Large scale production of C18 bound porous silica monolith stationary phase of enhanced separation performance in liquid chromatography

Synthesis of partially sub- 2µm Ground Silica monolith particlesPEG,Mn20,000+Urea+TMOS+0.01N Acetic acid

(Under ice cold conditions)

Multi steps heating of the mixture at 40C˚ and 120C˚ for 48 h respectively, then drying at 70C˚

Grinding and Calcination at 550C˚ for 72 h

A microscopic view of silica monolith particles (A) and SEM images of C18-bound silica monolith particles with different magnification (B, C, D). The scale bars are 2, 20, 10, and 2 μm for A, B, C, and D, respectively.

A

A B

D

BB

C

Experimental

Results & Discusions

Solute A a B b C aPhenol 17400±400 27000±500 46872±800

Acetophenone 17400±650 26900±600 41503±900

4-Methyl-2-nitroaniline

19000±700 29700±900 36034 ±1100

Benzene 18300±300 23800±900 42504±800

Toluene 19200±450 24600±600 38675 ±1400

Average 18300 26400 41100

Comparison of N-values for the column of current study with those of the phase of previous study and commercial C-18.

A. Commercial Lichorsorper RP18 (5 µm).

B. Monolithic silica (previous study, [1]), C18 bound, 3-5 µm.

C. Monolithic silica (current study), C18 bound, sub 2 µm.

Current study Previous study [1]

d(0.1)a d(0.5)b d(0.9)c d(0.1)a d(0.5)b d(0.9)c

Number based

0.776 1.214 2.481 0.855 1.348 2.984

Volume based

1.463 3.233 6.230 2.346 4.185 8.541

Particle size distribution of bare silica monolith particles

Comparison of BET/BJH data between current and previous studies of monolith particles

Bare silica particles

C18-bound silica particles

A B C A B C

Pore size (Å)

343 212 296 -- 146 216

Pore volume (cm3/g) 1.06 0.83 0.75 -- 0.53 0.63

Surface area (m2/g) 136 283 126 -- 161 115

AcknowledgmentsThis research was supported by the Basic Science Research program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2012 R1A1A2006066).References [1]. Lee, S. M.; Zaidi, S. A.; Cheong, W. J. Bull. Korean Chem. Soc.2010, 31, 2943-2948. [ 2].Han,K. M. and Cheong, W. J. Bull. Korean Chem. Soc.2008, 29(11), 2281-2283[3]. Ali, F.; Cheong, W. J.; Al Othman, Z.A.; Al Majid, A. M. J. Chromatogr. A. 2013, 1303, 9-17.

The plots of BJH adsorption pore size distribution of the bare silica monolith particles (closed circle) and the C18-bound silica monolith particles (open circle).

Figure Number based and volume based particle size distribution of bare silica monolith particles.

Abstract

Conclusion

Partially sub-2-micron porous silica monolith particles of relatively uniform

size have been prepared successfully in large scale by sol gel process followed

by grinding and

calcination at 550˚C. These particles were derivatized with a C18 reagent

(chlorodimethyl octadecylsilane) in anhydrous toluene under reflux and end-

capped with a misture of HMDS (hexamethyl disilazane) and TMCS (trimethyl

chlorosilane). The C18 bound phase was packed in a glass-lined stainless steel

micro-column (1.0 mm ID and 300 mm length) with a slurry packer under high

pressure. The separation efficiency as high as 130,000 N/m were achieved for a

test mixture containing benzene and its four derivatives using 60/40

acetonitrile/ water (v/v %) with 0.1% TFA at a flow rate of 25 µL/min. The

separation efficiency of current stationary phase is better than that of common

commercial C-18 phases.

Partially sub-2 µm silica monolith particles have been synthesized in relatively large scale in comparison to those of our previous studies. Those particles were chemically modified with C-18 alkyl ligand and end-capped. The resultant stationary phase after packing in a micro column (1.0 mm x 300 mm) showed better separation efficiency compared tothose of our previous studies for the same column dimensions. This study may be regarded as a step advance towards the realization of future disposable micro-columns.

0 5 10 15 20 25 30 35

min

C

B

A

a. Column dimensions and mobile phase compositions: 1.0 mm ID X 300 mm and 60/40 acetonitrile/water, 0.1% TFA, 214nm.b. Column dimensions and mobile phase composition: 0.5mm ID X 300mm and 70/30 acetonitrile/water, 0.1% TFA, 214nm.