Alternatives to Filter Paper
Mohammed Farooq
> I am doing a preliminary study on the removal and adsorption of copper
> at trace levels by sulfuric acid activated waste vegetable
> materials. However a seemingly unimportant problem is the filtration
> step. I was using 50 ppm copper solutions for adsorption experiments,
> in order to remove the adsorbent for further dilution and analysis by
> AAS I used unbranded filter papers however the adsorption of copper by
> filter paper was "significant", to test it, I prepared a 3 ppm solution
> and filtered it, the filterate was showing a concentration of 0.61 ppm
> on AAS. It means there is significant sorption of copper by the
> filter paper, this would introduce a systematic error in the
> results,leaving aside the adsorption by glass and other materials
> used. Could someone suggest a NONADSORBING filtering medium? What
> would be the best option from glass wool, centifuge, any other cheap
> materials. I assume that every filter paper eg. Whatman filter paper
> would adsorb .
I have tried some of the suggestions given in sci.chem and results are
given below, also found a single line mentioned about adsorption on
filter paper in an Atomic Absorption Spectroscopy text as "losses may
occur due to the adsorption during filteration" at least someone
acknowledged this fact. I don't why adsorption losses during
filteration are not discussed in detail in analytical chemistry texts.
Anyone has reference to an article about this problem?
Some good suggestions given in sci.chem were
1. Use a Whatman GF glass fiber filter and fritted glass disks Buchner
funnels, which is too expensive and difficult to obtain here.
2. Pretreatment of filter paper with a copper solution ( did not test
this suggestion, it would pose leaching problem). Another technique
was used related to pretreatment, the initial 10 ml of filterate was
rejected and the rest of the filtertate was used for further dilution,
again this did not work, I was getting low results.
3. The third idea was to use a centrifuge. It is posing two main
difficulties, I have been given a small centrifuge (it can accomodate
only six test tubes at a time) and the second thing is that the
adsorbent is so finely ground, that it does not settle well after
centrifuging at the highest possible speed of 4000 rpm, a thin
hydrophobic film of carbonized material tends to float on the top in
the test tubes, even if I try to decant it, it goes with the
centrifugate, so the very purpose of centrifuging is lost.I also tried
using a glass syringe to draw the liquid below the film, but it is
somehow tedious.
4.Glass wool was also tried but it was of low quality, turned the
flame of AAS yellow(heavy interference for the detection of copper by
AAS), thus very low results were obtained.
NEW SUGGESTION:
A book titled "Experiments in Physical Chemistry" by Cecil King and
Otto Steinbach, on page 91 it mentions the use of "sample withdrawing
tubes" in an experiment. The method of construction is given as:
Obtain glass tubing 6 X 20 mm, about 5 cm from the lower end, a
constriction is formed by heating uniformly and sucking in the walls
slightly. Place a small plug of cotton in the bottom of the sample
withdrawing tube and push up to the constriction with a glass rod.
Place a rubber policeman over the upper end. Connect the pipet with
the rubber policeman and withdraw the solution by suction.
This procedure seems to be very good, as a "very small amount" of
cotton or any filtering medium would be required and adsorption
effects would then be negligible, someone has given me QUARTZ WOOL of
Perkin-Elmer to try. I will try to construct such "sampling tubes" and
use quartz wool instead of cotton.
Has anybody used QUARTZ WOOL for filteration and tried this technique
for withdrawing sample solutions?
Mark Tarka
> faro...@hotmail.com (Mohammed Farooq) wrote in message news:<66756669.04031...@posting.google.com>...
> > I am doing a preliminary study on the removal and adsorption of copper
> I have tried some of the suggestions given in sci.chem and results are
> given below, also found a single line mentioned about adsorption on
> filter paper in an Atomic Absorption Spectroscopy text as "losses may
> occur due to the adsorption during filteration" at least someone
> acknowledged this fact. I don't why adsorption losses during
> filteration are not discussed in detail in analytical chemistry texts.
> Anyone has reference to an article about this problem?
Maaaaybeee ... the methods of analysis were developed
during a time _before_ trace analyses were contemplated.
As the amount of analyte decreased, losses by adsorption
became signicant.
Why not buy a good quality paper and make up surrogate
samples, do the analysis, determine the amount of loss
by adsorption correlated to the expected concentration
of your real samples, and make the obvious adjustments
to your final results. Document the method _you_ came
up with in your report and you're done.
Mark (... it's a fascinating place ... errrr ...
please excuse me, I feel the urge to
decant my bladder :-)
Coreleus Corneleus
> faro...@hotmail.com (Mohammed Farooq) wrote in message news:<66756669.04031...@posting.google.com>...
>
> difficulties, I have been given a small centrifuge (it can accomodate
> only six test tubes at a time) and the second thing is that the
> adsorbent is so finely ground, that it does not settle well after
> centrifuging at the highest possible speed of 4000 rpm, a thin
> hydrophobic film of carbonized material tends to float on the top in
> the test tubes, even if I try to decant it, it goes with the
> centrifugate, so the very purpose of centrifuging is lost.I also tried
> using a glass syringe to draw the liquid below the film, but it is
> somehow tedious.
'Somehow tedious'. What does that mean? Probably - 1. The length of
the needle does not correspond with the specific position in the
specific test tube that you are drawing from and the top of the
syringe is stopped by the test tube's opening. 2. The syringe is not
disposable and so you end up needing to rinse for purposes of
cross-contamination when you go from one sample to tne next. and/or
3. The viscosity of what you are drawing does not easily go through
the needle, and so it is not rapidly drawn.
Try 9 inch pasteur pipettes.
Mohammed Farooq
You guessed it right,
1. The top of the syringe is stopped by the centifuge tube's opening
and the needle just reaches the suface of the solution the maximum
volume that can be drawn using this technique is 2 ml.
2. The syringe is not disposable and needs to be rinsed everytime.
3. There is only one glass syringe available to me!
PJD
I thinks it' s important to say you have no means and to buy materials
is very difficult for you.
I believes many people , here, have not this parameter when they give
their ideas.
The pasteur pipettes is a good idea to replace syringe.
SNUMBER6
>Mohamed,
>I thinks it' s important to say you have no means and to buy materials
>is very difficult for you.
May be true ... but he'll become a more creative and adaptive Chemist because
of it ...
>I believes many people , here, have not this parameter when they give
>their ideas.
A lot of myopic people ...
I get very pissed off at some who do not want to make a process improvement ...
because "the capital cost is too high ..." ... then find other excuses when you
show you can do it with the equivalent of chewing gum and baling wire and have
a near infinite ROI ... Grabbing them by the throat does work sometimes ...
Be seeing you
In the Village
Number 6
Coreleus Corneleus
> faro...@hotmail.com (Mohammed Farooq) wrote in message news:<66756669.04031...@posting.google.com>...
> > I am doing a preliminary study on the removal and adsorption of copper
> > at trace levels by sulfuric acid activated waste vegetable
> > materials. However a seemingly unimportant problem is the filtration
> > step. I was using 50 ppm copper solutions for adsorption experiments,
> > in order to remove the adsorbent for further dilution and analysis by
> > AAS I used unbranded filter papers however the adsorption of copper by
> > filter paper was "significant", to test it, I prepared a 3 ppm solution
> > and filtered it, the filterate was showing a concentration of 0.61 ppm
> > on AAS. It means there is significant sorption of copper by the
> > filter paper, this would introduce a systematic error in the
> > results,leaving aside the adsorption by glass and other materials
> > used. Could someone suggest a NONADSORBING filtering medium? What
> > would be the best option from glass wool, centifuge, any other cheap
> > materials. I assume that every filter paper eg. Whatman filter paper
> > would adsorb .
>
> I have tried some of the suggestions given in sci.chem and results are
> given below, also found a single line mentioned about adsorption on
> filter paper in an Atomic Absorption Spectroscopy text as "losses may
> occur due to the adsorption during filteration" at least someone
> acknowledged this fact. I don't why adsorption losses during
> filteration are not discussed in detail in analytical chemistry texts.
> Anyone has reference to an article about this problem?
I am not sure if you are able to generate a concentration step
afterwards when you go through your filtration, ie, reduce the amount
of filtrate by vacuum distillation, evaporation, or the like,
especially if you are using an aquous solution. If you do, you have
the leisure to rinse the filter with your solvent to produce a maximum
recovery. If you do not, too much rinsing and the concentration goes
down, too little and the filter paper might still hold what is being
sent through. You might cheat some by including your rinsate in your
initial or final volume or concentration measurements and
calculations. I do not know if the parameters of your experiments
would allow changes in pHs, solvents, ionic strengths, or the like to
produce better 'eluting solutions' or not. (Look up the terms 'solid
phase extraction'.) Remember, the greater the amount of surface area
that your solution (even glass) can come in contact with, the greater
surface area that your solution can potentially adhere to. Remember
that scratches in glass can sometimes act as 'active sites'. Keep the
surface area of both the filter paper and funnel that you are using to
a minimum, in relation to the volume of solution that you are
ultimately working with, in order to keep these potential sources of
loss low. You can also try different types of filter paper.