I am currently doing research on the adsorption of heavy metal using magnetic reduce graphene oxide. I use AAS to determine the concentration of the heavy metal.
I prepare the Pb solution with an initial concentration of 60 ppm then I run an adsorption test with 30 min interval for screening testing. the dosage of the adsorbent is 1g/L. I run the test one day prior to AAS testing.
The problem is, when I do the AAS testing, the initial concentration of the solution was 30 ppm followed by 28 ppm for the first 30 min, and a negative result at 90 min.
Then I try another testing to see whether the problem is my dilution, and it shows that my dilution is correct. I also try dilute several stock solution to see if the problem is my stock solution but the result suggest my stock solution is ok.
does heavy metal solution degrade over time? or is it become precipitate which makes the concentration lower?
it may be that the AAS instrument was not properly calibrated with the working standard
A couple of options come to mind:
Can you elaborate on the experimental design please? Are you measuring the Pb concentration in the solution the adsorbent is placed in, or the Pb adsorbed on to the graphene oxide itself? If the purpose is the removal of Pb from the 60 ppm solution, then it seems that it is working fine. The negative result is odd, but could be explained, once we understand the rest of the experiment.
If the problem is the immediate change in concentration from 60 to 30 ppm, have you accounted for sample preparation for the AAS? Is there an internal standard you add, or is it mixing the graphene oxide (1g/L) mixed with Pb (60 µg/L) that dilutes it straight away?
Metals in solution are not going to go anywhere else in a significant way: elements don't break down, but as you suggest, may precipitate or adsorb to the wall of the container in some way. What sort of solution are you using? Acids are commonly used to keep metals in solution, but if you are using water only, then it is quite possible you are seeing adsorption on the wall of your sample container (plastic or glass).
If you can provide some more details, I'm sure we can help you solve your problem.
Matthew Wheal I use Pb(NO3)2 standard solution (1000ppm). I add 6ml of Pb(NO3)2 standard solution into a 100ml volumetric flask and fill it with deionized water (to produce 60ppm solution for experimental solution). I then take 15ml from the solution (before adding any adsorbent) to test the initial concentration. The result that I get from AAS should be around 60ppm because I didn't add any adsorbent yet, but I get 30ppm instead.
After that, I run my experiment by adding 1g/L of the adsorbent. I took a 15ml sample every 30minutes for AAS. I use a syringe filter when I extract the sample. (To measure the Pb concentration in the solution the adsorbent is placed in)
My standard solution is in acid but I change the pH from 2 to 6 by adding NaOH (in the experimental solution) before starting my experiment.
Edidiong Ikpe The equipment has been calibrated to the working standard
- Badges
- Science topic
- Similar topics
- Biological Science
- Kinesiology
- Running