Gels, cationic

Figure 8.12 Dowex Upcore Monosphere C-600, styrene-divinylbenzene gel cation resin (Dowex and Upcore are trademarks of Dow Chemical Company, Midland, MI).

Sodium softeners are used to treated RO influent water to remove soluble hardness (calcium, magnesium, barium, and strontium) that can form scale on RO membranes. Once known as sodium zeolite softeners, zeolites have been replaced with synthetic plastic resin beads. For sodium softeners, these resin beads are strongly acidic cation (SAC) polystyrene resin in the sodium form. The active group is benzene sulfonic acid, in the sodium, not free acid, form. Figure 8.12 shows styrene-divinylbenzene gel cation resin. Equation 8.4 shows the softening reaction for calcium exchange ... 

Figure 3.4 Strain patterns within a swelling gel cation exchange resin - 12% DVB...

A method for determination of cations and anions in a single run was described in Section 8.6. The column was packed with a polyacrylate gel cation exchanger. It appears that sample cations were separated by cation chromatography and anions by ion-exclusion chromatography. 

Macroporous cation resins are also available but are less widely used then the anion materials. This is because the standard gel cation resins are themselves very slroug and also because the poisoning of cation reains by large organic cations is virtually unknown. 

Carbohydrates are hydrolyzed by the action of acids. Since polymer acids are efficient catalysts for the hydrolysis of esters and amides, attempts have been made to use them for the hydrdysis of carbohydrates. Kern and co-workers (36) found that tlw catalytic activity of poly(styrenesulfonic acid) 2 in the hydrolysis of sucrose 25 was comparable to that of sulfuric acid. A sulfonated polystyrene gel (cation exchange resin) was sli tly more effective (37). 

It should be noted that defining the SNR (= 5) as the detection Hmit is an arbitrary decision. Recently, it was shown [104] that PI species can be easily monitored and even quantified in rather complex mixtures by using MALDI-TOF-MS, subsequent to the removal of interfering PC by its binding to a small column filled with a silica gel cation exchanger (SCX). A more comprehensive review of this important topic is available in Ref. [105]. 

Figure 3 Thermodynamic functions of ion exchange between amino acids and hydrogen forms of gel cation exchanger KU-2-8 (open symbols) and macroporous cation exchanger KU-23 (30/100) (filled symbols) Phe (left panels), Tyr (central panels), and ZyV (right panels)...

---