Eluents generation, electrolytic

Figure 26-7 Anion separation by ion chromatography with a gradient of electrolytically generated KOH and conductivity detection after suppression. Column Dionex lonPac AS11 diameter = 4 mm flow = 2.0 mL/min. Eluent 0.5 mM KOH for 2.5 min, 0.5 to 5.0 mM KOH from 2.5 to 6 min 5.0 to 38.2 mM KOH from 6 to 18 min. Peaks (1) quinate, (2) F, (3) acetate, (4) propanoate, (5) formate,...

With the advent of anion exchangers with an increased affinity for hydroxide and suppressors that tolerate a higher eluent concentration, the use of sodium or potassium hydroxide has become more popular. However, it is difficult to remove all of the carbonate from chemical solutions of sodium hydroxide. Electrolytic generation is now the preferred way to produce hydroxide eluents for IC. The product is almost entirely free of carbonate and the electrolytic generation provides excellent control of the concentration. Electrolytic generators are described in Chapter 1. 

Automated systems also generate KOH eluent electrolytically. It is only necessary to add deionized water to compensate for evaporation to allow an automated system with a 4-nun-diameter column to run for a month. 

Dionex offers a just add water system for electrolyte generation and purification of commonly used eluents such as KOH and methanesulfonic acid. Eluents are generated from deionized water using an Eluent Generator (EG) cartridge and then polished of contaminants using a continuous-regeneration trap column. 

Figure 3.202 Separation of inorganic anions with an electrolytically generated KOH eluent. Separator column lonPac AS11 eluent ...

Figure 3.203 Trace analysis of inorganic and organic anions with an electrolytically generated KOH eluent. Separator column lonPac AS15 column temperature 30°C eluent KOH (EG) gradient 9 mmol/L isocratically for 7 min and then to 46 mmol/L in 11 min flow rate 1.6mL/min detection suppressed...

Figure 3.230 Schematic of a HPAE-PAD system with vacuum degassed electrolytically generated hydroxide eluents.

By employing electrolytically generated hydroxide eluents (reagent-free ion chromatography, RHC) on hydroxide-selective stationary phases. 

This chapter reviews the underlying principles of ion chromatography and its application in pharmaceutical analysis. It provides an overview of eluent systems, applications of gradients, electrolytic eluent generation, suppressors, and stationary phases. Applications of ion chromatography to the confirmation of counter ions, active ingredient analysis, competitive analysis and development work are discussed. 

As the droplets move through the hot source area, they continue to vaporize. The electric field at the liquid surface increases until ions present in the eluent are ejected from the droplet. Ions are sampled through a conical exit aperture in the mass analyzer. The ionization of the analytes takes place by means of direct ion evaporization of the sample ion or by solvent-mediated CI reactions an ion of the electrolyte ejected from a droplet reacts with a sample molecule in the gas phase and generates a sample ion that is mass analyzed. In addition, fragment ions can be observed due to the high temperatures associated with TSP negative ions are also produced by TSP, and negative ion detection is recommended for acidic compounds. 

With TSP, ammonium acetate has emerged as the best general-purpose electrolyte for ionizing neutral samples. Improved ionization can be obtained by the use of a filament or discharge electrode to generate reactive ions for CI (87, 88). The processes involved in filament or discharge-assisted ionization must be used when operating in the absence of a buffer with nonaqueous eluents. With ionic analytes, the mechanism of ion evaporation is supposed to be primarily operative since ions are produced spontaneously from the mobile phase (89). Ion evaporation often yields mass spectra with little structural information in order to overcome this problem, other ionization modes or tandem MS have been applied (90). 

Figure 26-6 Electrolytic KOH eluent generator for ion chromatography. [Adapted from Y. Liu, K. Sriniyasan, C. PoN, and N. Avdalovic, "Recent Developments in Electrolytic Devices tor Ion Chromatography"J. Biochem. Biophys. Methods 2004,60.205]...

---