Lowering the concentration limits of detection by on-line solid-phase extraction-capillary electrophoresis-electrospray mass spectrometry.

The use of solid-phase extraction coupled on-line to capillary electrophoresis using electrospray mass spectrometry detection (SPE-CE-ESI-MS) is described for the analysis of peptides in dilute solutions. A SPE microcartridge or analyte concentrator containing C(18) derivatized silica particles as the extraction sorbent was easily constructed near the inlet of the separation capillary using commercially available materials. The reversed-phase sorbent selectively retained the target peptides, enabling large volumes of the sample to be introduced (>100muL). The captured analytes were eluted in a small volume of an appropriate solution (20-50nL). This resulted in sample clean-up and concentration enhancement, with minimum sample handling. As the SPE-CE conditions were compatible with on-line ESI-MS detection, the potential for identifying and characterizing the preconcentrated analytes by SPE-CE-ESI-MS using a sheath-flow CE-ESI-MS interface is also shown. Using separation electrolytes containing N-[carbamoylmethyl]-2-aminoethanesulfonic acid (ACES) at pH 7.4, an elution plug of 80:20 (v/v) (25mM of formic acid in MeCN):H(2)O and a sheath liquid of 20mM of acetic acid in 50:50 (v/v) methanol:H(2)O the concentration limits of detection for the analyzed peptides in the positive ion mode were lowered to nanogram per milliliter levels. The systematic optimization of the operational parameters involved in the development of the SPE-CE method is described in detail, in order to promote robust and quantitative SPE-CE-ESI-MS analysis and facilitate the widespread use of the technique.

Comparing cyclodextrin derivatives as chiral selectors for enantiomeric separation in capillary electrophoresis.

A total of 26 different cyclodextrin (CD) derivatives with different functional groups and degrees of substitution were tested against 35 basic pharmaceutical compounds in an effort to investigate their effectiveness as chiral selectors for enantiomeric separation in capillary electrophoresis (CE). Testing was performed under the same conditions using a low pH buffer (25 mM phosphate buffer at pH approximately 2.5). Five CD derivatives, namely, highly sulfated-beta-CD, highly sulfated-beta-CD, hydroxypropyl-beta-CD (degree of substitution approximately 1), heptakis-(2,6-O-dimethyl)-beta-CD, and heptakis(2,3,6-O-trimethyl)-beta-CD were identified to be most effective for enantiomeric separations and have a wide range of enantiomeric selectivity towards the model compounds. Over 90% of the model compounds were enantiomerically resolved with the five identified CD derivatives, at a minimum resolution of 0.5. An additional 20 compounds were also tested to demonstrate the validity of the identified CD derivatives. The five CD derivatives were recommended as the starting chiral selectors in developing enantiomeric separation methods by CE.

Efecto del ácido quenodesoxicólico sobre la composición de los ácidos biliares en bilis de hámster / Effect of chenodeoxycholic acid on the composition of biliary bile acids in hamster

Se investiga la modificación en la composición de los ácidos biliares de hámster por administración de altas dosis de ácido quenodeoxicólico (CDCA). Treinta hámster dorados, machos, fueron divididos en 5 grupos, uno de control y los otros cuatro recibieron 0,5g y 1g de CDCA por 100g de dieta estándar, durante 30 y 60 días. Luego de anestesia con éter se extrajo la vesícula y se aspiró la bilis inmediatamente. Los ácidos biliares se determinaron por cromatografía líquida de alta resolución (HPLC). Los conjugados del CDCA y del ácido litocólico (LCA) mostraron aumentos no relacionados con la dosis o el tiempo de tratamiento. También se observó un aumento moderado de los ceto derivados del CDCA, especialmente, uno de los glico conjugados. La relación cólico/queno disminuyó significativamente. Los ácidos taurolitocólico (TLCA) y glicolitocólico (GLCA) aumentaron significativamente en todos los grupos tratados. La relación glico/tauro conjugados de 1,17 en los controles aumentó a aproximadamente 3,0 en los tratados. Con respecto a la relación G/T del LCA de 0,38 en el grupo control aumentó a un valor cercano a 2,0 en los tratados.