I am trying to remove arsenic from laboratory water using iron nano particles. After treating with nano particles, do we need to digest the water sample using nitric acid? I have prepared my arsenic(III) standard solution from Sodium Arsenite Solution (0.05 mol/l) and added a few drops of dilute nitric acid to it. I have prepared working solutions of 1ppm, 3ppm and 5 ppm by diluting with de-ionized water and then I have done the treatment.
After treating the arsenic solution with nanoparticles I have separated them out by applying a magnetic field and then I am planning to do AAS analysis of the supernatant to check the amount of Arsenic removed by the nanoparticles.
In short "yes". Digestion with nitric acid is often done to ensure that all undissolved / solid particulates are dissolved, this is important when you are working with solid materials. Exceptions may include GFAAS in some samples. Your standard of 0.05 M solution contains 3.7 G/L arsenic -- which in my opinion is on the high side. Try diluting the standard and work on several concentration up to 500 microG/ mL (or less) -- working on several dilution will also let you figure out the linear working range of your system -- Beer's law. You also need to either add equal volumetric % of nitric acid (adjust the concentration accordingly) or calibrate separately for As content of nitric acid to correct your baseline -- this is to avoid / or correct for the possible contamination from Nitric acid itself. Ideally your calibration curve using the standard should cover the concentration range of your test samples (tap water for example). Here are a few links that may help:
http://cdn.intechopen.com/pdfs/26275/InTech-Atomic_absorption_spectrometry_aas_.pdf
http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3005a.pdf
http://www.pelagiaresearchlibrary.com/advances-in-applied-science/vol3-iss3/AASR-2012-3-3-1733-1737.pdf
http://water.epa.gov/type/rsl/monitoring/upload/2005_03_14_monitoring_wsa_WRS_lab_manual.pdf
I must add that I am not an expert in water analysis -- I am sure others will pitch in. This is mostly from what I do when I have to use AAS instruments to detect impurities.
Yes, if the particulate concentration is high, I think it will be better to digest samples with UV or with microwave.
Please write more details about info what do you want to do with this samples ?
step by step ...
Yes..at least if you want to measure total As. There are many methodologies in the literature for digestion of water samples but UV is the most frequently used.
I have modified the question and provided more details of my study.
What is the concentration of As in lab water ?
what type of detection (technique) are you using for determination ? (starting from 1 mg/L is quite high concentration for As)
If I understand correctly you want to make research on remadiation of As by nanoparticles ...
but I can not find the problem ? you have to make classical AAS calibration curve (based on standards) and sample determination from research ...
I just wanted to know whether digestion is required for my samples prior to AAS analysis, as I have seen that for clear samples i.e. less turbid samples digestion is not necessary.
In my opinion digestion is not necessary, If you use ET AAS with Ni as matrix modifier there is no need to digest the sample. Use pyro-coated graphite tubes with a L'vov platform. The only problem is the narrow linear range. The sample must be diluted accordingly. If you have any doubts, compare the results of determination with the callibration curve with the method of additions callibration. Best regards.
You dont have to digest system, if visible impurites are not present. once you have clear solution, you can go for AAS analysis. However, you can remove water by simply heating the solution till complete dryness and then add known volume of dilute solution of nitric acid from the all the side of appratus wall, since it may be possible that some of As may adsorbed on the glass surface. Addition of known volume will give exact result from calibration curve, as akif said.
Totally depends upon the particulate concentration. It is low use the treated water directly. Better use both the methods (with or without digest) and find the difference if any.
I will advise u to carry out all preparations including digestion (before analysis) on the standards used for the calibration of your AAS. And then do the same on your real samples. (i.e whatever preparation required for the determination of real samples must be carried out on the standards used for calibration). With that all errors are minimised.
As regards the work, i will be glad to see the outcome because my findings on nano iron oxide showed that nano iron oxide is positively charge (base on pH and pzc) and will be suitable to remove anionic complexes. It may remove As but the percentage remove may be very small (i.e +ve adsorbent and +ve pollutant). Part. Part. Syst. Charact. 29 (2012) 178–191.
I have used it to remove triphenyltin (organic compound) and it works fine (95.37 % removal). Clean -Soil Air Water, DOI: 10.1002/clen.201300180 (In press)
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