I've sent the following message to Hanna Instruments: Dear Sir or Madam:
I am the moderator of an online mailing list for people who are studying colloidal silver (CS). One of our goals is to test some of the many recipes that have been widely distributed in hopes of shedding some light on what is really being produced from them. One requirement for that effort is a simple, approximate measurement of concentration in the finished product. Several of our members have contacted you in the past about instruments for measuring concentration and have gotten more than one answer to their questions. I'd like to try to resolve this confusion so I can recommend the best instrument for the task. The samples we're trying to measure are assumed to be distilled water with moderately low concentrations of ionic silver and/or small charged silver particles in colloidal suspension. Concentrations that we expect are in the range of zero to a few tens of ppm. There should be only negligible amounts of any other material. The following instruments have been suggested to various people: TDS-1 DiST-1-WP PWT Several of our group already have the TDS-1. It is reasonably stable even though I know I'm at the very bottom of it's operating range. How can we *best* assure that we'll get sensible readings from one unit and/or measurement to the next? I dislike the idea of using an 800 ppm calibration solution (HI-7032P) when I am trying to measure 0-30 ppm. Assuming the TDS-1 also works by measuring conductivity, is it possible to use the HI-7033L conductivity standard (84 uS/cm) to calibrate the TDS-1? How linear is the TDS-1 at the low end, and how much zero error is possible? The DiST-1-WP seems to suffer from the same limitations as the TDS-1, only worse. The accuracy of the unit is 2% of full scale, which would amount to 40 ppm. Again, just how linear will it be if calibrated at the low end? The PWT *seems* to be more appropriate to our application. It is at least apparent we would be making better use of the electronics. I do not know the basis for the relationship between TDS readings and conductivity. Do the TDS-1 and DiST measure based on conductivity, and their calibration is a verifiable relationship for a specific material? Is a different calibration factor required for species with different molecular/atomic weights? Would it be practical to adjust the PWT calibration to show equivalent ppm directly? I fully recognize there are limits to the accuracy and precision of any instrument and measurement technique. Would you please provide me with whatever references or background you feel I need in order to understand the measurement technique used in these instruments enough to be sure we are applying the results correctly? Please contact me by e-mail or via telephone during business hours. I would appreciate as much detail as you can afford to share with me, so I may fully answer these questions for the members of our group. And please correct anything I've misunderstood in all of the second- and-third-hand information I have received. Be well, Michael Devour owner, silver-list -- 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: silver-list-requ...@eskimo.com -or- silver-digest-requ...@eskimo.com with the word subscribe or unsubscribe in the subject: line. To post, address your message to: silver-list@eskimo.com List maintainer: Mike Devour <mdev...@id.net>
