ATOMIC ABSORPTION SPECTROMETRY

INTRODUCTION

Atomic Absorption Spectrometry (AAS) is a technique which is used for the analysis of quantities of elements present in a sample by measuring the absorbed radiation by the chemical element of interest.

This is done by measuring the spectra produced when the sample is excited by radiation. The atoms absorb ultraviolet or visible light and get excited to higher energy levels. Atomic absorption technique measures the amount of energy in the form of photons of light that are absorbed by the sample.

A detector measures the wavelengths of light transmitted by the sample, and compares them to the wavelengths which originally passed through the sample. A signal processor then integrates the changes in wavelength absorbed, which appear in the readout as peaks of energy absorption at discrete wavelengths.

The energy required for an electron to leave an atom is known as ionization energy and is specific to each and every element. When an electron moves from one energy level to another within the atom, a photon is emitted with energy E. Atoms of an element emit a characteristic spectral line. Every atom has its own distinct pattern of wavelengths at which it will absorb energy, due to the unique configuration of electrons in its outer shell.

This enables the qualitative analysis of a sample. The concentration is calculated based on the Beer-Lambert law. Absorbance is directly proportional to the concentration of the analyte absorbed for the existing set of conditions. The concentration is usually determined from a calibration curve, obtained using standards of known concentration or certified reference materials (CRMs). However, applying the Beer-Lambert law directly in AAS is difficult due to:

·       variations in atomization efficiency from the sample matrix non-uniformity of concentration and path length of analyte atoms (in graphite furnace AA).

The chemical methods used are based on matter interactions, i.e. chemical reactions. For a long period of time these methods were essentially empirical, involving, in most cases, great experimental skills. In analytical chemistry, AAS is a technique used mostly for determining the concentration of a particular metal element within a sample. AAS can be used to analyse the concentration of over 62 different metals in a solution. Typically, the technique makes use of a flame to atomize the sample, but other atomizers, such as a graphite furnace, are also used. Three steps are involved in turning a liquid sample into an atomic gas:

1. Desolvation – the liquid solvent is evaporated, and the dry sample remains;

2. Vaporization – the solid sample vaporizes to a gas; and

3. Volatilization – the compounds that compose the sample are broken into free atoms.

To measure how much of a given element is present in a sample, first of all , we must establish a basis for comparison using certified reference materials or known quantities of that element to produce a calibration curve.

To generate this curve, a specific wavelength is selected, and the detector (Usually Photomultiplier tube detectors are used) is set to measure only the energy transmitted at that wavelength. As the concentration of the target atom in the sample increases, the absorption will also increase proportionally.

A series of samples containing known concentrations of the element to be measured are analysed, and the corresponding absorbance, which is the inverse percentage of light transmitted, is recorded.

The measured absorption at each concentration is then plotted, so that a straight line can then be drawn between the resulting points. From this line, the concentration of the substance under investigation is extrapolated from the substance’s absorbance. The use of special light sources and the selection of specific wavelengths allow for the quantitative determination of individual components in a multi-element mixture.

BASIC PRINCIPLE

The selectivity in AAS is very important, since each element has a different set of energy levels and gives rise to very narrow absorption lines. Hence, the selection of the monochromator is vital to obtain a linear calibration curve (Beers' Law), the bandwidth of the absorbing species must be broader than that of the light source; which is difficult to achieve with ordinary monochromators. The monochromator is a very important part of an AA spectrometer because it is used to separate the thousands of lines generated by all of the elements in a sample.

Without a good monochromator, detection limits are severely compromised. A monochromator is used to select the specific wavelength of light that is absorbed by the sample and to exclude other wavelengths. The selection of the specific wavelength of light allows for the determination of the specific element of interest when it is in the presence of other elements. The light selected by the monochromator is directed onto a detector,typically a photomultiplier tube, whose function is to convert the light signal into an electrical signal proportional to the light intensity. The challenge of requiring the bandwidth of the absorbing species to be broader than that of the light source is solved with radiation sources with very narrow lines.

The study of trace metals in wet and dry precipitation has increased in recent decades because trace metals have adverse environmental and human health effects. Some metals, such as Pb, Cd and Hg, accumulate in the biosphere and can be toxic to living systems.

Anthropogenic activities have substantially increased trace metal concentrations in the atmosphere. In addition, acid precipitation promotes the dissolution of many trace metals, which enhances their bioavailability. In recent decades, heavy metal concentrations have increased not only in the atmosphere but also in pluvial precipitation. Metals, such as Pb, Cd, As, and Hg, are known to accumulate in the biosphere and to be dangerous for living organisms, even at very low levels. Many human activities play a major role in global and regional trace element budgets. Additionally, when present above certain concentration levels, trace metals are potentially toxic to marine and terrestrial life. Thus, biogeochemical

perturbations are a matter of crucial interest in science.

The atmospheric input of metals exhibits strong temporal and spatial variability due to short atmospheric residence times and meteorological factors. As in oceanic chemistry, the impact of trace metals in atmospheric deposition cannot be determined from a simple consideration of global mass balance; rather, accurate data on net air or sea fluxes for specific regions are needed.

Particles in urban areas represent one of the most significant atmospheric pollution problems, and are responsible for decreased visibility and other effects on public health, particularly when their aerodynamic diameters are smaller than 10 μm, because these small particles can penetrate deep into the human respiratory tract. There have been many studies measuring concentrations of toxic metals such as Ag, As, Cd, Cr, Cu, Hg, Ni, Pb in rainwater and their deposition into surface waters and on soils. Natural sources of aerosols include terrestrial dust, marine aerosols, volcanic emissions and forest fires. Anthropogenic particles, on the other hand, are created by industrial processes, fossil fuel combustion, automobile mufflers, worn engine parts, and corrosion of metallic parts. The presence of metals in atmospheric particles are directly associated with health risks of these metals. Anthropogenic sources have substantially increased trace metal concentrations in atmospheric deposition.

The instrument used for atomic absorption spectrometry can have either of two atomizers. One attachment is a flame burner, which uses acetylene and air fuels. The second attachment consists of a graphite furnace that is used for trace metal analysis. Figure 1 depicts a diagram of an atomic absorption spectrometer.

Fig. 1. The spectral, or wavelength, range captures the dispersion of the grating across the linear array.

           

 Flame and furnace spectroscopy has been used for years for the analysis of metals. Today these procedures are used more than ever in materials and environmental applications. This is due to the need for lower detection limits and for trace analysis in a wide range ofsamples. Because of the scientific advances of Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), have left Atomic Absorption (AA) behind. This technique, however, is excellent and has a larger specificity that ICP does not have.

Figure 2 shows a diagram of an atomic absorption spectrometer with a graphite furnace.

 AAS is a reliable chemical technique to analyze almost any type of material. This post describes the basic principles of atomic absorption spectroscopy in the analysis of trace metals, such as Ag, As, Cd, Cr, Cu, and Hg, in environmental samples. For example, the study of trace metals in wet and dry precipitation has increased in recent decades because trace metals have adverse environmental and human health effects. Anthropogenic activities have substantially increased trace metal concentrations in the atmosphere. In recent decades, heavy metal concentrations have increased not only in the atmosphere but also in pluvial precipitation.

Many human activities play a major role in global and regional trace element budgets. Additionally, when present above certain concentration levels, trace metals are potentially toxic to marine and terrestrial life. Thus, biogeochemical perturbations are a matter of crucial interest in science.

The atmospheric input of metals exhibits strong temporal and spatial variability due to short atmospheric residence times and meteorological factors. As in oceanic chemistry, the impact of trace metals in atmospheric deposition cannot be determined from a simple consideration of global mass balance; rather, accurate data on net air or sea fluxes for specific regions are needed.

Particles in urban areas represent one of the most significant atmospheric pollution

problems, and are responsible for decreased visibility and other effects on public health, particularly when their aerodynamic diameters are smaller than 10 μm, because these small particles can penetrate deep into the human respiratory tract. There have been many studies measuring concentrations of toxic metals such as Ag, As, Cd, Cr, Cu, Hg, Ni, Pb in rainwater and their deposition into surface waters and on soils. Natural sources of aerosols include terrestrial dust, marine aerosols, volcanic emissions and forest fires. Anthropogenic particles, on the other hand, are created by industrial processes, fossil fuel combustion, automobile mufflers, worn engine parts, and corrosion of metallic parts. The presence of metals in atmospheric particles and the associated health risks of these metals.

Anthropogenic sources have substantially increased trace metal concentrations in

atmospheric deposition. In addition, acid precipitation favors the dissolution of many trace metals, which enhances their bioavailability. Trace metals from the atmosphere are deposited by rain, snow and dry fallout. The predominant processes of deposition by rain are rainout and washout (scavenging). Generally, in over 80 % of wet precipitation, heavy metals are dissolved in rainwater and can thus reach and be taken up by the vegetation blanket and soils. Light of a specific wavelength, selected appropriately for the element being analyzed, is given off when the metal is ionized in the flame; the absorption of this light by the element of interest is proportional to the concentration of that element.

Quantification is achieved by preparing standards of the element.

• AAS intrinsically more sensitive than Atomic Emission Spectrometry (AES)
• Similar atomization techniques to AES
• Addition of radiation source
• High temperature for atomization necessary
• Flame and electrothermal atomization
• Very high temperature for excitation not necessary; generally no plasma/arc/spark in AAS

We will discuss the Flame AAS technique and AAS with Graphite Furnace (GFAA) in the upcoming posts.

PORTABLE PHOTOSYNTHESIS SYSTEM : MEASUREMENT PRINCIPLE

MEASUREMENT THEORY

The PHOTOSYNTHESIS SYSTEM is a completely self-contained unit for measuring the CO2 assimilation (Photosynthesis and Respiration) and transpiration (water loss by evaporation of leaves of plants. These systems are designed specifically for use by students in Schools and Universities. It offers many of the facilities of instruments designed for research , but greatly simplifies the measurement procedure.

 

It operates on the Open System principle. The leaf is placed in a sealed enclosure with a window for illumination. This is referred to as the leaf cuvette. Through the cuvette is passed a measured flow of air. The CO2 / H2O concentrations of the air entering (reference air) and of the air leaving (analysis air) are measured. To measure the concentrations the PHOTOSYNTHESIS SYSTEM uses a single CO2 and H2O sensor and alternately switches the reference and analysis air. From the flow rate of air and the change in the concentration the assimilation and transpiration rates are calculated.

Though it is designed to supply ambient air to the cuvette, for the study of CO2 responses, it is possible to decrease the CO2 concentration in a series of steps. A similar provision is made for water vapour responses. It is supplied with a leaf cuvette which can be used for a wide variety of leaves. A light unit will be available shortly (LED) for use with the cuvette for manual control of cuvette light intensity.

CO2 /H2O ANALYSIS MEASUREMENT PRINCIPLE

Carbon Dioxide absorbs Infra-red radiation strongly at a wavelength of 4.26 microns. PHOTOSYNTHESIS SYSTEM uses this absorption to measure the CO2 concentration. The analyzer consists of a source of infra-red radiation (a small tungsten filament lamp) at one end of a highly polished, gold plated tube through which the air passes. At the other end of the tube is the infra-red detector which has a window through which only infra-red radiation at 4.26 microns can pass so that the responds only to the presence of CO2. The theoretical analysis range is from 0-100% CO2. However, because of the absorption characteristics of gases, the absorption path lengths, infrared source intensities, detector sensitivities and the S/N (Signal to Noise) ratio of the system define the effective range. The absorption path length of PHOTOSYNTHESIS SYSTEM is optimised for 2,000 volumes of CO2 per million volumes of air. This is correctly referred to as 2000 parts per million by volume or 2000 ppm. (Ambient air contains about 360 ppm.).

Temperature corrections are not required as the opto-electronics are thermostatted and the air is equilibrated to this temperature before entering the absorption cells. The built in transducer compensates for absolute pressure changes in the cell.

In part, the excellent stability of PHOTOSYNTHESIS SYSTEM is due to regular zeroing when CO2 free, air is passed through (referred to as ZERO). ZERO minimises the effects on span (gas sensitivity), of sample cell contamination, source ageing, and changes in detector sensitivity, amplifier gains, and reference voltages. It is done every approximately minute. The ZERO reading is used to compensate for changes in the signal level. From the relationship between absorptance and concentration, determined in the factory, and the current calibration factor, the sample concentration is determined.

Water vapor is measured using a high precision capacitive sensor. This consists of a small piece of glass coated first with a layer of metal, then with a polymer, followed by a second metal layer. Wires are soldered to the metal layers and the sensor is placed in a circuit that measures its electrical capacitance. The amount of water in the polymer depends on the water vapour content of the air and the electrical capacitance of the polymer depends on the water content. So with calibration, the water in the air can be measured. Water vapour concentration is again expressed as a volume/volume relationship but in parts per thousand, which is called millibars (mb)

Both CO2 and H2O measurements give the absolute concentrations for the reference air, and then the difference between the reference and the analysis concentration.

The complete PHOTOSYNTHESIS SYSTEM gas circuit with control valves is shown below.

CALIBRATION AND THE ROLE OF CALIBRATION SAMPLES IN METAL OPTICAL EMISSION SPECTROMETER.

THEORY OF CALIBRATION:

Concentration vs Intensity calibration curve

Calibration comprises measurement of calibration samples and determination of the functional relationship between the intensity ‘I’ of the line of an analyte and its concentration c in these samples. The functional relationship is the calibration function or calibration curve. It includes relationships between vaporisation, excitation, radiation offtake, dispersion and the measured value. Since spectrochemical analysis is a process of analysis is a process of analysis by comparison ( in contrast to absolute methods such as weighing ), it is necessary to carry out calibration with samples of accurately known concentration, the calibration samples.

The calibration function must not be confused with the function inverse to it-the read out or evaluation function. In the case of the calibration function I = f1 (c), the concentrations of the calibration samples are assumed to be free of error, and the errors (deviations from a best fit curve after correction of the intensities for systematic errors) are imputed entirely to the spectrometer method, so that the preconditions for regression calculations showing correlation coefficients as a quality index are useless. With the evaluation function c = f2 = ( I ) the concentration c of an analyte in an analytical sample is determined, which is accordingly subject to error, f2 = 1/f1.

For optical emission spectrometry there is no theory of calibration curves which can be used for practical purposes. There are formulae for which it is assumed that it is possible to represent the relationship between line intensity and concentration as a power function : I = I0 ck. The calibration function can be represented mathematically in various ways :

linear calibration function : I = f(c) = a0 + a1 c

non-linear calibration function : I =f(c) = a0 + a1 c +a2 c2+...+an cn

The extent to which the regression approaches the true course of the calibration

curve can be discerned from the residual scatter, namely at the point when the

addition of further terms to the approximation function does not produce any

further improvement in the residual scatter.

CALIBRATION SAMPLES

Fundamental role of the calibration samples is attested by international community and by International Standardisation Organization (ISO), which delivered the following definitions :

Reference Materials (RM) : they are Materials or substances whose properties are so well defined that they can be used to calibrate the instrument, verify the measure or assign values to the materials.

CRM sample with Spark analysis spots

Certified Reference Materials (CRM) : they are Materials whose values concerning one or more properties are certified by means of a valid technical procedure and equipped by a Certificate or other documents from a qualified technical Body ( public or private Organization or Society., which deliver a certificate for the Reference Material )

Calibration samples present three disadvantages :

1) They are expensive

2) Their dimensions and shapes are not always available for the sample-holder stand of the spectrometer.

3) They are available only for some elements and concentrations

In some cases calibration samples can be synthesised, for example by alloying or diluting part of a charge. Because of this manipulation, the calculated values are rarely reliable and their composition should be confirmed by chemical analysis.

RECALIBRATION SAMPLES

When calibrating spectrometers with calibration samples (reference samples)

Recalibration samples are measured a number of times in order to obtain a reliable nominal value suitable for calibration. The additive and/or multiplicative changes in the sensitivity of the spectrometer bring about displacements of the calibration curves in the linear scale of the co-ordinate system. In order to trace (calculate) the actual intensity values at any later time back to the nominal intensity values submitted at the time of calibration a low (LP) and a high (HP) intensity is required for each analyte channel. In metal analysis with spark discharge the low points of all the analyte channels are usually measured with the pure base (Fe, Al, Cu,...). The high points are usually measured from synthetic samples having as many elements as possible with good homogeneity and precision.

The synthetic composition is given as a guide analysis and the samples often do not lie on the calibration curves. Mathematical procedure of calibration is a automated process.

In emission spectrometry recalibration samples run out, because of the polishing of the surface before recalibration. When recalibration samples are replaced there is no guarantee that, even with the same sample number, the new sample concentrations will correspond exactly to the sample being replaced. For this reason when calibrating a spectrometer for metal analysis, a minimum supply of recalibration samples should be available, for example five recalibration samples for each type.

The frequency of recalibration depends on the instrument and its use.

Interdependence with the instrument means that devices of the same kind, specially because of different phototubes stability, must be recalibrated at different intervals. Interdependence with use means that, even if stability is the same, recalibration frequency depends on the kind of analysis (traces analysis, sorting analysis).

(Note: The above post is written in context to calibration of Spark Optical emission spectrometer for metal and alloy analysis.)

DIFFERENT NANO PARTICLES AND THEIR APPLICATIONS

Nanoparticle type	Applications
Alumino silicate nano particles	It can be used to reduce bleeding in trauma patients with external wounds by activating the blood clotting mechanism, causing blood in a wound to clot quickly. Z-Medica is producing a medical gauze that uses aluminosilicate nano particles for use on external wounds. For trauma patients with internal bleeding another way to reduce the blood loss is needed.  Also the researchers at Chase Western Reserve University are developing polymer nanoparticles that act as synthetic platelets. Lab tests have shown that injection of these synthetic platelets significantly reduces blood loss.
Polyethylene glycol-hydrophilic carbon clusters (PEG-HCC)	They have been shown to absorb free radicals at a much higher rate than the proteins out body uses for this function. This ability to absorb free radicals may reduce the harm that is caused by the release of free radicals after a brain injury.
Iron oxide nano particles	It can be used to improve MRI images of cancer tumours. The nanoparticle is coated with a peptide that binds to a cancer tumour, once the nanoparticles are attached to the tumour the magnetic property of the iron oxide enhances the images from the Magnetic Resonance Imagining scan.
Gold nano particles	A method being developed to fight skin cancer uses gold nanoparticles to which RNA molecules are attached. The nanoparticles are in an ointment that is applied to the skin. The nanoparticles penetrate the skin and the RNA attaches to a cancer related gene, stopping the gene from generating proteins that are used in the growth of skin cancer tumours.
Gold nano particles embedded in a porous manganese oxide	Using gold nanoparticles embedded in a porous manganese oxide as a room temperature catalyst to breakdown volatile organic compounds in air.
Palladium nano particles	A layer of closely spaced palladium nanoparticles that detect hydrogen. When hydrogen is absorbed the palladium nanoparticles swell, causing shorts between nanoparticles which lowers the resistance of the palladium layer.
Quantum Dots (crystalline nano particles)	Quantum Dots (crystalline nanoparticles) that identify the location of cancer cells in the body.
Gold nano particles with organic molecules	Combining gold nanoparticles with organic molecules to create a transistor known as a NOMFET (Nanoparticle Organic Memory Field-Effect Transistor).
Iron nano particles	Iron nanoparticles used to clean up carbon tetrachloride pollution in ground water.
Silicon nano particles coating	Silicon nanoparticles coating anodes of lithium-ion batteries to increase battery power and reduce recharge time.
Gold nano particles	Gold nanoparticles that allow heat from infrared lasers to be targeted on cancer tumours.
Silicate nano particles	Silicate nanoparticles used to provide a barrier to gasses (for example oxygen), or moisture in a plastic film used for packaging. This could reduce the possibly of food spoiling or drying out.
Zinc oxide nano particles	Zinc oxide nano particles dispersed in industrial coatings to protect wood, plastic and textiles from exposure to UV rays.
Silicon dioxide crystalline nano particles	Silicon dioxide crystalline nano particles filling gaps between carbon fibres strengthen tennis racquets.
Silver nano particles	Silver nano particles in fabric that kills bacteria making clothing odour-resistant.
Porous silica  Nano particles used to deliver chemotherapy drugs to cancer cells.	Porous silica nano particles used to deliver chemotherapy drugs to cancer cells.
Semiconductor nano particles	Semiconductor nano particles applied in a low temperature printing process that results in low cost solar cells.
Iron oxide nano particles	Iron oxide nano particles used to clean arsenic from water wells.
	Nano particles, when activated by x-rays, that generate electrons that cause the destruction of cancer cells to which they have attached themselves. This is intended to be used in place radiation therapy with much less damage to healthy tissue.
	A nano particle cream that releases nitric oxide gas to fight staph infections.
Gold-palladium	That can replace expensive and potentially toxic reagents that promote oxidation of aromatic primary alcohols to aldehydes, which is one of the crucial processes in the perfume production.

DIFFERENCE BETWEEN PHOTOMULTIPLIER (PMT) & CHARGED COUPLED DEVICE (CCD) DETECTORS

Some of the most common differences between Photo multiplier (PMT) detectors & Charged Coupled Device detector (CCDs)..


1.       Photomultiplier tubes (PMTs) and Charged coupled devices (CCDs) both give spectra. The difference is the PMT is used with a small slit in front of it to control the bandwidth of light being detected. The CCD takes advantage of the dispersed light fully. The pixel columns will each correspond to a wavelength (resolution and range depend on the grating used). A PMT requires scanning of the Monochromator to collect a spectra. The CCD takes a single snap shot and you have a spectrum. The CCD sensitivity and dynamic range is lower than a PMT.

2.     A photomultiplier tube is a detection device that is made from a glass vacuum tube with a series of metal plate electrodes. A CCD is a solid state detector made from semiconductor materials.

3.     The main difference is one of sensitivity. Generally speaking the better the spectral resolution of the instrument the lower the amount of light reaching the detector and so you need more sensitivity in your detector. A PMT measures a single point in the spectrum at a time whereas with a CCD the complete spectrum is imaged across the CCD and so can be measured all at the same time. 

4.     An instrument with a CCD is usually much faster and cheaper but will not have as good a spectral resolution (the ability to resolve absorbance peaks very close to each other).

5.     CCDs and photomultipliers vary in a number of aspects. One difference is gain, a photomultiplier has gain whereas a CCD does not (hence the multiplier bit of PMT). The PMT gain may be up to 10,000,000 and is available at high speeds and for large area detectors, which means that one can usually get close to the theoretical noise floor. On the other hand, PMTs have poor quantum efficiency compared to CCDs (25% typ against 85% typ) so you can sometimes get better performance with a CCD if you can go slowly enough.

6.     PMTs are also typically single channel devices, although 16 channel linear arrays are available. CCDs are usually linear or 2D arrays.

7.     In a dispersive spectrometer a linear CCD array can capture the entire spectrum in one measurement. A single channel PMT must have the spectrum scanned across it sequentially to produce the entire spectrum.

8.     PMT's are typically preferable to CCD's on spectroscopic application for several reasons. The ability to adjust the gain of each PMT allows a manufacturer to adjust the response of each PMT to the specific signal being measured, so every element you are trying to detect can be analyzed at optimum conditions. Solid state CCD's are a compromise. Every element detected has the same conditions, so most are compromised. 

9.     Also, PMT's can be heated and held at constant temperature (in well made instruments) to prevent drift caused by variation in temperature. If you try to heat a CCD, the noise level will go up, and the signal to noie ratio will degrade as a result. CCD's are sometimes cooled to try to improve their s/n ratio, but usually not cooled enough to really help much due to condensation issues that arise. 

10. A third advantage of PMT's is that they can be used in a vacuum chamber without long term degradation for decades of use. The surface of a CCD will degrade under vacuum over a few (8-15) years. Most manufacturers making CCD based instruments opt for a Nitrogen or Argon flush, rather than vacuum to displace the oxygen from the detector chamber. This method results in decreased performance compared to PMT's, and is used in lower performance less expensive spectrometers.

LASER INDUCED BREAKDOWN SPECTROSCOPY

LIBS, is a spectroscopy technique in which a short laser pulse beam is focused on a target sample. Laser energy ionizes the sample material by heating it,  creating small area of plasma. Excited ions in the plasma state emits light waves which are collected and the spectrum is resolved by a spectrometer and analyzed by suitably calibrated  photon or light detector. Each chemical element has a unique wavelength or signature which can be optically resolved from the obtained spectrum. As  result, the composition of the elements which constitutes in the target sample can be determined. Below provided some of the general information about the technique : i Advantages ii Considerations Spectral coverage vs. resolution Light sensitivity iii. General Applications I. Advantages LIBS is considered one of the most  efficient and user friendly analytical techniques for trace elemental analysis in gases, solids, and liquids. Some of its major advantages include: Real-time measurements: online monitoring and quality control of industrial processes Noninvasive, nondestructive technique: valuable samples can be reused, sensitive materials can be analyzed, suitable for in-situ biological analysis Remote measurements can be done from up to 50 meters distance: can be used in hazardous environments and for space exploration missions on other planets Compact and inexpensive equipment: can be widely used in industrial environments, perfect for field measurements High-spatial resolution: can obtain 2D chemical and mechanical profiles of virtually any solid material with up to 1 µm precision Non or very little sample preparation is required: reduced measurement time, greater convenience, less opportunity for sample contamination Samples can be in virtually any form: gas, liquid, or solids Analysis can be performed with a very small amount of sample (nanograms): very useful in chemistry for characterization of new chemicals and in material science for characterization of new composite materials or nanostructures Virtually any chemical element can be analyzed, such as heavier elements unavailable for X-ray fluorescence Analysis can be done on extremely hard materials like ceramics and superconductors; these materials are difficult to dissolve or sample to perform other types of analysis In aerosols both particle size and chemical composition can be analyzed simultaneously II. Considerations  Spectral Coverage vs. Resolution Compact echelle spectrometers designed for LIBS applications are offered by several manufacturers. In the rare occasion that an application requires even higher resolution, the Acton Series of spectrometers with their long focal lengths are extremely useful. The latest models  use toroid mirrors with improved spectral quality. For a  detector with 1024 horizontal pixels, each of which is 26 m wide, the theoretical field of view is 26.6 mm. But since a standard 25 mm intensifier is used, the field of view is 25 mm. For example, if you decided to utilize a 2400 groove/mm grating in the Acton Series 2500 in order to enhance resolution, the linear dispersion will be 0.6 nm/mm while the spectral coverage will be 0.6*25 = 15 nm. To cover a spectral range between 300 and 600 nm (for example), you will need to perform at least 20 laser shots each time, moving the spectrometer grating to a new position and "gluing" all 20 spectra together. This is a very standard procedure which can be done painlessly and automatically. The only disadvantage to this is that acquisition of one spectrum could take up to a few dozen seconds or longer, which is why the echelle spectrometer has become extremely popular, especially in industrial and field applications where real-time measurements such as online quality control is a must.  Light sensitivity Typically, the laser pulse in LIBS applications lasts for femto- to nanoseconds (10-15 to 10-9 s). Especially in applications where non-invasive and non-destructive analysis is required, a relatively small amount of laser energy is transferred to the sample. Therefore, one laser pulse produces a weak emission signal which is hard or impossible to collect with conventional CCD detectors. That is why intensified CCDs (ICCDs) are widely used in LIBS. To improve the emitting signal on the order of 10-30 times, a scheme with two orthogonal lasers beams is often used. In this dual-scheme, the first and usually more powerful laser pulse ablates and atomizes sample material while the second one heats the ablated material even further, allowing it to improve the intensity of atomic or ionic lines. Factors such as the level of laser excitation energy for both pulses and the time delay between the pulses play a crucial role in achieving signal intensity enhancement. This technique increases the sensitivity of LIBS by  at least one order of magnitude and allows for a greater possible number of applications. If measurement time duration is not an issue, a regular CCD, (1024x1024 pixels, 13 µm pixel size), can be used together with the an spectrometer for LIBS applications. To obtain the reasonable light level required for a non-intensified CCD, long exposure time measurements should be performed. In this case, plasma emission signal is accumulated on the CCD from a multiple laser pulse. However, one should be careful about excessive accumulation of background noise and low signal-to-noise ratio. It is especially important when performing measurements in the open air without an enclosed sample chamber. Since the CCD stays open for a long period of time, all sources of stray light in the room should be eliminated and measurements should be conducted in darkness.  CCD usually proves a more sophisticated system than the  ICCD because intensified CCDs are prone to permanent damage by excessive light levels. Extra care should be taken so as not to expose ICCDs to the bright sources of light like laser reflections. In the case of a regular CCD, it is difficult to damage with excessive light. III. General Applications The fact that LIBS generally requires little-to-no sample preparation, simple instrumentation, and can easily be performed on-the-field in hazardous industrial environments in real-time, it is a very attractive analytical tool. The following are a few examples of real life applications, where LIBS is successfully used: Express-analysis of soils and minerals (geology, mining, construction) Exploration of planets (such as projects using LIBS for analyzing specific conditions on Mars and Venus to understand their elemental composition) Environmental monitoring (Real-time analysis of air and water quality, control of industrial sewage and exhaust gas emissions) Biological samples (non-invasive analysis of human hair and teeth for metal poisoning, cancer tissue diagnosis, bacteria type detection, detection of bio-aerosols and bio-hazards, anthrax, airborne infectious disease, viruses, sources of allergy, fungal spores, pollen). Replacing antibody, cultural, and DNA types of analysis Archeology (analysis of artifacts restoration quality) Architecture (quality control of stone buildings and glasses restoration) Army and Defense (detection of biological weapons, explosives, backpack-based detection systems for homeland security) Forensic (gun shooter detection) Combustion processes (analysis of intermediate combustion agents, combustion products, furnace gases control, control of unburned ashes) Metal industry (in-situ metal melting control, control of steel sheets quality, 2D mapping of Al alloys) Nuclear industry (detection of cerium in U-matrix, radioactive waste disposal)