By Anonymous on Thursday, July 17, 2003 - 10:20 pm:
Hi,
Under what circumstances,and what is the chemistry behind using the halide salts in the mobile phase.What could be the equivalent alternative
By HW Mueller on Friday, July 18, 2003 - 07:37 am:
You may want to emulate body fluids, ionic strength, etc. I have used NaSCN with success, but one should better not work at acidic pH with that.
By Carlos Teixeira on Friday, July 18, 2003 - 08:30 am:
Hi Anon. 10:20
It is very important remember that Halide Salts can to attack the stainlees steel of your chromatographer.
Bye
By Chris Pohl on Friday, July 18, 2003 - 09:15 am:
The rationale for making use of electrolytes in liquid chromatography eluents depends entirely upon the retention mechanism. In reversed phase applications, electrolytes will lower the solubility of organic components and have been used to increase retention of weakly retained neutral analytes (otherwise known as salting out chromatography, renamed by the biologists as HIC).
In ion pair chromatography, adding electrolytes will both increase the partition coefficient of the ion pair reagent onto the surface of the reversed phase column (increasing capacity) and compete for retention sites on the surface (reducing retention). Generally chromatographic efficiency is improved in this mode by the addition of electrolytes.
Lastly, in ion exchange chromatography, adding electrolytes is a crucial component of the elution process and the proper choice of electrolyte plays a significant role in the dynamic capacity and selectivity of the analytical system, with the amount of electrolyte present regulating retention.
In all of the three cases above, it is feasible to replace halides with other electrolytes. Of course which electrolytes may be substituted is dependent upon which of the modes above your interested in. Generally, the best course of action is to choose an electrolyte with similar ion exchange selectivity as this is a good indicator of its relative hydration and such an electrolyte will be expected to behave similarly when substituting for a halide electrolyte. There are a number of references that provide the anion and cation selectivity order for ion exchange including Lange's Handbook of Chemistry.
By Anonymous on Saturday, July 19, 2003 - 12:22 am:
thanx chris,
thank you so much for your time
regards
-Karunai raj Michael