Micelle-enhanced and terbium-sensitized spectrofluorimetric determination of gatifloxacin and its interaction mechanism

Article abstract of DOI:10.1016/j.saa.2008.10.063

A terbium-sensitized spectrofluorimetric method using an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS), was developed for the determination of gatifloxacin (GFLX). A coordination complex system of GFLX-Tb³⁺-SDBS was studied. It wa

Full text of DOI:10.1016/j.saa.2008.10.063

Spectrochimica Acta Part A 72 (2009) 766–771
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Micelle-enhanced and terbium-sensitized spectrofluorimetric determination of
gatifloxacin and its interaction mechanism
a
a,∗
a
b,∗∗
, Lihong Sanga
Changchuan Guo , Lei Wang , Zhun Hou , Wei Jiang
a
School of Pharmacy, Shandong University, 44# West Wenhua Road, 250012 Jinan, PR China
School of Chemistry and Chemical Engineering, Shandong University, 250100 Jinan, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 June 2008
Accepted 29 October 2008
A terbium-sensitized spectrofluorimetric method using an anionic surfactant, sodium dodecyl benzene
sulfonate (SDBS), was developed for the determination of gatifloxacin (GFLX). A coordination complex
system of GFLX–Tb –SDBS was studied. It was found that SDBS significantly enhanced the fluorescence
3+
intensity of the complex (about 11-fold). Optimal experimental conditions were determined as follows:
Keywords:
Gatifloxacin
Terbium
Determination
Fluorescence
Luminescence
−4
−1
excitation and emission wavelengths of 331 and 547 nm, pH 7.0, 2.0 × 10 mol l terbium (III), and
−4
−1
2
.0 × 10 mol l SDBS. The enhanced fluorescence intensity of the system (ꢀIf) showed a good linear
10
−
−8
−1
relationship with the concentration of GFLX over the range of 5.0 × 10
to 5.0 × 10 mol l with a cor-
11
−
−1
relation coefficient of 0.9996. The detection limit (3ꢁ) was determined as 6.0 × 10
mol l . This method
has been successfully applied to the determination of GFLX in pharmaceuticals and human urine/serum
samples. Compared with most of other methods reported, the rapid and simple procedure proposed in
the text offers higher sensitivity, wider linear range, and better stability. The interaction mechanism of the
system is also studied by the research of ultraviolet absorption spectra, surface tension, solution polarity
and fluorescence polarization.
©
2008 Elsevier B.V. All rights reserved.
1
. Introduction
used to estimate GFLX in pharmaceutical formulations and biolog-
ical fluids [18–20]. Quinolones have suitable functional groups to
form stable complexes with Tb3+ and Eu . The presence of these
ions in quinolone solutions leads to the formation of complexes that
3+
Gatifloxacin[(± )-1-cyclopropyl-6-fluoro-1,4-dihydro-8-meth-
oxy-7-(3-methyl-1-piperazinyl)-4-oxo-3-quinoline carboxylic
acid, GFLX] (Fig. 1) is the fourth generation of a new class of syn-
thetic antibacterial fluoroquinolone agents. It is a novel extended-
spectrum fluoroquinolone with an improved Gram-positive
and anaerobe coverage compared with older agents such as
ciprofloxacin. GFLX acts intravenously by inhibiting topoisomerase
II (DNA gyrase) or topoisomerase IV. It does not appear to exert
phototoxic effects [1]. This fluoroquinolone is mainly excreted in
urine (>75%) in unaltered form, and no pharmacokinetic differ-
ences have been observed between oral and i.v. administration
absorb energy at the characteristic wavelength of the organic ligand
and emit radiation of the characteristic wavelength of Tb3+ or Eu
3+
.
These complexes show a large Stokes shift and narrow emission
bands. This technique has been widely utilized for the determi-
nation of quinolones norfloxacin [21], enoxacin [22], garenoxacin
[23], trovafloxacin [24], ciprofloxacin [25], etc. But the sensitiv-
ity is not very high as all the detection limits of these methods
−
9
−8
−1
are over the range of 1.2 × 10 to 4.7 × 10 mol l . However, the
micelle-enhanced and terbium-sensitized spectrofluorimetry that
the present paper describes could provide a much higher sensi-
[
2].
Various analytical techniques have been employed for the deter-
mination of GFLX such as high-performance liquid chromatography
HPLC) [3–9], spectrophotometry [10–12], high performance thin-
−
−1
11
−1
tivity. The detection limit (3ꢁ) could attain 6.0 × 10
mol l and
−
10
−8
the linear range is 5.0 × 10
to 5.0 × 10 mol l , which is at a
(
low concentration level. Furthermore, most of these references had
not discussed the luminescence mechanism except that [21] and
[22] merely studied it by the fluorescence spectra and ultraviolet
absorption spectra. But in the present paper the interaction mech-
anism of the fluorescence system is studied through the research
of surface tension, solution polarity and fluorescence polariza-
tion. Compared with most of other published procedures for the
determination of GFLX, the proposed method offers advantages in
higher sensitivity, wider linear range, and better stability. It has
been successfully applied to the determination of gatifloxacin in
layer chromatography (HPTLC) [13,14], microbiological assay [15],
voltammetry [16], and atomic absorption spectrometry [17]. Due to
its high sensitivity and selectivity, the spectrofluorimetry has been
∗
Corresponding author. Tel.: +86 531 8838 2330; fax: +86 531 8856 5167.
Corresponding author. Tel.: +86 531 8836 3888.
E-mail addresses: wangl-sdu@sdu.edu.cn (L. Wang), wjiang@sdu.edu.cn
∗
∗
(
W. Jiang).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.10.063

C. Guo et al. / Spectrochimica Acta Part A 72 (2009) 766–771
767
All reagents used were analytical grade unless otherwise indi-
cated. Redistilled water made in-house was used throughout the
study.
2.3. Methods
To a 10 ml volumetric flask, various solutions were added accord-
−
3
−1
3+
ing to the following order: 1.0 ml of 2.0 × 10 mol l Tb solution,
−
1
an aliquot of GFLX working standard solution, 1.0 ml of 0.1 mol l
−
3
−1
Tris–HCl buffer solution, and 1.0 ml of 2.0 × 10 mol l SDBS. The
resultant mixture was diluted to the volume with water and mixed
thoroughly by shaking, and then allowed to stand for 15 min at room
temperature. Final gatifloxacin concentrations were in the range
−
10
−8
−1
of 5.0 × 10
to 5.0 × 10 mol l . The fluorescence intensity was
measured in a 10 mm path-length quartz cell with excitation and
emission wavelengths of 331 and 547 nm, respectively.
Fig. 1. Chemical structure of gatifloxacin.
2
.4. Serum and urine sample preparation
pharmaceutical samples and human urine/serum samples, and the
interaction mechanism of the system is also discussed. To the best
of our knowledge, this is the first time that the terbium-sensitized
spectrofluorimetric determination of GFLX has been reported.
Each 1.0 ml of serum sample was deproteinized with 2.0 ml of
acetonitrile, followed by vortexing for 5 min and centrifuging for
5
urine samples. Further dilutions with water were made to ensure
that the concentrations of the drug in the sample solutions fall
within the linear range of the method.
min at 1500 × g [23]. No sample pretreatment was required for
2. Experimental
2.1. Apparatus
3. Results and discussion
Normal fluorescence measurements were recorded with a
Hitachi F-2500 Fluorescence Spectrophotometer (Japan), using a
standard 10 mm pathlength quartz cell with 10 nm bandwidths for
both the excitation and emission monochromators.
The fluorescence polarization spectra were obtained using an
ISS K2 multifrequency phase and modulation spectrofluorometer
3
.1. Spectral characteristics
ꢀ
3+
The excitation and emission spectra of GFLX (1, 1 ), Tb (2,
ꢀ
ꢀ
3+
ꢀ
3+
ꢀ
3+
2
4
), GFLX–Tb (3, 3 ), Tb –SDBS (4, 4 ), and GFLX–Tb –SDBS (4,
) system are shown in Fig. 2. The excitation spectrum of the
(
USA).
All absorption spectra were measured on a UV-2401PC spec-
3+
GFLX–Tb –SDBS system exhibited an excitation peak at 331 nm,
which was selected as the excitation wavelength. The emission
spectra obtained showed that neither GFLX aqueous solution (curve
trophotometer (Shimadzu, Japan) equipped with 10 mm pathlength
quartz cells.
ꢀ
3+
ꢀ
1
) nor Tb aqueous solution (curve 2 ) gave a strong fluorescence
The surface tension was measured on a Processor Tensiometer-
K12 (KRÜSS Corp., Germany) with the precise degree of the
3
+
peak at 547 nm. The characteristic fluorescence of Tb cannot be
observed. Curve 3 was the emission spectrum of GFLX–Tb sys-
tem. It can be seen that the native fluorescence of GFLX at 445 nm
ꢀ
3+
−1
measurement 0.01 mN m by the Wilhelmy plate.
The pH was measured using a Lei Ci pHs-3C pH-meter (Shanghai,
China).
decreased significantly in comparison with GFLX aqueous solution
ꢀ
(curve 1 ), while an emission peak was observed at 547 nm, which
Serum samples were centrifuged with a Xiang Yi TDZ4A-WS
brachytely desk centrifuge (Changsha, China).
3+
indicated that Tb could interact with GFLX and resulted in the
2.2. Reagents
A stock standard solution (1.0 × 10−3 mol l ) of GFLX (96.0%,
−1
National Institute for the Control of Pharmaceutical and Biologi-
cal Products) was prepared by dissolving 0.0391 g of GFLX in and
◦
diluting to 100 ml with water. The solution was kept at 4 C in the
refrigerator and protected from light. Working standard solutions
were obtained by making appropriate dilutions of the stock stan-
dard solution with water.
Stock standard solution of Tb3+ (2.0 × 10 mol l ) was pre-
−2
−1
pared by dissolving 0.3739 g Tb O7 (purity, 99.99%) in 1:1 HCl and
4
evaporating the solution to almost dryness before diluting to 100 ml
with water. The stock standard solution was kept in the refrigerator
◦
at 4 C. The working standard solutions were prepared by making
appropriate dilutions with water.
−3
−1
An SDBS solution (2.0 × 10 mol l ) was prepared by dissolv-
ing 0.0774 g SDBS (90.0%) in and then diluting to 100 ml with
water.
ꢀ
ꢀ
Tb3+
ꢀ
3
Fig. 2. Excitation spectra and emission spectra. 1,
1
GFLX; 2,
2
;
3,
A Tris–HCl buffer solution (pH 7.0, 0.1 mol l−1) was prepared
by dissolving 3.0437 g Tris(trihydroxymethyl aminomethane) in
GFLX–Tb ; 4, 4 Tb –SDBS; 5, 5 GFLX–Tb3+–SDBS. Experimental conditions:
3
+
ꢀ
3+
ꢀ
GFLX, 1.0 × 10 mol l ; Tb , 2.0 × 10−4 mol l−1; SDBS, 2.0 × 10 mol l ; Tris–HCl,
−6
−1
3+
−4
−1
−
1
2
50 ml water and then adjusting pH to 7.0 with 1:1 HCl.
0.01 mol l , pH 7.0.

768
C. Guo et al. / Spectrochimica Acta Part A 72 (2009) 766–771
Fig. 3. Ultraviolet absorption spectra. Experimental conditions: GFLX, 1.0 ×
−
5
−1
Tb3+, 4.0 × 10 mol l
−4
−1
−4
−1
Fig. 4. Effect of pH. Experimental conditions: GFLX, 5.0 × 10−6 mol l
−1
;
Tb3+
,
10
mol l
;
;
SDBS, 2.0 × 10 mol l
;
Tris–HCl,
−1
3+
3+
3+
−4
−1
−4
−1
.
0
.01 mol l , pH 7.0. (1) GFLX; (2) Tb ; (3) GFLX–Tb ; and (4) GFLX–Tb –SDBS.
2.0 × 10 mol l ; SDBS, 2.0 × 10 mol l
3+
energy transfer from the GFLX to Tb . Weak characteristic flu-
3
+
3+
orescence of Tb was observed in the Tb –SDBS system (curve
ꢀ
3+
4
), indicating that SDBS could also interact with Tb and emit
the characteristic fluorescence of Tb as a result of energy trans-
fer from SDBS to Tb . Curve 5 was an emission spectrum of the
GFLX–Tb –SDBS system with an excitation wavelength of 331 nm.
Strong emission peaks were observed at 491, 547, and 588 nm,
3+
3
+
ꢀ
3
+
3+
5
7
5
7
which corresponded to the Tb transitions of D – F , D – F5 and
D – F , respectively, while the native fluorescence peak of GFLX
4
6
4
5
7
4
4
at 445 nm was absent. Among these emission peaks the 547 nm one
displayed the strongest signal. Accordingly, 331 and 547 nm were
selected as the excitation wavelength and the emission wavelength,
respectively, for further study.
In order to study the interaction of GFLX, Tb3+, and SDBS, sev-
eral ultraviolet absorption spectra were recorded and are shown
in Fig. 3. It could be seen in Fig. 3 that there were two absorption
peaks of GFLX at 285 nm and 331 nm. With the addition of Tb3
+
,
the 285 nm absorption peak of the GFLX shifted to 290 nm while
the fluorescence intensity increased. When both Tb3 and SDBS
solution was added, the absorbance of GFLX increased significantly,
corresponding to a fluorescence enhancement of the fluorescence
excitation spectrum of the GFLX–Tb3 –SDBS system (see Fig. 2).
A red shift of the maximum absorption wavelength from 290 to
+
Fig. 5. Effect of Tb3+ concentration. Experimental conditions: GFLX, 5.0 ×
−
6
−1
−4
−1
−1
10
mol l ; SDBS, 2.0 × 10 mol l ; Tris–HCl, 0.01 mol l , pH 7.0.
+
tion of 1.5 × 10 mol L−1. Therefore, the Tb3+ concentration of
−4
−4
−1
2
.0 × 10 mol L was selected for further experiments.
2
[
94 nm indicated that a GFLX–Tb3+–SDBS complex was formed
26].
3.4. Effect of surfactants
3
.2. Effect of pH and buffers
The fluorimetric properties of GFLX were studied in a series of
−
6
−1
micellar media by preparing 5.0 × 10 mol L GFLX in the pres-
ence of various concentrations of the surfactants CTAB (cationic),
SDS (anionic), SDBS (anionic), GA (non-ionic), OP (non-ionic), and
-CD (non-ionic). The results are summarized in Table 1. It can be
seen that no significant fluorescence enhancement was observed in
The effect of pH values on the fluorescence emission of a
−
6
−1
5
.0 × 10 mol l GFLX solution is shown in Fig. 4. The data indi-
cated that the signal exhibited a maximum around pH 7.0, which
was chosen for further experiments. The effect of the follow-
ing buffer solution media on the fluorescence intensity was then
examined: NH Ac–HAc, NaAc–HAc, NH Cl–NH ·H O, Tris–HCl, and
␤
4
4
3
2
−
1
1
Table 1
KH PO –NaOH. It was found that 0.01 mol l Tris–HCl offered the
2
4
Effect of different surfactants.
−
highest sensitivity. Therefore, a 0.01 mol l Tris–HCl buffer solu-
tion of pH 7.0 was selected for the study.
Surfactants and the optimal concentration
Fluorescence
intensity
None
10.5
10.2
28.5
25.1
10.8
79.2
111.4
3
.3. Effect of terbium concentration
−
5
−1
Cetrimonium bromide (CTAB), 3.0 × 10 mol l
−
3
−1
Arabic gum (GA), 1.5 × 10 g ml
−
6
−1
With a fixed GFLX concentration of 5.0 × 10 mol l , the
Polyoxyethylene nonylphenol ether (OP), 2.5% (v/v)
3
+
−4
−1
effect of Tb
concentration on the fluorescence intensity of
␤-Cyclodextrin (␤-CD), 5.0 × 10 mol l
−
4
−1
Sodium dodecyl sulfate (SDS), 5.0 × 10 mol l
the system was studied. The results are shown in Fig. 5.
Fluorescence intensity reached a plateau with a Tb concentra-
−
4
−1
3
+
Sodium dodecylbenzene sulfonate (SDBS), 2.0 × 10 mol l

C. Guo et al. / Spectrochimica Acta Part A 72 (2009) 766–771
769
Table 2
Maximum permissible concentrations of interference species.
Interference species
Maximum permissible
Change of ꢀI (%)
−1
concentration (mol l
)
Cu2+, SO42−
Vitamin C
Fe , Cl
l-Methionine
4.0 × 10
−7
5.0
4.5
4.6
−4.5
−4.4
3.8
−4.2
−4.7
−4.3
−4.2
−5.0
−4.9
−4.5
−4.8
−4.7
−4.3
−
7
7.0 × 10
1.5 × 10
7.0 × 10
2.0 × 10
6.0 × 10
1.0 × 10
1.0 × 10
1.0 × 10
1.5 × 10
2.0 × 10
4.0 × 10
5.0 × 10
7.0 × 10
1.0 × 10
1.0 × 10
3
+
−
−6
−
6
2
+
2−
−5
−5
−4
−4
Zn , SO4
3
+
−
Al , Cl
2
+
−
Mg , Cl
Ca2+, Cl
−
−
4
l-Histidine
+
−
−4
Na , Cl
l-Glutamine
−
4
+
−
−4
K , Cl
−
−
4
l-Cysteine
4
Glycine
NH4 , Cl
+
−
−3
−
2
Glucose
Fig. 6. Effect of SDBS concentration. Experimental conditions: GFLX, 5.0 ×
−
6
−1
3+
−4
−1
−1
10
mol l ; Tb , 2.0 × 10 mol l ; Tris–HCl, 0.01 mol l , pH 7.0.
fore, was chosen for further research. The experiments also showed
that the fluorescence intensity of the system reached its maximum
in 15 min after all the reagents had been added and remained stable
for at least 3 h.
the presence of either cationic or non-ionic surfactants. However,
a significant increase in fluorescence was observed in the pres-
ence of anionic surfactants SDS and SDBS with the latter appeared
to be more effective. The effect of the SDBS concentration on the
fluorescence intensity was also determined (Fig. 6). Maximum flu-
orescence intensity was observed for an SDBS concentration of
3.6. Effect of interfering species
In order to assess the applicability of the proposed method in
biological samples, the effects of the potentially interfering species
such as metal ions, sugars, and amino acids were examined. The
results are summarized in Table 2. A 5% variation in intensity as a
result of interference is considered acceptable. The results indicated
that most species except for Cu2+, Fe and vitamin C have little
effect on the fluorescence intensity of the system.
−
4
−1
2
.0 × 10 mol l , which was chosen for further experiments.
The mechanism of SDBS effect was studied by investigating
the change of surface tension of the fluorescence system with an
increase of the SDBS concentration, as shown in Fig. 7. It can be seen
that the surface tension first decreased sharply, then an equilibrium
3+
−
5
−1
was reached at the SDBS concentration of 5.0 × 10 mol l , which
may be considered as the apparent critical micelle concentration
(
CMC) of SDBS in this system. Since the SDBS concentration selected
3
3
.7. Analytical application
−4
−1
for the study (2.0 × 10 mol l ) was well above the CMC, it can be
concluded that the formation of micelles had a great impact on the
enhancement of the fluorescence intensity of the system.
.7.1. Calibration curve and detection limit
Under optimal conditions, the enhanced fluorescence intensity
of the system (ꢀI ) showed an excellent linear relationship over
f
3
.5. Effect of reagent addition order and fluorescence stability
−10
−8
−1
the GFLX concentration range of 5.0 × 10
to 5.0 × 10 mol l
.
10
The linear equation was ꢀI = 6.35 + 1.97 × 10
C
, with a cor-
f
GFLX
The effect of the order of reagent addition on the fluorescence
relation coefficient of 0.9996. The detection limit (3ꢁ) was
intensity was studied. The result showed that an addition order of
Tb , GFLX, Tris–HCl, SDBS, offered the optimal performance, there-
−11
−1
.
6
.0 × 10
mol l
3+
In comparison with other methods reported, as shown in Table 3,
the rapid and simple method proposed in this paper offers higher
sensitivity and a wider linear range.
3.7.2. Recovery tests
GFLX is present in human serum and urine samples at the lev-
−
1
els of approximately 2–5 and 20–100 mg l , respectively [2] (viz.
−
6
−5
−1
−5
in serum: 5.3 × 10 to 1.3 × 10 mol l ; in urine: 5.3 × 10 to
−
4
−1
2
.7 × 10 mol l ). In order to make the analyte concentrations
fall within the linear range of the method, urine samples were
diluted 10,000-fold in water and then analyzed by standard addi-
tion method. Serum samples were deproteinized first and then
diluted 1000-fold prior to analysis. The results of spiked urine and
serum samples are shown in Table 4. All recoveries were in the range
of 95.3–103.2%.
3.7.3. Pharmaceutical sample analysis
Three batches of gatifloxacin sodium chloride injection (Xi’an
Wanlong Pharmaceutical Group Co. Ltd., China) were also analyzed
using the proposed procedure. The results are shown in Table 5.
The potencies of the products determined by the presented method
were in good agreement with the label claims.
Fig. 7. Effect to the solution surface tension with the addition of surfactant SDBS.
−6
−1
3+
−4
−1
Experimental conditions: GFLX, 5.0 × 10 mol l ; Tb , 2.0 × 10 mol l ; Tris–HCl,
−
1
0
.01 mol l , pH 7.0.

770
C. Guo et al. / Spectrochimica Acta Part A 72 (2009) 766–771
Table 3
Comparison of methods for the determination of GFLX.
Method
Detection
limit (mol l−1)
Linear range (mol l−1)
Application
References
[3]
−
7
−5
HPLC
2.7 × 10 to 2.7 × 10 (in human serum)
Human serum, human
urine
−
6
−4
2
.7 × 10 to 4.0 × 10 (in human urine)
7
7
4.3 × 10−7 to 1.3 × 10−5
HPLC
HPLC
3.2 × 10−
3.5 × 10−
Human serum
[4]
[5]
−
−
7
−5
−5
2.7 × 10 to 2.7 × 10 (UV detection)
Human
plasma
8
5
.3 × 10 to 1.3 × 10 (fluorescence detection)
HPLC
1.1 × 10−5 to 6.4 × 10−5
2.7 × 10− to 1.6 × 10−5
1.1 × 10− to 3.7 × 10−5
2.7 × 10−8 to 2.7 × 10−6
2.7 × 10−6 to 3.8 × 10−5
Tablet
[6]
[7]
[8]
[9]
[10]
7
HPLC
Human plasma
Tablet
5
HPLC
9
7
HPLC/ESI-MS/MS
UV
1.3 × 10−
2.6 × 10−
Human serum
Tablet, injection,
ophthalmic solution
Tablet
7
5.3 × 10−6 to 4.3 × 10−5
1.1 × 10− to 3.7 × 10−5
UV
6.2 × 10−
[11]
[12]
[13]
5
UV
Tablet
2.7 ng spot 1
−
400–1200 ng spot
−1
Bulk drug, polymeric
nanoparticles
Tablet
HP-TLC
40 ng spot 1
−
100–500 ng spot
−1
[14]
[15]
[16]
[17]
[18]
HP-TLC
5
Microbiological assay
Voltammetric method
Atomic absorption spectrometry
Spectrofluorimetry
1.1 × 10− to 4.3 × 10−5
8.0 × 10−9 to 4.0 × 10−7
2.7 × 10−5 to 4.0 × 10−4
5.3 × 10−8 to 1.2 × 10−6
Tablet
2.0 × 10−
4.5 × 10−
5.3 × 10−
8
Tablet, human urine
Tablet
6
9
Human serum, human
urine
Capsule, human serum,
human urine
Injection, human
serum, human urine
Injection, human
serum, human urine
9
1.1 × 10−7 to 2.7 × 10−6
1.0 × 10−8 to 8.0 × 10−7
5.0 × 10−10 to 5.0 × 10−8
Yttrium fluorescence probe spectrofluorimetry
Europium-sensitized spectrofluorimetry
Terbium-sensitized spectrofluorimetry
9.0 × 10−
1.0 × 10−
6.0 × 10−
[19]
9
[20]
11
Present paper
Table 4
Recovery of GFLX in spiked human urine and serum samples (n = 5).
Sample
Added (mol l 1
−
)
Found (mol l
−1
)
Recovery ± R.S.D. (%)
9
−9
−8
Urine 1
Urine 1
Serum 1
Serum 2
Serum 3
1.00 × 10−
0.953 × 10
95.3 ± 2.5
103.2 ± 1.8
98.0 ± 2.1
100.6 ± 2.6
97.8 ± 1.9
−
−
−
8
9
8
8
1.00 × 10
1.00 × 10
1.00 × 10
1.03 × 10
−9
−8
0.980 × 10
1.01 × 10
3.00 × 10−
2.93 × 10
−8
Table 5
Pharmaceutical sample analysis (n = 5).
Batch no.
70603-3
Mark concentration (mg/100 ml)
Found (mg/100 ml)
Average (mg/100 ml)
R.S.D. (%)
0
200.0
200.0
200.0
196.3, 198.6, 198.4, 200.8, 201.7
197.4, 195.1, 197.9, 199.2, 201.3
202.3, 203.2, 202.1, 198.9, 200.4
199.2
198.2
201.4
2.1
2.3
1.7
070604-3
070605-1
3
3
.8. Interaction mechanism
be seen that the absorption peak of GFLX shifted to longer wave-
length, as a result of the change in microenvironment of the
system. This change can also be demonstrated by the variation in
polarity and fluorescence polarization of the system as shown in
Table 6.
.8.1. Luminescence of Tb3+
In the GFLX–Tb3+–SDBS system, GFLX was excited to its excited
singlet state after absorbing light energy, and then changed to its
triplet state via an inter-system crossing. Subsequently, GFLX can
transfer its energy to the level 5D4 of Tb (III) via intra-molecular
energy transfer, resulting in the observation of the characteristic
fluorescence of Tb (III). This luminescence mechanism was also
called the Antenna Effect [27].
The ratio of the first to the third fluorescence bands of pyrene
monomer (I /I ) is a well-established parameter which reflects the
1
3
Table 6
Comparison of the polarity and fluorescence polarization of the systems.
System
GFLX–Tb3+
GFLX–Tb3+–SDBS
3
.8.2. The fluorescence enhancement of GFLX–Tb3+–SDBS system
I1/I3
P
1.721
0.163
1.327
0.332
Fig. 2 clearly shows that SDBS can greatly enhance the fluo-
rescence intensity of GFLX–Tb3 complexes. Furthermore, it can
+

C. Guo et al. / Spectrochimica Acta Part A 72 (2009) 766–771
771
polarity variation of a system experienced by the pyrene probe with
a lower value as an indication of a lower polar environment [28,29].
The microviscosity of the microenvironment can be estimated
using the fluorescence polarization of fluorescence probe according
to Perrin equation [30]. A higher value of polarization reflects a
higher microviscosity.
Natural Science Foundation of Shandong Province (China) (No.
Z2005B01). The authors would like to thank the Key Laboratory
of Education Ministry on Colloid & Interface Chemistry of Shan-
dong University for kindly loaning Processor Tensiometer-K12 for
the determination of the surface tension and ISS K2 multifrequency
phase and modulation spectrofluorometer for the measurement of
fluorescence polarization spectra.
Table 6 illustrates that, with the addition of SDBS to the
3
+
GFLX–Tb system, the value of I /I3 decreased and the value of
1
P increased. Therefore, it can be concluded that SDBS medium
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[
Acknowledgements
This project was supported by the National Natural Science
Foundations of China (Nos. 20875056 and 20775043) and the
[