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비아그라 구매 ï¿½ has quickly become just about the most popular and trusted drugs in the treating erectile dysfunction. 3 In parallel with the growth in its consumption, there was an increase in the quantity of cases of adulteration and falsification of this medication. 4 To date, there is an lack of a monograph and description of the official method for its analysis in the Brazilian pharmacopoeia and in the primary international works in this category. In view of these considerations, it is of paramount importance to ensure the quality of the merchandise sold for the protection of consumers’ health.
The techniques described in the literature for sildenafil citrate analysis include voltammetry, 5.6 high performance liquid chromatography with UV 7-9 detection or coupled to mass spectrometry, 10 micellar electrokinetic chromatography, 11 gas chromatography, 12 capillary electrophoresis, 13 spectroscopy of nuclear magnetic resonance 14 and spectrophotometry. 15-17 Chromatographic methods are the most found in the determination of sildenafil citrate in several matrices (pharmaceutical formulations, plasma and urine), 7-9,11as well as in the determination of pharmacokinetic parameters. These have low detection limits, which justifies their used in the analysis of biological fluids. However, they require a long time in the initial sample preparation steps, use greater amounts of solvents and the instrumentation is more expensive, which raises the ultimate cost of the analyzes. For the analysis of pharmaceutical formulations, it really is desirable that methods using low cost techniques and offering fast, precise and accurate email address details are available.
Molecular absorption spectrophotometry may be the instrumental technique of choice trusted for this purpose, getting the advantages of being simple, involving the use of low-cost equipment and to be able to be easily automated. The methods described in the literature for the determination of sildenafil citrate by spectrophotometry 15-17 are scarce plus they have some disadvantages, because they require heating for color development in acetonitrile medium 16 or involve laborious procedures with many stages of sample handling, including extractions with chloroform. 15
This work describes the development of a fast and simple spectrophotometric method based on the reaction between sildenafil citrate and p-chloranil 16 accelerated with the addition of hydrogen peroxide, instantly creating a stable violet complex ( ? max = 535 nm) at room temperature .
Materials and equipment
The volume measurements were made with class A burettes or Eppendorf micropipette (100-1000 ï¿½ L). The glassware used in the preparation of the solutions was grade A and the weighings were carried out on an analytical balance AG204, Mettler Toledo. Absorbance measurements were made using a Varian spectrophotometer model Cary 100 built with glass or quartz cuvettes with an optical path of 1 1 cm.
Reagents and solutions
All reagents and solvents used in this work were of analytical grade. Working solution 5.68 x 10 -3 mol L -1 of sildenafil citrate (given by Pfizer, 95%) was prepared in methanol (Mallinckrodt, Xalostoc, Mexico). This solution is stable for 15 days if stored in the refrigerator. 5 p-chloranil (Sigma, St. Louis, USA), working solution 1.00 x 10 -2 mol L -1 of p-chloranil (Sigma, St. Louis, USA) was prepared in dioxane (Mallinckrodt, Xalostoc, Mexico). Hydrogen peroxide solution 5.00 mol L -1was made by the appropriate dilution of the Peridrol solution (Merck, Darmstadt, Germany, 30% w / w) with methanol, previously standardized in line with the permanganimetric procedure. 18
so that its final concentration ranged from 8.52 x 10 -5 to 1 1.70 x 10 -3 mol L -1. The quantity of the flasks was completed with methanol sufficient and the absorbance measurements were made at 535 nm against a similarly prepared blank, but without the addition of sildenafil citrate. 비아그라 was constructed by plotting the absorbance values ??measured as a function of the sildenafil citrate concentration.
Sample preparation and analysis
Samples of drugs containing sildenafil citrate available on the market were purchased from local pharmacies and analyzed by the proposed method, within their expiration dates.
Sixteen tablets, from exactly the same batch, were weighed on an analytical balance and the mean mass value was determined. Subsequently, these were sprayed on agate grains until a fine powder was obtained. Some of sprayed sample equal to 20 mg of sildenafil citrate was exactly weighed and subjected to stirring with 5 ml of methanol in a magnetic stirrer for 15 min. This solution was used in a 10 mL volumetric flask and the volume made up with methanol until the meniscus. Then, the answer was filtered on Whatman 41 quantitative filter paper and a 750 ï¿½L aliquot was taken and analyzed according to the recommended process of the construction of the analytical curv