Applications of the Ion-Suppression Technique

Another application for neutral, non-polar stationary phases based on sUica or organic polymers is the separation of weak adds or bases in their molecrdar form. Their dissodation is suppressed by choosing the appropriate pH value. The solute interactions with the stationary phase are determined solely by their 

Applications of Multi-Dimensional Ion Chromatography on Multimode Phases 

They are also termed multimode phases, because they allow separations based on ion-exchange-, ion-pair-, reversed-phase-, and ion-suppression interactions, depending on the type of eluant. Any combinations of these interactions, at the same time or in succession, can also be employed to separate analyte species. 

OmniPac columns are probably the most fascinating separation materials in ion chromatography today. 

1 mmol/L TBAOH - acetonitrile (83 17 v/v) flow rate 1 mL/min detection suppressed conductivity analytes (1) fluoride, (2) chloride, (3) nitrite, (4) succinate, (5) sulfate, 

1 mL/min detection UV (280nm) injection volume 50 pL peaks lOOmg/L each of pyro-gallic acid (1), resorcinol (2), phenol (3), o-cre-sol (4), 2,4-dimethylphenol (5), -naphthol (6), 2,4-dichloro-3-nitrophenol (7), and thymol (8). 

5 pm eluent MeOH/water/acetic acid (38 62 1 v/v/v) flow rate 15mL/min  

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The ion suppression technique can be used to great effect for the analysis of weak acids or bases. For the analysis of acidic compounds the technique consists of the addition of a small amount of acetic or phosphoric acid to the mobile phase. By reducing the eluant pH dissociation of the sample molecules is suppressed. They thus have decreased affinity for the eluant and are retained to a greater extent by the ODS phase. The range of BPC is considerably extended using techniques such as ionic suppression and this mode of LC using ODS bonded phases finds wide application. 

Stockton and Irgolic separated As(III), As(V), arsenobetaine and arsenocholine by high performance liquid chromatography using a reversed-phase ion suppression technique. This method seemed applicable to the separation of these arsenicals with better resolution than the conventional ion-exchange chromatography using resins. 

ESI and MALDI have distinct advantages and disadvantages, such that they are complementary for many applications. Of the two techniques, ESI is the softer one, allowing for ionization of intact multi-molecule complexes however, in the presence of high concentrations of salts or other unwanted constituents, the formation of ions can be suppressed (making analysis impossible). This effect is less pronounced in MALDI, which can produce ionized products even in the presence of salts, but MALDI spectra tend to be very noisy in the mass range below 500 daltons (Da), due to the presence of matrix ions. MALDI usually... 

Phosphate is commonly determined by ion chromatography, both in suppressed and unsuppressed modes. The sensitivity of the conductivity detection techniques commonly used may be inadequate for direct application to the analysis of pristine waters. 

A detailed description of sources used in atmospheric pressure ionization by electrospray or chemical ionization has been compiled.2 Atmospheric pressure has been used in a wide array of applications with electron impact, chemical ionization, pressure spray ionization (ionization when the electrode is below the threshold for corona discharge), electrospray ionization, and sonic spray ionization.3 Interferences potentially include overlap of ions of about the same mass-charge ratio, mobile-phase components, formation of adducts such as alkali metal ions, and suppression of ionization by substances more easily ionized than the analyte.4 A number of applications of mass spectroscopy are given in subsequent chapters. However, this section will serve as a brief synopsis, focusing on key techniques. 

Ion chromatography has found widespread application for the analysis of inorganic and organic ions with pKa values less than 7. It combines the techniques of ion-exchange separation, eluent suppression, and... 

Ion chromatography has become an essential tool of the pharmaceutical analytical chemist. The high sensitivity of the technique, coupled with the wide dynamic operating range made possible with modern high-capacity stationary phases makes it ideal for the analysis of ions in pharmaceutical applications. The combination of gradients and suppressed conductivity detection provides a powerful screening... 

The dissolution of cellulose and other plant-based material in ILs has been studied by Moyna and Rogers [64-66]. Here, the application of NMR excluded fhe need for solvenf suppression techniques. In combination with and C1/ C1 relaxation measurements, it was found that dissolution of cellulose in [C4CiIm]Cl was promoted by the nonhydrated chloride ions, breaking up the hydrogen bonding networks via the cellulose hydroxyl groups. 

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