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

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.