J Pharm Anal Vol 1, No 1, 51- 56 (2011)
ORIGINAL ARTICLES
Flow injection chemiluminescence determination of loxoprofen and naproxen with the acidic permanganate-sulfite system
2 2 Li-Juan Wang· , Yu-Hai Thng *, Yang-Hao Lilt
I Medical School, Xi'an ]iaotong University, Xi'an 710061, China; 2 Institute of Analytical Sciences, Xi'an ]iaotong University, Xi'an 710061, China.
Abstract: A novel flow injection chemiluminescence (CL) method for the determination of loxoprofen and naproxen was proposed based on the CL system of KMnO, and Na,SOJ in acid media. The CL intensity of KMnO,-Na,SOJ was greatly enhanced in the presence of loxoprofen and naproxen. The mechanism of the CL reaction was studied by the kinetic process and UV-vis absorption and the conditions were optimized. Under optimized conditions, the CL intensity was 8 5 7 linear with loxoprofen and naproxen concentration in the range of 7.0 X 10- -1. 0 x 10- glmL and 2.0 x 10- - 4.0 X 10-· glmL with the detection limit of 2.0 x 10- 8 glmL and 3.0 x 10- 8 glmL (SIN = 3), respectively. The relative standard deviations were 2.39% and 1.37% for 5.0 x 10- 7 glmL naproxen and 5.0 x 10- 7 glmL loxoprofen (n = 10), respectively. The proposed method was satisfactorily applied to the determination of loxoprofen and naproxen in pharmaceutical prepa rations. Keywords: chemiluminescence; KMnO, ; loxoprofen; naproxen
1 Introduction which does not require sophisticated instruments and too many chemical reagents. CL method has been developed to Nonsteroidal anti-inflammatory drugs (NSAIDs) are a detect arylpropionic acid derivatives, such as ketoprofen, group of analgesics and anti-inflammatory drugs that are naproxen, ibuprofen, and fenbufen [21-25]. To the best of most commonly used around the world for treating inflam our knowledge, CL method for the detection of loxoprofen matory diseases and musculoskeletal injuries for their anal has not been reported. gesic and antipyretic effects. Recently, NSAIDs have In this paper, a novel flow injection chemiluminescence gained more attention because they can reduce the risk of method for the determination of loxoprofen and naproxen developing Alzheimer's disease and various tumors [1-5]. is proposed based on the CL reaction of KMn04 and NSAIDs are a large family of compounds according to their NazSQ in acid media. The CL intensity of KMnO,-NazSQ chemical structures. Regardless of their structural differ was greatly enhanced in the presence of loxoprofen and ences, NSAIDs induce mostly of the same therapeutic func naproxen. The mechanism of the CL reaction was studied tions as well as side effects [6]. and the conditions were optimized. The proposed method Loxoprofen and naproxen are well-established NSAIDs was applied to the determination of loxoprofen and naproxen which belong to the arylpropionic acid family, the struc in pharmaceutical preparations. tures as described in Figure 1. The two arylpropionic acid derivatives have been used widely in clinic and other fields. 2 Materials and methods Up to now, many researchers interested in their possible side effects considerably. At the same time, these com 2.1 Reagents pounds are environmental pollutants due to their residue 3 levels in water [7, 8]. Therefore, it is very important to The stock solutions (1.0 x 10- glmL) of loxoprofen and develop highly sensitive analytical methods for the analysis naproxen (National Institute for the Control of Pharmaceu of loxoprofen and naproxen. Many methods have been tical and Biological Products, Beijing, China) were pre developed for the assay of loxoprofen and naproxen, inclu pared by dissolving 0.1000 g of each compound in double ding spectrometry [9, 10], HPLC [11-13]' HPLC- MS [14 distilled water and diluting to 100 mL. The stock solutions 16], CE [17,18], and GC- MS [19,20]. Some of methods, were stored in a refrigerator and kept from light. The tes however, have shown considerable shortcomings, such as ting solutions were prepared by appropriate dilution of these bulky instrumentation, large sample, and time consump stock solutions with water before use. tion. KMn04 stock solution (0.01 M) was prepared by dissol Chemiluminescence (CL) is a simple and rapid method ving 0.1580 g of KMn04(Xi'an Chemical Reagent Factory, Xi'an, China) in a 0.1 M sulfuric acid solution and diluting 3 Received 1 December 2010; Accepted 8 January 2011 to 100 mL with water. A NazSQ stock solution (5 x 10- • Corresponding author. E-mail: [email protected] M) was prepared by dissolving 0.0630 g of sodium sulfite 52 Li-]uan Wang, et at.
(Xi'an Chemical Reagent Factory, Xi'an, China) in water Ten capsules (tablets) of loxoprofen and naproxen were and diluting to 100 mL with water. The working solutions accurately weighed, and then ground to fine powder, were obtained by a series of dilutions of the stock solution respectively. A tablet sample equivalent to approximately with water. 250 mg naproxen and 60 mg loxoprofen was weighed accu All chemicals used were of analytical grade. Double dis rately, and then dissolved in water. Each solution was fil tilled water was used during the entire experiment procedure. tered and the corresponding residue was washed several Naproxen tablets (250 mg/tablet) were provided by times with water. All the solutions were collected. When Shaanxi LanHuaQiFoShan Pharmaceutical Co., Ltd. the level of loxoprofen and naproxen was obove the cali (Shaanxi, China). Loxoprofen sodium capsules (60 mg/cap bration ranges, samples were appropriately diluted with sule) were provided by Shandong Qidu Pharmaceutical Co., water prior to the assay. Ltd. (Shandong, China).
Figure 1 Structures of loxoprofen and naproxen 4-(6-methoxy-2-naphthy 1)-2-butanone (+)-2-(6-methoxy-2-naphthy I) propionic acid Lexoprofen Naproxen
tion was injected into the NazSOJ solution stream. The 2.2 Apparatus stream was merged with KMn04 solution in the flow cell to Figure 2 is the schematic diagram of the flow injection CL produce CL emission. The signal was recorded using a com (FI-CL) system. A peristaltic pump was used for delivering patible computer connected to the PMT. The concentration the sample solution and NazSOJ solution. Another peristal of sample was quantified by the increase of CL intensity, tic pump was applied to deliver KMn04 solution. All com calculated as tJ = 1 - 10 , where 1 is the net CL signal of ponents were connected with PTFE tubing (0.8 mm i. d.) the system in the presence of sample and [0 is the CL inten in the flow system. Reagent solutions were injected into the sity of the system in the absence of sample. flow system by a six-way injection valve. A photomultiplier tube was employed to detect the CL intensity. The CL sig 3 Results and discussion nal was recorded and treated using IFFM-E type data pro cessing system (Xi'an Remax Electronic Science-tech Co. , 3.1 CL intensity-time profile Ltd., China). The CL kinetic characteristics of the KMnOr Naz SOJ sample system were investigated. The results are shown in :~I---CIDf-----, Figure 3 and Figure 4. The results showed that a strong enhancement of the CL emission of the KMnOr Naz SOJ reaction was observed in the presence of naproxen and lox -----0 V ,1 r.::::::l oprofen respectively. Therefore, the addition of two kinds c u '~ICOMI of arylpropionic acid derivatives could facilitate the KMnOrNazSOJ CL reaction and greatly enhance light P, W emission. Figure 2 Schematic diagram of the Fl-CL system for the determina tion of naproxen and loxoprofen. a, sample solution; b, NazSo. solu 1600 - _. KMnO,-Na,SO, reaction tion; c, KMnO. solution; PI and P , peristaltic pump; V, six-way C 1400 ...... KMnO,-Na,SO,-naproxen reaction z - KMnO,-naproxen reaction valve; F, flow cell; PMT, photomultiplier tube; COM, computer; ~ 1200 \ W, waste solution. .::....J 1000 \ The UV spectrum was obtained using an UV-vis spectro U., 800 photometer (Shanghai Spectrum Instruments Co., Ltd., .::: 600 China) . ~ 400 \ ~ 200 \ ...... 2.3 Procedures o 1.onn._;r;;.._...... _...u:;;;...__A_..,J,;;"""'"....-_"'.=--=="'-'''''"'~ o 2 4 6 8 10 As shown in Figure 2, flow lines were inserted into the Time(s) sample/standard solution, loxoprofen or naproxen solution, NazSOJ solution and KMn04 solution, respectively. The Figure 3 Kinetic CL intensity-time profile of KMnO.-NazSQ,- pump was started to wash the whole flow system until a naproxen reaction. stable baseline was recorded. Then a sample/standard solu- J PharmAnal Vall, No 1, February 2011 53
3.2 Optimization of experimental conditions added to the KMnO, solution to test the effect on the CL signal. The maximum and most stable CL signal was 3.2.1 Effect of instrumental parameters obtained when sulfuric acid was added. Hence, H2S04 was The instrumental parameters, including the flow rate, the chosen for further work. And then, the effect of H2S04 concentration on the CL intensity was studied over the ratio of peristaltic pump1 to peristaltic pump2 (Vj /V2), and the length (~) from three ways "T" to the flow cell, range of O. 01 M to O. 2 M. The results showed that the were optimized. The length (~) of 6 cm and the flow rate maximum CL intensity was obtained with O. 1 M H2S04 of 1.6 mUmin could give a steady baseline and the maxi (Figure 6). So, 0.1 MH2S04 was selected as the suitable mum CL intensity, which were chosen for further study. medium for subsequent work.
900 - _. KMnO,·Na,SO, reaction 180 ~ 800 ...... KMnO.,-Na,SO,-loxoprofen reaction 2:' 160 -- KMnO,-loxoprofen reaction V> .~ 140 c 700 The effect of V j /V2 on the CL signal was investigated in the range of 0.5 to 2, and the results showed that the maxi In this CL system, potassium permanganate in sulfuric mum CL emission intensity was obtained when the ratio was acid which is used as the oxidant can offer both the maxi up to 1. 0 (as shown in Figure 5). Therefore, the ratio of mum CL signal and the best signal to the background ratio. 1. 0 was selected for subsequent procedures. Therefore, the effect of KMn04 concentration in 0.1 M sulfuric acid medium on the relative CL intensity was stud 180 ied in the range of 1. 0 x 10- 6 M to 1. 0 x 10-2M. The results 160 are shown in Figure 7. The results showed that 1. 0 x 10- 4 M could give rise to the larger CL response and lower back 2:' 140 V> ground signal. So, the optimum concentration of KMnO, c HAc, and H2S04 ) with different concentrations were 54 Li-Juan Wang, et at. 3.3 Analytical characteristics lished by triplicate injections of different concentration samples. The linear dynamic range, regression equation, 3.3.1 Linearity correlation coefficient, and limit of detection (WD) of Under the optimized conditions, the calibration curves for each compound are listed in Table 1. the determination of naproxen and loxoprofen were estab- Thble 1 The linear dynamic range, regression equation, correlation coefficient, and LOD of naproxen and loxoprofen Regression equation Correlation LOD NSAIDs Linear range (gimL) (unit of C is f-lglmL) coefficient (glmL) Naproxen 7.0 x 10 8 - 1.0 x 10 5 M = 168. 58C + 44.6 0.9979 2.0x 10 8 Loxoprofen 2.0XlO- 7 -4.0xlO-8 M = 58.6C+ 13.0 0.9958 3.0X 10- 8 180 3.4 Analytical application $160 The proposed method was applied to the determination of .~ 140 naproxen and loxoprofen in commercial pharmaceutical ~ 120 formulations. The samples were determined by standard d 100 addition method. As shown in Table 3, the obtained recov ~ 80 eries were in the range of 98.5% to 104.0%. As shown in ;;; 60 Table 4, the results showed that there were no significant ~ 40 differences between the nominal content values and those 20 OL...---'-_-'-_-'------'L...---'-_-'-_-'------''----'-_....L..---l obtained by the proposed method. o 2 3 4 5 6 7 8 9 10 II Thble 3 Recovery rate of externally added (l x 1O-6g1mL) naproxen Na,SO, concentration (I O-'M) and loxoprofen in pharmaceutical preparations Original Added Found Recovery Average of Figure 8 Effect of Nazso, concentration on the relative CL intensity. recovery 6 NSAlDs concentration concentration concentration rate LOX 1O- M naproxen + LOX lO-'M KMnO, in 0.1 M HzSO, medium. (x 1O- 6g1mL) (x 1O- 6g1mL) (x 1O- 6g1mL) (%) rate (%) 3.3.2 Precision 0 0.97 1.0 1.99 102.0 Naproxen 1.0 101.8 The precision of the proposed method was obtained by 2.0 3.03 103.0 analyzing samples containing 5.0 X 10- 7 glmL naproxen and 3.0 3.98 100.3 5.0 x 10 -7 gImL loxoprofen respectively. On three consecu 0 0.95 tive days, each sample was injected ten times. The results 1.0 1.99 104.0 Loxoprofen 1.0 100.6 are listed in Table 2. 2.0 2.92 98.5 3.0 3.93 99.3 Thble 2 The precision in the determination of naproxen and loxopro fen standard substance Thble 4 Analysis results of the two NSAIDs in pharmaceutical Concentration Concentration found RSD NSAIDs preparations (XlO- 7 glmL) (x 10- 7 glmL) (%) NSAIDs pharmaceutical Nominal content Proposed FI-CL 0.8 0.81 ± 0.02 2.05 preperation (gltablet) method (gltablet) Naproxen 5.0 5.07±0.12 2.39 Naprofen tablets 0.25 0.23 ± O. 015 50 52.25±2.37 4.55 Loxoprofen tablets 0.060 0.058 ± O. 0014 1.0 1.00±0.03 3.19 Note: Values are the averages of three measurements ± SD (amount of Loxoprofen 5.0 5.05±0.07 1.37 NSAIDs tablets [g!tablet]) . 10 10.10±0.14 1.43 3.5 Possible mechanism 3.3.3 Interference Grinberg first used the potassium permanganate as the In order to assess the analytical application possibility of the chemiluminescence reagent in analytical chemistry in 1920. CL method described above, the interference of different And then, there are some discussions about the mechanism metal ions and some excipients used in pharmaceutical prep of this kind of reaction and the corresponding emitting arations on the CL intensity was investigated by analyzing species in the literature. The emitting species of the potassi the solutions of 1.0 p.gI mL naproxen and 1.0 p.gImL loxo um permanganate CL reaction can be broadly grouped as profen, respectively. The tolerable limit of a foreign follows: manganese species, singlet oxygen, analyte oxida species was taken as a relative error less than 5%. The tion products, and compounds that receive energy from an results showed that no interference could be observed when excited intermediate of the reaction [26]. Excited sulphur 2 the sample included up to a 1000-fold Mt + , ea + , Na + , dioxide molecules are often considered as the CL emitters 3 2 NOJ -, 100-fold Al +, starch, glucose, lO-fold COJ -, when sodium sulfite reacts with potassium permanganate sucrose, and uric acid. [27]. Meixner and Jaeschke [28] proposed an alternative J P/w,,.,,, Anal Vol I, No 1, February 2011 55 mechanism, which can be explained as follows: good linearity, higher sensitivity, and good precision. The HSO, - + MnO. --'HSO, + MnO.' proposed method has been satisfactorily applied to the 2HSO,'-S,Q;'- +2W determination of loxoprofen and naproxen in pharmaceuti s,Q;'- -SO.'- +SO" • cal preparations. Moreover, the possible mechanism of this SO" •-SO" + hy CL system is proposed. It is supposed that sulfite acts as a reductant to produce 3.0 an excited molecule of sulfur dioxide, which emits radiation ------. KMn04-Na SOJ in the range of 450 - 600 nm [29]. The emission intensity 2.5 z could be sensitized with fluorescent compounds and non - KMn04-N3zS0J-loxoproxen .~ .. Na S0 -!oxoproxen fluorescence compounds [30,31]. 2.0 Z 3 jj ._ •..•_•._--- KMn0 -loxoproxen In this work, it was found that naproxen and loxoprofen c 4 ';;;; 1.5 could increase the CL intensity of potassium permanganate o and sulfite. In order to illustrate the possible mechanism of 'eo the CL reaction, UV-vis absorption spectra of different ~ 1.0 :jl systems were studied. As shown in Figure 9, the results showed that naproxen could react with KMnO. while it 0.5 \ could not react with Na,SO". Figure 10 shows that loxopro oLl:\(g:::::~:=~=--=-_---=-, fen could also react with KMnO. while it could not react 200 300 400 500 600 700 with Na,SO". So, we deduced that the two CL reaction Wavelength (run) mechanisms are the same because the two arylpropionic acid derivatives can react with KMnO.. 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