Resonance light scattering method for the determination of anionic ...

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Spectrochimica Acta Part A 71 (2008) 398–402
Resonance light scattering method for the determination of
anionic surfactant with acridine orange
Xilin Xiao a,b , Yongsheng Wang a,∗ , Zhangming Chen c , Qiangxiang Li d , Zhihuo Liu d ,
Guirong Li a , Changyin Lü a , Jinhua Xue a , Yanzhi Li a
a College of Public Health, University of South China, Hengyang 421001, PR China
b College of Chemistry and Chemical Engineering, University of South China, Hengyang 421001, PR China
c Changsha Medical College, Changsha 410219, PR China
d Xiangya Hospital, Central South University, Changsha 410219, PR China
Received 3 December 2007; received in revised form 27 December 2007; accepted 1 January 2008
Abstract
The resonance Rayleigh scattering (RRS), second-order scattering (SOS) and frequency-double scattering (FDS) spectra of sodium dodecylbenzene
sulfonate (SDBS) (anionic surfactant (AS)) with acridine orange (AO) system were studied. Experimental results showed that when
λ em = λ ex = 537 nm, the RRS peak of AO was greatly enhanced with the increase of SDBS concentration at a pH range of 1.8–4.0. The linear range
of the calibration curve for SDBS was 0.028–8.71 mg L −1 with a detection limit of 8.36 gL −1 when the AO concentration was 2.5 × 10 −5 mol L −1 .
The method has been applied to the determination of trace amount of AS in environmental water samples with satisfactory results. In addition,
when λ em = 321 nm and λ ex = 642 nm, the intensity of FDS was proportional to the SDBS concentration ranging from 0.014 to 8.71 mg L −1 and the
correlation coefficient was 0.993 with a detection limit of 4.31 gL −1 ; when λ em = 642 nm and λ ex = 321 nm, the intensity of SOS was proportional
to the SDBS concentration ranging from 0.050 to 8.71 mg L −1 , and the correlation coefficient was 0.993 with a detection limit of 14.9 gL −1 .
© 2008 Elsevier B.V. All rights reserved.
Keywords: Anionic surfactant; Acridine orange; Resonance Rayleigh scattering; Resonance nonlinear scattering
1. Introduction
With the extensive application of synthetic detergent in daily
life, the analysis of trace anionic surfactant (AS) in water
has become an indispensable topic [1] in the environmental
monitoring. In recent years, most of resonance light scattering
technologies had been applied to the research of biologic
molecule such as protein [2–5] and nucleic acid [6–10], and
the huge advantage and potential application value had been
embodied and shown. In order to overcome the disadvantages
of methylene-blue colorimetric method that needs the organic
agent for its extraction and of tedious operation, the direct measurement
of AS in the environmental water samples by the water
phase was reported [11–15], but the Resonance light scattering
method for the direct determination of anionic surfactant with
acridine orange was not reported so far. No need of organic agent
∗ Corresponding author. Tel.: +86 734 8280312.
E-mail addresses: xiaoxl2001@163.com (X. Xiao),
yongsheng.w@tom.com (Y. Wang).
for the extraction for the new method mentioned in this thesis
and the operation was simple and quick and the sensitivity was
high. This method had been applied to the determination of AS
in the water environment, with a satisfactory result.
2. Experimental
2.1. Main instruments and reagent
970 CRT spectrofluorophotometer (Shanghai Sanco Instruments
Co. Ltd.), UV8500 ultraviolet visible range spectrophotometer
(Shanghai Techcomp Holding Ltd.), PB-20 standard pH
meter (Sartorius Scientific Instruments (Beiing) Co. Ltd.), and
AB204-S electronic analytical balance (Mettler-Toledo Instruments
(Shanghai) Co. Ltd.) were used in this experiment.
Sodium dodecyl benzene sulfonate (SDBS, analytic reagent,
China National Medicine Group Shanghai Chemical Reagent
Company) standard solution: the concentration of stock
solution was 5.00 × 10 −3 mol L −1 , concentration of working
solution was 5.00 × 10 −4 mol L −1 , concentration of AO solu-
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2008.01.002

tion was 5.00 × 10 −3 mol L −1 , which was diluted into the
working solution of 5.00 × 10 −4 mol L −1 , Tris(hydroxymethyl)
aminomethane buffer solution: 0.1 mol L −1 , which was mixed
by Tris and 0.1 mol L −1 HCl. The remaining reagents were all
analytic reagent, and experiment water adopted the secondary
distilled water.
2.2. Experiment method
X. Xiao et al. / Spectrochimica Acta Part A 71 (2008) 398–402 399
2.2.1. Determination of resonance Rayleigh scattering
Added 0.50 mL AO solution and 0.50 mL Tris buffer solution
(pH2.0) into the 10 mL colorimeter tube, joggled the tube
to mix the solutions evenly, and then added certain SDBS standard
solution or sample solution, and joggled the tube after the
solutions were diluted behind the scale. Put the mixed solution
at the place of λ em = λ ex for synchronous scanning, and then the
resonance Rayleigh scattering (RRS) spectrum can be obtained.
Measured the scattering light intensity at the 537 nm of the RRS
peak, marked it as I 1 ; meanwhile measured the scattering light
intensity of reagent blank, marked it as I 0; I RRS = I 1 − I 0. Both
excitation slit width and emission slit width were all 5.0 nm.
2.2.2. Determination of resonance nonlinear scattering
Used the method of above Section 2.2.1 to make the test
solution, and used λ em = 1/2λ ex and λ em =2λ ex to measure the
intensities I FDs (frequency-double scattering) and I SOS (secondorder
scattering) of two resonance nonlinear scattering lights.
FDS and SOS spectrograms can be made by plotting the corresponding
wavelengths of I FDs and I SOS . Measured the scattering
intensities I FDs and I SOS of ion-associated complex at FDS peak
and SOS peak as well as the scattering intensities IFDs 0 and
ISOS 0 of reagent blank, then ΔI FDs = I FDs − IFDS 0 and ΔI SOS =
I SOS − ISOS 0 . Excitation slit width and emission slit width were
both 5.0 nm.
3. Results and discussion
Fig. 1. Resonance Rayleigh scattering spectra of AO–SDBS system at pH
2.0: SDBS, (2); AO, (3); AO–SDBS ((AO): 1.00 × 10 −5 mol L −1 ; (SDBS):
1.00 × 10 −5 mol L −1 ).
ence and accordingly increase the RRS strength. Therefore, this
experiment adopted λ em = λ ex = 537 nm as the study wavelength.
From the absorption spectrogram, we saw that, with the gradual
increase of adding quantity of SDBS, absorbance light of AO
at 490 nm constantly reduced, this was because that AO reacted
with SDBS to generate the ion-associated complex. The reason
that RRS signal increases may be that positive ion dye stuffs AO
and SDBS in the water solution generated the ion-associated
complex through the reactions such as water repellent, electrostatic
reaction or charge transfer complex [16], resulted in the
enhancement of RRS signal intensity at 537 nm.
Mole-ratio method was used to study the composition of ionassociated
complex: fixed SDBS concentration, changed the AO
concentration, measured and determined the I RRS of corresponding
reagent blanks and various solution groups at 537 nm,
plotted the I–V diagram. Result showed that a turning point
occurred in case of mole ratio 1.2:1 for AO and SDBS, namely,
3.1. Resonance Rayleigh scattering spectra properties of
SDBS–AO system
The experimental method was used to measure the RRS spectrum
for AO–SDBS system, as shown in Figs. 1 and 2 was the
ultraviolet-visible range spectrum for AO–SDBS system. From
Fig. 1, we knew that the RRS signals of SDBS and AO were
both weaker. AO had a stronger resonance Rayleigh scattering
signal near 512 nm, which was corresponding to the wide peak
valley of ultraviolet-visible spectrum at 520 nm. With the addition
of SDBS, stronger RRS peaks occurred at both 337 nm
and 537 nm. The two RRS peaks (337 nm and 537 nm) in the
RRS spectra was on the right of corresponding absorption peak,
this was a characteristic “absorption-scattering” phenomenon
of RRS spectra. Compared to RRS signal of acridine orange,
RRS signal at 537 nm was stronger than that at 337 nm. If measuring
the signal at the stronger wavelength, it may not only
avoid the adverse reaction from the higher radiant energy of
short wavelength, but also reduced the background interfer-
Fig. 2. Absorption spectra of AO–SDBS system at pH 2.0: (AO),
1.00 × 10 −5 mol L −1 ; (SDBS)/×10 −5 mol L −1 ; (1) 0.00; (2) 0.25; (3) 0.50; (4)
0.75; (5) 1.00; (6) 1.25.

400 X. Xiao et al. / Spectrochimica Acta Part A 71 (2008) 398–402
Fig. 3. Spectra of frequency-double scattering (FDS) for SDBS–AO system:
(1) 0.20 mL AO; (2) 1 + 0.20 mL SDBS; (3) 1 + 0.40 mL SDBS ((AO):
5.00 × 10 −4 mol L −1 ; (SDBS): 5.00 × 10 −4 mol L −1 ).
the composition ratio of AO and SDBS in the ion-associated
complex is 1.2:1. In case of any change of SDBS concentration,
its ratio changed too, and this was because that there was
a ratio difference between AO monomer and dimer, which was
identical to the study of He et al. [17].
3.2. Resonance nonlinear scattering spectra properties of
SDBS–AO system
When incident ray of different wavelengths passed through
the reagent blank and solution of ion-associated complex, we
recorded the scattering light intensity of incident ray at places
of 1/2 or tow times wavelength, and plotted the corresponding
wavelength diagrams according to scattering light intensity,
and then we could get the spectrograms of FDS and SOS
(Figs. 3 and 4). From the two figures, we saw that: (1) in FDS
spectrum, when λ em = 321 nm and λ ex = 642 nm, I FDs maximized,
and it was proportional to the matter concentration in
the solution under certain condition. In SOS spectrum, when
λ em = 642 nm and λ ex = 321 nm, I SOS maximized, and it was
proportional to the matter concentration in the solution under
certain condition. (2) FDS and SOS of acridine orange were
both weak. When adding the SDBS into acridine orange to generate
the ion-associated complex, the FDS and SDBS enhanced
greatly. FDS maximum peak of ion-associated complex was at
321 nm and SOS maximum peak was at 642 nm. FDS maximum
peak wavelength was 1/2 of SOS maximum peak wavelength.
The radiation peak occurred near 542 nm should be the fluorescence
peak [18], and therefore, there was a similarity between
FDS peak and SOS peak. (3) I FDs > I SOS , FDS had a higher
sensitivity and FDS used the long wavelength of low energy as
the incident ray, which was more beneficial to determining some
systems that are easy to generate the photochemical reaction. As
a result, FDS was preferred for the determination study under
the general condition.
Fig. 4. Spectra of second-order scattering (SOS) for SDBS–AO system:
(1) 0.20 mL AO; (2) 1 + 0.20 mL SDBS; (3) 1 + 0.40 mL SDBS ((AO):
5.00 × 10 −4 mol L −1 ; (SDBS): 5.00 × 10 −4 mol L −1 ).
FDS and SOS were all nonlinear scatterings caused from
the resonance scattering. The above experiment results showed
that the resonance nonlinear scattering and resonance Rayleigh
scattering of AO itself were all weaker. After adding SDBS,
the three scatterings were all greatly enhanced and were in a
linear relation with the added quantity. Therefore, there was a
correlation between RRS and the two scatterings, which synchronously
change with the generation and changes of RRS. The
increase of molecular polarizability was an important factor [19]
for the enhancement of RRS, and the sharp increase of molecular
polarizability however was exactly the important condition for
generating the nonlinear scatterings such as frequency-double
scattering, second-order scattering, etc. Therefore, a stronger
interdependent relationship may be existed among them.
3.3. Experiment of condition optimization
The experiment of condition optimization was made on the
basis of RRS method.
3.3.1. Influence of acidity
Used the experimental method and took “Tris–HCl and
Tris–NaOH” buffer solution to adjusted pH value of this solution,
we determined the RRS intensity under different acidities
and the intensity was among the range of pH 1.8–4.0, and I of
this system maximized and kept the constant value. Hence, this
experiment selected Tris buffer solution at pH 2.0 to control the
acidity of the solution.
3.3.2. Influence of dosage of acridine orange
With the SDBS of 1.00 × 10 −5 mol L −1 , we tested the influence
of dosage of acridine orange, and the result showed that
when AO dosage was 0.50 mL, the resonance light scattering of
this system enhanced maximally.

X. Xiao et al. / Spectrochimica Acta Part A 71 (2008) 398–402 401
Table 1
Analytical parameters
Method
Concentration of AO
(×10 −5 mol L −1 )
Linear range
(mg L −1 )
Linear regression
equation ρ (mg L −1 )
Correlation
coefficient r
Limit of determination
(3δ) ((g L −1 )
RRS 2.50 0.028–8.71 I = −18.1 + 31.2ρ 0.992 8.36
FDS 2.50 0.014–8.71 I = 0.02 + 6.1ρ 0.993 4.31
SOS 2.50 0.050–8.71 I = 0.19 + 4.3ρ 0.993 14.9
Table 2
Determination results of water samples (n =6)
Sample
Found
(mg L −1 )
R.S.D.
S r (%)
SDBS
added (g)
Recovery of
SDBS (g)
Recovery
R (%)
Methylene-blue
method ρ (mg L −1 )
t
Running water 0.057 4.0 1.74 1.64 94.3 0.059 1.01
Xiangjiang river water 0.079 3.0 1.74 1.68 96.6 0.082 2.12
Pond water 0.109 1.8 1.74 1.81 104.0 0.112 1.69
3.3.3. Influence of reaction temperature, standing time and
adding sequence
We tested the influence of temperature on the intensity of
resonance light scattering of this reactive system. 15 ◦ C was the
optimal reaction temperature. The reaction could be generated
instantly and the standing time should last 2 h. This experiment
preferred 10 min as the determining time.
Three adding sequences of reagents were tested in this experiment:
first, mix AO and SDBS and then added the buffer
solution; second, added AO into buffer solution and then
feeded SDBS; thirdly, added SDBS into buffer solution and
then added AO to mix them evenly. The result showed that
theI RRS of the second adding sequence maximized, and so, we
selected the reagent adding sequence of AO – buffer solution –
SDBS.
3.4. Standard curve
Under the optimal condition of the experiment, plotted the
standard curve. Put 5.00 × 10 −4 mol L −1 SDBS into 10 mL colorimeter
tube, and then measured its intensity of scattering light
in terms of the test method. The result was shown in Table 1.
After being compared with other methods, the linear range of
this study were wider than absorption spectra method [20],
and the limits of determination (3σ) of this study were come
up to direct measurement methods [11–15] had been reported
approximately. It would be very good for applying this study to
environmental water AS detection.
3.5. Influence of co-existent ions
With 1.00 × 10 −5 mol L −1 SDBS, we researched the influence
of various co-existent matters on the determination of
resonance light scattering method. The relative error was no
more than ±5%. The allowable quantities (mg) of the following
ions or matters were respectively: Na + (1.2), K + (2.04), Mg 2+
(1.0), AI 3+ (1.2), NH 4 + (3.0), Pb 2+ (0.01), Ba 2+ (1.6), Mn 2+
(0.5), Co 2+ (1.6), Zn 2+ (1.2), Cu 2+ (0.4), Ca 2+ (2.0), F − (0.05),
HCO 3− (2.0), EDTA (2.25), Cl − (1.9), Br − (2.5), Fe 2+ (0.2),
S0 4 2− (2.5), Ag + (1.2), Hg 2+ (0.02), Ni 2+ (1.6), oxalic acid (2.0),
and citric acid (5.0).
3.6. Precision and detection limit
Under the optimal condition of the experiment, prepared 11
samples of 1.00 × 10 −5 mol L −1 SDBS in parallel, and then conducted
the precision detection after the determination by RLS
method. The relative standard deviation was 3.5%. Through 11
blank parallel experiments, the detection limit (see Table 1)
of the RLS method was calculated by the formula C L =3S b /k
(S b represents the standard deviation of blank solution and k
represents the slope of working curve).
3.7. Sample analysis
Sample analysed by RRS method. Water sampler was used
to collect water samples at different environments. After filtering,
accurately gather adequate water sample and adjust its pH
value to 8.0 and then re-filter it (most of heavy metal ions were
subsided at pH 8.0.). Carefully heat it to compress it for five
times, and determined the capacity by 5.00 mL distilled water
in terms of the test method. And the calibration and recovery
experiment was carried out. Working curve method was used
to calculate the AS concentration in the water (by SDBS), and
meanwhile, the comparison test was conducted in accordance
with the current standard method—methylene-blue colorimetric
method. Experiment data were handled by statistics and the
result was shown in Table 2. Table shows that t 0.05(10) = 2.228,
and t < t 0.05(10) . To sum up, there was no significant difference
for the determination result of the two methods.
Acknowledgements
We are grateful for the financial support from the National
Science Foundation of China under the grant 20775024 and the
Hunan Provincial Natural Science Foundation of China under
the grant 03JJY3030.

402 X. Xiao et al. / Spectrochimica Acta Part A 71 (2008) 398–402
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