CHAPTER 9 



ION EXCHANGE 



General Methods — Cation Exchangers; Anion Exchangers. General Tech- 

 niques — Apparatus; Procedures. Physical Basis of Separation — Ions of Opposite 

 Charge; Ions from Nonelectrolytes; Substances of Different Acidic or Basic Strength; 

 Ions of Different Size; Conversion of Nonelectrolytes to Ions by Complex Formation. 

 Types of Applications — Removal of Impurities or Interfering Substances: Concen- 

 tration of Trace Constituents; Separation of Materials; Estimation of Total Salt 

 Concentration; Properties of Complex Ions; Miscellaneous Applications. 



As the name implies, this method is based on the exchange of ions 

 in a solution for ions of the same charge from an ion exchanger. Ion 

 exchangers are insoluble substances from which ions may be readily and 

 reversibly replaced by others from solutions that are brought into contact 

 with the exchanger. The occurrence of ion exchange between soil par- 

 ticles and soil solution has been recognized for more than a hundred years, 

 and the agricultural application contributed the first systematic study of 

 the phenomenon. 



Exchange has been shown to occur with many types of substances, such 

 as cellulose, lignin, wool, protein, bone, resins, and inorganic precipitates. 

 The relatively recent development of synthetic exchange resins having 

 optimum physical and chemical properties for specific applications has 

 extended the use of exchange techniques for analytical and biological pur- 

 poses, in addition to promoting increased industrial usage. The texts of 

 Kunin and Myers (1), Samuelson (2), Lederer and Lederer (3), Cassidy 

 (4), and Nachod (5) may be consulted for historical and operational 

 details. 



Ion exchange offers many of the advantages mentioned for paper chro- 

 matography, namely, simplicity of equipment, rapidity, and ease of 

 manipulation. Also, less skill and judgment are required on the part of 

 the analyst than for conventional analytical techniques. A primary con- 

 sideration is that ion exchange permits separations or concentrations that 

 would otherwise be impracticable or time-consuming. In comparison 

 with paper chromatography, ion-exchange methods are not generally so 

 applicable but do allow larger amounts of substances to be fra(;tionated 

 and collected. Thus ion-exchange methods offer many advantages in 



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