J.-h. Yu et al. / Spectrochimica Acta Part A 72 (2009) 17–21
19
Table 2
Determination of samples and result of recovery.
Water
sample
Founda
Added
Founda
Recovery (%)
Official
method
(g L−1
)
(g L−1
)
(g L−1
)
(g L−1
)
1
2
3
0.337
2.014
0.745
3.00
6.00
8.00
3.168
8.179
9.007
95.6
102.3
103.1
3.103
8.335
9.182
a
Average of six measurements.
KIO4 (2.0 × 10−3 mol L−1
) amount was examined during the
range 1.8–2.2 mL. And 4.0 × 10−4 mol L−1 of KIO4 was selected to
get the maximal fluorescence emission intensity. The effect of
2ClRAAP (2 × 10−5 mol L−1) amount was investigated in the range
0.8–1.2 mL. The results showed that the maximal fluorescence
emission peak could be obtained when the amount of 2ClRAAP was
1.0 mL. Therefore, 2 × 10−6 mol L−1 2ClRAAP was chosen for further
study.
Fig. 2. Excitation spectra and emission spectra of system: (1, 1ꢀ) 2 × 10−6 mol L−1
2ClRAAP–4.0 × 10−4 mol L−1 KIO4–5.0 g L−1 Sb(III); (2, 2ꢀ) 2 × 10−6 mol L−1
2ClRAAP–4.0 × 10−4 mol L−1 KIO4; (3, 3ꢀ) 2 × 10−6 mol L−1 2ClRAAP–buffer solution;
(4, 4ꢀ) 2 × 10−6 mol L−1 2ClRAAP.
3.2.3. Effect of heating parameters
was produced at 410 nm (curves 1, 1ꢀ), which was much stronger
than the fluorescence emission peak of 2ClRAAP–KIO4 (curves 2,
2ꢀ). According to what is shown in Fig. 2, 308 and 410 nm have been
chosen to be the wavelength of excitation peak and emission peak,
respectively at which the fluorescence intensity reached maximum
when determination for trace antimony by 2ClRAAP was carried
out.
The influence of temperature was studied during the range of
70–100 ◦C. It comes to a conclusion that the reaction speeds up in
the temperature range of 80–100 ◦C. Relative fluorescence intensity
was enhanced as the temperature goes upper, and it had a linear
relationship against temperature. The regression equation of the
system was calculated to be −ln ꢁF = 6.67 × 103/T − 23.04 accord-
ing to formula of Arrhenius and temperature curve with the relative
coefficient r of 0.9983, and the active energy was 51.20 kJ mol−1
.
Both the catalyzed system and uncatalyzed system were tested
with the proposed method at 100 ◦C for every 5 min during
the range 5–30 min, respectively. It was found that the rela-
tive fluorescence intensity ꢁF is directly proportional to heating
time t when the solution was heated for 5–15 min, from which
it can be investigated that at the initial state, the reaction of
2ClRAAP–KIO4–Sb(III) was zero record, whose regression equa-
tion was ꢁF = 8.15t (min) + 57.23 with relative coefficient r = 0.9977.
The reaction rate constant k is 1.36 × 10−2 s−1. The fluorescence
intensity was found to stay steady when heated for from 15
to 21 min, and finally the reaction was made to be heated for
18 min.
The following conditions were optimumed in order to obtain the
greatest sensitivity by conducting a series of experiments using a
1.0 g L−1 antimony standard solution. The optimumed conditions
are shown in Table 1.
3.2.1. Optimum of pH
Initially, the fluorescence intensity of antimony with oxi-
dant and 2ClRAAP in different buffer mediums were tested,
which were: potassium hydrogen phthalate–NaOH buffer system,
acetic acid–sodium acetic acid buffer system, disodium hydro-
gen phosphate–citric acid buffer system, and tartaric acid–sodium
tartaric acid buffer system. It was found that the Sb(III) solution
emitted the most intense fluorescence in the potassium hydrogen
phthalate–NaOH buffer system. The proper pH was investigated to
be 5.2, and the proper amount of buffer solution was to be 1.2 mL.
The enhanced fluorescence intensity of 2ClRAAP–KIO4–Sb(III)
ꢁF could stay invariable for more than 24 h.
3.2.4. Analytical performance
The proposed spectrofluorimetry method was studied for lin-
earity, precision, and sensitivity. Under the optimumed conditions,
a linear relationship between antimony concentration and rel-
ative fluorescence intensity was obtained over the range of
0.2–10 g L−1, with a regression equation of ꢁF = 2.453 + 13.77ꢂ
(g L−1) and correlation coefficient (r) of 0.9980. The low detection
limit of antimony was found to be 1.65 × 10−10 g mL−1 according
3.2.2. Optimum of other chemicals
The influence of other chemicals was studied at pH 5.2.
H2O2, KIO4 and KBrO3 have been tested as oxidants, and
it was investigated that the fluorescence intensity was the
strongest and steadiest with KIO4 as oxidant. The effect of
Table 1
Optimization of the proposed spectrofluorimetry for antimony determination.
Variable
Studied range
5.0–5.4
Optimum conditions
5.2
pH
Buffer solution
Potassium hydrogen phthalate–NaOH; acetic acid–sodium acetic acid; disodium hydrogen
Potassium hydrogen phthalate–NaOH
phosphate–
citric acid; tartaric acid–sodium tartaric acid
Buffer solution amount (mL)
Oxidant
1.0–1.8
H2O2; KIO4; KBrO3
3.6–4.4
1.6–2.4
70–100
1.2
KIO4
4.0
2.0
100
18
Oxidant amount (×10−4 mol L−1
)
)
2ClRAAP amount (×10−6 mol L−1
Temperature (◦C)
Heating time (min)
15–21