From: '''newspam'''@nonad.co.uk   
      
   On 06/05/2021 00:38, M P wrote:   
   > I'm working on detecting a particular metal ion using fluorescent   
   > dyes in conjunction with absorbance and emission spectroscopy, and I   
   > need to test the chosen dye over a range of pH values (i.e. 10-14). I   
   > first create the dye solution in a beaker and adjust its pH using   
   > NaOH (lets say one dye solution at 12.5 and one at 13.0), then I add   
   > 1.9 mL of this to a cuvette along with 0.1 mL of a metal ion in acid   
   > solution. However, the cuvette's pH always drops to the same value   
   > (typically 12.3) once I add my 0.1 mL metal ion in acid solution. I'm   
   > assuming this is because pH is logarithmic, to reiterate the   
   > proportions are 1.9 mL of the dye solution to 0.1 mL of the metal ion   
   > in acid solution.   
      
   Why don't you do it the other way round?   
      
   Make the dye and metal ion solution in bulk first and then add N-n drops   
   of 1M NaOH and n drops of 1M HCl to each sample aliquot in a cuvette.   
   Then measure the pH of each test specimen after stirring.   
      
   > Any suggestions on resolving this? I cannot titrate a solution in a   
   > small, 2.5 mL cuvette. I've considered using a buffer from what I've   
   > read but I do not know how to select one, or if they affect   
   > absorbance/emission data.   
      
   Alkaline buffers tend to be something like glycine/NaCl/NaOH eg   
      
   https://www.thomassci.com/scientific-supplies/Ph-Buffer-13   
      
   You would have to test if it affects your choice of fluoro dye(s).   
      
   > I do not have a background in chemistry but I've been on this project   
   > and am now hitting a brick wall. Any advice or guidance is much   
   > appreciated.   
      
   AA spectroscopy or ICPMS might be an alternative option for metals.   
      
   --   
   Regards,   
   Martin Brown   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)