Comparison between Single Beam and Double Beam Atomic Absorption Spectrometer Systems

Spectroscopic analysis has seen growth in a number of application oriented domains such as UV – Visible, Infrared, Raman, Atomic Absorption Spectroscopy, etc.

Design of spectroscopic systems is based on the fundamental principle of light absorption by absorbing species-the Beer Lambert law. Over the years basic design has been based on single beam or double beam optics with the latter gaining prominence due to its distinct advantages. Advances in electronics and detection systems have contributed further to the popularity of double beam systems. In the present article  the discussion will be limited  to Atomic Absorption Spectroscopy systems.

It is important to understand the optical layout of both single beam and double beam systems before you begin to appreciate the advantages of one over the other.

Single Beam Systems

Single Beam Schematic Diagram

Single Beam Schematic Diagram

The light source comprising of a hollow cathode lamp emits sharp atomic line of the element whose determination is required. The light is modulated (switched on and off) rapidly by means of a rotating chopper located between the light source and the flame. Modulation can also be achieved by pulsing the power (switched on and off rapidly) to the light source. Modulation serves to differentiate the light coming from the source lamp from the emission from the flame. The modulated light is led to the flame where ground state atoms of the element of interest are present and after absorption is led to the monochromator which isolates the wavelength of interest which is then led to the detector.

Advantages of Single Beam Systems

  • Single beam instruments are less expensive
  • High energy throughput due to non-splitting of source beam results in high sensitivity of detection

Disadvantages

Instability due to lack of compensation for disturbances like electronic circuit fluctuations, voltage fluctuations, mechanical component’s instability or drift in energy of light sources. Such drifts result in abnormal fluctuations in the results.

Double Beam Systems

Double Beam AAS Schematic Diagram

Double Beam AAS Schematic Diagram

The light beam from the source is split into sample beam and reference beam by the mechanical chopper. The reference beam monitors the lamp energy whereas the sample beam reflects sample absorption. The observed absorbance measurement is the ratio of the sample and reference beams which are recombined before moving to the monochromator. This arrangement compensates the effects due to drift in lamp intensity, electronic and mechanical fluctuations which affect both the sample and reference beams equally.

Advantages of Double Beam Systems

  • Modern improvements in optics permit high level of automation and offer the same or even better level of detection as compared to earlier single beam systems. Instability factors due to lamp drift, stray light, voltage fluctuations do not affect the measurement in real-time.
  • Little or no lamp warm up time is required. This not only improves throughput of results but also conserves lamp life

We have seen that the double beam system design features far outweigh the advantages offered by single beam systems. The cost factor is more than offset by the advantages offered by modern double beam systems and therefore these have become the preferred choice.

The topic is open for discussion and you may offer your valued comments.

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. solomon uzoaru says:

    Dear Sir, I’ve background in Physics. Recently,my school bought an AAS and no one has been able to install it and I do not know anything about it but would like to know so as to be able to use it for analysis. Please,what do I do in other to become proficient in using the AAS for analysis?

    • Dear Solomon,
      You can make a start by registering for the AAS free course . It will introduce you to the basic components and their role. Next you can enrol for the advanced level certificate course on AAS which is to be launched in near future.The content of this course will be interesting and the visuals will explain the operational aspects.I am sure it will meet your desired goal.
      In case you have any queries please feel to contact me on my e-mail as well.
      Regards

      • Shivananda K.S says:

        Dear Sir,

        I am an instrumentation Engg.,
        please give me the dis-advantages of Double beam AAS .

        with regards,
        Shivananda

        • Dear Shivananda,
          The disadvantage, if you may say so, is only reduction in sensitivity due to splitting of beam into two portions. These days due to advances in electronics and improvements in sensitivity of detection systems even this disadvantage has been overcome and today all manufacturers are providing double beam systems.
          Regards

      • Ravishankar says:

        Sir,
        We have purchased AAS. What is difference in oxy-acetylene and pure acetylene gas used in aas. Also can you tel me the application of different gases used in AAS

        • The term oxy-acetylene refers to the flame. The gases used for sustaining combustion in this case are acetylene which is fuel gas and air which has presence of oxygen which acts as oxidant to support the flame ignition. Majority of elements can be studied with acetylene and air combinations.Pure oxygen is not used due to high flame velocity of acetylene-oxygen flame which can result in flashback and explosive bang in the burner chamber.The other common combination is acetylene and nitrous oxide.In this case the oxidant required to support combustion is nitrous oxide , This flame results in higher temperature than air -acetylene flame. Such temperatures are necessary to decompose metals forming stable oxides(refractory elements)

  2. al-amin says:

    very nice

  3. Dear sir,
    I am planing to purchase a new spectrophotometer for my Biochemistry lab.
    I am working on capsanthin analysis.
    Kindly suggest , should I go with single beam or double beam is more beneficial.
    Pls replay.

    Thank you
    Jaishri

  4. sidhartha singh says:

    Dear Dr/

    I am working as an assistant professor in India and i am interested in buying a spectrophotometer for my lab. Which one do you think is the best for my lab. I have a budget of 8 lacs. My lab involves working with nucleic acids, enzymes, proteins. Also since bachelor students of biotechnology program will be also using this machine for their routine practicals so kindly keep this in mind before suggesting anything.

    Thank in advance. I would really appreciate your help.

    • Dear Prof Singh,
      From your required applications details it seems that you should go for a UV- VIS Spectrophotometer instead of AAS.Please confirm the same so that we may suggest a suitable configuration.

  5. Dear Dr Thanks this is pretty good.We also do trainings on analytical techniques of measurement.How do we partner with you.

    Thanks
    John

  6. Patrick Ogu says:

    Hello Dr. I am a technologist in the chemistry laboratory of a polytechnic where I work. we have a DLC-20 HPLC instrument that has never been used because it has not been installed, an sadly I can not operate it!!! can I get a customized training on the above HPLC instrument in your facility? Please furnish me on how I can go about arranging such training. ?

  7. Gina Catalan says:

    We are planning to buy a UV-Vis spectrophotometer and we want to establish whether to have a single or double beam optics. We will be using this for P and Mo analysis in ferrous metals. Please advise..Thanks.

    • Hi Gena,
      You should undoubtled go for double beam system as a combination of sophisticated modern day optics and electronics offers same sensitivity and interference free performance as single beam systems.
      Regards

  8. Oyebanji Oyekunle Sunday says:

    How do I contact you one on one for AAS training especially with regard to geological science am a geology lab technologist.

  9. Dear friend ,
    I am a service engineer for analytical instrument . I have worked since 1989 .
    I work now for my own, istanbul , Turkey.
    I still to learn more and more. I just meet this website while look for chopper funtions in the instrument.
    Best Regarda
    Mehmet

  10. BADMUS Gabriel says:

    I just want to say thank you for been responsive on this forum.

    Thanks Prof. for your contribution.
    I hope to be a Prof in years to come.

  11. Dr. B.S. Sandhu says:

    Dr. D. Bhanot deserves a world of great appreciation for sharing his knowledge of instrumentation.We have made up our mind to purchase double beam over single beam.

    Thanks Dr. Sahib.

  12. the singel beam and duble beam structure are not correct. I got zero in my exam. The sample cell should be after the monochromator.

  13. sir

    what is diffrence between singal and double beam of instrument ??

    • In single beam instruments the light beam is passed through the sample without splitting whereas in double beam instruments the beam is split in two . One portion passes through the sample and the other through a reference blank. Double beam instruments give benefit of blank correction in real time.

  14. Use nitous oxide as oxidant in place of air. Tems are above 2000 deg C

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