A Fast Fluorimetric Flow Injection Method to Determine Ibuprofen

A fluorescência natural da ibuprofeína foi melhorada quando foi formado um complexo convidado-hospedeiro com a beta-ciclodextrina (beta-CD). A partir disso, foi desenvolvido um método por injeção em fluxo para a determinação de ibuprofeína em diferentes preparações farmacêuticas, com detecção fluorescente (λ em 287 nm, λ ex 233 nm). A curva de calibração foi linear no intervalo entre 6,00 a 60,0 mg L de ibuprofeína, com limite de detecção (LOD para S/N=3) de 4,5 mg L. O desvio padrão relativo foi de 1,2% e a velocidade de determinação de 240 amostras por hora. O método foi validado pela comparação do método proposto, e do usado oficialmente, em amostras comerciais preparadas.


Introduction
Ibuprofen (2-(4-isobutyl)-propionic acid) is a nonsteroidal anti-inflammatory drug that is available in a variety of preparations.Usually, it is used in treatment of pain and inflammation for rheumatoid arthritis and other musculoskeletal disorders. 1][4][5][6][7][8][9] Hergert and Escandar 10 have developed a spectrofluorimetric method for the determination of ibuprofen.This method is based on the host-guest complexation of the analyte with β ciclodextryn (β-CD).It was possible to improve the analytical parameters of the method because the fluorescent properties of the inclusion complex were better than those of the free compound.
Quality control in pharmaceutical preparations requires analytical methods for routine that should be accurate, simple, and economical in time and cost.Moreover, they should be capable to monitor a large number of samples and to detect the analyte over the established range.The automation of the laboratory process allows to attain these objectives.Flow injection analysis (FIA) is an appropriate methodology to automate analytical methods due to its extreme versatility, simplicity and inexpensive lab ware. 11,12n order to contribute to the quality control of pharmaceutical preparations, an automated spectrofluorimetric FIA method to determine ibuprofen in tablets and syrups was developed.It was based on the inclusion complex formation studied by Hergert and Escandar 10 and the measurements were done at λ em 287 nm (λ exc 223 nm).
The method was validated by comparing the obtained results with those obtained by official British Pharmacopoeia method. 13

Instrumentation
An Aminco Bowman Serie 2 luminescence spectrophotometer controlled by a computer and equipped with a Hellma 176752 -QS flow cell with an inner volume of 25 μL was used.
All the reaction coils were made of PTFE tubing (i.d.0.5 mm).
A Gilson Minipuls 3 peristaltic pump and a home made proportional double injection valve 14 were used.

Reagents and solutions
Analytical grade reagent and ultra pure water (18MΩ cm -1 ) were always used.Ibuprofen (99.9%) was obtained from Marsing & Co (Denmark).
An alkaline stock solution of Ibuprofen was prepared by weighing 0.0375 g and diluting to 25 mL with NH 3 (Merck) 0.05 mol L -1 , approximately.Standard solutions were daily prepared by appropriate dilution of the stock solution.

Sample preparation
Twenty tablets were weighed to calculate the average tablet weight.They were finely powdered and homogenised.In order to obtain approximately 20 mg of ibuprofen in 25 mL of NH 3 (0.05 mol L -1 ), a suitable amount of the powder was accurately weighed.To obtain the same concentration of ibuprofen when Ibupirac syrup was prepared, 1 mL of the syrup was diluted to 25 mL with NH 3 (0.05 mol L -1 ).
Appropriated dilutions of these solutions were made to determine the ibuprofen concentration.

Procedure
The double injection FIA manifold used for the determination of ibuprofen in pharmaceutical preparations is depicted in Figure 1.The same volume (200 μL) of sample and β-CD was simultaneously injected by using a proportional injector, in an ammonium hydroxide solution (0.05 mol L -1 ) and water streams respectively.Both carriers were flowing at the same flow rate (2.1 mL min -1 ), and they went across an equal distance from the injection point up to the confluence point, where both streams were mixed in the R reactor (300 mm).The increased fluorescence signal was measured at λ em =287 nm (λ exc =223 nm).

Selection of FIA manifold
Two configurations for FIA system were proved.In the first one, a sample volume of ibuprofen was injected in an ammonium hydroxide carrier solution.Then, this solution merged with a stream of β-CD solution in a reactor, and the inclusion complex was formed.
In the other one, a double injection was used.The same volume of ibuprofen and β-CD was inserted simultaneously in ammonium hydroxide and water carrier solutions respectively.
A best reproducibility and enhance signal intensity were attained with the last configuration (Figure 1).

Influence of chemical and FIA variables
The variables influencing the performance of the method were optimised by the univariant method.By considering the reproducibility of the signal, and the shape and height of the peak, the optimum values were selected.
Different concentrations of the ammonium hydroxide carrier solution were tested between 0.02 and 0.08 mol L -1 .When 0.02 mol L -1 concentration was used it was observed the formation of a precipitate into the reactor.At higher concentrations than 0.05 mol L -1 , signals were not increased.Thus, 0.05 mol L -1 was used.
The β-CD concentration influence on fluorescent signal was studied.For that purpose concentrations from

Table 3 .
Determination of ibuprofen in pharmaceutical preparations (tablets) a Standard deviations (n=5); b the recoveries are based on the labelled amount.

Table 1 .
Optimization of FIA variables