Comparison of nonporous silica‐based ion exchangers and monolithic ion exchangers in separations of inorganic anions

Abstract

Original PaperComparison of nonporous silica-based ion exchangers and monolithic ion exchangers in separations of inorganic anions Low capacity anion exchangers for IC have been prepared by modification of nonporous uniformed silica MICRA microbeads and by modification of the organic polymeric monolithic matrixes prepared in situ in quarz capillary. Due to the small particle size (1.5 lm) high-performance adsorbents were prepared allowing to obtain up to 190 000 tp/m. However, the column possesses a very high back-pressure and can be used in a short length up to 50 mm only to meet the requirements of conventional chromatographic equipment. An analysis of a test mixture of seven anions was completed within 3 min with a back column pressure of about 350 bar (HETP of about 5.5 lm, where HETP is the height equivalent to the theoretical plate). Monolithic capillary columns provide lower efficiency per column unit length than MICRA columns; however, they can be used at a longer length because of their low flow resistance. Monolithic column of ca. 40 cm length has workable pressure below 10 bar and allows separation of a five anions test mixture within less than 10 min. A better efficiency of monolithic column (HETP l75 lm) can be achieved at reduced flow rates when the analysis time is not a critical parameter.

High‐performance separation of small inorganic anions on a methacrylate‐based polymer monolith grafted with [2(methacryloyloxy)ethyl] trimethylammonium chloride

“…Here, it is well removed for the void peak with a capacity factor of 2.5 which compares very favourably with recent work by Kanatyeva et al [13] who achieved a capacity factor of only 0.3 for fluoride on a monolith aminated with a mixture of polyethyleneimine and dimethylamine. On the monolith reported herein, baseline resolution is also achieved for chloride and nitrite.…”

Separation of inorganic anions on a high capacity porous polymeric monolithic column and application to direct determination of anions in seawater

“…Bromide was the only analyte that showed improved efficiency using the more concentrated eluent. These efficiency values are considerably improved over previously published data obtained using capillary formats [4,10,11].…”

“…However, improvements in efficiency gained through this approach come at the expense of increased back pressure and this frequently requires the use of more expensive instrumentation or the use of very short columns. By using 1.5 lm nonporous silica particles, Kanatyeva et al [4] were able to achieve plate heights as low as 5.5 lm but required operating pressures as high as 5800 psi for a 4.6 mm id column that was only 50 mm long. Furthermore, such silica-based particles are limited in their application as they are incompatible with alkaline eluents.…”

“…Hutchinson et al [11] performed postpolymerisation modification of a reactive monolith containing glycidyl methacrylate to produce a significant increase in ion exchange capacity compared with previous methods and also a slight improvement in efficiency. More recently, Kanatyeva et al [4] achieved 14 300 plates/m in a postpolymerisation modified column using 5 mM potassium phthalate solution as the eluent. While all these results have demonstrated that the application of polymer monoliths to the separation of inorganic ions is promising, one of the greatest obstacles to the further development of this technology is that until now all this work has been done in the capillary format due to the technical difficulties associated with preparing columns in typical analytical column dimensions.…”

“…The efficiency of polymer particulate stationary phases is improved significantly by the use of pellicular stationary phases, in which the packing material consists of a nonpermeable core particle coated with a thin layer of stationary phase [2]. The core particles can be dynamically coated [3,4], permanently coated with latex nanoparticles by electrostatic attraction [2] or chemically modified by grafting functional groups to their surface [3]. Recent developments in IC have focused on the use of smaller diameter core particles since the efficiency of particle-packed columns can be improved by using smaller particle sizes.…”