ABSTRACT Risperidone, an antipsychotic drug, was determined in human serum, using an optimized liquid-liquid extraction for isolation from biological fluid, with ethyl acetate as extraction solvent. This sample extraction method was chosen to increase extraction efficiency and reduce matrix interferences. Quantitation was achieved by LC/DAD at 294 nm over the concentration range of 1 ng/mL to 60 ng/mL (r=0.999). Desipramine was used as internal standard (tR for Risperidone: 4.23; tR Desipramine: 7.31). Mobile phase was water: acetonitrile: triethilamine: glacial acetic acid (70:29.16:0.52: 0.33 v/v), using a Purosphere STAR RP-18e 250 × 4.5 mm (5µ) column. RSD, for the intra-assay study, was between 0.52 % – 2.09 % (n=3), and between 0.79 % −3.25 % (n=9) for the inter-assay. LOD was 0.40 ng/mL and LOQ was 0.87 ng/mL. Recovery percentage for the accuracy study was between 90.82% and 98.56% ((RSD ≤ 3.93). The method is simple, fast, precise, accurate, sensible and selective. This method was successfully applied to quantify risperidone in patient serum samples. In conclusion, the method is useful for quantitative determination of risperidone in human serum.

ABSTRACT Acetazolamide (ACZ) is a carbonic anhydrase inhibitor that exhibits diuretic activity. In medicine, it is principally used in open-angle glaucoma, for prevention or amelioration of symptoms associated with acute high-altitude sickness and as an adjunct to other anticonvulsants in centrencephalic epilepsies. Furthermore, ACZ is sometimes used by athletes to mask the presence of doping substances, so its use has been banned in competitions. The aim of this work was the development of a sensor to determine ACZ in pharmaceuticals, as quality control way, and serum, for clinical and doping analyzes. The sensor has been developed modifying a glassy carbon electrode with carbon nanofibers. The electrochemical characterization of the sensor was performed by cyclic voltammetry using the redox mediator potassium ferrocyanide. ACZ electrochemical behavior was studied as well. Measurements were performed in a conventional three electrodes cell using differential pulse voltammetry. The influence of some experimental variables involved in the preparation and performance of the sensor –amount of modifier, supporting electrolyte, pH, scan rate and pulse amplitude– were optimized. This methodology provided a linear calibration plot for ACZ in the 1 – 17 µM concentration range. Furthermore, the proposed sensor exhibited suitable analytical properties, with detection and quantification limits of 0.06 µM and 0.2 µM respectively; analytical sensitivity of 1.142 µA/µM, repeatability of 0.72 %, and it was applied to determine ACZ in pharmaceuticals (tablets) and spiked human serum, being an excellent tool to perform quality control and antidoping control.

ABSTRACT A stability-indicating LC method was developed and validated for the determination of risperidone in tablets. Quantitation was achieved by LC/DAD at 294 nm over the concentration range of 25.00 μg/mL to 250.00 μg/mL. Mobile phase was a mixture of water: glacial acetic acid 0.50 %: triethylamine 0.80 %: acetonitrile (65.00: 0.32: 0.52: 34.16, v/v), using a Purosphere STAR RP-18e 250 × 4.5 mm (5μ) column, and paroxetine as internal standard. The method exhibited an adequate linearity (r = 0.999), selectivity, precision (RSD ≤ 0.847 %) and accuracy (recoveries from 99.55 % to 101.35 %). Risperidone was subjected to the stress conditions of oxidative, acid, base, thermal and photolytic degradation. Risperidone was found no degrade in basic or acid stress conditions, neither in thermal stress exposition (50, 70 and 100 °C) no at visible or UV stress conditions, during the time of the study. Only two degradation products were observed with peroxide oxidation, well resolved from analyte peak, proving the stability-indicating power of the method. The proposed method was found to be suitable for quantitative determination and the stability studies of risperidone in tablets.

A high performance thin-layer chromatographic (HPTLC) method for quantitative analysis of trazodone in human serum has been developed and validated. Trazodone was extracted with n-hexane: isoamyl alcohol (99:1). Chromatographic separation was performed on silica gel 60 F 254 HPTLC plates, with toluene: acetone: ethanol: ammonium (9:7:2:0.5, v/v/v/v) as mobile phase. Densitometric evaluation was carried out at 290 nm. There was no chromatographic interference between trazodone and its major metabolite, m-chlorophenilpiperazine (Rf 0.82 and 0.39, respectively). Regression analysis of the calibration plot revealed good linearity (r=0.999) over the range of 20.00 and 200.00 ng/band, corresponding to 0.20 and 2.00 ng/µL of trazodone in human serum after extraction process and applying 10 µL to the chromatographic plates. The % RSD of intra-assay and inter-assay precision, were in the range of 0.98% to 2.97% (n=3) and 1.06% to 3.54% (n=9), respectively. LOD and LOQ were found to be 0.016ng/µL, and 0.048ng/µL, and the recovery values, of trazodone from serum, were between 92.52 % and 96.73 %. This method was successfully applied to quantify trazodone in patient serum samples. In conclusion, the developed method might be useful for the quantitative determination of trazodone in human serum, as a tool to evaluate patient adherence to their pharmacotherapy with this drug.

A method using HPTLC for quantitation of nifedipine in serum was developed and validated. It includes a liquid-liquid extraction, and carbamazepine as internal standard. Chloroform: ethyl acetate: cyclohexane (19:2:2, v/v/v) was the mobile phase. The method showed good relationship (r = 0.996) (2.00 to 25.00 ng/band, corresponding to 0.02 and 0.25 ng/µL in serum). The % RSD of intra-assay and inter-assay, were between 0.57 and 3.56 and 1.16 to 3.60, respectively. LOD and LOQ were 0.72 and 0.86 ng/band, respectively. The recovery values were between 93 and 102%. Rf for nifedipine and carbamazepine were 0.31 and 0.10, respectively.

The chemical stability of enalapril drug substance and tablets was studied by a stability-indicating liquid chromatographic method. Stress testing was performed on drug substance under various conditions. Accelerated stability testing was carried out for different formulations of enalapril tablets. Chromatographic separation was achieved on a RP-18 column, using a mobile phase of methanol phosphate buffer at 1.0 mL min"1 and UV detection. Degradation of the drug substance was greater under hydrolytic conditions. After 180 days of accelerated stability testing most enalapril tablets showed more than 10% of degradation. Enalapril drug substance and tablets showed instability under stress and accelerated testing respectively, with possible implications on the therapeutic activity.