Viviana Rodríguez

In vitro measurement of available iron in fortified foods

Abstract The objective of this study was to investigate the influence of base systems used to regulate pH values of digests on iron dialysability as an indicator of bioavailable iron. We studied the pertinence of measuring titratable acidity to pH 7.5 with KOH to calculate mEq of NaHCO 3 to be used for pancreatic digestion/dialysis. The pH achieved using the same mEq of each base was lower when using NaHCO 3 than when using KOH. The discrepancy between achieved and attempted pH was uneven for several iron sources. Differences in pH regulation procedure, including type and concentration of base or buffer added to the pepsin digest rendered different final digest/dialysate pH values, thus affecting dialysable iron. A modification of in vitro equilibrium dialysis method is proposed using PIPES buffer of sufficient molarity to obtain a uniform final pH of 6.5 in digest/dialysate systems. The main factors taken into account to calculate buffer concentration were buffer capacity of food matrix (HCl mEq required to reach pH 2), HCl mEq included in the aliquot of pepsin suspension, acid or base mEq generated through enzymatic hydrolysis during in vitro digestion and intrinsic food pH (HCl mEq to adjust food matrix pH to 6.5). With these data buffer molarity for each food matrix can be calculated. Modifications suggested for the equilibrium dialysis method allowed development of a uniform final pH of the digest/dialysate system in a variety of foods assayed.

Analysis of cis-trans isomers and enantiomers of sertraline by cyclodextrin-modified micellar electrokinetic chromatography

In this work development, optimization and validation of a cyclodextrin-modified micellar electrokinetic chromatography (CD-modified MEKC) method is proposed to resolve separation of the sertraline hydrochloride and synthesis-related substances. Sertraline hydrochloride, the cis-(1S,4S) enantiomer form, is used as an antidepressant therapeutic agent. A buffer concentration composed of 20 mM sodium borate, pH 9.0 with 50 mM sodium cholate, 15 mM sulfated beta-cyclodextrin and 5 mM hydroxypropyl-beta-cyclodextrin was found to be the most suitable background electrolyte. Quantitation of the impurities at levels of 0.1% in different samples of the bulk drug was determined. A comparison of the results with those obtained by HPLC methodology was also accomplished. The method proved appropriate for testing the purity of sertraline hydrochloride in bulk drug.

Determination of bile acids in pharmaceutical formulations using micellar electrokinetic chromatography

A micellar electrokinetic chromatography method (MEKC) has been developed and validated for the determination of bile acids (BA) such as ursodeoxycholic acid (UDCA), dehydrocholic acid (DHCA) and deoxycholic acid (DCA) in pharmaceuticals for quality control purpose. The background electrolyte consisted of 20 mM borate-phosphate buffer containing 50 mM sodium dodecylsulfate (SDS), and acetonitrile as additive. UV detection was set at 185 nm. Selectivity, linearity, range, repeatability, intermediate precision and accuracy showed good results. Comparison of the values obtained by MEKC and HPLC methods were in close agreement.

Application of extraction disks in dissolution tests of clenbuterol and levothyroxine tablets by capillary electrophoresis

Sample preparation procedures using octadecyl (C18) extraction disks were developed to obtain accurate and reproducible results for determinations of clenbuterol(20 micrograms per dose) and levothyroxine (100 micrograms per dose) in dissolution media of solid oral dosage forms. Preconcentration of samples allowed final concentrations of 1.1 micrograms/ml of clenbuterol and 4.0 micrograms/ml of levothyroxine to be reached prior to CE analysis. The results obtained by CE were in good agreement with those of HPLC. The precision of the migration time, peak area, peak height and accuracy were determined in both intra-day (n = 6) and inter-day (n = 18) assays. Linearity was demonstrated over the ranges 0.5-80.0 micrograms/ml of clenbuterol and 1.0-30.0 micrograms/ml of levothyroxine. The mean recoveries were higher than 94.0%, ranging from 50 to 125% levels with respect to dose potencies. The proposed methodology may be generally applied to determine drugs at ng/ml concentrations.

Analysis of immunosuppressive drugs and their pharmaceuticals by micellar electrokinetic chromatography

SummaryA simple and practical micellar electrokinetic capillary chromatography (MEKC) method is proposed for the quantitation of immunosuppressive drugs such as azathioprine (AZA), mycophenolate mofetil (MMF), cyclosporine A (CyA) and tacrolimus (FK 506). The electrophoretic separation of the analytes was performed with a background electrolyte containing 20 mM phosphate buffer at pH 7.5, 50 mM SDS and methanol as an organic modifier. Fused silica capillaries 75 μm i.d. and 60 cm in length were employed and detection of analytes was performed at 214 nm.Thorough validation according to international guidelines showed that the proposed method is reliable and appropiate for the routine analysis of immunosuppressants. Moreover, it may be an advantageous alternative to the traditional chromatographic methodologies currently employed in the pharmaceutical and bioanalysis fields.