Elena Bossù

Determination of optical purity by nonenantioselective LC using CD detection

The use of a circular dichroism (CD) based HPLC detection system was recently described by some authors and proposed for a nonenantioselective HPLC enantiomeric purity determination. Indeed the system, measuring both CD and UV signals simultaneously, allows the evaluation of the g anisotropy factor. In order to experimentally support such an analytical procedure as an alternative to the enantioselective chromatographic method currently found in some pharmacopoeial monographs, we have studied its application to the analysis of dexchlorpheniramine maleate, an active substance which exhibits a poor CD signal in the 250-270 nm spectral region with a g value of the order of 10(-4). The results reported indicate that the suitability of the studied procedure for the enantiomeric purity determination is obtained only when the CD-detector reaches high stability; indeed a certain time lag is systematically necessary to obtain stable responses, i.e. adequate precision. The enantioselective HPLC procedure seems to be more precise for enantiomeric purity values < or = 2% than the CD based detection system; such a disadvantage might be counterbalanced by the use of non chiral stationary phases.

Determination of MPTP, a toxic impurity of pethidine

Pethidine, predominantly a mu-receptor agonist, is a phenyl-piperidinic synthetic drug. It is used in the management of moderate to several pain. A possible hydrolytic degradation of an ester group can generate a very toxic compound, the N-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) which contaminates the drug. Because of the toxicity of MPTP a suitable method for its determination must be selective and sensitive. Afterwards we propose simple methods to determine pethidine and MPTP by capillary electrophoresis (CE), MECK and RP-high performance liquid chromatography (HPLC) looking at the limit of detection obtained using these three techniques. CE was carried out using as running buffer ammonium acetate (pH 8.3). MECK was performed with a borate buffer (pH 8.3) containing sodium dodecylsulphate and trimethyl-beta-cyclodextrins. RP-HPLC was carried out on a RP18 stationary phase, using as mobile phase a mixture of phosphate buffer (pH 7) containing acetonitrile and 1% of diethylamine.

The indirect UV detection in the analysis of ursodeoxycholic acid and related compounds by HPCE

A high-performance capillary zone electrophoretic (HPCE) assay has been developed for the determination of ursodeoxycholic acid (UDCA) and its usual impurities. Considering the low molecular absorptivity of UDCA and its related compounds indirect UV detection was used. The electrophoretic capillary was filled with a background electrolyte (BGE) containing an UV absorbing ion: benzoic acid (BA) or 5,5-diethylbarbituric acid (DBA). To enhance the selectivity of the assay diimethyl-beta-cyclodextrines (D-beta-CDs) or trimethyl-beta-cyclodextrines (T-beta-CDs) have been added to the running buffer together with methylcellulose or urea. All considered impurities were well resolved with two buffers studied, with the exception of methylursodehoxycholate, a neutral compound.

Capillary electrophoresis as a tool for the characterization of pentosan nanoparticles

Because capillary zone electrophoresis (CZE) showed higher resolution for highly charged large carbohydrates and complex structures when compared to other chromatographic separation methods, it was chosen for the characterization of nanoparticles (NPs) of pentosan polysulfate (PPS). Thus, using the CZE technique, we developed a reliable, sensitive and rapid protocol that allowed the detection and characterization of PPS NPs. This protocol was able to determine the profile of both the NPs and the species of PPS entrapped into them, and to quantify free and bound PPS showing high reproducibility, acceptable accuracy and a good degree of precision. Moreover, it allowed the evaluation of the size and charge of the NPs. This protocol might be suitable for the characterization of other kinds of NPs also.

Simple and rapid analysis of methyldibromo glutaronitrile in cosmetic products by gas chromatography mass spectrometry

A simple and rapid gas chromatography (GC) method with mass spectrometry (MS) detection has been developed for the determination of methyldibromo glutaronitrile (MDBGN) in cosmetic products. The presence of this preservative in commercial cosmetic samples is prohibited since 2007 because of its allergenic properties. The analyzed products were opportunely diluted in methanol and MDBGN was separated by fused silica capillary column and detected by electron impact (EI)-MS in positive ionization mode with a total run time of 7 min. The assay was validated in the range 0.005-0.100 mg MDBGN per g of examined product with good determination coefficients (r(2)≥0.99) for the calibration curves. At three concentrations spanning the linear dynamic range of the calibration curves, mean recoveries were always higher than 95% for MDBGN in the tested cosmetics. This method was successfully applied to the analysis of cleansing gels, shampoo and solar waters to disclose the eventual presence of MDBGN illegally added in cosmetic products.

Determination of fenticonazole and its impurities by capillary electrophoresis and high performance liquid chromatography

Fenticonazole, a topical antifungal agent containing a stereogenic centre, is used in therapy as a racemic mixture. Five related compounds can be found as impurities in the drug. We propose a HPLC method using as stationary phase a RP-8 column eluted with different gradients of acetonitrile/phosphate buffer (pH 6) for simultaneous determination of the drug and these impurities. We also studied a high performance capillary electrophoresis (HPCE) method for quality control of fenticonazole. The separation of fenticonazole from all its impurities by HPCE was obtained in a relative short capillary (40 cm, effective length 34 cm, 50 μm ID) with a running buffer of 30 mM phosphate (pH 3) containing 8 mM trimethyl-β-cyclodextrin. Under these experimental conditions very good separation of fenticonazole from each individual impurity is obtained in less than 20 minutes. The choice of cyclodextrin added to the running buffer was dictated by the chiral nature of fenticonazole; trimethyl-β-cyclodextrin is mainly used as chiral selector. The optimised HPLC and HPCE methods are compared.

Quantitative analysis of iobitridol in an injectable preparation by 1H NMR spectroscopy

Nuclear magnetic resonance spectroscopy was used for direct quantitative determination of iobitridol in an injectable formulation. The method was developed on a medium field strength magnet (400MHz) and validation was performed by assessing specificity, accuracy, precision, linearity, stability of samples and robustness. Validation data confirm that the method is highly appropriate for direct quantification of iobitridol in the final formulation. Moreover the method has a good potential for rapid screening analyses due to straightforward experimental setup and lack of any sample pretreatment.