Applied Chemistry,

Vol. 15, No. 1, May 2011, 29-32

29

Salicylic Acid 정량을 위한 Europium-Salicylic Acid 복합체의 계면활성제

증감 형광법에 관한 연구

MD R-Mahmnur Alam⋅Mohammad Kamruzzaman⋅김소연⋅조해진⋅이상학†⋅김영호*,†⋅서정기**

경북대학교 화학과, *경북대학교 차세대에너지기술연구소, **한국표준과학연구원 삶의질측정표준본부

Study of Surfactant Sensitized Fluorescence of Europium-Salicylic

Acid Complex for the Determination of Salicylic Acid

MD R-Mahmnur Alam⋅Mohammad Kamruzzaman⋅So Yeon Kim⋅Hae Jin Jo⋅Sang Hak Lee†⋅

Young Ho Kim*,†⋅Jung Kee Suh**

Department of Chemistry, Kyungpook National University, Daegu 702-701, Korea,

*Research Institute of Advanced Energy Technology, Kyungpook National University, Daegu 702-701, Korea,

**Health Metrology Group, Korea Research Institute of Standards and Science, Daejeon 305-600, Korea

Abstract

Surfactant enhanced fluorescence (FL) of europium-salicylic acid (SA) complex has been

studied. It was observed that weak FL of Eu(III) at the wavelength of 589 nm and 612 nm

was found to be enhanced after addition of salicylic acid and cetyltrimethylammonium

bromide (CTAB) surfactant upon excitation at 395 nm. Under optimized condition, FL

intensity of Eu(III) at 612 nm responded linearly with the concentration of SA in the range

of 5.5×10-9

to 1.5×10-6

M of SA. The detection limit was calculated from the calibration

curve(3Sb/m) as 9.27×10-9

M.

Keywords: Fluorescence, Europium, Salicylic Acid, Cetyltrimethylammonium Bromide

1. Introduction

The salicylic acid (SA) and its salts-salicylates are naturally available in many plants such

as willow bark and oil of wintergreen[1]. It is the main metabolite of acetylsalicylic acid

(ASA) which is the most widely used drug as a painkiller and anti-inflammatory[2]. ASA is

hydrolyzed to salicylate in the stomach and as soon as it enters in blood circulation[3].

Spectrofluorometric method is widely used in different fields of the chemical analysis owing

to its high sensitivity and selectivity and simple instrumentation. Several fluorimetric

methods have been reported for the determination of SA[4-6]. It is reported that lanthanide

ions have an important role as a fluorescence (FL) probe in bioanalytical applications

because of their high sensitivity and selectivity[7]. Lanthanide sensitized FL provide large

Stokes shift, narrow emission bands, and long FL lifetimes[8]. In this study, cetyltrimethy-

lammonium bromide (CTAB) enhanced fluorescence of Eu(III) - SA complex has been

proposed for the determination. The influence of the solutions on the FL intensity was

investigated.

30 MD R-Mahmnur Alam⋅Mohammad Kamruzzaman⋅김소연⋅조해진⋅이상학⋅김영호⋅서정기

2. Experimental

2.1. Reagents and Standard Solutions

Deionized water (DI) was used throughout the experiments. SA (Sigma-Aldrich) stock

solution of 1×10-3

M and Eu(III)(Sigma-Aldrich) solution of 1×10-2

M was prepared by

dissolving the appropriate amount in DI water. A stock solution of 1×10-2

M CTAB was

prepared by dissolving the required amount in warm DI water. Tris-HCl buffer was prepared

by dissolving appropriate amount of tris(hydroxymethyl)aminomethane in DI water and pH

was adjusted using 0.1 M HCl. Other reagents used for this study were of analytical grade

purity from a standard supplier.

2.2. Apparatus and Procedure

FL measurements were conducted with a spectrofluorimeter (F-4500, Hitachi, Japan)

equipped with a 150 W xenon lamp and photomultiplier tube (Model R 928, Hamamatsu,

Japan). A pH meter (Orion, 520A, USA) was used for pH adjustment. The following

procedure was adopted for FL measurements in this study. A certain volume of Eu(III)

solution, 1.0 ml of buffer (pH, 8.5), appropriate volume of CTAB solution and finally SA

were added to a 10 mL volumetric flask. Next, the FL spectra of the system were measured

in a 1 cm quartz cell with the excitation and emission wavelengths of 395 nm and 612 nm

respectively.

3. Results and Discussion

3.1. Characteristics of FL Spectra

Excitation and emission spectra of Eu(III), Eu(III)-CTAB and Eu(III)-CTAB-SA were

recorded. The results indicated that FL of Eu(III) has very weak intensity to be observed

(Fig. 1a). After incorporation of CTAB in Eu(III) solution in presence of buffer solution,

characteristic FL intensity of Eu(III) is found to be enhanced at the wavelength of 595 nm

and 612 nm (Fig. 1b), corresponding to 5D0-

7F1 and

5D0-

7F2 transition of Eu(III). It was

interesting to observe that addition of SA solution into the mixture of Eu(III)-CTAB caused

the enhancement of FL intensity of the system several times (Fig. 1c). This speculation was

the basis of the proposed method for the determination of SA in trace amount.

3.2. Influence of pH

The FL intensity was examined over the pH range from 7 to 10 to observe the influence

of pH. The intensity is significantly enhanced by increasing the pH of the tris buffer solution

from 8 to 9. Fluorescence intensity was maximized at pH 8.5. Thus pH 8.5 was chosen for

this study.

3.3. Influence of Concentration Eu(III) Solution

The influence of the concentration in the range of 9.0×10-3

to 5.5×10-4

M of Eu(III) was

31Salicylic Acid 정량을 위한 Europium-Salicylic Acid 복합체의 계면활성제 증감 형광법에 관한 연구

investigated as shown in Fig. 2. Results showed that FL intensity reaches maximum when 5

×10-3

M Eu(III) solution has been used. Therefore, 5×10-3

M Eu(III) was used in following

experiments as optimum concentration.

Fig. 1. Emission Spectra (a) Eu(III), (b) Eu

(III)-CTAB and (c) Eu(III)-CTAB-SA.

Conditions: [Eu(III)], 5×10-3

M; [CTAB],

3.5×10-6

M; [SA] 3.5×10-6

M; pH 8.5.

Fig. 2. Influence of Concentration of Eu(III).

Conditions: [CTAB], 3.5×10-6

M; [SA],

3.5×10-6

, M ; pH 8.5.

3.4. Influence of Concentration of Surfactant

Several kinds of surfactant such as SDS, CTAB, SDBS, and Triton-X 100 were examined

on the FL intensity of the system. The best result was achieved using CTAB. Next, the

system intensity was verified by changing the concentration of CTAB from 9.0×10-5

M to

1.0×10-8

M. The strongest intensity was obtained from 3.5×10-4

M of CTAB. Thus this

concentration was considered as optimum value for this study.

Fig. 3. Calibration curve for the determination of SA. Conditions: [Eu(III)], 5×10-3 M; [CTAB],

3.5×10-6

M; [SA], 5.5×10-9

to 1.5×10-6

M; pH 8.5.

3.5. Calibration Curve and Detection Limit

Under aforementioned optimal condition FL intensity against the concentration of SA was

linear (Fig. 3) in the range of 5.5×10-9

to 1.5×10-6

M with regression equation of

32 MD R-Mahmnur Alam⋅Mohammad Kamruzzaman⋅김소연⋅조해진⋅이상학⋅김영호⋅서정기

Y=223+2.75×108CSA (R=0.9997) where CSA is the concentration of SA in M and Y is the FL

intensity. The limit of detection as defined by IUPAC, CLOD=3 Sb/m (where Sb is the

standard deviation of the blank signals and m is the slope of the calibration curve) was

calculated to be 9.27×10-9

M. The relative standard deviation (RSD) was 1.27%.

4. Conclusion

The determination of SA by surfactant enhanced fluorescence of Eu(III) has been

proposed. In presence of buffer solution, Eu(III), CTAB and SA produce fluorescence

complex. The obtained limit of detection was at nano molar level.

Acknowledgement

This Research was supported by Kyungpook National University Research Fund, 2009.

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