научная статья по теме FLUORESCENCE SENSOR FOR NITROFURAZONE BASED ON 4-METHYL-7-ALLYLOXYNAPHTHO[1,2-B]PYRAN-2-KETONE AS SENSING CARRIER Химия

ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2010, том 65, № 3, с. 266-271

ОРИГИНАЛЬНЫЕ СТАТЬИ =

УДК 543

FLUORESCENCE SENSOR FOR NITROFURAZONE BASED ON 4-METHYL-7-ALLYLOXYNAPHTHO[1,2-B]PYRAN-2-KETONE

AS SENSING CARRIER © 2010 Lixin Chena, Chenggang Niub, Zhimin Xiea, Nianyuan Tana

aDepartment of Chemistry and Chemical Engineering, Hunan institute of engineering 411104, P. R. China, Xiangtan bDepartment of Environmental Science and Engineering, Hunan University 410082, P. R. China, Changsha Received 12.05.2009; in final form 25.06.2009

4-methyl-7-allyloxynaphtho[1,2-b]pyran-2-ketone (MANPK), a naphthopyran derivative, was synthesized as a fluorescent carrier for the preparation of an optical chemical sensor for nitrofurazone. To prevent the leakage of the fluorophore, MANPK with a terminal double bond was photo-copolymerized with 2-hydroxypropyl methacrylate on the silanized glass surface. The response of the sensor is based on fluorescence quenching of MANPK by nitro-furazone. The sensor shows sufficient reproducibility, selectivity and a long lifetime. Nitrofurazone can be determined in the range from 6.0 x 10-6 to 8.0 x 10-4 M with a detection limit of 4.5 x 10-6 M at pH 6.0. The sensor has been applied to the direct determination of nitrofurazone in pharmaceutical preparations and urine samples.

In recent years, owing to outstanding features such as high sensitivity and reasonable selectivity, the development of fluorescence chemical sensors is a subject of growing interest. A variety of fluorescence reagents including fluorescein and its derivatives [1—3], aromatic compounds [4—8], porphyrins and their metal complexes [9—11] were synthesized and employed as sensing materials in the fluorescence sensor preparation. The search for a new type of sensing reagent for fluorescence sensor design is of considerable interest.

Naphthopyran derivatives are a category of fluorescence reagents. They have been the subject of a number of investigations due to their photochromic properties and biological activities [12—14]. Also, the fluorescence properties of naphthopyran have been extensively studied [15]. Owing to their high quantum yield and stability, it is possible for naphthopyran derivatives to be used as sensing materials. In a search of useful naph-thopyran derivatives as fluorescent carriers for chemical sensors, starting from 1,5-naphthalenediol, we synthesized 4-methyl-7-hydroxynaphtho[ 1,2-b]pyr-an-2-ketone(MHNPK). The presence of a hydroxy group in the molecule of MHNPK makes it suitable for covalent immobilization. Among various ways of immobilization of fluorescent carriers, covalent binding seems to be the most efficient method which can effectively prevent the leakage of the fluorescent dye from the sensor membrane, a phenomenon that shortens the long-term stability of many chemical sensors [16—18]. In order to introduce into the molecule a terminal double bond capable of covalent immobilization, MHNPK was reacted with allyl bromide to form 4-methyl-7-ally-loxynaphtho [1,2-b] pyran-2-ketone (MANPK). Under UV radiation, MANPK was photo-copolymerized with

2-hydroxyethyl methacrylate, acrylamide and 1,2-cyclo-hexanediol diacrylate on the glass surface treated with a silanizing agent. It has been shown experimentally that the sensing membrane prepared in such a way shows strong fluorescence, which can be quenched by nitro-fUrazone. The quenching effect can be utilized for fluoro-metric determination of nitrofurazone.

Nitrofurazone is a broad-spectrum antibiotic commonly used in human and veterinary medicine. Its potential harmful effects on animal growth and human health have been described in a number of papers [19]. Methods reported for the determination of nitrofurazone include high-performance liquid chromatography [19, 20], paper chromatography [21] and ultraviolet spectroscopy [22]. Fluorescence sensor is an alternative method for nitro-furazone assay, though few attempts have been directed toward this end [23].

In this paper, a new fluorescence sensor based on MANPK through covalent immobilization is described for the determination of nitrofurazone. The performance characteristics of the sensor with long-term stability, good selectivity and fast response for nitrofurazone were evaluated.

EXPERIMENTAL

Materials and apparatus. Nitrofurazone was purchased from Suzhou Chemicals (Jiangsu, China) and

3-(trimethoxysilyl)propyl methacrylate (TSPM) was from ACROS (Sweden). Allyl bromide was synthesized according to a method described elsewhere [24]. 2-Hy-droxyethyl methacrylate, acrylamide and 1,2-cyclohex-anediol diacrylate were ofanalytical reagent grade used in the membrane matrix preparation without further purifi-

O

OCH2CH=CH2

Fig. 1. Synthesis scheme of 4-methyl-7-allyloxynaphtho [1,2-b] pyran-2-ketone.

cation. The prepared stock solution of 2.0 x 10-2 M ni-trofurazone was stored in a refrigerator to protect from exposure to light. The working solutions were obtained by series dilutions with Britton—Robinson (B—R) buffer solution. B—R buffer solutions of different pH were prepared by mixing appropriate amounts of phosphoric acid, acetic acid, and boric acid and adjusting to the desired pH with 0.2 M sodium hydroxide. Other reagents and solvents were of analytical regent grade. Doubly distilled water was used throughout.

All fluorescence measurements were conducted on a Hitachi F-4500 spectrofluorimeter (Japan). The solution pH was measured using a PHS-3C pH meter (Shanghai analytical instruments, China).

The fluorescent carrier synthesize. The general scheme of the synthesis is shown in Fig. 1.

MHNPK was prepared by the method reported by Adam et al. [25]. To a mixture of 4.00 g of1.5-naphtha-lenediol (25.0 mmol) and 3.60 g of ethyl acetoacetate (28.4 mmol) was added 10 mL of concentrated H2SO4 (98%) within 30 min at 0°C. The reaction mixture were stirred for 3 h and after the addition of ice/water (100 mL) extracted with ether (3 x 200 mL), washed with water (3 x 20 mL), and dried, and the solvent was removed to give 2.30 g ofproduct as yellow needles, with a nominal yield of 81.8%; Mp 148°C; MS: base peak 166, M+: 116.

MANPK was prepared according to reference [26]. 1.0 g of MHNPK obtained and anhydrous potassium carbonate (2.8 g) were mixed with 2 mL of allyl bromide and refluxed for 2.5 h at 90°C in 60 mL of butanone. After removing solvent, the mixture was poured into 50 mL of water and filtered. The residue was dissolved in 60 mL of ammonia, filtered, dried over anhydrous bitter salt to give 1.15 g of yellow product, MANPK, with a nominal

yield of 84.3%. Mp 130-131°C, Ms: base peak 44, M+ 226.

Silanization of the glass surface. The glass surface was modified by silanization as described in the litera-ture[16, 17, 27] with some modifications. Conventional glass plates (diameter 13 mm) were immersed successively in 3% HF and 10% H2O2 for 30 min each and then washed with doubly distilled water. A solution of TSPM was prepared by mixing 0.2 mL of TSPM, 2 ml of 0.2 M HOAc-NaOAc buffer solution of pH 3.6 and 8 mL ofdoubly distilled water. After sufficient mixing, the glass plates were soaked in this mixture for 2 h, then washed with doubly distilled water and dried at room temperature.

1.02 г

1.00 -

0 2 4 6 8 10 12 14 pH

Fig. 2. Effect of pH on F0/F for nitrofurazone concentration of 2.0 x 10-4 M.

268

LIXIN CHEN и др.

300 г

250 -

Рн

50 -

ol-1-1-1

400 450 500

Wavelenth, nm

Fig. 3. Fluorescence excitation (left) and emission spectra (right) of the sensor on exposure to (from top to bottom): blank solution, 1.25 x 10-4 M, 2.5 x 10-4 M, 4.0 x 10-4 M, 6.0 x 10-4 M, 8.0 x 10-4 M, 1.0 x 10-3 M nitrofurazone solutions.

Preparation of the sensing membrane. The sensing membrane was prepared according to the following procedure. Acrylamide (200 mg) was dissolved in 0.20 ml of N,N-dimethylformamide (DMF), with subsequent addition of 2-hydroxyethyl methacrylate (0.25 mL), 1,2-cyclohexanediol diacrylate (0.10 mL), MANPK (10 mg), benzoin ethyl ether (10 mg), and diphenyl diketone (15 mg). Drops of the solution were taken onto a cleaned poly(tetrafluorethylene) plate, then silanized glass plates were placed over the droplets. After the UV irradiation (254 nm, 30 W, 10 cm over the glass plates) for about 2 h, the glass plates with the membrane were washed with water and methanol to remove any unre-acted species, then dried and stored for use.

Fluorescence measurements. The fluorescence measurements were conducted on a Hitachi F-4500 spec-trofluorimeter controlled by a personal computer data processing unit with both excitation and emission slits set at 10 nm. The fluorescence of the membrane was measured at the wavelength of maximum emission of 454 nm and a wavelength of maximum excitation of 402 nm. A homemade poly(tetrafluoroethylene) flow-cell and a bifurcated fiber were used for the nitrofurazone sensing measurements [28]. The excitation light was carried to the cell through one arm of the bifurcated optical fiber and the emission light collected through the other. A glass plate (diameter 13 mm) covered with sensing membrane was fixed on the top of the flow chamber by the mounting screw nut with the membrane in contact with the sample solution. The sample solution was driven through the flow cell by a peristaltic pump (GuoKang Instruments, Zhejiang, China) at a

log [nitrofurazone]

Fig. 4. Relative fluorescence values (a) as a function of log [nitrofurazone].

1 - m : n = 2 : 1, k = 3.8 x 106; 2- m : n = 1 : 1, k = 2000 ; 3 - m : n = 1 : 2, k = 2.2 x 105; 4- m : n = 1 : 3, k = 3.2 x 107.

flow rate of 2.0 mL/min. The sensor membrane was equilibrated with the sample solution for obtaining a stable fluorescence signal. After each measurement, the fluorescence intensity of the sensing membrane was recovered by pumping the blank solution through the cell prior to the next measurement.

RESULTS AND DISCUSSION

Effect of acidity. The fluorescence intensity of the sensing membrane was found to be

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