Influence of the BGE composition on analyte response in CD-mediated NACE-MS

in Electrophoresis (2010), 31(7), 1157-1161

The influence of the BGE composition, including the addition of a single-isomer sulfated beta-CD derivative, on the ionization performance of the model compound carvedilol in NACE-ESI-MS was studied using ... [more ▼]

The influence of the BGE composition, including the addition of a single-isomer sulfated beta-CD derivative, on the ionization performance of the model compound carvedilol in NACE-ESI-MS was studied using an alternative infusion method. This approach employs voltage-induced infusion of the BGE containing the analyte, and takes into account the effects of variations in EOF and effective analyte mobility on the ESI-MS intensity. First, the optimal composition of the sheath liquid for CE-MS in terms of signal abundance and stability was determined. The BGE ammonium formate, acetate, and camphorsulfonate were found to have similar effects on analyte ionization. Addition of single-isomer sulfated beta-CD derivatives (available as sodium salt) to the BGE revealed that the anionic CD derivatives did not give rise to the same ionization suppression effect. This result can be attributed to differences in the dissociation state of these sodium salts. Finally, it is shown that information about chiral selectivity can also be obtained with the applied infusion method. [less ▲]

On-line coupling of cyclodextrin mediated nonaqueous capillary electrophoresis to mass spectrometry for the determination of salbutamol enantiomers in urine

in Journal of Pharmaceutical & Biomedical Analysis (2006), 40(3), 752-757

The usefulness of the on-line coupling of nonaqueous capillary electrophoresis (NACE) with electrospray ionization (ESI) mass spectrometry (MS) using heptakis(2,3-di-O-acetyl-6-O-sulfo)-beta-cyclodextrin ... [more ▼]

The usefulness of the on-line coupling of nonaqueous capillary electrophoresis (NACE) with electrospray ionization (ESI) mass spectrometry (MS) using heptakis(2,3-di-O-acetyl-6-O-sulfo)-beta-cyclodextrin (HDAS-beta-CD) was demonstrated for the enantioselective determination of low concentrations of salbutamol in human urine. After optimization of several parameters, such as sheath-liquid composition and flow rate, nebulizing gas pressure, CE counter-pressure and position of the CE capillary outlet, a limit of quantification of 18 and 20 ng/ml was obtained for salbutamol enantiomers. Moreover, the relative standard deviation values for repeatability at a concentration of 30 ng/ml were below 7% for both enantiomers. Typical regression lines obtained after application of a simple linear regression model revealed a pod relationship between peak area and analyte concentration (with 0.9988 and 0.9966 as coefficients of determination). This paper proposes an easy to use and sensitive NACE-MS method to determine enantiomers of a basic chiral drug in biological fluids preceded by solid-phase extraction as sample cleanup. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

Interlaboratory study of a NACE method for the determination of R-timolol content in S-timolol maleate: assessment of uncertainty.

in Electrophoresis (2006), 27(12), 2386-99

Analyses of statistical variance were applied to evaluate the precision and practicality of a CD-based NACE assay for R-timolol after enantiomeric separation of R- and S-timolol. Data were collected in an ... [more ▼]

Analyses of statistical variance were applied to evaluate the precision and practicality of a CD-based NACE assay for R-timolol after enantiomeric separation of R- and S-timolol. Data were collected in an interlaboratory study by 11 participating laboratories located in Europe and North America. General qualitative method performance was examined using suitability descriptors (i.e. resolution, selectivity, migration times and S/N), while precision was determined by quantification of variances in the determination of R-timolol at four different impurity levels in S-timolol maleate samples. The interlaboratory trials were designed in accordance with the ISO guideline 5725-2. This allowed estimating for each sample, the different variances, i.e. between-laboratory (s2(Laboratories)), between-day (s2(Days)) and between-replicate (s2(Replicates)). The variances of repeatability (s2r) and reproducibility (s2R) were then calculated. The estimated uncertainty, derived from the precision estimates, seems to be concentration-dependent above a given threshold. This example of R-timolol illustrates how a laboratory can evaluate uncertainty in general. [less ▲]