicular to each other. One of the dispersing devices is, in general, an echelle grating which is a very course grating in comparison to the normal diffraction grating. The echelle grating separates the polychromatic radiation by wavelengths and produces multiple, overlapping spectral orders. The second dispersing device, either a grating with a ruling density greater than 350 gr/mm or a prism, separates or cross disperses the overlapping orders into a two dimensional pattern called an echellogram. A typical optical configuration for this echelle type of spectrometer is illustrated in Figure 15.

Echelle grating-based spectrometers offer some distinct advantages over the conventional spectrometers. Firstly, the optics results in very good efficiency in each of the spectral orders. Conventional diffraction gratings are generally optimized at a particular wavelength, called the blaze wavelength, and for a particularly order which is usually the first order. Secondly, the system has excellent resolution since it is generally used in the higher spectral orders. (Resolution enhancements are exhibited with increasing order.) Because of the use of higher orders with better resolution, the physical size of the instrument may be reduced thus producing a small instrument footprint. ⁽¹⁸⁾

Advanced Array Detectors

In the 1960s, solid-state devices were introduced into the electronics industry. These devices, such as transistors and diodes, were based on the properties of silicon but were relegated to research and aerospace applications that could afford the relatively high cost of these components. As their use expanded to the digital electronics industry in the form of integrated circuits (ICs), not only did the cost of the devices become affordable but the cost of systems using the ICs such as digital computers were drastically reduced⁽¹⁹⁾.

It was also discovered that silicon-based sensors responded to light and were quickly integrated into linear and two-dimensional arrays called solid-state imagers or detectors. Consequently, three generic, advanced solid-state detectors with high sensitivity and resolution for spectroscopic applications have been developed –

· The photodiode array (PDA),

· The charge-injection device (CID)

· The charge-coupled device (CCD).

Figure No.16. Metal Oxide - Silicon (MOS) capacitor.

Figure.No.17. Photon absorption by silicon crystalline lattice and the formation of electron-hole pairs.

The CID and CCD devices are based on the light-sensitive properties of solid-state silicon and belong to the broad class of silicon-based devices called charge transfer devices (CTD).To illustrate the principals associated with CTDs, a block of very high purity crystalline silicon is considered (Figure 16). Onto this silicon substrate is grown an insulating layer of silicon dioxide (SiO₂). As shown in the pictorial Figure 17, each silicon atom in the substrate is bonded to its adjacent silicon atom in a three dimensional lattice. The silicon-silicon bond may be broken by energy of sufficient strength such as photons with visible or ultraviolet wavelength. When the bond is broken, an electron is released within the lattice structure and a subsequent hole in the crystalline structure is formed. This is called an electron-hole pair.

If a voltage is applied across the block of silicon (Figures 16 and 17), the freed electrons will move in the opposite direction of the applied electric field or toward the silicon-silicon dioxide interface while the holes will move in the other direction or in the same direction as the electric field and leave a region depleted of positive charge. This electron and hole motion within the crystalline lattice creates a current which is proportional to the amount of photons impinging on the structure. That is, the more light absorbed by the silicon, the more electrons are captured at the silicon silicon oxide interface. ⁽²⁰⁾

The CTDs elements, called pixels, may vary in size from 6 to 30 microns and arranged generally in a two-dimensional silicon wafer configuration from 512 x 512 to 4096 x 4096 pixels. Each of these pixels is capable of storing photon- generated charge

In general, each pixel of the two-dimensional Charge Injection Devices (CIDs) may be randomly interrogated to determine the amount of charge that has been accumulated during a measured time to which the device has been exposed to light (called the integration time). With the advent of high speed microprocessors, individual pixels may be examined even during the integration time to determine the accumulated charge. This process of examining the contents does not destroy the contents and, hence, is known as a non-destructive read-out mode. However, even though the CID has a random access and non-destructive read-out, it has an inherently higher noise level or dark current than, for example, a CCD, and requires cooling to liquid nitrogen temperatures to effectively decrease this noise. The dark current of any device is the electronic current that flows in a detector when operating voltages are applied but no light is present.⁽²¹⁾

Figure No.18. Segmented array charge-coupled device detector (SCD)

Figure No.19. SCD Detector Subarray

3.4. Signal processing and instrument control

Signal Processing

The electronics used for signal processing in ICP-OES systems utilizing PMT detection are generally straight forward. The electrical current measured at the anode of the PMT is converted into information that can be used by a computer.²² The first step is to convert the anode current, which represents emission intensity, into a voltage signal and utilize digital signal processing, the voltage signal is converted into digital information via an analog-to-digital, or A/D, converter. This digital information can then be used by a computer for further processing, the end result being information passed on to the computer.

Computers and Processors

An important part of any ICP-OES instrument is the computer control incorporated into the instrument. The majority of automated functions of an ICP-OES instrument are directly controlled by an on-board computer.At the simplest level of multi element ICP-OES instrumentation, a computer is needed to handle the massive amounts of data that such an instrument generates. While virtually every commercial ICP-OES instrument available today uses some type of computer to control the spectrometer and to collect, manipulate, and report analytical data, the amount of computer control over other functions of the instrument varies widely from model to model.⁽²⁶⁾

Software

ICP-OES instrument would be that it could prepare the standards and samples, develop the analytical method, analyze the samples, report the results, and make decisions based on those results all from a single keystroke.

The objective of a good software package is not only to control the automated features of the instrument during collection of analytical data but to simplify the overall operation of the instrument. Areas in which this is important include not only running an analysis but developing analytical methods and reporting results. The methods development task involves selecting proper operating parameters for an analysis, such as wavelengths, PMT voltages, background correction points, and standards concentrations. The ability to view spectral data displayed graphically with a minimum of effort is indispensable during the selection of these parameters.

4. ICP-OES Methodology:

The first step in an analysis is to prepare the samples and standards for introduction to the ICP. This step depends on the physical and chemical characteristics of the samples and from simple dilution to a complex series of chemical reactions and other preparation steps. The next step in the analysis concerns the sample introduction method and hardware to be used. For most ICP-OES analyses, the standard sample introduction system provided with the instrument will be sufficient.

The next step in the development of an analysis methodology is to program the instrument, using the computer software provided with the instrument, to perform the data collection and processing steps. To do this, decisions must be made concerning the operating conditions, wavelength selection, instrument calibration, emission measurement, and the actual sample analysis. For many analyses, the default conditions recommended by the instrument manufacturer will provide satisfactory results.

Once the samples and standards are prepared, the hardware is set up properly, and the computer is programmed, the analysis may begin. The analyst usually starts by introducing the first standard solution to the plasma and pressing a key on the computer. Assuming everything is found to be working properly, the analyst continues by introducing further standards (if used) and a blank solution to complete the calibration of the instrument. If no other calibrations or checks are required, the calibration is followed by introduction of samples. Once the analysis of samples is completed, the results can be tabulated and reported as necessary.⁽²⁴⁾

5. Applications:

1) Agricultural and Foods:

· The ICP-OES technique has been applied to the analysis of a large variety of agricultural and food materials. Types of samples include soils, fertilizers, plant materials, feedstuffs, foods, animal tissues, and body fluids. Analysis of infant formula for Ca, Cu, Fe, Mg, Mn, P, K, Na and Zn;

· Determination of trace metals in beer and wine.⁽²⁵⁾

2) Biological and Clinical:

· The use of surgical equipment, such as scalpels, needles, scissors, and forceps, often contaminates the sample with trace quantities of the very elements being determined in the sample.

· Determinations of Cr, Ni and Cu in urine.

· Determination of Al in blood.

· Determination of Cu in brain tissue.

· Determination of Se in liver.

· Determination of Ni in breast milk.

· Determination of B, P and S in bone.

· Determination of trace elements in oyster and tuna tissues.

3) Geological

· Determination of major, minor and trace compositions of various rocks, soils, sediments, and related materials.

· The major use of ICP-OES in this field is mainly used for prospecting purposes.

· The technique is also used for applications such as determining origins of rock formations and for marine geochemistry.

· Determination of U in ore grade material.

· Analysis of river sediments for several metals.

· Analysis of carbonate drill cores for major, minor and trace elements.

· Determination of rare earth elements in rock formations.

· Analysis of plankton for several elements.⁽²⁶⁾

4) Environmental and Waters:

· Analyses of sewage sludge, domestic and industrial refuge, coal and coal fly ash, and dust and other airborne particulates.

· Various water quality analyses as required by the U.S. Environmental Protection Agency.

· Determination of Fe, Cd, Cu, Mo, Ni, V, and Zn in seawater.

· Determination of phosphorus in municipal wastewater.

· Determination of heavy metals in inner-city dust samples.

· Trace metal analysis of coal fly ash.

5) Metals:

· Determination of toxic, trace and major constituents in coal and slags.

· Analysis of low alloy steels for As, B, Bi, Ce, La, P, Sn and Ta; high-precision determination of Si in steels;

· Determination of contaminants in high-purity Al.

· Analysis of superconducting materials for trace contaminants.⁽²⁷⁾

6) Organics:

· Analysis of organic solutions by ICP-OES is important not only for analyzing organic-based materials such as petroleum products but also for a wide variety of other applications. ⁽²⁸⁾

· The analysis of used lubricating oils for trace metal content is one of the more popular applications for organics analysis by ICP-OES. Some other applications include analysis of solvent-extracted geological materials for trace elemental composition.

· Determination of lead in gasoline;

· Determination of Cu, Fe, Ni, P, Si and V in cooking oils.

· Analysis of organophosphates for trace contaminants.

· Determination of major and trace elements in antifreeze.^(29,30)

CONCLUSION:

As Inductively coupled plasma-optical emission spectrometry (ICP-OES) is an attractive technique that has led many analysts to ask whether it is wiser to buy an ICP-OES or to stay with their trusted atomic absorption technique (AAS) and one of the sophisticated analytical techniques used now a days by many pharmaceutical industries. Being having the vast number of applications in the analysis of the samples of foods, agriculture etc, it is the choice by many analysts. The multielement analysis of water is one of the major applications for inductively coupled plasma-optical emission spectroscopy (ICP-OES), describes the analysis of metals and trace elements in drinking water in terms of sensitivity, precision, and accuracy. The modern ICP-OES method can success fully be used to assess content and fine the profile of many trace elements in organs and body fluids both in clinical analyses and in organic toxicological analysis for forensic purposes. Concentrations of elements in biological material obtained by this method can be used to interpret results of analyses in cases of suspicion of poisoning by in organic compounds. The ICP-OES method, similarly to other methods, has certain limitations. ICP optical emission spectrometry is now highly rated as a multipurpose analysis technique and there are over 2,000 units of ICP-OES in use in Japan. It is well regarded as an environmental measurement technique, along with atomic absorption spectrometry and ICP mass spectrometry, and its use is expected to expand even further in the future.

REFERENCES:

1. Charles B. Boss and Kenneth J. Fredeen, Concepts, Instrumentation and Techniques in Inductively Coupled Plasma Optical Emission Spectrometry, Second Edition, Perkin elmer, Pg 36-71.

2. Xiandeng Hou and Bradley T. Jones, Inductively Coupled Plasma/Optical Emission Spectrometry, Pg no 2.

3. Available at http://www.cetac.com/pdfs/AP_LSX-213_Plastics.pdf DATE; 21-1-2012 time 10pm.

4. Thomas J. Gluodenis, Dennis A. Yates, Zoe et al ,Determination of metals in TCLP extracts using RCRA ICP-OES, Perkin Elmer Instruments, http://www.perkinelmer. com.cn/CMSResources/Images/4674210APP_MetalsInTCLPExtracts.pdfdate 21 time 10.18

5. Rodolfo Fernández-Martínez,quel Caballero et al,Application of ICP-OES to the determination of CuIn_1−xGa_xSe₂ thin films used as absorber materials in solar cell devices

Analytical and Bio analytical Chemistry, 2005, Volume 382, Number 2, Pages 466-470

6. Yodalgis Mosqueda, Mario Pomares et al, Determination of major, minor and trace elements in cobalt-substituted lithium nickelate ceramic powders by inductively coupled plasma optical emission spectrometry, Pages 1855-1862.

7. Ahmet Aksoy, Zeliha Leblebici