Thanks Marshall, The pictures and plots are very informative. I believe you are right about trying to measure ppm without digesting the silver won't work. Your explanation has helped tremendously in understanding the theory and operation of colorimeters and spectrophotometers. - Steve N
-----Original Message----- From: Marshall Dudley [mailto:[email protected]] Sent: Thursday, December 18, 2008 2:17 PM To: [email protected] Subject: Re: CS>Measuring CS with a spectrophotometer or colorimeter 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 >>> >>> > > > -- > The Silver List is a moderated forum for discussing Colloidal Silver. > > Instructions for unsubscribing are posted at: http://silverlist.org > > To post, address your message to: [email protected] > > Address Off-Topic messages to: [email protected] > > The Silver List and Off Topic List archives are currently down... > > List maintainer: Mike Devour <[email protected]> > > > > > > . > >
