Synthesis and characterization of β-cyclodextrin modified hyperbranched carbosilane as stationary phase for GC

Article abstract of DOI:10.1016/j.cclet.2012.09.012

A new β-cyclodextrin modified hyperbranched carbosilane stationary phase for gas chromatography was synthesized by substituting the OH groups of β-cyclodextrin with hyperbranched carbosilane and was coated on the inner wall of fused silica capillary column for gas chromatography. The chromatographic behaviors of the stationary phase were studied. The initial testing results showed that it possessed good separation abilities for several kinds of mixtures, such as benzenes, acrylates, ketones and alkylchlorides.

Full text of DOI:10.1016/j.cclet.2012.09.012

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 1259–1262
www.elsevier.com/locate/cclet
Synthesis and characterization of b-cyclodextrin modified
hyperbranched carbosilane as stationary phase for GC
b,
Guo Wen Chen a,b, Chen Zhang a, Wen Jie Li a, Chuan Jian Zhou a, , Sheng Yu Feng
*
*
a School of Materials Science and Engineering, Shandong University, Jinan 250061, China
b Key Laboratory of Special Functional Aggregated Materials, Ministry of Education of China, Jinan 250100, China
Received 10 May 2012
Available online 23 October 2012
Abstract
A new b-cyclodextrin modified hyperbranched carbosilane stationary phase for gas chromatography was synthesized by
substituting the –OH groups of b-cyclodextrin with hyperbranched carbosilane and was coated on the inner wall of fused silica
capillary column for gas chromatography. The chromatographic behaviors of the stationary phase were studied. The initial testing
results showed that it possessed good separation abilities for several kinds of mixtures, such as benzenes, acrylates, ketones and
alkylchlorides.
# 2012 Chuan Jian Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Hyperbranched carbosilane; Cyclodextrin; Stationary phase; Gas chromatography
Derived cyclodextrins are among the most popular phases in chromatography, such as gas chromatography [1–4],
liquid chromatography [5–8] and electrochromatography [9]. Due to the strong hydrogen bonds formed between the
polar hydroxyl groups in the cyclodextrins, the melting point of this material is usually very high. This makes the
column coating process difficult to manipulate. Derived cyclodextrin could decrease the coating temperature and
produce more homogeneous and special functional membrane for different kinds of separations. Hyperbranched
polymers [10–12] have highly branched structure. The branches grow in three different dimensional directions and
thus less entangled with each other. This affords the polymer with low viscous property. Large amount of the end
groups at the peripheral of the hyperbranched structure could be modified according to the separational requirements.
These are precious characteristics for trace level analysis. In addition, the hyperbranched polymers could be
synthesized by one-pot. Compared with dendrimers which are synthesized step by step (or generation after
generation), the synthesis of hyperbranched polymers is less laborious, less organic solvent and time-consuming.
These characteristics make the irregular three-dimensional polymer more suitable for large scale production with less
environmental impaction.
In this work, b-cyclodextrin was modified by hyperbranched carbosilane and was packed into fused silica capillary
column. The chromatographic performance was tested by separation of several kinds of analogs such as acrylates,
ketones, chloroalkanes, and benzenes.
* Corresponding authors.
E-mail addresses: zhouchuanjian@sdu.edu.cn (C.J. Zhou), fsy@sdu.edu.cn (S.Y. Feng).
1001-8417/$ – see front matter # 2012 Chuan Jian Zhou. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
http://dx.doi.org/10.1016/j.cclet.2012.09.012

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1. Experimental
All the chemicals are analytical pure. Methyldichlorosilane was purchased from Aladdin Reagent Co. Ltd.,
Shanghai. Hydrochloric acid (36–37%), magnesium chips, allylchloride, dichloromethane and tetrahydrofuran (THF)
were products purchased from Sinopharm Chemical Reagent Co. Ltd., Shanghai. Hydrogen-containing siloxane oil
(1%, weight percentage) was purchased from Ruizhiyuan Chemicals Co. Ltd., Jinan. Fused silica capillary column
with diameter of 250 mm was purchased from Yongnian Ruipei Co. Ltd., Hebei. Chromatography tests were carried
out on a N1690 Chromatography Instrument, a product of Kexiao Instruments, with a flame ionization detector.
All the reactions were carried out with N2 protection except for hydrosilylation reactions which were carried out in
sealed Kontes tubes. THF was dried by Na through refluxing till the drying indicator of diphenylmethanone turned
blue.
To a 250 mL three-necked flask equipped with a condenser and a drop funnel was charged with 10.69 g magnesium
turnings, 100 mL THF and a magnetic stirrer. 1/10 amount of 36 mL allylchloride in 100 mL THF was added in
advance to initiate the reaction at 35–40 8C. After the solution turned gray, the remainder of the allylchloride/THF
solution was added dropwisely into the system. The reaction was carried on for 4 h without additional heating. At the
end of the reaction, the temperature was raised to keep the system slightly refluxing for 30 min. Remnant
magnesium:1.63 g (product rate: 84.76%).
MeHSiCl2 (20 mL) in 50 mL THF was added dropwisely into pre-ice cooled allylmagnesium chloride solution in
THF (1.89 mol/L) with stirring. The reaction was carried out overnight and was terminated by 50 mL saturated
NH4Cl/H2O solution. After fully standing, the upper layer was separated carefully and was dried over anhydrous
MgSO4 for 4 h. MeHSi (CH2–CH CH2)2 was obtained by rotating evaporation of THF at 80 8C.
IR: 3077, 2956 (s, –C–H), 894 cmꢀ1 (b, C–H), 2921 cmꢀ1 (vs, –C–H), 2116.91 cmꢀ1 (s, Si–H), 1631 cmꢀ1 (s,
C C), 1254 (b, Si–CH3), 816 cmꢀ1 (s, Si–CH3); 1H NMR (500 MHz, CDCl3): d 0.00–0.07 (s, 3H, Si–Me), 1.78–1.87
(t, 4H, J = 5 Hz, CH2–CH CH2), 3.74 (s, 1H, SiH), 4.83–4.91 (d, 2H, J = 8 Hz, CH2–CH CH2), 4.93 (s, 2H, CH2–
CH CH2), 5.73–5.84 (m, 2H, –CH2–CH CH2); 13C NMR (CDCl3): d 19.81 (Si–CH3), 20.8 (CH2–CH CH2), 113.42
(CH2–CH CH2), 134.35 (CH2–CH CH2).
Methyldiallylsilane (2 mL) was added to a clean and dry Kontes tube containing 10 mL THF and 2 drops of
Karstedt catalyst. The reaction was carried out for 10 h at 75–80 8C. FT-IR was used to monitor the reaction till the
disappearance of Si–H peak at 2114 cmꢀ1. Allyl-ended hyperbranched carbosilane (HBP-allyl) was obtained after
evaporation of THF at 70 8C.
IR: 3077, 2955, 2914, 2875(s, –C–H), 2993 (s, C–H), 1155, 990, 931, 893 (s, Si–CH2–CH CH2), 1630, 1418,
1393 (s, –C C), 1252 (s, Si–CH3); 1H NMR (500 MHz, CDCl3): d 0.04 (m, 3H, Si–Me), 0.838–0.882 (m, 2H, CH2–
CH2–CH3), 1.194–1.286, (m, 2H, CH2–CH2–CH3), 1.573–1.650, (m, 3H, CH2–CH2–CH3), 1.573–1.650, (m, 2H,
CH2–CH2 CH2), 4.833–4.874 (m, 2H, CH2–CH CH2) 4.903–4.934 (CH2–CH CH2) 5.704–5.847 (–CH2–
CH CH2); 13C NMR (CDCl3): d ꢀ2.75 (Si–CH3), ꢀ7.22 (Si–CH3), 20.82 (CH2–CH CH2), 113.26 (CH2–
CH CH2), 134.13 (CH2–CH CH2).
HBP-allyl (6.30 g), MeHSiCl2 (7.50 mL), 2 drops of Karstedt catalyst and THF (20 mL) were added to a 100 mL
fully dried Kontes tube. The reaction was carried out at 75–80 8C with stirring for 10 h. FT-IR was used to detect the
disappearance of allyl groups. Chloride-ended hyperbranched carbosilane (HBP-Cl) was obtained after the solvent and
redundant reactants were evaporated at 70 8C.
b-Cyclodextrin (0.2 g), triethylamine (2 mL) and THF (10 mL) were added to the Kontes tube containing HBP-Cl.
The reaction was carried out at 80–90 8C with stirring overnight and was then fully cooled in ice-bath. Undried THF
(5 mL) and H2O (15 mL) were added to the tube sequentially with care and were fully stirred for 30–40 min. The
polymer peel formed at the surface of the liquid was removed by filtration. The upper organic liquid was separated by
centrifugation and was dried over anhydrous MgSO4 for 4–5 h. After filtration and removal of the solvent, a slight
yellow viscous liquid was obtained.
A Ø250 mm ꢁ 15 m fused silica capillary column was washed by 20 mL CH2Cl2 and was dried by N2 for 30 min.
The b-cyclodextrin modified HBP liquid was poured into a dry and clean reagent bottle. The liquid was then pressured
into the capillary column by home-made packing equipment. It stayed in the column for 20 min and was pressured out
by N2. The column was then aged at 220 8C for 3 h with N2 running through. It was then cleaned by 10 mL CH2Cl2 and
was dried by N2 before use.

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Chromatographic behaviors of the column were characterized by the separation of several different kinds of analog
mixtures, such as aromatics, acrylates, ketones and chloroalkanes. Chromatography conditions varied with different
mixtures.
2. Results and discussion
The column was preliminary tested by separation of several different analog mixtures (Figs. 1–4).
Sharp and symmetrical peaks showed good separations were obtained for analog mixtures of acrylates, ketones,
chloroalkanes and benzenes. Isomers of xylene were separated with good resolution. The hyperbranched carbosilane-
modified cyclodextrin is competent for room temperature coating, which is a precious property for cyclodextrin-based
stationary phases. In consideration that these separations are realized on a 15 m capillary column, extraordinary high
column efficiency and excellent chromatography properties are expected when longer column with hyperbranched-
bearing structure is applied.
Fig. 1. Separation of acrylate analog mixture on CD/HBP column. 1: methyl acrylate; 2: methyl methacrylate; 3: butyl acrylate. Injector
temperature: 200 8C, detector temperature: 200 8C, oven: 100 8C, pressure before the column: 0.08 MPa, split ratio: 600.
Fig. 2. Separation of ketone analog mixture on CD/HBP column. 1: acetone; 2: butanone. Injector temperature: 200 8C, detector temperature:
200 8C, oven: 90 8C, pressure before the column 0.06 MPa, split ratio: 600.

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Fig. 3. Separation of chloroalkane analog mixture on CD/HBP column. 1: dichloromethane; 2: trichloromethane; 3: tetrachloromethane. Injector
temperature: 200 8C, detector temperature: 200 8C, oven: 60–70 8C (1 min) at 5 8C/min, pressure before the column: 0.06 MPa, split ratio: 600.
Fig. 4. Separation of benzene analog mixture on CD/HBP column. 1: benzene; 2: toluene; 3,30: xylene; 4: naphthalene. Injector temperature:
200 8C, detector temperature: 200 8C, oven: 80–220 8C at 40 8C/min, pressure before the column: 0.08 MPa, split ratio: 600.
Acknowledgments
We acknowledge financial support from the National Natural Science Foundation of China (No. 20874057) and the
Key Natural Science Foundation of Shandong Province of China (No. ZR2011BZ001).
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