Separation of inorganic anions on reversed-phase C18 columns with a phosphomolybdate mobile phase

Reversed-phase high performance liquid chromatography (RP-HPLC) is the most widely used chromatographic method. In addition to hydrophobic interactions, additional interactions such as electrostatic interactions may participate in the retention behaviour of an analyte. This makes it possible to use RP-HPLC for many types of analyte. We describe a simple method for separating inorganic anions on a C18 column, in which retention of inorganic anions is almost entirely due to electrostatic interactions. This leads to rapid separations as well as higher theoretical plate numbers. We used 2 mM phosphoric acid containing a low concentration of disodium molybdate as the mobile phase, which allows UV detection of non-UV-absorbing anions. With this method, we determined eight inorganic anions including several non-UV-absorbing anions photometrically at 220 nm. The detection limits of the examined eight inorganic anions calculated at a signal-to-noise ratio of 3 were between 0.3 and 10 μM. The detector response was linear over three orders of magnitude of inorganic anion concentration. The proposed RP-HPLC/UV method was successfully applied to determine inorganic anions in some water samples.

Mixed-mode chromatographic performance using nicotinic acid-functionalized chito-oligosaccharide-bonded Ti/Si hybrid monolithic capillary columns

This article describes the fabrication of porous nicotinic acid-functionalized chito-oligosaccharide-bonded titania/silica hybrid monoliths (TiO2/SiO2@ChO-N) through a co-gelation sol-gel process. A capillary monolith with a well-defined and homogeneous structure was obtained by controlling the hydrolysis speed of titanium alkoxides in a sol mixture by using glycerol and acetylacetone. As a result of the functionalization with chito-oligosaccharides (ChO)-modified nicotinic acid, the obtained stationary phase provides superior physiochemical properties, such as a cationic hydrophilic surface, porosity, and mechanical strength. Scanning electron microscope and attenuated total reflectance-infrared spectroscopy were used to characterize the functionalized monolithic columns. The produced capillary columns showed high chromatographic performance with acceptable selectivity for charged analytes as well as organic polar compounds such as nucleic bases, nucleosides, carbamate pesticides, and strobilurin fungicides. The obtained results also indicated that the functionalized ChO's amino, amide, hydroxyl, and pyridinium ring moieties served as hydrophilic electrostatic traps for charged substances, in addition to stroing π-π interaction with the carbamate pesticides and strobilurin fungicides analytes via hydrogen bonding.

Poly(ethylene glycol) Methyl Ether Methacrylate-bonded Stationary Phase in Ion Chromatography and Its Application to Seawater Samples

A fast and simple ion chromatographic method for the determination of iodide in seawater is reported using poly(ethylene glycol) methyl ether methacrylate-bonded stationary phase. Poly(ethylene glycol) methyl ether methacrylate was reacted with primary amino groups of aminopropylsilica in N,N-dimethylformamide at 80°C. The prepared stationary phases were evaluated by analyzing several inorganic anions and the retention behavior was observed. Various chromatographic parameters were optimized for the separation of these anions. Although there were no ion-exchange sites on the resulted stationary phases, the results obtained suggested that an ion-exchange mechanism was involved in the retention of analyte anions. With 0.15 μL injection, the limit of quantitation of iodide was 26 μg L^-1 when 200 mM NaCl was selected as the eluent. This stationary phase was applied to the analysis of direct and fast determination of iodide in real seawater samples successfully with the recovery rates of 98.1 and 104.9%.

Advanced analytical methods and sample preparation for ion chromatography techniques

The recently developed advanced ion chromatography techniques and the various sample preparation methods have been summarized in this mini-review.

Polymer monolithic methacrylate base modified with tosylated-polyethylene glycol monomethyl ether as a stationary phase for capillary liquid chromatography

A polyethylene glycol (PEG) monolithic column was successfully prepared in situ for the separation of inorganic anions in ion exchange capillary chromatography. By attaching PEG-groups into the methacrylate-based polymer, the number of theoretical plates was improved from 1433 to 3346 plates/m (when nitrate was used as the analyte). The retention behavior of iodate, bromate, nitrite, bromide and nitrate was observed under various salt aqueous solutions. The retention was based on cations trapped among PEG chain and the positively charged pyridine that work as the anion exchange sites in the PEG monolith. The relative standard deviations (RSDs, for n=7) of retention time, peak height and peak area were less than 2.27% for all the analyte anions. The PEG monoliths showed satisfactory mechanical stability and did not swell or shrink significantly with swelling propensity value of 0.34 and 0.64 for methanol and THF, respectively. This stationary phase was successfully applied to the determination of these anions in seawater as well as public drinking water samples.