Ion pair equlibria, mathematical modelling of data - Please help

Gabriel L Pitts glp at helium.gas.uug.arizona.edu
Fri Mar 26 03:46:33 EST 1993

In article <1993Mar18.122756.24525 at kth.se> tomas_e at LINK.Physchem.KTH.SE writes:
>In article <1993Mar18.155857.898 at otago.ac.nz>, alastair at farli.otago.ac.nz (Alastair Thomson), University of Otago, Dunedin, New Zealand writes:
>>We have been examining an ion-pair between eosin (anion) and  
>>cetylpridinium chloride (cation) (a quaternary ammonium compound) by  
>>spectrophotometry (542 nm) and are seeking to determine the ion-pair  
>>association constant (K).
>>What we want to know is the ion-pair constants for both the 1:1 (K1) and  
>>1:2 (K2) complexes.  Does anyone have a mathematical model we could use to  
>>calculate these constants, and if so, can we use it?
>This sound like a fairly standard evaluation of stability constants of 
>complex formation. (Nevertheless, the actual computation of several K's 
>simulataneously can be numerically very troublesome.) There are several 
>different computer programs that are used to evaluate this kind of data, 
>most commonly for ligand bonding to metal ions. Since this is a typical 
>inorganic chemistry thing, I would recommend you to contact the 
>inorganic chemistry department closest to you. I'm sure they will know 
>someone who has the appropriate complex constant evaluation programs, 
>and know how to use them.
>Tomas Eriksson                                          tomas_e at physchem.kth.se
>            Surface Force Group, Department of Physical Chemistry,
>               Royal Institute of Technology, Stockholm, Sweden
>"These latter-day practitioners of surface chemistry reflect a lingering of the
>adventurous spirit of the Enlightment" -- Charles Tanford

If you need help with the chemistry itself I would suggest the following ref:
Ionic Equilibria in analytical chemsitry by Henry Freiser and Quintus
Fernando.  If you need just software to figure out your solubility equations
than I suggest Mathematica.  I have used this software to create programs which
determine pka and pHs of pharmaceutical dosage formulations, which can get
quite complex!!  The last eqn I created was a quarktic expression!  It took
Mathematica, on a Mac SE/30, about 3 hrs to solve.  Good luck

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