The development and optimization of a novel UV spectrophotometric methodology was proposed for simultaneous analysis of ethambutol (ETB), isoniazid (ISO), rifampicin (RIF) and pyrazinamide (PYR), using multivariate calibration based on the partial least squares method (PLS). The methodology was successfully applied for analysis of four-drug fixed dose combination (4-FDC) tablets used for tuberculosis treatment. A 34 Box-Behnken design, with triplicate in central point, was used for sample preparation in the calibration step. In the present case, nine latent variables were chosen for the model development that presented the smallest RMSECV and explain 98.76% of data variance in Y block (concentrations of ETB ISO, RIF and PYR) and 99.93% of data variance in X block (spectral data). PLS models for ETB, ISO, RIF and PYR presented RMSEP and R2 values of 0.23 mg L−1 and 0.971; 0.14 mg L−1 and 0.731; 0.11 mg L−1 and 0.990 and 0.57 mg L−1 and 0.972, respectively. A validation step was performed based on the comparison between the UV spectrophotometric proposed methodology and capillary zone electrophoresis (CZE) in 4-FDC real samples and no significant difference was found between two methodologies at 95% of confidence level. [...]
An alternative method for extraction optimization of C18:2 n-6 and C18:3 n-3, the main precursors for the synthesis of conjugated linoleic acid (CLA), in Brachiaria ruzizienses forages was proposed. Three methods of lipid extraction were tested: 1. Hara & Radin, 2. Micro Folch and 3. Bligh & Dyer. The preliminary test showed the Hara & Radin method as the most promising procedure. Then, a 33 Box Behnken design with triplicate in the central point was applied in Hara & Radin method in order to optimize the extraction procedure. The optimization extraction was monitored by quantification of C18:2 n-6 and C18:3 n-3 through capillary zone electrophoresis (CZE). The results obtained by CZE were compared to gas chromatography (AOCS official method) in real samples using the paired t-test. No significant difference between methods was found within a 95% confidence interval (p-value= 0.937). The alternative CZE method for Brachiaria ruzizienses forages analysis has some advantages in comparison with official GC method such as, short analysis time (10 min), no derivatization step for sample preparation, absence of specific separation columns, lower analytical cost and high throughput. [...]
Ethambutol (ETB) is a first-line antitubercular drug effective against actively growing Mycobacterium tuberculosis. Resistance of the mycobacterium to ethambutol among tuberculosis (TB) patients results from inadequate or inappropriate dosing of treatment or using low quality medication. It is therefore necessary to develop reliable methods for determining ethambutol metabolic profiles of patients at point of care for proper dosing. Herein an efficient ETB sensor device is illustrated. It consists of a graphite-polyurethane composite electrode. In order to characterise the electrochemical behaviour of ethambutol at pH = 8.0 voltammetric studies were performed. The detector was assembled in a flow injection apparatus and operated at +1.2 V (vs. Ag/AgCl(NaCl sat.)). The influence of sample volume and flow rate was studied. The linear response for the method was extended up to a 1.1 mmol L−1 ethambutol solution with a detection limit of 0.0634 mmol L−1. The reproducibility of current responses for injections of 0.7 mmol L−1 ethambutol solution was evaluated to be 5.1% (n = 30) and the analytical frequency was 161 determinations h−1. Two different samples were successfully analysed and the results were in good agreement with those obtained using capillary zone electrophoresis (CZE). [...]
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