An Appraisal Of The Chemical And Thermal Stability Of Silica Based Reversed-phase Liquid Chromatographic Stationary Phases Employed Within The Pharmaceutical Environment

Mobile phase pH and temperature are major factors in determining retention, selectivity and chromatographic performance of ionizable compounds. This imposes a requirement that stationary phases must ideally be stable in both acidic and basic conditions coupled with good thermal stability, in order to be able to chromatograph these compounds in either their ionized or ion-suppressed modes. The development of a range of new high and/or low pH stable silica based RPLC stationary phases (including sub-2 μm fully porous and sub-3 μm fused core-shell materials), which are specially designed for the analysis of ionizable compounds and their chemical and thermal stability is reviewed. The ability to utilize both pH and temperature as selectivity variables allows the chromatographer to exploit a much wider method development design space including previously prohibited alkaline conditions. 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Comparison Of Classical Chromatographic Tests With A Chromatographic Test Applied To Stationary Phases Prepared By Thermal Immobilization Of Poly (methyloctylsiloxane) Onto Silica

Stationary-phase evaluation in reversed-phase liquid chromatography (RP-LC) is not a straightforward process. A number of tests to characterize and classify stationary phases have been suggested. The results of these various tests, however, do not always describe the real properties of the stationary phase. This study critically compares several tests for RP-LC stationary phases, including the Engelhardt, Tanaka, and SRM 870 tests, as well as an in-house test, with emphasis on the stationary-phase descriptors of hydrophobicity and silanol activity. The stationary phases were prepared by thermal immobilization of poly(methyloctylsiloxane) onto silica. Hydrophobicity data fromthe tests were generally good and interchangeable between the several tests. In contrast, the silanol activity results of the various tests differ significantly. As a consequence, stationary phase classification with respect to silanol activity depends considerably on the test method applied. A new classification method for silanol activity is proposed. © Springer-Verlag 2012.4041029853002Marchand, D.H., Carr, P.W., McCalley, D.V., Neue, U.D., Dolan, J.W., Snyder, L.R., (2011) J Chromatogr A, 1218, pp. 7110-7129Vyňuchalová, K., Jandera, P., (2011) Anal Lett, 44, pp. 1640-1662Lämmerhofer, M., Nogueira, R., Lindner, W., (2011) Anal Bioanal Chem, 400, pp. 2517-2530Borges, E.M., Euerby, M.R., Collins, C.H., (2012) Anal Bioanal Chem., , doi:10.1007/s00216-011-5674-zNémetha, T., Haghedoorena, E., Noszálc, B., Hoogmartensa, J., Adams, E., (2008) J Chemometrics;, 22, pp. 178-185Buszewski, B., Kowalska, S., Krupczynska, K., (2007) Crit Rev Anal Chem, 35, pp. 89-116Lesellier, E., West, C., (2007) J Chromatogr A, 1158, pp. 329-360De Matteis, C.I., Simpson, D.A., Euerby, M.R., Shaw, P.N., Barrett, D.A., (2012) J Chromatogr A., , doi:10.1016/j.chroma.2011.12.090Engelhardt, H., Jungheim, M., (1990) Chromatographia, 29, pp. 59-68Schmitz, S.J., Zwanziger, H., Engelhardt, H., (1991) J Chromatogr, 544, pp. 381-391Engelhardt, H., Arangio, M., Lobert, T., (1997) LCGC Int, 10, pp. 803-812Sander, L., Wise, S.A., (2003) J Sep Sci, 26, pp. 283-294Rimmer, C.A., Lane, C., Sander, L.C., (2009) Anal Bioanal Chem, 394, pp. 285-291(2002) SRM 870, Column Performance Test Mixture, , National Institute of Standards and Technology, Gaithersburg, MDAccessed on April 2011, , http://www.usp.org/USPNF/columnsDB.htmlKimata, K., Iwaguchi, K., Onishi, S., Jinno, K., Eksteen, R., Hosoya, K., Arki, M., Tanaka, N., (1989) J Chromatogr Sci, 27, pp. 721-728Euerby, M.R., Petersson, P., (2000) LC-GC Eur, 13, pp. 665-677Euerby, M.R., McKeown, A.P., Petersson, P., (2003) J Sep Sci, 26, pp. 295-306Euerby, M.R., Petersson, P., (2003) J Chromatogr A, 994, pp. 13-36Euerby, M.R., Petersson, P.W., Campbell, W., Roe, W., (2007) J Chromatogr A, 1154, pp. 138-151Euerby, M.R., James, M., Petersson, P., (2011) J Chromatogr A., , doi:10.1016/j.chroma.2011.05.105Accessed On: April 2011, , http://www.acdlabs.com/resources/freeware/Neue, U.D., Van Tran, K., Iraneta, P.C., Alden, B.A., (2003) J. Sep Sci, 26, pp. 174-186Rogers, S.D., Dorsey, J.G., (2000) J Chromatogr A, 892, pp. 57-65Visky, D., Heyden, Y.V., Ivany, T., Baten, P., De Beer, J., Kovacs, Z., Noszal, B., Hoogmartens, J., (2002) J Chromatogr A, 977, pp. 39-58Van Stratenma, C., Cramers, C.A., Jezierska, M., Buszewski, B., (1998) J Chromatogr A, 826, pp. 135-156Rogers, S.D., (2003), http://etd.lib.fsu.edu/theses/available/etd-08192004-103718/unrestricted/ Rogers_S.pdf, Doctoral thesis, The Florida State University, Tallahassee. Accessed on: May 2011(2008) Comparison Guide to C18 Reversed Phase HPLC Columns, , http://www.mac-mod.com/pdf/technical-report/036-ColumnComparisonGuide.pdf, MAC-MOD Analytical, Chadds Ford, PA, June, Accessed on: January 2012Stella, C., Rudaz, S., Veuthey, J.L., Tchapla, A., (2001) Chromatographia Supplement 1, 53, pp. S113-S131McCalley, D.V., (1999) J Chromatogr A, 844, pp. 23-38McCalley, D.V., (2010) J Chromatogr A, 1217, pp. 858-880Okusa, K., Suita, Y., Otsuka, Y., Tahara, M., Ikegami, T., Tanaka, N., Ohira, M., Takahashi, M., (2010) J Sep Sci, 33, pp. 348-358Borges, E.M., Collins, C.H., (2012) J Chromatogr A., , doi:10.1016/j.chroma.2012.01.001Borges, E.M., Silva, C.G.A., Collins, C.H., (2010) Microchem. J, 96, pp. 120-125Borges, E.M., Collins, C.H., (2011) J J Sep Sci, 34, pp. 1141-1148Tonhi, E., Collins, K.E., Collins, C.H., (2002) J ChromatogrA, 948, pp. 97-107Bachmann, S., Melo, L.F.C., Silva, R.B., Anazawa, T.A., Jardim, I.C.S.F., Collins, K.E., Collins, C.H., Albert, K., (2001) Chem.Mater, 13, pp. 1874-1879Hu, Y., Yang, X., Carr, P.W., (2002) J Chromatogr A, 968, pp. 17-2

Characterization Of A Mixed-mode Reversed-phase/cation-exchange Stationary Phase Prepared By Thermal Immobilization Of Poly(dimethylsiloxane) Onto The Surface Of Silica

A novel stationary phase prepared by the thermal immobilization of poly(dimethylsiloxane) onto the surface of silica (PDMS-SiO 2) has been described, evaluated and compared with 229 commercially available RP-LC stationary phases using the Tanaka column classification protocol. The phase exhibited many unique chromatographic properties and, based on the phases in the database, was most similar to the fluoroalkylated phases (aside from the obvious lack of fluoro selectivity imposed by the C-F dipole). The phase exhibited classic reversed-phase behaviour in acid mobile phase conditions and mixed-mode reversed-phase/cation-exchange retention behaviour in neutral mobile phase conditions. The phase exhibited acceptable stability at both low and intermediate pH, conditions which should impart optimum chromatographic selectivity to the phase. Retention of basic analytes was shown to occur by a "three site model" as proposed by Neue. This new PDMS-SiO 2 stationary phase is extremely interesting in that the dominancy of its hydrophobic and ion-exchange interactions can be controlled by the influence of mobile phase pH, buffer type and concentration. The PDMS-SiO 2 stationary phase may provide a complementary tool to reversed-phase and HILIC stationary phases. The present results highlight the fact that the type of buffer, its concentration and pH can not only affect peak shape but also retention, selectivity and hence chromatographic resolution. Therefore, in method development and optimization strategies it is suggested that more emphasis should be given to the evaluation of these mobile phase operating parameters especially when basic solutes are involved. © 2012 Springer-Verlag.402620432055Abbood, A., Herrenknecht, C., Proczek, G., Descroix, S., Rodrigo, J., Taverna, M., Smadja, C., (2011) Anal Bioanal Chem, 400, pp. 459-468. , 10.1007/s00216-011-4762-4 1:CAS:528:DC%2BC3MXitFKisro%3DAgrafiotou, P., Ràfols, C., Castells, C., Bosch, E., Roses, M., (2011) J Chromatogr A, 1218, pp. 4995-5009. , 10.1016/j.chroma.2010.12.119 1:CAS:528:DC%2BC3MXoslCgur0%3DBachmann, S., Melo, L.F.C., Silva, R.B., Anazawa, T.A., Jardim, I.C.S.F., Collins, K.E., Collins, C.H., Albert, K., Synthesis and solid-state NMR investigations of radiation-immobilized polysiloxanes on bare, titanium-grafted, and zirconium-grafted silicas (2001) Chemistry of Materials, 13 (5), pp. 1874-1879. , DOI 10.1021/cm001179fBorges, E.M., Collins, C.H., (2011) J Sep Sci, 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high-performance liquid chromatography (1998) Journal of Chromatography A, 826 (2), pp. 135-156. , DOI 10.1016/S0021-9673(98)00749-3, PII S0021967398007493Collins, K.E., Franchon, A.C., Icsf, J., Radanovic, E., Gonçalves, M.C., (2000) LCGC, 18, pp. 106-117. , 1:CAS:528:DC%2BD3cXhtlaitrg%3DCollins, C.H., Silva, C.R., Faria, A.M., Collins, K.E., Icsf, J., (2009) J Braz Chem Soc, 20, pp. 604-612. , 10.1590/S0103-50532009000400004 1:CAS:528:DC%2BD1MXms1Gksbs%3DDai, J., Carr, P.W., (2009) J Chromatogr A, 1216, pp. 6695-6705. , 10.1016/j.chroma.2009.07.062 1:CAS:528:DC%2BD1MXhtV2rsLbMEngelhardt, H., Arangio, M., Lobert, T., (1997) LCGC Int, 10, p. 803Euerby, M.R., James, M., Petersson, P., (2011) J Chromatogr A, , doi: 10.1016/j.chroma.2011.05.105Euerby, M.R., McKeown, A.P., Petersson, P., Chromatographic classification and comparison of commercially available perfluorinated stationary phases for reversed-phase liquid chromatography using principal component analysis (2003) Journal of Separation Science, 26 (3-4), pp. 295-306. , DOI 10.1002/jssc.200390035Euerby, M.R., Petersson, P., (2000) LCGC Eur, 13, pp. 665-677Euerby, M.R., Petersson, P., Chromatographic classification and comparison of commercially available reversed-phase liquid chromatographic columns using principal component analysis (2003) Journal of Chromatography A, 994 (1-2), pp. 13-36. , DOI 10.1016/S0021-9673(03)00393-5Faria, A.M., Collins, C.H., Icsf, J., (2009) J Braz Chem Soc, 20, pp. 1385-1398. , 10.1590/S0103-50532009000800002 1:CAS:528:DC%2BD1MXhtlGjsrnMhttp://www.acdlabs.com/resources/freeware/, AccessedinApril2011http://www.usp.org/USPNF/columnsDB.html, AccessedinApril2011Kimata, K., Iwaguchi, K., Onishi, S., Jinno, K., Eksteen, R., Hosoya, K., Arki, M., Tanaka, N., (1989) J Chromatogr Sci, 27, pp. 721-728. , 1:CAS:528:DyaK3cXhsFWjsro%3DLämmerhofer, M., Nogueira, R., Lindner, W., (2011) Anal Bioanal Chem, 400, pp. 2517-2530. , 10.1007/s00216-011-4755-3Lesellier, E., West, C., Description and 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Migration behaviour of weakly retained, charged analytes in voltage-assisted micro-high performance liquid chromatography

The application of voltage in micro-high performance liquid chromatography (micro-HPLC) creates a system where separation is governed by a hybrid differential migration process, which entails the features of both HPLC and capillary zone electrophoresis (CZE), i.e., chromatographic retention and electrophoretic migration. In this paper, we use our previously published approach to decouple these two mechanisms via analysis of the input data for estimation of electrokinetic parameters, such as conductivity, equivalent lengths, mobilities and velocities. Separation of weakly retained, charged analytes was performed via voltage-assisted micro-HPLC. Contrary to conclusions from data analysis using the conventional definitions of the retention factor, it is shown that our approach allows us to isolate the “chromatographic retention” component and thus, investigate the “modification” of the retention process upon application of voltage in micro-HPLC. It is shown that the traditional approaches of calculating retention factor would erroneously lead to conclusion that the retention behavior of these analytes changes upon application of voltage. However, the approach suggested here demonstrates that under the conditions investigated, most of the charged analytes do not show any significant retention on the columns and that all the changes in their retention times can be attributed to their electrophoretic migration