Norton, Steve wrote:
Re.: "picking the right frequency,"
I'm glad you brought that up. If one was to consider calibrating a
spectrophotometer to use for measuring ppm as well as particle size
distribution, there is the problem that light absorption by a sample of
CS at a specific wavelength could vary from lot to lot based on the
particle size distribution of the sample. Should one make the ppm
measurement at the point of maximum absorption, at some intermediate
"average" point or would one need to make measurements over the
distribution and average the results.
I assume that the colorimeter avoids this problem because by digesting
the silver, you convert all the silver to the same "particle size". Do
you know what wavelength your colorimeter uses when making the
measurement for silver?
Thanks,
Steve N
If you run it on plain old EIS, then you can get a curve which will give
you some idea of the particle sizes. For ppm measurement, you first
digest the silver. Thus you have no particles at all, it is 100% silver
salts. I use nitric acid, and thus it is silver nitrate. Then chemicals
are added that give it a very strong color, if I remember right it turns
violet. The wavelength that is then used is for the violet color that
the chemical changes the silver to. I doubt you could come up with a
good way to get ppm from a curve of the undigested and treated EIS,
absorption changes so much depending on size and shape of the
particles. To see some typical curves of different ppm and particle
size of EIS see the following:
http://silver-lightning.com/hach/oral.GIF
http://silver-lightning.com/hach/oral2.GIF
http://silver-lightning.com/hach/oral3.GIF
http://silver-lightning.com/hach/topical.GIF
These are in ever increasing particle size. The leftmost peak is the
absorption of the silver ion, that is ionic silver. All other peaks
correspond to particles, with larger being more to the right generally.
HIf you look at http://silver-lightning.com/hach/agno3.GIF that is the
absorption of silver nitrate. The reason that this one appears so much
wider than the others is that I expanded the X axis to show more detail
since there was no absorption at the longer wavelengths (that is all the
absorption was in the uv range.
You can see the changes in the color of CS as particle size increases
here: http://silver-lightning.com/cs-color.jpg and the actual absorption
curves vs particl size here http://silver-lightning.com/cs-curves.jpg
Marshall
-----Original Message-----
From: Marshall Dudley [mailto:[email protected]]
Sent: Thursday, December 18, 2008 10:29 AM
To: [email protected]
Subject: Re: CS>Measuring CS with a spectrophotometer or colorimeter
Norton, Steve wrote:
Thanks Marshall,
That helps. The info online relative to colorimeters does mention
digesting substances but I was unclear on how that might apply to
silver measurement. There are old manual, analog meter, Hach
colorimeters available for a low cost on eBay. Any reason they would
not work? One could replace the analog meter with a precision resistor
and a digital multimeter and probably gain some accuracy for a very
low additional cost.
They should work, if you have the proper reagents. Mine is digital and
computer controlled, so it does all the work itself as far as
calibration, picking the right frequency, and figuring out the
concentration of silver.
The spectrophotometers allow you to vary the wavelength of the light
used. Does varying the light wavelengths and measuring the light
absorbtion at each wavelength provide particle size distribution
information? At least a rough estimation? Again, there are old manual,
analog meter, spectrophotometers available for a low cost on eBay and
one could make the DMM modification.
Yes, it is quit good for assisting in particle size distribution. The
unit I have prints out the curve of amplitude of absorption vs
wavelength from the infrared through the uv range.
Marshall
Thanks for your help,
Steve N
-----Original Message-----
From: Marshall Dudley [mailto:[email protected]]
Sent: Thursday, December 18, 2008 7:01 AM
To: [email protected]
Subject: Re: CS>Measuring CS with a spectrophotometer or colorimeter -
need help
Norton, Steve wrote:
>From what I can gather, to measure ppm with a spectrophotometer you
must measure a solution with a known ppm first. You then measure the
unknown solution and then using a formula you can calculate the ppm
of
the unknown solution. If you have multiple known solutions of CS of
different ppms, you can plot a conversion chart that gives more
accuracy than the formula. Is that correct?
Does the colorimeter use the same methodology?
That Hach unit I have is calibrated, so you do not use a solution with
a known ppm. You put in a control, which is the same distilled water
that the CS was made from, and let it run the baseline, then put in
the one with CS in it, and it displays the ppm directly. However all
the silver must be digested first, using nitric acid.
Marshall
Thanks,
Steve N
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