A simple and sensitive kinetic spectrophotometric method was developed for the determination of ciclopirox olamine in pharmaceutical formulations (cream). The method is based on the oxidation of ciclopirox olamine with KMnO4 in alkaline medium to form K2MnO4, a bluish green color compound, at ionic strength controlled and room temperature. The reaction is monitored measuring the rate of change of absorbance at 610 nm. The absorbance-concentration plot corresponding to synthetic pharmaceutical samples (cream) was rectilinear, over the range of 0.32 - 10.0 μg mL-1, with detection and quantification limits of 0.095 μg mL¹ and 0.32 μg mL¹, respectively. Different experimental parameters affecting the development and stability of the reaction product were carefully studied via factorial screening and optimized by univariate method. The determination of ciclopirox olamine by the fixed time method is feasible and more advantageous with the calibration equation obtained at 30 min. The proposed method was validated for the application of the determination of the drug in pharmaceutical sample (cream).

In this work are presented two methods for the simultaneous determination of 17α-ethinylestradiol (EEL) and chlormadinone acetate (CMA) by second order derivative spectrophotometry. The first analytical method proposed is based in the dissolution and extraction of both drugs in acetonitrile. The solution was directly evaluated by second order derivative spectrophotometry with a smoothing factor of 8,000 and a scale factor of 10,000. The determination of EEL and CMA was carried out to 296,6 and 291.8 nm, respectively. The detection limits (3.3 σ criterion) for EEL and CMA were 6.9 x 10-7 and 9.8 x 10-8 mol/L, respectively. Furthermore, a study of the effect of the excipients containing in the pharmaceutical formulation was included. Polyvidone presents greater tendency to produce interference, but its spectral bands are located between 215 and 240 nm, so these bands do not interferes spectrally in the simultaneous determination of EEL and CMA. Both drugs were extracted from the pharmaceutical formulation with acetonitrile, obtaining a good recovery relative to the nominal content. The second method is a screening method and was applied in fortified drinking water. In this method, drugs were extracted in chloroform, which was then removed with N2 and the residue was redissolved in acetonitrile. Due to the difference in the procedure in relation to the pharmaceutical formulation a new analytical parameters were obtained. For EEL this parameters were very similar to those obtained directly in solution, however these were higher for CMA, which could be attributed to that under these conditions was found a higher standard deviation of the blank. Recoveries of fortified samples were 81.8 ± 1.5% and 101.1 ± 0.73% for EEL and CMA, respectively.

This work proposes a method for the co-determination of praziquantel and fenbendazole in veterinary pharmaceutical formulations (VPF) by second-derivative spectrophotometry at 226.4 nm (Zero-crossing method) and 324.6 nm (Graphic method), respectively. The excipients commonly used in VPF do not interfere. To obtain the optimal determination conditions, studies of solvent and light effects, were performed. The results of the light effects show that the expose of both drugs to indirect light and darkness does not produce any chemical change, since their zero-order spectra remained unchanged during the experiment. However, the exposition to the direct light only affects the fenbendazole. The zero order spectrum of FBZ in EtOH-HCl, present two broad bands (200 to 240 nm and 260 to 330 nm), these signals disappear and appear others totally different, at 230 nm and other with two peaks (285 and 295 nm). The FT-IR spectrum shows characteristics signals of the FBZ structure as the amide-NH group (3336.3 cm¹), this signal disappear indicating the bond break of the amide group caused by the exposition to sunlight for a time. These spectral changes evidenced a structural transformation as a result of photochemical decomposition in acid medium.

This work presents a rapid and simple method for the parallel determination of Desogestrel (DSG) and 17a-Ethinylestradiol (EE2) by second order derivative spectrophotometry and its application in pharmaceutical formulations. Study of the effect of the solvents, excipients and spectral behavior is also included. Acetonitrile was selected as a solvent; subsequently the samples were evaluated by second order derivatives, using a smoothing factor of 8,000 and a scale factor of 10(4). The EE2 determination was carried out using the graphical method at 288 nm and DSG by the zero-crossing method at 220 nm. The determination ranges were found to be between 1.5 10-6 and 5 10-4 mol/L and 1.710-7 to 1.010-3 mol/L for DSG and EE2, respectively. The homogenized tablets are divided in two fractions, the first, called sample A, was dissolved in acetonitrile, which contains the absorbents species that is polyvidone, DGS and EE2, the latter is determined directly at 288 nm. Meanwhile, in the second fraction (sample B), after extract with water the polyvidone and partially EE2, it is possible determine DGS at 220 nm. When the pharmaceutical formulation contains Vitamin E (Vit. E) is necessary to use an equations system to be evaluated in sample B.

Biosolid model samples (BMSs) were developed to study the capacity of various matrixes to adsorb polybrominated diphenyl ethers (PBDEs) as a function of their composition. A commercial standard reference samples for biosolids containing a certified amount of PBDEs is currently not available for extraction evaluation. Therefore, this study will allow for the selection of an appropriate concentration of PBDEs to produce a reference material for analytes associated with the matrix. The sorption of PBDEs increased clearly concomitantly with the amount of organic matter present in the model, revealing that organic matter rather than the inorganic fraction is mainly responsible for the analyte-matrix interaction. Hydrophobic interactions are predominant in the retention of PBDEs in the biosolid matrix because more hydrophobic congeners are generally sorbed to a higher extent than those that are less hydrophobic. In order to know the probable PBDE sorption mechanism on the model sample of biosolid, the Gibbs free energies were calculated using the Freundlich model, giving values between -8 and -10 kJ/mol. These results suggest that the sorption mechanism of the PBDEs is through physiosorption. Therefore, the Freundlich model should be satisfactory for describing the analyte behavior.

In this paper, a simple and rapid method was developed for the simultaneous determination of Piperacillin (PIP) and Tazobactam (TAZ) by second-order derivative spectrophotometry. Water was selected as a solvent for extraction and determination of both analytes. Further studies of photo-stability and forced degradation for both drugs were also performed. The spectral variables were optimized, a smoothing factor of 8·10³ and a scaling factor of 1·10(4) were selected and the analytical signals were evaluated at 296.3 nm and 233.3 nm for PIP and TAZ, respectively. The detection and quantification limits for PIP and TAZ were: 3.2•10-7 to 9.5•10-7 and 2.7•10-7 to 8.9•10-7 mol/L, respectively. The levels of repeatability (RSD) were 1.5% and 2.4% for PIP and TAZ respectively. The method was applied to the pharmaceutical formulation TAZONAM NF® Wyeth. USA, with a nominal content of 4.0 g of PIP, 0.5 g of TAZ, 0.139 g of citric acid and 1 mg of EDTA. A study of excipients was carried out and it was found that they do not interfere with quantification. By applying this method, a content of 3.96 ± 0.04 g and 0.57 ± 0.01 g was found of PIP and TAZ, respectively.

This paper analyses several mathematical approaches for simultaneous determination of dibucaine (D) and chlorphenamine maléate (CM). The different calibration methods utilised were: first derivative spectrophotometry (FDS), classical least squares (CLS), regression of partial least squares (PLS), and principal components regression (PCR). For the multivariated methods, the limits of detection (LOD) for multivariate calibrations were determined creating a surrogate signal variable (SSV). The recoveries were selected to confirm the validity of the models. In general, the CLS model presents the poorest recovery. In order to compare the exactitude of the different calibration methods, a one-way ANOVA test was performed. In these analyses, only the CLS calibration method produced a significantly different prediction. The lowest LODs were achieved by CLS and FDS, although the former method presented lower precision and poor prediction. Therefore, the FDS method is proposed as a pure binary calibration method for D-CM mixed samples, including the prepared according to a medical prescription and plasma samples simulating an event of intoxication.

In this work is proposed, a simple experiment for the simultaneous determination of losartan (L) and hydrochlorothiazide (H) in synthetic and real samples by derivative spectrophotometry technique. For the students it is relevant to know this technique for simultaneous determinations of drugs, allowing that the students recognize that this technique is simple, rapid and applicable to quality control. This experimental work, it is proposed in order to being applied to undergraduates into laboratories of analytical chemistry. Furthermore, it is given the integration of the theoretical knowledge with the experimental work; this correlation is of interest for the students.

A rapid method for the simultaneous determination of acetaminophen (A) and tramadol (T) by second derivative spectrophotometric has been developed. From a solvent effect studies and the spectral behaviours of A and T, ethanol was selected as solvent. For a Δλ value of 210 nm a smoothing factor of 8,000 and scale factor of 1,000,000 were selected, because in these conditions the signal/noise ratio was favoured in order to avoid error. In these conditions also it is possible the simultaneous determination of A/T in a molar relation of 17/1 contained in pharmaceutical formulations. At 285.7 nm the second derivative value is T concentration dependent, corresponding to zero-crossing point of A. On the other hand, T does not absorb between 296.0 to 400.0 nm, thus 308.0 nm was selected for A determination by graphic method. The determination ranges for A and T were 8.1x10-7 - 5 1x10-5 mol/L and 3.4 x10-7 - 5.0 x10-5 mol/L, respectively and can be determined with good precision and accuracy, without previous separation. A study of interferents, was carried out by using the excipients Zafin® tablet. The recoveries were 97.4 ± 2.0% and 100.6 ± 1.7% for A and T, respectively. This tablet containing both drugs was assayed using the methods developed, showing a good accuracy and precision.

The concentration of trace elements and other analytes of environmental interest was determined in waters and sediments of the Coya and Cachapoal rivers (VI Region, Central Chile), which corresponds to a location highly polluted by copper mining activity. Analysis showed the highest pollution at the sampling station closest to the copper smelter (Caletones), then pollutant concentrations decrease at sites far away from this source. The statistical correlation between the different variables determined in waters and sediments was carried out through a principal components analysis (PCA). It was observed that the parameters fell into three groups: (a) analytes present in waters and sediments which come from the mining wastes (b) analytes of lithoge-nic character present in waters plus alkaline and alkaline earth metals plus organic matter present in sediments and waters, and (c) lithogenic elements present in sediments. On the other hand, by using cluster analysis (CA), it was possible to group the different sampling stations according to their extent of pollution

The 3-[2´-thiazolylazo]-2,6-diaminopyridine or 2,6-TADAP have been used as chromophore reagent for the determination of metals of the platinum group. In this work a study of the stability of the 2,6-TADAP is included, a synergetic action of the temperature, the reaction time and the acidity of the medium was found. According to spectral behavior it can be postulated that 2,6-TADAP ligand suffers structural changes, having as consequence the formation of another azocompound. Besides, the mechanism of decomposition and characterization of the formed compound was also included. The characteristic chemical of new azocompound is appropriate for the development of analytic methods for the determination of metals belonging to the platinum group, using the new ligand called 3-[N,N-ethyl-met-azo]-2,6-diaminopyridine or 2,6-DAPEMA

A direct and simple second derivative digital spectrophometric method has been developed for the simultaneous determination of the sulfamethoxazole and trimethoprim in pharmaceutical formulation. A study of the spectral behavior of these drugs in different solvents is included, in order to select the best conditions for their simultaneous determination. Acetonitrile was used as solvent to extract the drugs from the pharmaceutical formulations and then to evaluate directly by second derivative spectra. This sumultaneous determination was carried out by the zero crossing approach, at 272,8 nm for sulfamethoxazole determination and at 256,0 nm for trimethoprim determination. The determination range for sulfamethoxazole was from 6,31x10-8 to 1,20x10-4 mol/L and for trimethoprim from 2,47x10-7 to 1,20x10-4 mol/L, and the detection limits for sulfamethoxazole and trimethoprim were 1,89x10-8 mol/L and 7,40x10-8 mol/L, respectively. The method was applied successfully in pharmaceutical formulations (tablets). Besides a study of photo-stability of both drugs with standard solutions and real pharmaceutical formulations was performed

RESUMEN En este trabajo, se propone un método simple y directo para la determinación simultánea de sulfametoxazol y trimetoprim en formulaciones farmacéuticas por espectrofotometría derivada digital de segundo orden. Se incluye además, un estudio de la conducta espectral de estas drogas en diferentes solventes, con el objeto de seleccionar las condiciones óptimas para su determinación simultánea. Acetonitrilo fue utilizado como solvente para extraer las drogas desde las formulaciones farmacéuticas y luego evaluar directamente las segundas derivadas espectrales. Esta determinación simultánea fue realizada por la aproximación de "zero crossing" a 272,8 nm para la determinación de sulfametoxazol y a 256,0 nm para la determinación de trimetoprim. Se encontró un rango de determinación para sulfametoxazol desde 6,31x10-8 a 1,20x10-4 mol/L y para trimetoprim desde 2,47x10-7 a 1,20x10-4 mol/L siendo los límites de detección 1,89x10-8 mol/L para sulfametoxazol y 7,40x10-8 mol/L para trimetoprim. El método propuesto fue aplicado exitosamente en formulaciones farmacéuticas (tabletas). Además se realizó un estudio de la foto-estabilidad de ambas drogas con soluciones estándares y en formulaciones farmacéuticas reales