Separator Universal Anion

A HEMA-based anion exchanger developed by Alltech has been described as a universal stationary phase for the separation of a wide variety of anions [6,7]. This anion-exchange resin has been compared to agglomerated peUicular anion exchangers for the separation of anions by chemically suppressed 1C. The HEMA-based columns exhibit higher capacities for all anions and particularly for weakly retained anions such as fluoride and formate, which were completely resolved. The HEMA columns could be used for both isocratic and gradient techniques. 

R. Saari-Nordhaus, I. K. Henderson and J. M. Anderson, Jr., Universal stationary phase for the separation of anions on suppressor-based and single-column ion chromatographic systems,. /. Chromatogr... 546, 89, 1991. 

Over the past 5 years, Metrohm (Herisau, Switzerland) also developed a number of surface-aminated PS/DVB-based resins. Metrosep A Supp 1 is a medium-capacity universal anion exchanger with a special selectivity in that bromide elutes behind nitrate. It is predominantly used both for anion analysis in samples with large concentration differences and for separating oxyhalide ions such as bromate, chlorite, and chlorate. 

Metrosep A Supp 15 is a mediuni Capacity universal anion exchanger designed for high mechanical and chemical stability. Therefore, this separator column can be used for standard applications as well as for highly complex separation problems. It exhibits a special selectivity to separate glycolate, formate, and acetate to baseline under isocratic conditions being illustrated in Figure 3.10. 

Quitasol and Krastins [504] used a polyhydroxyethylmethacrylate (Universal Anion, Grace Alltech, USA) as a stationary phase 5 mmol/L potassium nitrate adjusted to pH 3.5 with nitric acid serving as an eluent. Under these chromatographic conditions, the organic phosphate can be separated to baseline from orthophosphate and orthophosphite within 10 min. Because Quitasol and Krastins determined only the drug component in various pharmaceutical formulations, they used a refractive index detector for the sake of simplicity. This procedure can be validated in terms of precision, accuracy, and linearity without any difficulties. 

Fig. 3 -19. Separation of various inorganic anions on Alltech Universal Anion. - Separator 150 mm X 4.6 mm i. d. Universal Anion eluant 5 mmol/L p-hydroxybenzoic acid, pH 7.9 with LiOH flow rate 1 mL/min detection direct conductivity injection volume 100 pL solute concentrations 10 mg/L fluoride (1),...

When it was introduced, the lonPac AS12A was clearly the most modem latexed anion exchanger for the separation of fluoride, oxyhalides, and mineral acids. The latest development in the field of universal anion exchangers for water analysis is the lonPac ASM discussed in Section 3.4.1, which is based on a support material with a covalently bonded ion-exchange polymer (see Fig. 3-33 in Section 3.4.1). 

By using an anionic collector and external reflux in a combined (enriching and stripping) column of 3.8-cm (1.5-in) diameter with a feed rate of 1.63 ni/n [40 gal/(h ft )] based on column cross section, D/F was reduced to 0.00027 with C JCp for Sr below 0.001 [Shou-feld and Kibbey, Nucl. AppL, 3, 353 (1967)]. Reports of the adsubble separation of 29 heavy metals, radioactive and otheiwise, have been tabulated [Lemlich, The Adsorptive Bubble Separation Techniques, in Sabadell (ed.), Froc. Conf. Traces Heavy Met. Water, 211-223, Princeton University, 1973, EPA 902/9-74-001, U.S. EPA, Reg. 11, 1974). Some separation of N from by foam fractionation has been reported [Hitchcock, Ph.D. dissertation. University of Missouri, RoUa, 1982]. 

Metal nanotube membranes with electrochemically suitable ion-transport selectivity, which can be reversibly switched between cation-permeable and anion-permselective states, have been reported. These membranes can be viewed as universal ion-exchange membranes. Gold nanotube molecular filtration membranes have been made for the separation of small molecules (< 400 Da) on the basis of molecular size, eg. separation of pyridine from quinine (Jirage and Martin, 1999). 

For the cationic surfactants, the available HPLC detection methods involve direct UV (for cationics with chromophores, such as benzylalkyl-dimethyl ammonium salts) or for compounds that lack UV absorbance, indirect photometry in conjunction with a post-column addition of bromophenol blue or other anionic dye [49], refractive index [50,51], conductivity detection [47,52] and fluorescence combined with postcolumn addition of the ion-pair [53] were used. These modes of detection, limited to isocratic elution, are not totally satisfactory for the separation of quaternary compounds with a wide range of molecular weights. Thus, to overcome the limitation of other detection systems, the ELS detector has been introduced as a universal detector compatible with gradient elution [45]. 

When the kinetics of a sorption process do appear to separate according to very small and very large time scales, the almost universal inference made is that pure adsorption is reflected by the rapid kinetics (16,21,22,26). The slow kinetics are interpreted either in terms of surface precipitation (20) or diffusion of the adsorbate into the adsorbent (16,24). With respect to metal cation sorption, "rapid kinetics" refers to time scales of minutes (16,26), whereas for anion sorption it refers to time scales up to hours TT, 21). The interpretation of these time scales as characteristic of adsorption rests almost entirely on the premise that surface phenomena involve little in the way of molecular rearrangement and steric hindrance effects (16,21). 

Phillip A. Drake (1990), Master s Thesis Anion Chromatography with Variable Capacity Separators Based on Macrocyclic Complexes, Brigham Young University. 

Robert G. Smith (1993), PhD Dissertation Anion Separations Using Macrocycle-Based Ion Exchange Columns, Brigham Young University. 

Ion-pair chromatography provides a useful alternative to ion-exchange chromatography. The selectivity of the separation in ion-pair chromatography is mainly determined by the make-up of the mobile phase, thus both anionic and cationic compounds can be separated. This universal applicability has helped ion-pair chromatography reach its present significance. 

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