Mike, & Joe and All, What you are describing is the way it is done. You react the silver with reagents which produce a color whose intensity varies with the concentration available silver. This can be roughly evaluated by eyeball. I play a little game of guessing the mg/L when the color appears in the process, before measuring the absorbance with the meter. If you had a set of tubes of permanent colors matching concentrations, you could do quite well with visual comparison. That is how it was originally done.
The spectrophotometer just quantifies this by measuring the amount of light of a particular wavelength/frequency/color which gets through the solution, which tell you how much was absorbed by the solution. Darker solution absorbs more, and the intensity of the color was determined originally by how much silver was in the sample to react with the dye-forming reagents. All it would take is a high-accuracy set of printed color patches to get you in the ballpark with the Hach reagents. I think you could judge it certainly to within 2 PPM and possibly within 1 PPM. James Osbourne Holmes [email protected] -----Original Message----- From: M. G. Devour [SMTP:[email protected]] Sent: Thursday, November 11, 1999 1:16 AM To: [email protected] Subject: Re: CS>wet chem > Shouldn't there be a way to perform some regular wet chemistry test > to determine PPM? Something like a simple titration or something? > joe... Joe, I've been asking that question on and off for 2 1/2 years, and I've never gotten a good answer. The analogy of titration was always the first thing to come to mind. Shoot, I'd expect you could create a kit of dyes and reagents similar to that used to test a swimming pool and be able to get crude readings by color. Even that much would be helpful. Even if you had a fairly complex setup using a number of reagents and a bunch of glassware, it would still be cheaper than some of the instruments folks have had to buy. I'd like to see us do a survey of analysis techniques and maybe create a table of equipment cost, cost per sample, accuracy and precision, complexity, safety, etc. At least over narrow ranges of process conditions there *is* a correlation between conductivity and concentration. But to peg that measurement to anything *known* still requires other methods for calibration. It's a great question. I hope we're closer to finding an answer. Be well, Mike D. [Mike Devour, Citizen, Patriot, Libertarian] [[email protected] ] [Speaking only for myself... ] -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] List maintainer: Mike Devour <[email protected]>
