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
-----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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