In a batch adsorption system, we need to take samples from the solution at different time intervals (for kinetics study) or at the end of the experiment.
My question is, how should we take those samples? Do we need to wait till the adsorbents settle down or we can do it with filter papers? Considering that the filter papers themselves adsorb to some extent.
Many published works reported the use of filter papers in their adsorption studies. But in my case, if I use filter papers, there is no metal (my experiment of interest) residues (almost 100 % adsorption).
On the contrary, without filter papers, the initial concentration doesn't change a bit (100% remaining).
I'm so very confused! Can anyone clarify this phenomenon?
I would be thankful to know some answers from your own experience.
As salamualaikum, filtration is very important step during adsorption study. your adsorbent remains suspended in the solution, so they can interfere in the result. For example, if the adsorbent is suspended, it will be accompanied by adsorbed metal/adsorbate. You may consider following which is a standard method of filtration in adsorption studies even if it also adsorb some adsorbate.
http://www.google.com.hk/imgres?imgurl=http%3A%2F%2Fwww.millipore.com%2Fimages%2Fxl%2F904201-06%255B659-ALL%255D.jpg&imgrefurl=http%3A%2F%2Fwww.millipore.com%2Fcatalogue%2Fitem%2Fslgv033rs&h=600&w=467&tbnid=tBZ_2iIKCWbhoM%3A&zoom=1&q=0.22u%20microfilters&docid=4AKz8JeRVzmSWM&hl=zh-CN&ei=4IuGU9LsAYzn8AW_8IGYDA&tbm=isch&ved=0CFMQMygAMAA&iact=rc&uact=3&dur=327&page=1&start=0&ndsp=19&biw=1366&bih=643
Another widely used method is to take sample at desired times and centrifuge them if you think filter is not working in your work. You can take samples at different time intervals, collect them and then centrifuge together. This will save your time.
Thank you Mr. Asif. Alhamdulillah, I've got desired results this morning using filter papers of 0.4 micrometer retention capacity. You recommended the membrane filter with 0.22 micrometer retention. Since I couldn't make that way,,,I tried with that and finally got the results.
Thanks again for your valuable suggestion.
Agreed with Asif Mahmood. He gave clear-cut explanation of this aspect.
Hello Sirajus,
You must filter the samples at the end of an experiment as well as in a batch kinetic run. This is to prevent any more adsorption reactions from taking place as well as to prevent solids from entering the analytical instrument's uptake system thus blocking it. The easiest and quickest way is to use a syringe mounted disposable filters of 0.45 microns. I hope this helps.
Filtration pr centrifugation is must to sepaprate the adsorbent from the aqueous system containing metal. if by chance a small particle of the adsorbent remains in your aliquot from which you estimate amount of residual metal, there may be interference in measurement or you may get false results(probably higher than actual concentration of metal) due to presence of the sorbed adsorbent particle (this may not happen always, so you should be able to distinguish).
I support Asif Mahmood.
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