Transport Characteristics of Aromatic Acids in the Capillary Electrochromatography with Mixed Magnetic Nanoparticles Coating as Stationary Phase

Abstract

In this paper, novel open-tubular electrochromatographic system with core/shell magnetic nanoparticles modified by amino and C 18 functional groups as mixed stationary phase by using a series of permanent magnets to immobilize nanoparticles into the capillary were investigated. The new system showed high separation ability and efficiency due to high specific surface area of nanomaterial and mixing separation mechanism. The transport equations of aromatic acids using the open-tubular electrochromatographic column with magnetic nanoparticle coating as stationary phases were derived under isocratic and double stepwise gradient elutions, and the retention characteristics of organic acids separated by the columns were further investigated. The results showed that the electroosmotic flow gradually decreased with the increase of Fe 3 O 4 @SiO 2-NH 2 in the mixed stationary phases, and the direction of electroosmotic flow reversed eventually. The capacity factor was relevant to the ratio of ion-exchange and reversed-phase stationary phases. Furthermore, experiments confirmed that the capacity factor of solute had a good linear relationship with the ratio of mixed stationary phases, and the correlation coefficient was greater than 0.9166 after fitting. Under the double stepwise gradient elution condition, the migration time of solute can be predicted by its elution time under isocratic elution. After the solutes were eluted by phosphate buffer stepwise gradient elution, the relative errors between predicted retention time and actual retention time of solute were less than 8.0%. After they were eluted by organic modifier concentration stepwise gradient elution, the relative errors between two values of solute were less than 10%. After they were eluted by pH value stepwise gradient elution, the relative errors between two values of solute were less than 5.8%. Rhizoma gastrodiae was separated by the constructed system under the optimized chromatographic condition, the main components of gastrodin, vanilla alcohol and citric acid were identified based on retention time of standards, and the relative errors between predicted value and actual value of citric acid was 11%. The open-tubular electrochromatographic system shows great potential in the method development of analysis of complicated samples.

Open tubular‐capillary electrochromatography: Developments and applications from 2013 to 2015

“…Zhu and coworkers have separated neutrals and aromatic acids using core‐shell magnetic nanoparticles (Fig. ) with octadecyl (C 18 ) and amino functionalities . The separation mechanism of organic acids changed with the proportion of amino and C 18 groups.…”

“…A number of nanomaterial‐based SP materials have also been used as noncovalent coatings, including nanolatex particles, nano‐chitosan particles , and MNPs . For example, nanolatex or latex particles possess a large surface‐to‐volume ratio.…”

“…Retention time RSDs were less than 0.44% and 1.65% for five consecutive runs and 10.20% and 4.29% for five columns using series/mixed SPs, respectively, with no change in resolution observed for at least 30 consecutive runs. The transport properties of the organic acids were subsequently investigated using isocratic and double stepwise gradient elution . On the other hand, Wang and coworkers have used externally placed magnets to pack dopamine‐imprinted magnetic NPs (Fe 3 O 4 @PDA) into PDMS microchannels .…”