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Cite this: Analyst, 2013, 138, 5555
Received 26th June 2013 Accepted 26th July 2013
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Polyhedral oligomeric silsesquioxane (POSS)-based multifunctional organic–silica hybrid monoliths† Xucong Lin,* Na Zheng, Jinzhen Wang, Xiao Wang, Yanqiong Zheng and Zenghong Xie
DOI: 10.1039/c3an01243c www.rsc.org/analyst
A facile polyhedral oligomeric silsesquioxane (POSS)-based hybrid monolith with multiple mechanisms was developed by an in situ polymerization. High mechanical stability and good separation capabilities to polar and hydrophobic analytes were successfully achieved. An ideal versatile organic–silica hybrid monolith was presented for easy access to the efficient separation of various analytes.
Organic–silica hybrid monoliths, which possess the merits such as wide-pH-range tolerance, high mechanical stability and good permeability, have been studied intensively as a new stationary phase and attract great attention.1 Numerous silica hybrid monoliths with typical reversed-phase mode for the efficient separation of hydrophobic and weak polar analytes,2 or with a hydrophilic interaction for highly polar and charged analytes,3 have been developed respectively. However, the extent of chromatographic retention for highly polar analytes in hydrophobic monoliths with reversed-phase mode was weak, and the separation capacity of polar monoliths to hydrophobic analytes was also poor. The analytical coverage of various compounds with different polarities on the common hybrid monoliths with single retention mode was somewhat limited. Seeking a functional hybrid monolith with multiple modes to match a wide application to polar and hydrophobic analytes is expected. To date, several functional silica hybrid monoliths have been fabricated for multiple separation modes via the sol–gel process with a post-column modication of an imidazolium ionic liquid4 or a dipyridyl-immobilized ionic liquid.5 Multiple modes including hydrophilic interactions, hydrogen bonding, p–p and electrostatic interactions could be involved in a monolithic column, and a broad analytical coverage was achieved, which shed light on the research of multiple separations with an intact silica column. However, it was still time-consuming to prepare a
Institute of food safety and environmental monitoring, Fuzhou University, 350108, China. E-mail: [email protected]; Fax: +86-591-22866131; Tel: +86-591-22866131 † Electronic supplementary 10.1039/c3an01243c
information
(ESI)
available.
This journal is ª The Royal Society of Chemistry 2013
See
DOI:
post-column modied monolith with multiple steps of chemical reactions, and the precise control over the quantity of the functional sites was not easy to be achieved in the multiple-step modication.6 Developing a facile versatile silica hybrid monolith for the efficient separation of various compounds has become an interesting point. Polyhedral oligomeric silsesquioxane (POSS)-based silica hybrid monolith is an ideal choice, which possesses unique properties including facile polymerization, good rigidity, and abundant functional moieties for the exible modication.7 With a simple in situ polymerization, many functionalized POSS-based silica hybrid monoliths have been fabricated conveniently with good robustness, high column efficiency and signicant reproducibility, and used for capillary liquid chromatography or electrochromatography with hydrophilic interactions (HI),8 reversed-phase/ion exchange (RP-IE),9 and hydrophilic interaction/ion exchange (HI-IE),10 respectively. It avoids the drawbacks in the post-column modication and has become one of the hottest topics in the region of silica hybrid monolith.7,8 However, POSS-based silica hybrid monoliths for multiple separation mechanisms are still absent. Developing a facile POSS-based silica hybrid monolith for easy access to the versatile analysis of various compounds is attractive. Herein, by an in situ polymerization of the monomers of POSS-methacryl substituted (POSS-MA) and vinylbenzyl trimethyl-ammonium chloride (VBTA), a facile versatile POSSbased hybrid monolith has been developed for multiple separation interactions (Fig. 1). p–p conjugated interactions, hydrophilic interactions and cationic sites could be provided by VBTA monomers, and polar ester groups for hydrogen bonding interactions and rigid silica cubes for the excellent stability could be afforded by POSS-MA monomers. In this work, with the optimum polymer recipe, the functional POSS-based monolith was prepared with multiple retention mechanisms. A characterization of the resultant monolith was studied in detail. By means of multiple retention mechanisms, a good chromatographic property and satisfactory versatility for the efficient separations of various analytes were well achieved.
Analyst, 2013, 138, 5555–5558 | 5555
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Fig. 2 Capillary liquid chromatography of phenols (I) and amides (II). (I) Mobile phase, ACN–buffer (5 mM ammonium formate, pH 5.0) ¼ 70/30 (v/v). (II) Mobile phase, ACN–buffer (5 mM ammonium formate, pH 6.5) ¼ 80/20 (v/v); pressure: 100 psi, pump flow rate: 0.1 mL min1.
Fig. 1
Scheme for hybrid monolith and potential multiple interactions.
In Tables S1, S2 and Fig. S1†, effects of polymer recipes and the characteristics of the obtained POSS-based monolith were investigated respectively. Under optimum conditions, a homogeneous morphology with spherical units agglomerated into larger clusters inter-dispersed by large-pore channels was observed in Fig. S1.† A good permeability of 1.19 1013 m2 and theoretical plates of 78 000 m1 were achieved for capillary liquid chromatography (cLC) (Table S2†, column B). The linear dependence of column pressure on the ow rate in different mobile phases is also presented (Fig. S2†), which denotes an excellent mechanical stability of the resultant POSS-based monolith in these solutions. Besides, a signicant reproducibility was achieved with RSD% of run-to-run (n ¼ 6), day-to-day (n ¼ 5), column-to-column (n ¼ 6), and batch-to-batch (n ¼ 4) less than 2.6%, 3.1%, 3.6% and 4.6%, respectively (Table S3†). A series of experiments were further studied to indicate that the retention mechanisms existed in the POSS-based monolith. A typical HILIC was observed when the ACN in the mobile phase exceeded 65% (Fig. S3†). The efficient separation of neutral polar phenols was also achieved (Fig. 2I). In Fig. 2I, with the amount of hydroxyl groups increasing, the retention of polar phenols was enhanced. The elution of phenols was in the order of their polarity. Hydrophilic interactions would be responsible for the separation of polar phenols. The selectivity parameters such as a(OH) and a(OH)2, which were dened as kresorcinol/ kphenol and kphloroglucinol/kphenol and affected by the amount of hydroxyl groups, were 5.9 and 24.4 respectively. Hydrophilic interactions for the efficient separation of polar phenols were proved in this POSS-based monolith. In Fig. 2II, polar amides were also used to evaluate the chromatographic performance of the POSS-based monolith, and the separation with an acceptable resolution was achieved. The elution of polar amides such as acrylamide (octanol–water
5556 | Analyst, 2013, 138, 5555–5558
partition coefficient, log P ¼ 0.78), acetamide (log P ¼ 1.23) and formamide (log P ¼ 1.51), which possessed primary amine groups, was in the order of the degree of hydrophilic properties. Hydrophilic interactions were responsible for the separation of these polar solutes. Interestingly, dimethylformamide (log P ¼ 1.01) acting as a tertiary amine and methylene bisacrylamide (log P ¼ 1.44) acting as a secondary amine were eluted prior to acrylamide (log P ¼ 0.78). The elution order was listed as tertiary amine, secondary amine and primary amine. It went with the amount of H atoms on the acrylamide groups, which indicated that hydrogen bonding existed and played an active role. Hydrophilic interaction and hydrogen bonding could be involved in the resultant POSSbased monolith. A subsequent evaluation of p–p conjugated interactions has been carried out by using hydrophobic estrogens as model analytes. As seen in Fig. 3, the elution of hexestrol (log P ¼ 5.6) and bisphenol A (log P ¼ 3.3) is in agreement with the degree of hydrophilic ability. However, for 4-tert-octylphenol, hexestrol, diethylstilbestrol and dienestrol, the values of log P were similar (5.8, 5.6, 5.1 and 5.4, respectively), and their elution in the resultant POSS-based monolith was not in good agreement with their hydrophilic properties. These estrogens possessed various efficient p–p conjugated structures, and their elution was more likely in the order of the degree of p–p conjugation. It indicated that p–p conjugated interactions between estrogens and
Fig. 3 Capillary liquid chromatography of hydrophobic estrogens. Mobile phase, buffer (5 mM, pH 7.0), ACN : buffer ¼ 70 : 30, v/v; pressure: 100 psi, pump flow rate: 0.1 mL min1. Solutes: 1, 4-tert-octylphenol; 2, hexestrol; 3, diethylstilbestrol; 4, dienestrol; and 5, bisphenol A.
This journal is ª The Royal Society of Chemistry 2013
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Fig. 4 Effects of pH (I) and buffer concentration (II) on the retention factor (k) of organic acids. Mobile phase: (I) ammonium formate buffer (80 mmol L1) with various pH in ACN : buffer ¼ 75 : 25, v/v; (II) ammonium formate (pH 5.0) with various concentrations in ACN : buffer ¼ 75 : 25, v/v; pressure: 100 psi, pump flow rate: 0.1 mL min1.
aromatic groups of VBTA monomers might play an effective role in the separation with this POSS-based monolith. Besides, the ion-exchange mode for charged analytes was also evaluated. Effects of buffer concentrations and pH values on the retention factor (k) were studied. In Fig. 4, k values of benzoic acids decreased obviously with the augment of salt concentration or the decrease of pH values, which indicated that anion exchange between acidic solutes and ammonium groups on the POSS-based monolith was active. In this work, with the buffer concentration increasing, ion-exchange interactions of anionic benzoic acids and cationic ammonium groups became weaker and resulted in a faster elution. In the buffer with a lower pH, the deprotonation of benzoic acids was restrained and less negative charges were produced, thus resulting in a weaker ion exchange. It was in agreement with a typical ion-exchange chromatography reported previously.6,10 Therefore, the resultant POSS-based monolith possessed multiple interactions including hydrophilic interactions, hydrogen bonding, p–p conjugation and anion exchange. To further evaluate its application to various compounds, analyses of hydrophobic anthraquinones or highly polar nucleobases and nucleosides were studied. In Fig. 5, a baseline separation of anthraquinones was achieved with HILIC. Hydrophilic interaction and hydrogen bonding might occur attributing to the
Analyst
Fig. 6 Capillary liquid chromatography of nucleobases and nucleosides. Mobile phase, ammonium formate buffer (5 mM, pH 4.5), ACN : buffer ¼ 85 : 15, v/v; pressure: 100 psi, pump flow rate: 0.1 mL min1.
abundant –OH groups of anthraquinones. Hydrophobic analytes (chrysophanol and physcion) were eluted prior to the less hydrophobic solutes (aloe-emodin and emodin). The –O–CH3 group in physcion (2) and –CH3 group in emodin (4) acting as electron donors could reinforce p–p conjugation on the anthracene ring. And by means of p–p conjugation, an efficient separation of pairs of chrysophanol (1)–physcion (2) or aloeemodin (3)–emodin (4) was achieved. Additionally, in Fig. 6, highly polar and charged nucleobases and nucleosides were effectively separated in 12 min. Effects of ACN, pH and buffer concentration were studied from Fig. S4–S6.† Nucleosides possessing more hydrogen bond donors were eluted aer the corresponding nucleobases. An increasing retention factor (k) could be observed with the increasing ACN content from 75% to 95% or the decreasing buffer concentration from 25 mmol L1 to 5 mmol L1. Multiple mechanisms such as HI, hydrogen bonding, p–p conjugation and electrostatic interactions were achieved for the efficient separation, which was in agreement with previous reports.6 Compared with the typical amide-80 and ZIC-HILIC polar columns, the satisfactory selectivity factors of ribose a(ribose) dened as k(nucleoside)/k(nucleic base) were achieved in the resultant POSS-based monolith (Table S4†). In summary, a facile versatile poly(POSS-MA-co-VBTA) silica hybrid monolith was developed. The merits including good rigidity, high column efficiency and favorable versatility were obtained. Multiple mechanisms could occur in a column, and a broad analytical coverage from highly polar and charged to hydrophobic compounds was achieved. An ideal versatile organic–silica hybrid monolith was presented for easy access to the efficient separation of various compounds and could be promising to be used for a wide analysis. This work was supported by NCFS (81001634, 21177022, 21277026), R&D Projects (2011YQ150072 and 2011J01042).
Notes and references Fig. 5 Capillary liquid chromatography of anthraquinones. Mobile phase, ammonium formate buffer (5 mM, pH 7.0), ACN : buffer ¼ 70 : 30, v/v; pressure: 100 psi, pump flow rate: 0.1 mL min1. Solutes: 1, chrysophanol; 2, physcion; 3, aloe-emodin; and 4, emodin.
This journal is ª The Royal Society of Chemistry 2013
1 (a) M. Chen, J. Zhang, Z. Zhang, B. Yuan, Q. Yu and Y. Feng, J. Chromatogr., A, 2013, 1284, 118; (b) X. Wang, Y. Zheng, C. Zhang, Y. Yang, X. Lin, G. Huang and Z. Xie, J. Chromatogr., A, 2012, 1239, 56. Analyst, 2013, 138, 5555–5558 | 5557
View Article Online
Published on 29 July 2013. Downloaded by University of Arizona on 10/09/2013 10:05:02.
Analyst 2 Z. Zhang, H. Lin, J. Ou, H. Qin, R. Wu, J. Dong and H. Zou, J. Chromatogr., A, 2012, 1228, 263. 3 (a) M. Wu, R. Wu, F. Wang, L. Ren, J. Dong, Z. Liu and H. Zou, Anal. Chem., 2009, 81, 3529; (b) H. Huang, Y. Jin, M. Xue, L. Yu, Q. Fu, Y. Ke, C. Chu and X. Liang, Chem. Commun., 2009, 6973. 4 (a) P. Zhang, J. Chen and L. Jia, J. Chromatogr., A, 2011, 1218, 3459–3465; (b) H. Han, Q. Wang, X. Liu and S. Jiang, J. Chromatogr., A, 2012, 1246, 9. 5 S. Tang, L. Wang, H. Han, H. Qiu, X. Liu and S. Jiang, RSC Adv., 2013, 3, 7894.
5558 | Analyst, 2013, 138, 5555–5558
Communication 6 (a) J. Lin, J. Lin, X. Lin and Z. Xie, J. Chromatogr., A, 2009, 1216, 7728–7731; (b) X. Lin, J. Lin, Y. Sun, Y. Li and Z. Xie, Analyst, 2013, 138, 771. 7 H. Lin, J. Ou, Z. Zhang, J. Dong and H. Zou, Chem. Commun., 2013, 49, 231. 8 X. Lin, X. Wang, T. Zhao, Y. Zheng, S. Liu and Z. Xie, J. Chromatogr., A, 2012, 1260, 174. 9 M. Dong, M. Wu, F. Wang, H. Qin, G. Han, J. Dong, R. Wu, M. Ye, Z. Liu and H. Zou, Anal. Chem., 2010, 82, 2907. 10 H. Lin, J. Ou, S. Tang, Z. Zhang, J. Dong, Z. Liu and H. Zou, J. Chromatogr., A, 2013, 1301, 131.
This journal is ª The Royal Society of Chemistry 2013
Published on 29 July 2013. Downloaded by University of Arizona on 10/09/2013 10:05:02.
COMMUNICATION
Cite this: Analyst, 2013, 138, 5555
Received 26th June 2013 Accepted 26th July 2013
View Journal | View Issue
Polyhedral oligomeric silsesquioxane (POSS)-based multifunctional organic–silica hybrid monoliths† Xucong Lin,* Na Zheng, Jinzhen Wang, Xiao Wang, Yanqiong Zheng and Zenghong Xie
DOI: 10.1039/c3an01243c www.rsc.org/analyst
A facile polyhedral oligomeric silsesquioxane (POSS)-based hybrid monolith with multiple mechanisms was developed by an in situ polymerization. High mechanical stability and good separation capabilities to polar and hydrophobic analytes were successfully achieved. An ideal versatile organic–silica hybrid monolith was presented for easy access to the efficient separation of various analytes.
Organic–silica hybrid monoliths, which possess the merits such as wide-pH-range tolerance, high mechanical stability and good permeability, have been studied intensively as a new stationary phase and attract great attention.1 Numerous silica hybrid monoliths with typical reversed-phase mode for the efficient separation of hydrophobic and weak polar analytes,2 or with a hydrophilic interaction for highly polar and charged analytes,3 have been developed respectively. However, the extent of chromatographic retention for highly polar analytes in hydrophobic monoliths with reversed-phase mode was weak, and the separation capacity of polar monoliths to hydrophobic analytes was also poor. The analytical coverage of various compounds with different polarities on the common hybrid monoliths with single retention mode was somewhat limited. Seeking a functional hybrid monolith with multiple modes to match a wide application to polar and hydrophobic analytes is expected. To date, several functional silica hybrid monoliths have been fabricated for multiple separation modes via the sol–gel process with a post-column modication of an imidazolium ionic liquid4 or a dipyridyl-immobilized ionic liquid.5 Multiple modes including hydrophilic interactions, hydrogen bonding, p–p and electrostatic interactions could be involved in a monolithic column, and a broad analytical coverage was achieved, which shed light on the research of multiple separations with an intact silica column. However, it was still time-consuming to prepare a
Institute of food safety and environmental monitoring, Fuzhou University, 350108, China. E-mail: [email protected]; Fax: +86-591-22866131; Tel: +86-591-22866131 † Electronic supplementary 10.1039/c3an01243c
information
(ESI)
available.
This journal is ª The Royal Society of Chemistry 2013
See
DOI:
post-column modied monolith with multiple steps of chemical reactions, and the precise control over the quantity of the functional sites was not easy to be achieved in the multiple-step modication.6 Developing a facile versatile silica hybrid monolith for the efficient separation of various compounds has become an interesting point. Polyhedral oligomeric silsesquioxane (POSS)-based silica hybrid monolith is an ideal choice, which possesses unique properties including facile polymerization, good rigidity, and abundant functional moieties for the exible modication.7 With a simple in situ polymerization, many functionalized POSS-based silica hybrid monoliths have been fabricated conveniently with good robustness, high column efficiency and signicant reproducibility, and used for capillary liquid chromatography or electrochromatography with hydrophilic interactions (HI),8 reversed-phase/ion exchange (RP-IE),9 and hydrophilic interaction/ion exchange (HI-IE),10 respectively. It avoids the drawbacks in the post-column modication and has become one of the hottest topics in the region of silica hybrid monolith.7,8 However, POSS-based silica hybrid monoliths for multiple separation mechanisms are still absent. Developing a facile POSS-based silica hybrid monolith for easy access to the versatile analysis of various compounds is attractive. Herein, by an in situ polymerization of the monomers of POSS-methacryl substituted (POSS-MA) and vinylbenzyl trimethyl-ammonium chloride (VBTA), a facile versatile POSSbased hybrid monolith has been developed for multiple separation interactions (Fig. 1). p–p conjugated interactions, hydrophilic interactions and cationic sites could be provided by VBTA monomers, and polar ester groups for hydrogen bonding interactions and rigid silica cubes for the excellent stability could be afforded by POSS-MA monomers. In this work, with the optimum polymer recipe, the functional POSS-based monolith was prepared with multiple retention mechanisms. A characterization of the resultant monolith was studied in detail. By means of multiple retention mechanisms, a good chromatographic property and satisfactory versatility for the efficient separations of various analytes were well achieved.
Analyst, 2013, 138, 5555–5558 | 5555
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Published on 29 July 2013. Downloaded by University of Arizona on 10/09/2013 10:05:02.
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Fig. 2 Capillary liquid chromatography of phenols (I) and amides (II). (I) Mobile phase, ACN–buffer (5 mM ammonium formate, pH 5.0) ¼ 70/30 (v/v). (II) Mobile phase, ACN–buffer (5 mM ammonium formate, pH 6.5) ¼ 80/20 (v/v); pressure: 100 psi, pump flow rate: 0.1 mL min1.
Fig. 1
Scheme for hybrid monolith and potential multiple interactions.
In Tables S1, S2 and Fig. S1†, effects of polymer recipes and the characteristics of the obtained POSS-based monolith were investigated respectively. Under optimum conditions, a homogeneous morphology with spherical units agglomerated into larger clusters inter-dispersed by large-pore channels was observed in Fig. S1.† A good permeability of 1.19 1013 m2 and theoretical plates of 78 000 m1 were achieved for capillary liquid chromatography (cLC) (Table S2†, column B). The linear dependence of column pressure on the ow rate in different mobile phases is also presented (Fig. S2†), which denotes an excellent mechanical stability of the resultant POSS-based monolith in these solutions. Besides, a signicant reproducibility was achieved with RSD% of run-to-run (n ¼ 6), day-to-day (n ¼ 5), column-to-column (n ¼ 6), and batch-to-batch (n ¼ 4) less than 2.6%, 3.1%, 3.6% and 4.6%, respectively (Table S3†). A series of experiments were further studied to indicate that the retention mechanisms existed in the POSS-based monolith. A typical HILIC was observed when the ACN in the mobile phase exceeded 65% (Fig. S3†). The efficient separation of neutral polar phenols was also achieved (Fig. 2I). In Fig. 2I, with the amount of hydroxyl groups increasing, the retention of polar phenols was enhanced. The elution of phenols was in the order of their polarity. Hydrophilic interactions would be responsible for the separation of polar phenols. The selectivity parameters such as a(OH) and a(OH)2, which were dened as kresorcinol/ kphenol and kphloroglucinol/kphenol and affected by the amount of hydroxyl groups, were 5.9 and 24.4 respectively. Hydrophilic interactions for the efficient separation of polar phenols were proved in this POSS-based monolith. In Fig. 2II, polar amides were also used to evaluate the chromatographic performance of the POSS-based monolith, and the separation with an acceptable resolution was achieved. The elution of polar amides such as acrylamide (octanol–water
5556 | Analyst, 2013, 138, 5555–5558
partition coefficient, log P ¼ 0.78), acetamide (log P ¼ 1.23) and formamide (log P ¼ 1.51), which possessed primary amine groups, was in the order of the degree of hydrophilic properties. Hydrophilic interactions were responsible for the separation of these polar solutes. Interestingly, dimethylformamide (log P ¼ 1.01) acting as a tertiary amine and methylene bisacrylamide (log P ¼ 1.44) acting as a secondary amine were eluted prior to acrylamide (log P ¼ 0.78). The elution order was listed as tertiary amine, secondary amine and primary amine. It went with the amount of H atoms on the acrylamide groups, which indicated that hydrogen bonding existed and played an active role. Hydrophilic interaction and hydrogen bonding could be involved in the resultant POSSbased monolith. A subsequent evaluation of p–p conjugated interactions has been carried out by using hydrophobic estrogens as model analytes. As seen in Fig. 3, the elution of hexestrol (log P ¼ 5.6) and bisphenol A (log P ¼ 3.3) is in agreement with the degree of hydrophilic ability. However, for 4-tert-octylphenol, hexestrol, diethylstilbestrol and dienestrol, the values of log P were similar (5.8, 5.6, 5.1 and 5.4, respectively), and their elution in the resultant POSS-based monolith was not in good agreement with their hydrophilic properties. These estrogens possessed various efficient p–p conjugated structures, and their elution was more likely in the order of the degree of p–p conjugation. It indicated that p–p conjugated interactions between estrogens and
Fig. 3 Capillary liquid chromatography of hydrophobic estrogens. Mobile phase, buffer (5 mM, pH 7.0), ACN : buffer ¼ 70 : 30, v/v; pressure: 100 psi, pump flow rate: 0.1 mL min1. Solutes: 1, 4-tert-octylphenol; 2, hexestrol; 3, diethylstilbestrol; 4, dienestrol; and 5, bisphenol A.
This journal is ª The Royal Society of Chemistry 2013
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Fig. 4 Effects of pH (I) and buffer concentration (II) on the retention factor (k) of organic acids. Mobile phase: (I) ammonium formate buffer (80 mmol L1) with various pH in ACN : buffer ¼ 75 : 25, v/v; (II) ammonium formate (pH 5.0) with various concentrations in ACN : buffer ¼ 75 : 25, v/v; pressure: 100 psi, pump flow rate: 0.1 mL min1.
aromatic groups of VBTA monomers might play an effective role in the separation with this POSS-based monolith. Besides, the ion-exchange mode for charged analytes was also evaluated. Effects of buffer concentrations and pH values on the retention factor (k) were studied. In Fig. 4, k values of benzoic acids decreased obviously with the augment of salt concentration or the decrease of pH values, which indicated that anion exchange between acidic solutes and ammonium groups on the POSS-based monolith was active. In this work, with the buffer concentration increasing, ion-exchange interactions of anionic benzoic acids and cationic ammonium groups became weaker and resulted in a faster elution. In the buffer with a lower pH, the deprotonation of benzoic acids was restrained and less negative charges were produced, thus resulting in a weaker ion exchange. It was in agreement with a typical ion-exchange chromatography reported previously.6,10 Therefore, the resultant POSS-based monolith possessed multiple interactions including hydrophilic interactions, hydrogen bonding, p–p conjugation and anion exchange. To further evaluate its application to various compounds, analyses of hydrophobic anthraquinones or highly polar nucleobases and nucleosides were studied. In Fig. 5, a baseline separation of anthraquinones was achieved with HILIC. Hydrophilic interaction and hydrogen bonding might occur attributing to the
Analyst
Fig. 6 Capillary liquid chromatography of nucleobases and nucleosides. Mobile phase, ammonium formate buffer (5 mM, pH 4.5), ACN : buffer ¼ 85 : 15, v/v; pressure: 100 psi, pump flow rate: 0.1 mL min1.
abundant –OH groups of anthraquinones. Hydrophobic analytes (chrysophanol and physcion) were eluted prior to the less hydrophobic solutes (aloe-emodin and emodin). The –O–CH3 group in physcion (2) and –CH3 group in emodin (4) acting as electron donors could reinforce p–p conjugation on the anthracene ring. And by means of p–p conjugation, an efficient separation of pairs of chrysophanol (1)–physcion (2) or aloeemodin (3)–emodin (4) was achieved. Additionally, in Fig. 6, highly polar and charged nucleobases and nucleosides were effectively separated in 12 min. Effects of ACN, pH and buffer concentration were studied from Fig. S4–S6.† Nucleosides possessing more hydrogen bond donors were eluted aer the corresponding nucleobases. An increasing retention factor (k) could be observed with the increasing ACN content from 75% to 95% or the decreasing buffer concentration from 25 mmol L1 to 5 mmol L1. Multiple mechanisms such as HI, hydrogen bonding, p–p conjugation and electrostatic interactions were achieved for the efficient separation, which was in agreement with previous reports.6 Compared with the typical amide-80 and ZIC-HILIC polar columns, the satisfactory selectivity factors of ribose a(ribose) dened as k(nucleoside)/k(nucleic base) were achieved in the resultant POSS-based monolith (Table S4†). In summary, a facile versatile poly(POSS-MA-co-VBTA) silica hybrid monolith was developed. The merits including good rigidity, high column efficiency and favorable versatility were obtained. Multiple mechanisms could occur in a column, and a broad analytical coverage from highly polar and charged to hydrophobic compounds was achieved. An ideal versatile organic–silica hybrid monolith was presented for easy access to the efficient separation of various compounds and could be promising to be used for a wide analysis. This work was supported by NCFS (81001634, 21177022, 21277026), R&D Projects (2011YQ150072 and 2011J01042).
Notes and references Fig. 5 Capillary liquid chromatography of anthraquinones. Mobile phase, ammonium formate buffer (5 mM, pH 7.0), ACN : buffer ¼ 70 : 30, v/v; pressure: 100 psi, pump flow rate: 0.1 mL min1. Solutes: 1, chrysophanol; 2, physcion; 3, aloe-emodin; and 4, emodin.
This journal is ª The Royal Society of Chemistry 2013
1 (a) M. Chen, J. Zhang, Z. Zhang, B. Yuan, Q. Yu and Y. Feng, J. Chromatogr., A, 2013, 1284, 118; (b) X. Wang, Y. Zheng, C. Zhang, Y. Yang, X. Lin, G. Huang and Z. Xie, J. Chromatogr., A, 2012, 1239, 56. Analyst, 2013, 138, 5555–5558 | 5557
View Article Online
Published on 29 July 2013. Downloaded by University of Arizona on 10/09/2013 10:05:02.
Analyst 2 Z. Zhang, H. Lin, J. Ou, H. Qin, R. Wu, J. Dong and H. Zou, J. Chromatogr., A, 2012, 1228, 263. 3 (a) M. Wu, R. Wu, F. Wang, L. Ren, J. Dong, Z. Liu and H. Zou, Anal. Chem., 2009, 81, 3529; (b) H. Huang, Y. Jin, M. Xue, L. Yu, Q. Fu, Y. Ke, C. Chu and X. Liang, Chem. Commun., 2009, 6973. 4 (a) P. Zhang, J. Chen and L. Jia, J. Chromatogr., A, 2011, 1218, 3459–3465; (b) H. Han, Q. Wang, X. Liu and S. Jiang, J. Chromatogr., A, 2012, 1246, 9. 5 S. Tang, L. Wang, H. Han, H. Qiu, X. Liu and S. Jiang, RSC Adv., 2013, 3, 7894.
5558 | Analyst, 2013, 138, 5555–5558
Communication 6 (a) J. Lin, J. Lin, X. Lin and Z. Xie, J. Chromatogr., A, 2009, 1216, 7728–7731; (b) X. Lin, J. Lin, Y. Sun, Y. Li and Z. Xie, Analyst, 2013, 138, 771. 7 H. Lin, J. Ou, Z. Zhang, J. Dong and H. Zou, Chem. Commun., 2013, 49, 231. 8 X. Lin, X. Wang, T. Zhao, Y. Zheng, S. Liu and Z. Xie, J. Chromatogr., A, 2012, 1260, 174. 9 M. Dong, M. Wu, F. Wang, H. Qin, G. Han, J. Dong, R. Wu, M. Ye, Z. Liu and H. Zou, Anal. Chem., 2010, 82, 2907. 10 H. Lin, J. Ou, S. Tang, Z. Zhang, J. Dong, Z. Liu and H. Zou, J. Chromatogr., A, 2013, 1301, 131.
This journal is ª The Royal Society of Chemistry 2013
