Brief introduction to Inductively coupled plasma- Atomic emission spectrometry (ICP-AES/ICP-OES)

Sorry, I know this post is all about science, but I thought it could help some people who don’t know about this analytical technique (like me).

Inductively coupled plasma- Atomic emission spectrometry (ICP-AES)

(By Zoobia Nadeem)

ICP-AES is a type of emission spectrometry designed for determination of the amount (concentration) of a test element in a sample. This characterization technique involves the atomization and excitation of the test element by inductively coupled plasma (ICP) and determination of amount (concentration) of test element from the intensity of atomic emission spectral line.

ICP-AES can detect more than 70 elements and offers several advantages over other techniques such as Atomic Absorption Spectroscopy. Some of these advantages include:

  • Possibility of rapid and simultaneous multi-elemental analysis.
  • Atomic emission source (ICP) is relatively free of chemical interference owing to its high temperature (6000 to 10,000 K).
  • Low detection limits.
  • Good accuracy and precisions.
  • Elements that are difficult to be determined through AAS, such as Boron and Vanadium, can be measured (Charles & Ferdeen, 1997).1.png

Figure 1: Elements of the periodic table which can be analyzed using ICP-AES (Charles & Ferdeen, 1997).

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Figure 2: Steps in analysis of samples by ICP-AES (Agilent technologies, 1999).

1.1         Instrumentation

An ICP-AES instrument typically involves the following components:

1.1.1        Sample introduction system

Test sample is pumped into a nebulizer, where it is converted into a fine aerosol spray by a stream of argon (Ar) gas. This aerosol enters the plasma through inner tube of the plasma torch.

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Figure 3: Components of ICP-AES (Agilent technologies, 1999).

1.1.2        The ICP discharge system

Following steps are involved in the generation of ICP:

  • Ar gas is directed through a torch comprising three concentric tubes made of quartz or any other appropriate material. The upper portion of this torch is surrounded by a copper coil (load coil) which is connected to a radiofrequency generator.
  • When RF power (700 to 1500 watts) is applied to the load coil, RF electric and magnetic fields are set up in the upper region of the torch.
  • An electric charge is applied to the Ar gas circulating through the torch, which leads to the stripping of electrons from Ar atoms.
  • The stripped electrons are caught up in and accelerated by magnetic field. The increase of energy of electrons by the use of coil in this manner is known as inductive coupling. The high energy electrons then collide with other Ar atoms and strip off more electrons.
  • The process continuous in a chain reaction to generate an inductively coupled plasma consisting of electrons, Ar ions and Ar atoms. The functions of high temperature ICP discharge involve desolvation (removal of solvent to generate microscopic particles), vaporization (decomposition of particles into stream of individual molecules), atomization (disassociation into atoms), excitation and ionization of test sample (Charles & Ferdeen, 1997).

1.1.3        Optical Spectrometer

As mentioned above, in ICP-AES, light emitted by the excited atoms and ions in the plasma is measured to determine the composition of test sample. On the basis of mode of operation, ICP-AES can be divided into two types, which are simultaneous and sequential instruments. Simultaneous instruments detect several spectral lines simultaneously using a polychromater with a detector for each spectral lines. Sequential instruments are relatively more suited for laboratories as they allow the freedom of selection of a set of analytical wavelengths using some monochromater (Agilent technologies, 1999).

Both these types of ICP-AES instruments use focusing optics, a grating spectrometer and a detector. Focusing optics (lenses or mirrors) collect and focus the light emitted from the plasma onto the entrance slit of spectrometer. A grating spectrometer then generates a spectrum of the focused light so that the intensity of light can be measured at very precisely defined wavelengths. Specific wavelengths are then detected using photo-sensitive detectors such as photo-multiplier tube (PMT), charge-induction device (CID), or charge-coupled device (CCD) (Charles & Ferdeen, 1997).

1.1.4        Computers

Computers are used to perform several functions such as background correction, preparation of calibration graphs, calculation and analysis of results. These are also used to access databases and control the instrument (Agilent technologies, 1999).

1.2         Applications

Some of the applications of this technique have been listed in the following table (Agilent technologies, 1999):

Field Applications
Agriculture, food and beverages Determination of micronutrient and toxic elements in agricultural

samples such as soil, plant tissue, grains, forages, animal feeds,

fertilizers, milk, etc.

Biology Determination of essential elements and non-essential elements in human urine, blood, soft and hard tissues, animal samples.
Geology Determination of minerals and radioactive elements in rocks, minerals, ores, concentrates, coal, fly ash, etc.
Water For the monitoring and analysis of surface water, freshwater, drinking water, etc.
Organics Determination of metals in cooking oils, antifreeze, pesticides, etc.

2           References

Charles, B., & Fredeen, K. J. (1997). Concepts, instrumentation and techniques in inductively

coupled plasma optical emission spectrometry. Shelton, CT: Perkin Elmer Corporation.

Agilent technologies. (1999). Liberty II: Analytical methods book. Victoria, VIC: Varian

Australia Private Limited.

 

 

 

 

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Can Carbon Cycle Save Us from Climate Change???

I was preparing for Atmospheric Chemistry’s exam when this question popped up in my mind. So, first of all, I hope you all know about our beloved Carbon Cycle. You should also know that carbon dioxide is a major greenhouse gas and recently its concentration in atmosphere has increased to 400ppm mainly due to human activities.

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So, now comes the question how carbon cycle acts as a thermostat for our Earth? It does so mainly by positive and negative feedback mechanisms. In positive feedback, the processes that are occurring in nature are enhanced (for example, upon increase in temperature these mechanisms support warming), while in negative feedback mechanisms, the processes are opposed (for example, upon increase in temperature these mechanisms support cooling). Maybe this figure will explain them better than I can!!

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Here Albedo means the reflectance of radiations from ice surfaces, thus decreased albedo means high absorbance of radiation. 

 

Now let’s observe how climate change affects carbon cycle and its feedback mechanisms.

  1. Terrestrial Environment 

carbon_cycle-animated_forest

In some areas where temperature increases due to climate change, there will be an increase in respiration by plants and this will reduce carbon storage in plants, releasing more carbon dioxide to the atmosphere (positive feedback). Though, in other areas where decrease in temperature occurs, the period of photosynthesis will increase as respiration will be slow, thus carbon will be stored from atmosphere (negative feedback). More carbon dioxide concentrations also support higher rate of photosynthesis.

Similarly, soil stores more carbon at colder temperature and high precipitation as rate of decomposition is reduced. 

This table clearly represents how various factors effect feedback mechanisms.

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2. Ocean Feedbacks
CO2 is far more soluble in colder water than in warmer water, thus warmer sea surface temperatures will affect the oceans’ ability to dissolve CO2 and their carbon chemistry. A warmer ocean might cause dissolved organic carbon to decompose faster and convert to CO2, reducing the amount of atmospheric CO2 that can be absorbed by the oceans (a positive feedback). Warming might also cause a decrease in the extent of sea ice, which could increase plankton and other marine growth in high-latitude regions. This would result in a greater uptake of atmospheric CO2, thereby acting as a negative feedback (Read more here).

Evidence exists that the relationship between climate change and carbon cycle will be very important in the future for determining emissions and carbon dioxide concentrations in the atmosphere.

Increasing Efficiency of Solar Cells by Mimicking Cabbage White Butterflies

A team of researchers from the University of Exeter has shown that the efficiency of solar panels can be increased by nearly 50% by mimicking the v-shaped posture adopted by Cabbage White butterflies to heat up their flight muscles before take off.

08-sn-univ-butterflies-fig1                              butterfly-technique

The angle at which these butterflies hold their wing is approximately 17 degrees. This is the reason due to which these butterflies take flight before other butterflies on cloudy days.

The research team analyzed and tried to replicate the butterfly wing structure to create a new lightweight reflective material with the capability to produce solar energy. The process produces not only lighter, but also more efficient panels.

 

srep12267-f4

 

 

Use of Mercury for Artisanal and Small-Scale Gold Mining

This specific issue became evident to me when I surfing twitter. Artisanal and small-scale gold mining (ASGM) is the extraction of minerals by miners working in small and medium sized operations, using rudimentary techniques.  Simple practices with minimum economic investment are employed be these miners. It is the largest intentional-release source of mercury in the world.

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How can mercury be used for gold-mining? Mercury is used to separate and collect the gold from the rocks. Mercury binds with gold to form an amalgam which facilitates it to separate from rock, sand or other material. The amalgam is then heated to vaporize the mercury leaving the gold behind.

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Mercury is a powerful neurotoxin that is harmful to people, especially to developing fetuses, and young children. Once emitted, it can travel great distances through the atmosphere, causing global contamination of ecosystems, fish, birds, mammals, and the human food chain.Local exposures in mining communities that use mercury can be acute.

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What to do now?

  1. The most important measure a mining community can take to reduce its mercury use is to concentrate the gold-containing portion of the ore before adding mercury. This can be done by crushing and grinding the ore and then using carpeted or magnetic sluice boxes or gravity concentration techniques such as panning or centrifuges. In this way, more gold will be captured, less mercury will be required and residual mercury can be more completely captured.
  2. Protective measures include the use of retorts when burning amalgam and the use of gloves by those handling mercury or amalgam.
  3. Most promising technology to replace the use of mercury is cyanidation, but this method may not be affordable or technically available to all artisanal miners. Also, cyanidation methods must be used with care and carefully introduced due to its significant risks to human health and the environment.

For further info check reference texts http://www.unep.org/hazardoussubstances/Portals/9/Mercury/AwarenessPack/English/UNEP_Mod3_UK_Web.pdf

http://www.unep.org/hazardoussubstances/Portals/9/Mercury/Documents/ASGM/Techdoc/UNEP%20Tech%20Doc%20APRIL%202012_120608b_web.pdf

Cloud Seeding (Artificial Induction of Rain) – An Interesting Phenomena

Are you curious about how we can artificially induce rainfall??? How can we bring rain to an area where it usually doesn’t rains or an area which experiences less rainfall??? Well, read this article and find out. I hope you’ll find it interesting and informative.

Before going towards cloud seeding you need to know that how rain is formed. I’ll explain it in as easy words as possible.

  1. First of all, air currents enter water vapors into the atmosphere.
  2. Then, these water vapors condense onto small particles that are known cloud condensation nuclei (CCN). These particles are less than a micron (10^-6) in diameter. The condensation takes place just like water vapors condense on a sauce pan’s lid when water is boiled in it. In the same way, water vapors condense when they collide with CCN.RTEmagicC_Clouds_2_CCN.jpeg

 Now, this is the step at which cloud seeding kicks in.

  1. After this step the raindrop is formed and it starts to grow in the size.collision
  2. When the droplet gains enough weight to exert force downwards and to cancel the upward thrusting force (More weight will overcome the upthrusting force), the raindrop falls to the ground. Upthrust

Now that you know the whole process, you can easily understand how we can artificially induce rain.

Sometimes it doesn’t rains in an area just because there are no CCN particles for the water vapors to condense. Or it rains less in an area because of less CCN particles in the atmosphere.

What we do in cloud seeding is that we artificially introduce CCN in the atmosphere. Once CCN particles are introduced, the water vapors begin to condense on them and the water droplet forms. After growing to its size, the rain drops fall to the ground as rain. CCN particles can be silver iodide particles, potassium chloride particles, etc. This picture perfectly represents the process of cloud seeding.

This is the perfect representation of cloud seeding

This is the perfect representation of cloud seeding

And yes even atmospheric pollutants, such as aerosols, can act as CCN. But if there are more aerosols than a certain threshold limit then they will stop clouds from raining and the cloud will continue to grow until it reaches a certain temperature, at which rainfall occurs. Now, this can affect badly, because at first there will be drought and afterwards there will be a very heavy rainfall (as the overly grown and high energy containing cloud will rain), which may result in flood. If you want to know more about this effect click here.

The lower one shows how aerosols can delay rainfall

The lower one shows how aerosols can delay rainfall

Is cloud seeding a new terminology for you? Or, did you know it before? Even if you know more information about this topic, do tell me.