From: michalp717@gmail.com   
      
   [[Mod. note --   
   1. I have manually re-wrapped over-long lines.   
   2. This post isn't really within the scope of this newsgroup, but   
   alas the logical newsgroup for this material, /sci.chem/, has a poor   
   signal/noise ratio (lots of irrelevant posts).  So... let's talk   
   about chemistry a bit!   
   -- jt]]   
      
   Goal:   
   -Need to generate a pH vs. Fluorescent Intensity calibration curve   
   using a spectrofluorometer for a particular fluorescent dye with   
   an analyte (metal ion).   
      
   Method:   
   -Generating pairs of samples at varying pH (9, 9.5, 10, etc) with one   
   sample being a blank and the other containing the analyte.   
   1. First mix the dye with ethanol and HNO3 in a beaker to dissolve.   
   2. Next, 2.0 mL of this dye solution is added to two cuvettes as a pair.   
   This is repeated for varying pHs by adding base.   
   3. Finally, 0.1 mL of the analyte suspended in 3% or 0.3% nitric acid   
   (required to solubilize) is added to one cuvette (test sample), and 3%   
   or 0.3% nitric acid is added to the other cuvette (blank sample). This   
   changes the pH yet again, so it's measured in the cuvette. Of course,   
   the cuvette pH is always lower than that of the beaker since the analyte   
   is in acidic solution.   
      
   Problem:   
   -The analyte can only be managed in a separate facility, so I cannot add   
   it to the beaker solution. It must be added to the cuvette in the final   
   step.   
   This creates the issue: I cannot adjust the pH in the cuvette given   
   its small volume, so whatever pH it ends up being after addition of the   
   analyte, I have to accept. This prevents me from adjusting the final pH   
   to my desired outcome.   
   -This is made even more difficult with the equivalence point, preventing   
   me from reaching pHs of ~10 and 11 since the addition of the analyte in   
   acid results in a drastic pH decrease and even 0.1 mL is proportionally   
   large compared to 2.0 mL of the dye solution..   
      
      
   Attempts to resolve:   
   -Tried using the analyte suspended in 0.3% acid solution rather than 3%   
   acid solution, but this doesn't fix the problem, only reduces the decrease   
   in pH.   
      
   Ideally, whatever the pH of my beaker solution is, I could just add that   
   to the cuvettes that contains the analyte and the dye solution. Is this   
   really the only way? I feel I have been using my method for so long that   
   I do not see another way.   
      
   Thanks for reading   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)