Elimination of adsorption effects in the analysis of water-soluble vitamins in pharmaceutical formulations by capillary electrophoresis

Abstract

A tendency to an increase in migration times was observed when different water-soluble vitamins were analysed repeatedly in pharmaceutical preparations by capillary electrophoresis. In order to better understand the origin of this effect, the influence of the vitamins and the excipients, such as cellulose derivatives, was investigated. These studies indicated that the increase in analyte migration times was most probably due to the adsorption of different kinds of constituents to the capillary wall. Different rinsing procedures were tested in order to eliminate these unfavourable effects. A rinse of the capillary with a 25 mM sodium dodecyl sulfate (SDS) solution in the running buffer between successive runs was found to be particularly effective when the analysis was performed by free solution capillary zone electrophoresis (CZE). When the vitamins were determined by micellar electrokinetic chromatography (MEKC) using SDS as surfactant, a short capillary rinse with the running buffer was sufficient to obtain reproducible migration times. The CZE and MEKC methods developed were validated and compared. Both methods could be applied to the determination of water-soluble vitamins in different multivitamin formulations.

Determination of water‐soluble vitamins in soft drinks and vitamin supplements using capillary electrophoresis

“…Following each run, the capillary was washed for 2 min with buffer containing 25 mm SDS. This SDS content, which is already included in the buffer for the MEKC method, is sufficient for cleaning the capillary between the analyses, so that no further washing steps with acid or alkali are required [4]. The samples were applied to the capillary using the hydrodynamic mode with an overpressure of 0.5 psi for 5 s. The applied voltage was 30 kV and detection was carried out at 214 nm.…”

Separation of three water‐soluble vitamins by poly(dimethylsiloxane) microchannel electrophoresis with electrochemical detection

“…Moreover, 10 mM L-cysteine [26,27] was added to all solutions in order to prevent water-soluble vitamins, especially VC, from oxidation in the experimental environment. All solutions were freshly prepared in amber volumetric flasks in the dark every day, and stored in a refrigerator prior to analysis.…”

Separation of thiamin and its phosphate esters by capillary zone electrophoresis and its application to the analysis of water-soluble vitamins

“…The amounts of free thiamin in selected commercial tablets determined experimentally are presented in Table 2. It was also observed that tablet samples or matrix components appeared to be adhering to the capillary walls, causing irreproducibility in both migration times and peak areas from run-to-run [30,39]. By reconditioning the capillary as described in Section 2 prior to commercial-tablet sample analyses, an improvement in migration times and peak area precision was obtained (R.S.D.…”