Yanting Song

Integration of pillar array columns into a gradient elution system for pressure-driven liquid chromatography.

A gradient elution system for pressure-driven liquid chromatography (LC) on a chip was developed for carrying out faster and more efficient chemical analyses. Through computational fluid dynamics simulations and an experimental study, we found that the use of a cross-Tesla structure with a 3 mm mixing length was effective for mixing two liquids. A gradient elution system using a cross-Tesla mixer was fabricated on a 20 mm × 20 mm silicon chip with a separation channel of pillar array columns and a sample injection channel. A mixed solution of water and fluorescein in methanol was delivered to the separation channel 7 s after the gradient program had been started. Then, the fluorescence intensity increased gradually with the increasing ratio of fluorescein, which showed that the gradient elution worked well. Under the gradient elution condition, the retention times of two coumarin dyes decreased with the gradient time. When the gradient time was 30 s, the analysis could be completed in 30 s, which was only half the time required compared to that required for an isocratic elution. Fluorescent derivatives of aliphatic amines were successfully separated within 110 s. The results show that the proposed system is promising for the analyses of complex biological samples.

Amino acids analysis using a monolithic silica column after derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F).

A fast HPLC method using a monolithic silica column was developed for the measurement of amino acids. The amino acids were pre-column derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) and separated on a monolithic silica column (MonoClad C18-HS, 250 mm × 3 mm I.D.). The separation of 19 NBD-amino acids was achieved within 18 min, which was only one-fifth of the time taken by the methods using a conventional particle-packed column, with the gradient elution of a mobile phase at the flow rate of 1.4 mL/min. The sensitivity was good with a limit of detection for the individual amino acids ranging from 2.94 to 53.4 fmol. The calibration curves for all the amino acids were found to be linear in the range of 200 fmol to 20 pmol with correlation coefficients of 0.997 or better. The analytical method was successfully applied to determine the amino acids in a mouse plasma sample.

Amino acid analysis using core–shell particle column☆

In this study, the separation efficiency of a core-shell particle column was compared with particle-packed and monolithic silica columns, which showed that the core-shell particle column had a smaller theoretical plate height and that its separation efficiency was not affected significantly by the increase in flow rate. A fast HPLC method using a core-shell particle column was developed for the determination of amino acids. 4-Fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was used as a fluorescence derivatization reagent for amino acids, followed by separation on a core-shell Kinetex C18 column. The analysis time for 21 NBD-amino acids was within 7min, which was faster than that in our previous studies with conventional particle-packed columns or monolithic silica columns. The linearities of the calibration curves for all the amino acids were found to be good over a range of injection amounts from 40fmol to 40pmol. The accuracies for the amino acid determinations were 90.9-107%. The method was proved to have potential for the fast determination of amino acids in biological samples.

MEMS LC microchip with low dispersion and low pressure drop turn structure using distribution controlled micro pillar array

MEMS liquid chromatography (LC) microchip with low dispersion and a low pressure drop turn structure was fabricated. In the turn structure, we used higher density pillar array at the inner side while lower density pillar array was used at the outer side to control inner and outer speed of a sample flow. An LC chip with an improved turn structure can obtain similar theoretical plate number (1233) compared to the previously proposed tapered turn (1135). The necessary inlet pressure is also reduced from 2.7 to 0.4 MPa under a flow rate of 10 μL/min. These results show the improved turn structure is applicable for fast analysis time under high flow rate conditions.