Interferences in Atomic Absorption Spectroscopy

Interference is a phenomena that leads to changes in intensity of the analyte signal in spectroscopy. Interferences in atomic absorption spectroscopy fall into two basic categories, namely, non-spectral and spectral.

Non-spectral interferences affect the formation of analyte items and spectral interferences result in higher light absorption due to presence of absorbing species other than the analyte element.

Interference in Atomic Absorption Spectroscopy

Interference in Atomic Absorption Spectroscopy

Non-spectral interferences

Matrix interference

When a sample is more viscous or has different surface tension than the standard it can result in differences in sample uptake rate due to changes in nebulization efficiency. Such interferences are minimized by matching as closely as possible the matrix composition of standard and sample

Chemical interference

If a sample contains a species which forms a thermally stable compound with the analyte that is not completely decomposed by the energy available in the flame then chemical interference exists. Refractory elements such as Ti, W, Zr, Mo and Al may combine with oxygen to form thermally stable oxides. Analysis of such elements can be carried out at higher flame temperatures using nitrous oxide – acetylene flame instead of air-acetylene to provide higher dissociation energy. Alternately an excess of another element or compound can be added e.g. Ca in presence of phosphate produces stable calcium phosphate which reduces absorption due to Ca ion. If an excess of lanthanum is added it forms a thermally stable compound with phosphate and calcium absorption is not affected.

Ionization interference

Ionization interference is more common in hot flames. The dissociation process does not stop at formation of ground state atoms. Excess energy of the flame can lead to excitation of ground state atoms to ionic state by loss of electrons thereby resulting in depletion of ground state atoms. In cooler flames such interference is encountered with easily ionized elements such as alkali metals and alkaline earths. Ionisation interference is eliminated by adding an excess of an element which is easily ionized thereby creating a large number of free electrons in the flame and suppressing ionization of the analyte. Salts of such elements as K, Rb and Cs are commonly used as ionization suppressants.

Spectral Interferences

Spectral interferences are caused by presence of another atomic absorption line or a molecular absorbance band close to the spectral line of element of interest. Most common spectral interferences are due to molecular emissions from oxides of other elements in the sample.

The main cause of background absorption is presence of undissociated molecules of matrix that have broad band absorption spectra and tiny solid particles, unvaporized solvent droplets or molecular species in the flame which may scatter light over a wide wavelength region. When this type of non-specific adsorption overlaps the atomic absorption of the analyte, background absorption occurs. The problem is overcome by measuring and subtracting the background absorption from the total measured absorption to determine the true atomic absorption.

Interferences are corrected using background correction techniques which are discussed in the next module.

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.


  1. Roan Birgen says:

    great site to polish and get deeper into the analytical field.keep it up

  2. al-amin says:

    I want to know about physical interference & refractory compound

    • Hello Al-Amin,
      Interferences in AAS analysis are basically spectroscopic and non-spectroscopic.I am not very clear on what you are refering to when you say physical interferences.Kindly elaborate so that I may comment.
      Refractory compounds,particularly oxides are those that do not decompose at normal air -acetylene flame temperatures and require higher temperatures to decompose and form free atoms.These temperatures are achieved by using nitrous oxide-acetylene flames.

  3. In chemical interference , we add one substance in excess amount to reduce interference of other. There is example of lanthanum with phosphates. Can lanthanum affect the result?

  4. Lin Weng says:

    Hi Dr Deepak Bhanot, I would like to ask why the absorbance of Antimony in a nickel concentrated matrix decreases when the analysis is repeated? Is this a normal sign?

    • Dr. Saurabh Arora says:

      Hi, most probably your solution is not stable and there might be precipitation. You need to establish the solution stability and add a stabilizer if needed.

  5. Is maximum sample uptake rate always be used in AAS?

    • Hi Nandini,
      It is not advisable to use maximum uptake rate always because the gain in sensitivity can be off-set by several other factors such as extinguishing of flame due to excessive solvent introduction or simultaneous increase in background interference and parallel increase in interference due to interfering elements introduced along with the sample.It is for this reason that variable intake provisions are provided on all instruments.

  6. Which could be the easiest way to assign species to an infra red spectrum?

    • The easiest way is to overlay the sample spectrum on the standard compound spectrum and match the degree of closeness of ovelap of peaks. It may not be a 100% overlay but you will come to know about your sample. Most systems come with a figure on correlation in the software which gives you a degree of match of the two spectra

  7. How can the interference of AA measurements by EA signals be removed?

  8. Martin kituyi says:

    Hi Dr, how can u prevent refractory compound in AAS?.

    • Refractory elements form stable oxides which do not decompose under normal operation using air- acetylene flames and will not be a matter of concern as you are looking for the element whose hollow cathode lamp has been selected.Under higher temperature operation you can remove interfering elements which have potential of contributing to interference by extraction and refining techniques specific to such elements prior to analysis.

  9. What about interference effect of phosphate on calcium? And then with releasing agents such at EDTA and strontium?

    • You are referring to chemical interferences where an element or complexing agent combines and forms a stable compound which reduces the absorption due to the element of interest. Such interference can be reduced by adding another element or chemical which forms preferentially a thermally stable compound with the interferent . An example is Ca in presence of phosphate. Phosphate produces stable calcium phosphate which reduces the absorption signal due to Ca.Addition of excess of Lanthanum forms thermally lanthanum phosphate and the effect of phosphate interference on Ca gets eliminated.

  10. Shinji Sudoyo says:

    Hi Dr. Deepak Bhanot, i just happened to have a problem with a flame AAS. During analysis of any elements which have a maximum wavelength below 300nm, i get this random sudden drop of absorbance. So out of nowhere 0.0005-0.0010 Abs could get to -0.0100 and then goes back up to 0.0005. It happens quite often during analysis and it prolonged my analysis time because i have to re-aspirate and re-read all the samples again. What could be the problems? thank you

    • My advise would be to check performance of your UV lamp source and see if it is nearing end of its useful rated life.It is easy if it has a built in energy meter. In case it has outlived its lifespan best would be to replace it. If problem persists get in touch with your service engineer.

  11. Barath Vasudevan says:

    Hi Dr. Deepak Bhanot, I would like to ask how to prevent the ash formation in AAS. Thank you

    • Ash formation is not a commonly encountered problem.However, as a preventive measure keep your burner slots clean using the cleaning wire. please do let me know your specific analysis where you faced such a problem.

  12. Richa Shrivastava says:

    In an ILC conducted on herbal samples for lead in different labs my brand new AAS is giving higher results than other labs. What could be the possible reason?

    • There could be more than one reason.Hope you calibrated the AAS with a standard from a reliable source and also used calibrated volumetric glassware.Use of high purity reagents is also recommended . lastly hope you made use of Electrodeless discharge lamp as light source instead of a hollow cathode lamp.

  13. Does lanthanum oxide help to reduce the interference? I don’t understand the ionization effect of lanthanum oxide.

    • Lanthanum compounds are easily ionizable and therefore help suppress ionization of other compounds with low ionization potentials.Thus there is no loss of the analyte compound ions due to ionization and their atoms in ground state are available for absorption of radiation from the source.

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