The authors have declared that no competing interests exist.
A hybrid monolithic column was prepared using octavinyloctasilasesquioxane (OVS) as a monomer, benzoyl peroxide/dimethylacetamide (BPO/DMA) as initiator, ethylene glycol dimethacrylate (EDMA) as cross-linker, 1-dodecanol as porogenic agent and dimethylbenzene as cosolvent. A tidy skeleton, much bigger specific surface area (22.4 m
Emerged in 1990s
Polyhedral oligomeric silsesquioxanes (POSS), a series of cage-like three-dimensional oligomeric, organosilicon compounds, were used for the preparation of hybrid monoliths with free radical polymerization via “one-pot” process
In this study, a facile approach for preparation of hybrid monolithic columns with and without OVS added was adopted via thermal-initiation. Chromatographic assessments and applications were carried out to determine the chromatographic performance of the obtained monolithic columns.
Materials used in the work were AR grade except methanol and acetonitrile, which was HPLC grade. Octavinyloctasilasesquioxane (OVS) used in this study was produced from Aladdin Industrial Corporation (Shanghai, China). The reagent including acetonitrile, methanol, dimethylbenzene and 1-dodecanol were bought from Tianjin kermel chemical reagent co., Ltd. (Tianjin, China). Ethylene glycol dimethacrylate (EDMA) was purchased from Acros (New Jersey, USA). Benzoyl peroxide (BPO) and dimethylacetamide (DMA) were bought from Tianjin Guangfu Fine Chemical Research Institute
All chromatography experiments were conducted on two Thermo Unitmate 3000 system (Thermo scientific, USA) equipped with solvent delivery pumps, pump mixers, well-plate autosamplers and UV detectors. Ultrasonic cleaning machine was bought from Kun Shan Ultrasonic Instruments Co., Ltd (Jiangsu, China). Deionized water with an electrical resistivity of 18.25 mΩ/cm was prepared by a Up-pure Deionizer (Chengdu, China), and an automatic potentiometric titrator, which had been calibrated before used, was purchased from Shanghai Grows Precision Instrument Co., Ltd. (Shanghai, China). The freeze dryer was a product of Gold Sim (Gold Sim, USA). The thermostat water bath was tailor-made from Nanjing Startlab Co., Ltd. (Jiangsu, China). The vacuum drying oven with an oil pump was purchased by Shanghai Boxun Industry &Commerce Co., Ltd. (Shanghai, China)
The preparation was carried out with the method of in-situ polymerization in stainless steel columns (50x4.6 mm i.d.). A certain amount of OVS was first dissolved in a certain amount of dimethylbenzene (0.30 mL), and followed with the addition of desired amount of crosslinker, porogenic solvent (EDMA and 1-dodecanol). Then with BPO (0.0045 g) added, the mixture was sonicated for 15 min under nitrogen below 30 ℃ to obtain a homogeneous solution. And finally, with addition of DMA (40 𝜇L) and vortex for 10 seconds, the polymerization mixture was poured in a stainless steel column with stoppers at the both sides to let the polymerization carry on. After being synthesized for 2.5 h at 35 ℃ in an oven, the obtained monolithic column was connected with the HPLC system and washed with ethanol (0.20 mL/min for 30 min) and methanol(10.00 mL/min for 60 min) to remove 1-dodecanol, dimethylbenzene and other soluble compounds present in the polymeric rod.
The poly(OVS-co-EDMA) monolith was firstly eluted with methanol for 5h and dried under freezing for 48h. Then it was observed on a JEOL SEM 6700 microscope operating at 10kV
Fourier-transform infrared spectra (FTIR) were recorded by a Varian 640-IR instrument (Varian America) with a resolution of 4 cm-1 for 32 scans over a wave number range of 4000–400 cm-1. The tablets were prepared with the mixture of KBr and samples, both of which were dried under 80 ℃ for 48h in a vacuum oven.
The detection of specific surface area of the dry bulk monoliths was performed by nitrogen adsorption-desorption on a MicromeriticsTristarⅡ3020 (Micromeritics, USA). The samples with different amount of OVS were dried under freezing for 48h and then purged on a Micromeritics flow prep 060 (Micromeritics, USA) with nitrogen for 6 h under 50 ℃..
Single factor experiment was introduced for the optimization conditions to prepare poly(OVS-co-EDMA) hybrid monolithic column. With the consideration that the ratio between crosslinker, monomer and porogenic agent representing great affection to the polymer skeleton and also its chromatographic behaviors, several columns were prepared under different ratios between EDMA, OVS and 1-dodecanol illustrated in
Column | EDMA (ml) | 1-Dodecanol (ml) | Dimethylbenzene (ml) | OVPOSS (mg) | BPO/DMA (mg/µl) | Mechanical/ Physical properties
(s |
Backpressure |
A | 0.40 | 1.20 | 0.30 | 20 | 4.5/40 | d | x |
B | 0.50 | 1.10 | 0.30 | 20 | s | x | |
C | 0.60 | 1.00 | 0.30 | 20 | n | 7 | |
D | 0.70 | 0.90 | 0.30 | 20 | hh | 14 | |
E | 0.80 | 0.80 | 0.30 | 20 | hhh | 19 | |
F | 0.55 | 1.05 | 0.30 | 30 | d | x | |
G | 0.55 | 1.05 | 0.30 | 20 | n | 8 | |
H | 0.55 | 1.05 | 0.30 | 10 | n | 7 | |
I | 0.55 | 1.05 | 0.30 | 0 | s | x | |
J | 0.6 | 1.00 | 0.30 | 40 | d | x | |
K | 0.6 | 1.00 | 0.30 | 30 | h | 9 | |
L | 0.6 | 1.00 | 0.30 | 10 | n | 7 | |
M | 0.6 | 1.00 | 0.30 | 0 | s | x | |
N | 0.65 | 0.95 | 0.30 | 40 | hhh | 20 | |
O | 0.65 | 0.95 | 0.30 | 30 | hh | 15 | |
P | 0.65 | 0.95 | 0.30 | 20 | h | 11 | |
Q | 0.65 | 0.95 | 0.30 | 10 | n | 8 | |
R | 0.65 | 0.95 | 0.30 | 0 | n | 12 |
theMechanical/physical properties of monolith is soft.
the Mechanical/physical properties of monolith is not soft or hard.
the Mechanical/physical properties of monolith is hard.
deposition of OVS from mixture happened.
Back pressure was obtained with methanol as the mobile phase at 1.00 mL/min and temperature at 25℃.
Opinions above could be illustrated in
FTIR was used to confirm the group composition in the monolith with and without OVS added. The result was shown in
In liquid chromatography, the mobile phase can diffuse into and even swell the polymer monolith. It means that the volume and morphology of monolithic column can be different between the monolith in dry and wet state
The swelling properties of the obtained monolithic column with and without OVS added was measured using different acetonitrile-water mixtures as the mobile phase. Thiourea, a non-retained compound for reversed-phase liquid chromatography, was injected to measure the porosity of monolith
Plate height of the obtained monolithic column along flow rate was examined with the elute of acetonitrile and water (75/25, v/v) at 25℃. Five compounds (1,2-Diaminobenzene, p-Nitrophenol, (Dichloromethyl)benzene, Naphthalenol, 1-Aminonaphthalene) were used to examine the performance of obtained monolithic column, which is shown in
Fully consideration above, the flow rate of 1mL/min was taken for the following experiments.
To compare the chromatographic performance of the home-made monolithic column with OVS with without OVS added, several small molecules including neutral, basic and acidic compounds were used as the test compounds. The eluting sequence of molecules on both columns were: 1,2-Diaminobenzene > p-Nitroaniline > Benzene > 1-Naphthylamine > 4-Chloronitrobenzene > Naphthalene > Diphenyl > Phenanthrene. From
A new kind of hybrid organic-silica monolithic column was prepared successfully with OVS added as a monomer. Three different polymer skeletons were obtained with different amount of monomer added. The monolith with OVS added showed stronger rigidity. The classical RPLC mode was observed during the experiment of swelling test. Under the optimization conditions, small molecules were separated successfully.
The authors would like to gratefully acknowledge financial support received from the National Natural Science Foundation of China (no. 21175031, 21575033, 21505030), the Natural Science Foundation of Hebei Province (no. B2013201082, B2015201024) and the Natural Science Foundation of Hebei University (no. 2014-05).