Design of experiments applied to stress testing of pharmaceutical products: A case study of Albendazole

Forced degradation tests are studies used to assess the stability of active pharmaceutical ingredients (APIs) and their formulations. These tests are performed submitting the API under extreme conditions in order to know the main degradation products in a short period of time. The results of these studies are used to assess the degradation susceptibility of APIs and to validate chromatographic analytical methods. However, most of degradation studies are performed using one-factor-at-the-time (OFAT) which does not consider the interactions between degradation variables. This work proposes the use of Design of Experiment (DoE) approach in forced degradation of albendazole (ABZ). It was used a central composite design (CCD) to evaluate the forced degradation in a multivariate way. Experiments were performed taking into account the variables pH, temperature, oxidizing agent (H₂O₂) and UV radiation. It was verified the influence of the variables and their interactions on the ABZ degradation. The ABZ oxidation showed to be the main degradation route for ABZ, which is strongly influenced by the temperature. The hydrolysis was relevant at alkaline medium and high temperature. LC-IT-MSⁿ was used to identify the degradation products. It was found three known degradation products (albendazole-2-amino, albendazole sulfoxide and albendazole sulfone) and a new derivate of albendazole molecule (albendazole sulfoxide with a chlorine). This last one was isolated and characterized by UPLC-QToF-MS and NMR analyses.

Determination of B-complex vitamins in pharmaceutical formulations by surface-enhanced Raman spectroscopy

The aim of this work was to quantify B-complex vitamins in pharmaceutical samples by surface enhanced Raman spectroscopy technique using gold colloid substrate. Synthesis of gold nanoparticles was performed according to an adapted Turkevich method. Initial essays were able to suggest the orientation of molecules on gold nanoparticles surface. Central Composite design was performed to obtain the highest SERS signal for nicotinamide and riboflavin. The evaluated parameters in the experimental design were volume of AuNPs, concentration of vitamins and sodium chloride concentration. The best condition for nicotinamide was NaCl 2.3×10^-3molL^-1 and 700μL of AuNPs colloid and this same condition showed to be adequate to quantify thiamine. The experimental design for riboflavin shows the best condition at NaCl 1.15×10^-2molL^-1 and 2.8mL of AuNPs colloid. It was possible to quantify thiamine and nicotinamide in presence of others vitamins and excipients in two solid multivitamin formulations using the standard addition procedure. The standard addition curve presented a R² higher than 0.96 for both nicotinamide and thiamine, at orders of magnitude 10^-7 and 10^-8molL^-1, respectively. The nicotinamide content in a cosmetic gel sample was also quantified by direct analysis presenting R² 0.98. The t-student test presented no significant difference regarding HPLC method. Despite the experimental design performed for riboflavin, it was not possible its quantification in the commercial samples.

Cluster analysis of commercial samples of Bauhinia spp. using HPLC-UV/PDA and MCR-ALS/PCA without peak alignment procedure

INTRODUCTION

Bauhinia forficata Link. is recognised by the Brazilian Health Ministry as a treatment of hypoglycemia and diabetes. Analytical methods are useful to assess the plant identity due the similarities found in plants from Bauhinia spp. HPLC-UV/PDA in combination with chemometric tools is an alternative widely used and suitable for authentication of plant material, however, the shifts of retention times for similar compounds in different samples is a problem.

OBJECTIVE

To perform comparisons between the authentic medicinal plant (Bauhinia forficata Link.) and samples commercially available in drugstores claiming to be "Bauhinia spp. to treat diabetes" and to evaluate the performance of multivariate curve resolution - alternating least squares (MCR-ALS) associated to principal component analysis (PCA) when compared to pure PCA.

METHODOLOGY

HPLC-UV/PDA data obtained from extracts of leaves were evaluated employing a combination of MCR-ALS and PCA, which allowed the use of the full chromatographic and spectrometric information without the need of peak alignment procedures.

RESULTS

The use of MCR-ALS/PCA showed better results than the conventional PCA using only one wavelength. Only two of nine commercial samples presented characteristics similar to the authentic Bauhinia forficata spp., considering the full HPLC-UV/PDA data.

CONCLUSION

The combination of MCR-ALS and PCA is very useful when applied to a group of samples where a general alignment procedure could not be applied due to the different chromatographic profiles. This work also demonstrates the need of more strict control from the health authorities regarding herbal products available on the market.

Determination of acetylsalicylic acid in commercial tablets by SERS using silver nanoparticle-coated filter paper

In this work, filter paper was used as a low cost substrate for silver nanoparticles in order to perform the detection and quantification of acetylsalicylic acid by SERS in a commercial tablet. The reaction conditions were 150mM of ammonium hydroxide, 50mM of silver nitrate, 500mM of glucose, 12min of the reaction time, 45°C temperature, pretreatment with ammonium hydroxide and quantitative filter paper (1-2μm). The average size of silver nanoparticles deposited on the paper substrate was 180nm. Adsorption time of acetylsalicylic acid on the surface of the silver-coated filter paper was studied and an adsorption time of 80min was used to build the analytical curve. It was possible to obtain a calibration curve with good precision with a coefficient of determination of 0.933. The method proposed in this work was capable to quantify acetylsalicylic acid in commercial tablets, at low concentration levels, with relative error of 2.06% compared to the HPLC. The preparation of filter paper coated with silver nanoparticles using Tollen's reagent presents several advantages such as low cost of synthesis, support and reagents; minimum amount of residuals, which are easily treated, despite the SERS spectroscopy presenting fast analysis, with low sample preparation and low amount of reactants as in HPLC analysis.

Square-wave adsorptive stripping voltammetric determination of nanomolar levels of bezafibrate using a glassy carbon electrode modified with multi-walled carbon nanotubes within a dihexadecyl hydrogen phosphate film

A glassy carbon electrode modified with carbon nanotubes is applied for bezafibrate sensing.