A fast fluorimetric flow injection method to determine ibuprofen

Abstracts

The native fluorescence of ibuprofen was enhanced when a host-guest complex of the analyte with beta cyclodextrin (beta-CD) was formed. So, based on this fact, a flow injection method to determine ibuprofen in different pharmaceutical preparations with fluorescence detection (lambdaem 287 nm, lambdaexc 223 nm) was developed. The calibration curve was linear over the range 6.00 - 60.0 mg L-1 of ibuprofen and the detection limit (LOD) for S/N=3 was 4.5 mg L-1. The relative standard deviation was 1.2% and the sample throughput 240 h-1. The method was validated by comparing the proposed and the official method to commercial preparation samples.

ibuprofen; FIA; spectrofluorimetry; pharmaceutical preparation

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 (lambdaem 287 nm, lambdaex 233 nm). A curva de calibração foi linear no intervalo entre 6,00 a 60,0 mg L-1 de ibuprofeína, com limite de detecção (LOD para S/N=3) de 4,5 mg L-1. 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.

ARTICLE

A fast fluorimetric flow injection method to determine ibuprofen

Adriana G. Lista; Miriam E. Palomeque^*; Beatriz S. Fernández Band^*

FIA Laboratory, Department of Chemistry, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahía Blanca, Argentine

ABSTRACT

The native fluorescence of ibuprofen was enhanced when a host-guest complex of the analyte with b cyclodextrin (b-CD) was formed. So, based on this fact, a flow injection method to determine ibuprofen in different pharmaceutical preparations with fluorescence detection (l_em 287 nm, l_exc 223 nm) was developed. The calibration curve was linear over the range 6.00 – 60.0 mg L^-1 of ibuprofen and the detection limit (LOD) for S/N=3 was 4.5 mg L^-1. The relative standard deviation was 1.2% and the sample throughput 240 h^-1. The method was validated by comparing the proposed and the official method to commercial preparation samples.

Keywords: ibuprofen, FIA, spectrofluorimetry, pharmaceutical preparation

RESUMO

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 (l_em 287 nm, l_ex 233 nm). A curva de calibração foi linear no intervalo entre 6,00 a 60,0 mg L^-1 de ibuprofeína, com limite de detecção (LOD para S/N=3) de 4,5 mg L^-1. 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 non-steroidal 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 Several methods have been developed to determine ibuprofen in pharmaceutical formulations and biological fluids specially by using gas liquid or high performance liquid chromatography.^2-9

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 b ciclodextryn (b-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.^11,12

In 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 l _em 287 nm (l _exc 223 nm).

The method was validated by comparing the obtained results with those obtained by official British Pharmacopoeia method.¹³

Experimental

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 valve¹⁴ were used.

Reagents and solutions

Analytical grade reagent and ultra pure water (18MW cm^-1) were always used. Ibuprofen (99.9%) was obtained from Marsing & Co (Denmark).

b-CD (Aldrich, Milwaukee, WI, USA) was doubly recristalized from water and an aqueous 1 ´ 10 ^–3 mol L^-1 solution was prepared.

An alkaline stock solution of Ibuprofen was prepared by weighing 0.0375 g and diluting to 25 mL with NH₃ (Merck) 0.05 mol L^-1, approximately. Standard solutions were daily prepared by appropriate dilution of the stock solution.

The pharmaceutical samples were Teprix (Gramon), Ibupirac 600 (Sintyal), Ibupirac syrup (Monsanto Argentina SAIC) and Causalon gesic (Phoenix).

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 NH₃ (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 NH₃ (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 b-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 l_em=287 nm (l_exc=223 nm).

Results and Discussion

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 b-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 b-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 b-CD concentration influence on fluorescent signal was studied. For that purpose concentrations from 0.5´10^-3 to 2.0´10^-3 mol L^-1 were tested. The best signal was obtained with 1x10^-3 mol L^-1.

The range of the FIA variables studied and their optimum values are listed in Table 1.

Analytical parameters

With selecting experimental conditions above described, the calibration curve was linear over the range 6.00 – 60.0 mg L^-1 of ibuprofen and the detection limit (LOD) for S/N=3 was 4.5 mg L^-1. The calibration line was y = (1.653 ± 0.030) x + (2.294 ± 1.126) (where y is the fluorescence signal and x the concentration of ibuprofen in mg L^-1), with a correlation coefficient of 0.9993. The reproducibility was 1.2% (n=11 duplicates of 18 mg L^-1) and the sample throughput 240 h^-1.

Applications to real samples

In order to detect the absence of interference from the matrix, the standard addition calibration method was applied to different real samples. The relative systematic errors can be evaluated by comparing the slopes of the standard addition lines and an aqueous calibration line.¹⁵ If the matrix does not interfere, both lines must have the same slope. Table 2 shows the slopes of calibration lines obtained with the proposed method and with the standard addition method applied to different pharmaceutical samples. The slopes comparison was done by applying the "t" test. As can be seen, the slopes were not significantly different.

In order to validate the proposed method, the samples were also analyzed by using the official British Pharmacopoeia method.¹³Table 3 shows the obtained results by both methods. The proposed method agrees with the standard method, and there are very good recovery values, all in the range recommended by Pharmacopoeias for this kind of analyses.

Conclusions

The proposed method is an excellent alternative to determine ibuprofen mainly in routine tasks, due to the highlight feature that is the high sample throughput. Moreover, the good reproducibility, low cost and easy implementation makes it an outstanding method for quality control. It is a simple method and free of interferents, as was showed in the analysis of different medicaments.

The advantages above mentioned and considering that the official method is more complicated, requires a technique more expensive and spent too much time for the analysis, the proposed method could be adapted easily in the pharmaceutical laboratory.

The method was validated by using real samples and the official method.¹³

Acknowledgments

B.S. Fernández Band express her gratitude to Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) de la República Argentina.

This work was totally supported by the Universidad Nacional del Sur, Bahía Blanca, Argentina.

Received: February 23, 2006

Published on the web: October 10, 2006

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Publication Dates

• Publication in this collection
  29 Jan 2007
• Date of issue
  Dec 2006

History

• Received
  23 Feb 2006
• Accepted
  10 Oct 2006