furantoin is absorbed after oral intake, however it does not reach therapeutic concentrations in the plasma and in the tissues since it is rapidly eliminated through both renal and biliary routes after rapid absorption in the gastro-intestinal tract.2 Since macrocrystalline nitrofurantoin is more slowly absorbed and presents less collateral effects, it is usually commercialized in this form [2,6].Some analytical methods are employed for the determination of nitrofurantoin in pharmaceutical preparations. For example: spectrophotometric [7][8][9][10]; spectrofluorimetric [11,12]; voltametric [13,14]; chromatographic [15,16], methods have been described.The development of simple and rapid analytical methods is always interesting. Diffuse reflectance spectroscopy in the ultraviolet and visible region of the spectrum frequently allows the direct quantitative analysis of analytes with a minimum of treatment, with consequent decreases in manipulation and in the use of organic solvents and chemical reagents. The diffuse reflectance spectroscopy using spot tests has been used with success in quantitative analysis of many drugs [17][18][19][21][22][23][24].In aim of the present work was the development of a quantitative diffuse reflectance method, in the ultraviolet-visible range of the spectrum, for the deter-
IntroductionNitrofurantoin,[N-(5-nitro-2-furyldine)-1-aminohydantoin], C 8 H 6 N 4 O 5 , whose structural formula is shown in Figure 1, is a nitro compound very active against gram-positive and gram-negative bacteria [1]. It is also effective against Proteus and Pseudomonas aeruginosa, particularly in the acidic medium of the urinary treat. This drug is used as antibacterial agent in urinary infections with doses from 5 to 10 mg per day [2,3]. The mechanism of action of the 5-nitrofuranic derivatives is not yet completely elucidated [4,5]. NitroTwo quantitative analytical methods for the determination of nitrofurantoin in pharmaceutical preparations in the visible-ultraviolet range of the spectrum are reported. One of them uses the diffuse reflectance technique and the other transmittance measurements in aqueous solution. Both procedures are very simple to be performed and also present green characteristics as only polyethylene glycol and water are used as solvents. Commercial pharmaceutical preparations of the drug were analyzed using the proposed methods. The results were compared with those obtained when the HPLC procedure recommended by the USP was applied. Statistical comparison using the paired Student's t test and the Snedecor's F test showed good agreement between all the methods.Keywords: nitrofurantoin ; UV-visible diffuse reflectance ; transmittance, pharmaceutical preparations
GREEN AND SIMPLE UV-VISIBLE DIFFUSE REFLECTANCE AND TRANSMITTANCE METHODS FOR THE DETERMINATION OF NITROFURANTOIN IN PHARMACEUTICAL PREPARATIONS
This article reports a microgravimetric method for the quantitative determination of metformin in bulk and in pharmaceutical preparations. The analysis is simple and relatively rapid. A complete analysis can be performed in only an hour and thirty minutes due to the drying procedure of the precipitate. However a sample can be treated every each five minutes. The method is based on the reaction of nickel (II) with metformin that in basic medium forms an orange precipitate. The reaction is performed in a plastic syringe. The filtration was done in a glass tube containing a sintered glass disk or in Millipore® syringe filters, with posterior weighing after drying. The analytical results were statistically compared with that obtained with a HPLC and with the titrimetric method suggested by the United States and by the Japanese pharmacopoeias.
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