Metal finishing Q&As since 1989
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Chromium Analysis using AAS Technique
Q. I am a Electronic Engineer in Customer Support of Company manufacturing Analytical Instruments Viz. AAS , GC.
I have a query about Chromium Analysis using AAS Technique .
We are using Air-Acetylene flame for Chromium analysis. But result are varying and the Co-efficient of Variance is 1.8 for 10 no. of standard analysis . Kindly advise what should be the correct method to get CV value less than 1 .
Vinay NAik- NASHIK, MAHARASHTRA, INDIA
2004
First of two simultaneous responses --
A. What wavelength are you using and how old is your lamp?
James Totter, CEF
- Tallahassee, Florida
2004
Second of two simultaneous responses --
A. Assuming that the AAS is being properly operated, then the problem is in the control of your sample, IE: more chrome in solution on some samples than on others. (if this is flame AAS)
James Watts- Navarre, Florida
2004
A. There are two very important variables in Cr analysis via flame AAS. 1) Flame conditions. Sensitivity increases radically when a rich (high acetylene) flame is used. However, the effect of interferences is also increased. I'd recommend using as lean a flame as is consistent with your required sensitivity. 2) Chloride content. Chloride increases the degree of atomization of chromium such that the results can be 30 - 50% higher than the true value.The way around this is to add 0.5 % w/v ammonium chloride to the blank, all standards, and all samples.
Dave Wichern
Consultant - The Bronx, New York
A. WHAT IS THE AMOUNT OF Cr YOU ARE READING. HOW MUCH ABSORBANCE YOU GET.? WHAT OXIDATION STATE (III) OR (VI)? ARE YOU READING THE SAME SAMPLE TEN TIMES?ARE YOU MAKING ANY DILUTION? I'VE BEEN WORKING IN AAS SEVERAL YEARS AND I WOULD LIKE TO TRY TO HELP.
HECTOR LONGUEIRA- ANTOFAGASTA, CHILE
2005
April 8, 2010
If we do have a mixture of Cr3+ and Cr6+, can it be a problem or during the atomization process.....
Perkin Elmer said that its recommended to get Cr6+ by adding an oxydant agent...
Can the KMnO4 should be used to transform Cr3+ to Cr6+?
Or can anyone suggest anything else?
Chemist - CANADA
Q. Hi,
I am an Researcher working in an educational institution.
I am analyzing tannery effluent samples through AAS to determine the chromium concentration in it. But there is a problem in calibration curve set up While using 357.8 nm wavelength. We have also tried 428.9 nm, but still there is a deviation up to ± 0.5 ppm from the true value. Its a new instrument and the alignment has been checked by the service engineer. We are using the standard solution of Sigma Aldrich make. Please guide me to solve this problem.
Research Scholar - TamilNadu, India
May 11, 2011
A. It is really pricey but if you do much AAS work, you should try to get a copy of "Atomic Absorption Spectroscopy" by Welz and Sperling. It tells you everything and includes the advantages and disadvantages of using the alternate wavelengths, different fuel mixtures, all of the interferences and ways to correct for them, and on and on. I would be able to answer your question directly if I still had access to my copy, but sadly I don't
Jon Barrows, MSF, EHSSC
GOAD Company
Independence, Missouri
First of two simultaneous responses -- May 13, 2011
aTry adding 0.5% ammonium chloride to both standards and samples. Chloride tends to enhance the atomization of Cr in the flame, and if it is present in the samples but not the standards you will get erroneous results.
It is advisable to use as lean (air rich) a flame as is consistent with sensitivity requirements. A fuel rich flame will give higher absorbance values but also aggravates the effect of interferences.
Dave Wichern
Consultant - The Bronx, New York
Q. I am doing research on Cr(VI)removal from polluted water and optimized parameters such contact time, pH, initial concentration and amount of dose. After dilution the same was subjected to AAS but the concentration that AAS gave was greater than the original. Why was this problem?
Dessalew Berihun- Addis Abeba, Ethiopia
April 16, 2013
A. AAS gives results for total Cr, not just Cr+6
James Totter, CEF
- Tallahassee, Florida
First of two simultaneous responses -- April 19, 2013
A. Hello Dessalew,
I would do the AAS analysis again, I don't think you can make chromium from nowhere! You should standardize the method and measure both solutions in the same routine, so you can compare with the same instrument, the same calibration and the same lamp and flame. Then you can make assumptions.
But when you dilute you should get lower concentrations of everything! Exceptions: oxygen, carbon, and some other pollutants in the dilution water...
Hope you can solve this mystery! Regards,
- Cañuelas, Buenos Aires, Argentina
Second of two simultaneous responses -- April 22, 2013
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