Flame Atomic Absorption Spectroscopy

“Formal education will make you a living, self education will make you a fortune”

— Jin Rohn 

Sample atomisation produces ground state atoms that are necessary for atomic absorption to take place. This involves application of thermal energy to break the bonds that hold the atoms together.

The complete atomisation assembly comprises of:

  • Nebuliser
  • Spray chamber
  • Burner Head

Each of the components of the atomisation assembly are discussed in detail below:

Nebuliser

AAS Nebulizer

AAS Nebulizer Schematic

AAS Nebulizer Schematic

AAS Nebulizer

Nebuliser converts the liquid sample into a fine spray or aerosol. In order to provide efficient nebulisation for different sample solutions (aqueous or organic, acids or bases, etc) the nebuliser should be adjustable and corrosion resistant. Stainless steel is commonly used but for corrosive solutions other corrosion resistant materials such as inert plastic, Pt/Ir or Pt/Rh alloy are also used. High sensitivity in combination with inert ceramic bead can be used to enhance nebulisation efficiency for lowest detection limits.

Spray Chamber

Spray Chamber

Spray Chamber

Aerosol from the nebuliser is led to the mixing or spray chamber. In this chamber the aerosol is mixed with fuel and oxidant gases and carried to the burner head. Only a fraction of the sample introduced by the nebuliser is used for analysis. An impact device prevents larger droplets from reaching the burner as these would delay sample vaporisation and atomisation through short transit through the flame. Only fine sized droplets are carried to the burner head

An impact device such as a flow spoiler or an impact bead is aligned at the exit of the aerosol stream of the nebulizer. A flow spoiler is more efficient at removing large droplets whereas the impact bead removes fewer large droplets and exhibits better sensitivity since more sample is led to the burner. However, the increased number of large droplets may have undesirable effects and increase interference.

Glass and ceramic impact beads can cause memory and contamination problems compared to the chemically inert flow spoiler and for this reason flow spoiler is preferred for routine work and for greater sensitivity impact bead is preferable. The excess sample is removed from the pre-mix chamber through a drain. The drain uses a liquid trap to prevent combustion gases from escaping through the drain line. The inside of the spray chamber is coated with wettable plastic material to provide free drainage of excess sample and prevent burner chamber memory. A freely draining burner chamber rapidly reaches equilibrium typically in less than two seconds for response to sample changes.

Burner Head

Burner Head

Burner Head

Burner heads are constructed of titanium to provide extreme resistance to heat and corrosion. A 10 cm single slot burner is recommended for air- acetylene flames. Its long length provides best sensitivity. A special 5 cm burner head is recommended for nitrous oxide –acetylene flame applications. The flame can be rotated to provide reduced sensitivity

Single slot 5 cm air-acetylene burner head is available when reduced sensitivity is required. It can be rotated to provide further sensitivity redaction and it has a wide slot to prevent clogging

A 3- slot burner head is designed for analysis of samples having high concentration of dissolved solids.

Majority of elements can be an analysed using air – acetylene flames which have high temperature range of 2150° C – 2300° C. Nitrous oxide – acetylene flames attain temperatures of 2600°C- 2800° C and can be used for analysing refractory elements which form stable oxides at lower temperatures.

The next module will introduce you to high sensitivity graphite furnace atomization.

About Dr. Deepak Bhanot

Dr Deepak Bhanot is a seasoned professional having nearly 30 years expertise beginning from sales and product support of analytical instruments. After completing his graduation and post graduation from Delhi University and IIT Delhi he went on to Loughborough University of Technology, UK for doctorate research in analytical chemistry. His mission is to develop training programs on analytical techniques and share his experiences with broad spectrum of users ranging from professionals engaged in analytical development and research as well as young enthusiasts fresh from academics who wish to embark upon a career in analytical industry.

Comments

  1. Michael Sperling says:

    Unfortunately the drawing of a nebulizer is totally wrong and therefore not instructive at all. It is not clear that and how the nebulizing gas is creating the aerosol.

    • Hi Micheael,
      The diagram was meant to be a simple schematic to show how the sample in the liquid carrier stream is converted to a fine aerosol before entering the spray chamber.Oxidant gas which is air in case of air-acetylene in case of air-acetylene flame or nitrous oxide in case of nitous oxide -acetylene flame enters the nebulizer through the side arm. This oxidant gas is also termed as the nebulizer gas.It shears the incoming sample liquid stream to form fine liquid droplets which are then led into the spray chamber where the fuel gas mixes with the stream on way to the burner head.Hope I have been able to clear your doubt. Please feel free to contact if still further explanation is required.

      • Dear Dr Bhanot,
        Could you please explain in detailled way how to mount an impact bead into a spray chamber.
        Thank you

        • Dear Awaleh,
          I shall explain it in the following steps:
          1.Ensure system and flame are shut then remove safety cover to expose burner chamber.
          2.Disconnect the waste drain tube alongwith the leak drain sensor.
          2.Loosen the end cap and move up the safety latch on top .
          3.Slide out the nebulizer inlet and with the help of spacer fix the impact bead to the end and reassemble the burner chamber end cap.
          4.Refix the drain pipe and the leak sensor.
          5.Put the protection shield in place before start-up of the system.
          Regards

  2. Abdalla Mohammed says:

    I have a problem in the flow rate of sample is very weak
    How to solve this problem ?

    • Dear Abdalla,
      If I have understood you correctly I believe your flow of sample into the spray chamber is either slow or erratic.You need to inspect the tubing first to see if there are any blocks or bends which are preventing the free flow.In case you do not find any problem here try running blank for about 5 minutes. Any blockages in nebulizer can then be cleared using a cleaning wire and once more flushing with blank or pure water.

  3. The flame AAS acetylene gas was in used (analysing samples) and suddenely the flame when out during the analysis. The gas bottle was installed outside the building however we discovered that the gas was completely empty as there was no gas gauge inside the building to indicate the gas volume.
    On start up after refulling the gas the next day the flame cannot be ignighted.

    Does that means impurities of other gas or debries from the gas bottle might have cause the inflow of gas and air pressure to drop?

    What would be the best option to rectified or solved this problem?

    • Dear Patrick,
      Acetylene gas cylinders generally contain water as impurity and this vapour on reaching the burner can extinguish the flame.The problem will not occur repeatedly if you monitor cylinder pressure regularly and replace the cylinder when pressure falls below 100 psi.Now even on cylinder replacement the flame is not igniting because there is water inside the supply line to the instrument.You should open the line and flush it with acetone and then fix it up again. This will help you to overcome the problem.

  4. Ms. Erfan Seyedin says:

    Hi
    would you mind sending me some text that tells me how can I start up the Atomic Absorpbtion Spectroscopy device ?
    I have perkin elmer 3300
    please, please, please help me

    • Hi Erfan,
      I would recommend you joining our certificate program on AAS. It covers all the material that could be of use to you. Besides it is developed around Perkin Elmer Model 400 AAS and Winlab 32 software. The setup and operation are clearly explained through videos in the program. In case you require further details about the program please do not hesitate to contact

  5. Thandeka Adonisi says:

    Hi i have a GBC 904 AAS I have noticed that the EHT meter reading is increasing in my AAS. I do not know what is causing that and what effect will that have on my analysis?

  6. Ramadani says:

    Hi..i have SensAA from GBC..and my aas flame not work..liquid trap icon is blinking..how i can fix it..thanks

    • Hi,
      First of all you should empty out the waste drain container. Ensure the drain pipe is free of kinks or bends and lastly clean the spray chamber with a mild detergent solution.Hope this will help you recover from the problem and improve the system performance as well.

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  8. It is really a great and helpful piece of information. I
    am happy that you shared this useful info with
    us. Please keep us up to date like this. Thank you for sharing.

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