M. Hoshino et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 117 (2014) 814–816
815
enhancing the sensitivity and repeatability of the determination
method. Furthermore, because a crystalline MCPF was obtained,
structural analysis by X-ray diffractometry was performed.
tem. A Shimadzu spectrophotometer (Model UV-160) with 1.0 cm
matched silica cell was used for absorbance measurements. All pH
measurements were conducted using a Horiba (F-11) pH meter in
combination with a calomel glass electrode.
Experimental
Standard procedure for the determination of H2O2
Synthesis of m-carboxyphenylfluorone
The following components were mixed in a 10 mL volumetric
According to a method described in literature [12], 1,4-benzo-
quinone was dissolved in 20 mL of acetic anhydride and 1 mL of
sulfuric acid, and the solution maintained at 30–50 °C for 30–
60 min. The reaction mixture was poured into 1 L of water to afford
a white precipitate that was filtered and washed with water. 1,2,4-
Benzenetriol triacetate was obtained after drying the precipitate
under reduced pressure for 5 h. In the synthesis of MCPF, 5 g of
m-carboxybenzaldehyde and 15 g of 1,2,4,-benzenetriol triacetate
were dissolved in 150 mL of 20% ethanol and 2 mL of concentrated
sulfuric acid. The solution became red upon heating in a steam
bath. This solution was subsequently allowed to stand in a cool,
dark place for several weeks. The crude MCPF (4.0 g) obtained
was collected and dissolved in a solution of 200 mL ethanol with
1 mL of hydrochloride acid, using a steam bath. Then, the resultant
solution was concentrated under reduced pressure to half of its ori-
ginal volume. Next, the precipitate obtained by adding pure water
into the concentrated reaction solution was redissolved in a 5:5:2
methanol/ethanol/water mixture. The solution was allowed to
stand in a cool, dark place for several days. The precipitate was fil-
tered and washed with pure water to yield pure MCPF (2.4 g) that
was subsequently dried under reduced pressure. 1H NMR (d6-
DMSO, 500 MHz) d ppm: 8.20 (1H, d), 8.00 (1H, s), 7.80 (1H, t),
7.73 (1H, d), 6.73 (1H, s) 6.33 (1H, s). MS (SIMS): m/z = 365.
flask: a solution containing 0.20–4.08 lg of H2O2, 3.0 mL of 5.0%
CTAC solution, 3.0 mL of 0.2 M CH3COOH-CH3COONa buffer solu-
tion (pH 3.3), 1.0 mL of a 1.0 ꢂ 10ꢁ3 mol Lꢁ1 MCPF solution, and
0.5 mL of a 1.0 ꢂ 10ꢁ3 mol Lꢁ1 Os(VIII) solution. The mixture was
diluted to 10 mL with water, transferred to a test tube, mixed well,
and maintained at room temperature for 20 min. The absorbance
of the resulting solution was measured at 580 nm against a reagent
blank without osmium ions.
Result and discussion
Optimization of experimental conditions
Analysis of the effect of pH showed that the optimal pH was
approximately 3.3, which was achieved using 3.0 mL of 0.2 mol Lꢁ1
CH3COOH/CH3COONa solution. After investigating the effects of
several acidic media, including CH3COOH/CH3COONa, HCl/Na3
(C3H5O(COO)3), HCl/Glycine/NaCl, HCl/C6H4(COOH)(COOK), and
HCl/Na2B4O5(OH)4ꢃ8H2O solutions, the effect of dispersing agents
on the H2O2-osmium(VII)-MCPF reaction was examined using
cationic surfactants (CTAC, stearyltrimethylammonium chloride,
cetylpyridinium chloride, and dimethylbenzyltetradecylammoni-
um chloride), an anionic surfactant (sodium dodecylsulfate), an
amphoteric surfactant (Swanol AM-101), and non-ionic surfactants
(methylcellulose, polyethylene glycol mono-p-isooctylphenyl
ether, poly(N-vinylpyrrolidone), polyvinyl alcohol, and polyoxy-
ethylene sorbitan monolaurate). A maximum and constant absor-
Reagents and chemicals
A H2O2 solution was prepared using suitably diluted reagent-
grade 30% H2O2. An osmium(VIII) standard stock solution
(1.0 ꢂ 10ꢁ3 mol Lꢁ1) was prepared in water. The working solution
bance difference (DAbs) value was obtained by adding more than
3.0 mL of 5.0% CTAC to 10 mL of MCPF-osmium(VIII)-H2O2
solution. The recommended procedure for the assay of H2O2 is as
follows: The following components were mixed in a 10 mL volu-
metric flask: a solution containing 0.20–4.08 lg of H2O2, 3.0 mL
of 5.0% CTAC solution, 3.0 mL of 0.2 M CH3COOH–CH3COONa buffer
was prepared by suitable dilution of this stock solution.
A
1.0 ꢂ 10ꢁ3 mol Lꢁ1 solution of MCPF, which had been synthesized
according to a method described in the literature, was prepared
in methanol, and a 5.0% aqueous solution of CTAC was prepared
by direct dissolution in water. A pH 4.2 buffer solution was pre-
pared by mixing appropriate amounts of 0.2 mol Lꢁ1 CH3COOH
and CH3COONa solutions. Reagent-grade chemicals were utilized
throughout the study. Ultrapure water was prepared immediately
before use, by purifying deionized water using a Milli-Q Labo sys-
Table 1
Effect of foreign substances on
DAbs at 580 nm and percent recovery.
Substance
Molar ratio (substance/
H2O2)
D
Abs at
Recovery
(%)
580 nm
None
Ca(II)
Mg(II)
Zn(II)
Fe(II)
Fe(III)
Cu(II)
NaCl
NaH2PO4
Na2SO4
KNO3
NaF
Citric acid
Tartaric acid 10
Oxalic acid
Ascorbic
acid
–
0.313
0.313
0.313
0.313
0.227
0.267
0.313
0.313
0.313
0.324
0.313
0.313
0.216
0.313
0.237
0.276
100
100
100
100
73
2.0
100
100
100
1
B
1.0
10
85
100
1000
100
1000
1000
100
10
100
100
100
103
100
100
69
100
76
88
A
0.0
C
-1.0
400
1
10
500
600
700
Wavelength (nm)
Glucose
EDTA
1000
10
0.313
0.313
100
100
Fig. 1. Absorption spectra of MCPF-osmium(VIII)–H2O2 solutions. Parameters:
H2O2: 1.8 ꢂ 10ꢁ5 mol Lꢁ1; Os(VIII): 0.5 ꢂ 10ꢁ4 mol Lꢁ1; CTAC: 1.5%; MCPF: 1.0 ꢂ
10ꢁ4 mol Lꢁ1; pH: 3.3; Curve A: MCPF–Os(VIII)–H2O2 solution; Curve B: MCPF–
Os(VIII) solution; Curve C: Curve A minus Curve B
H2O2: 0.6 ꢂ 10ꢁ5 mol Lꢁ1
;
Os(VIII): 0.5 ꢂ 10ꢁ4 mol Lꢁ1
;
CTAC: 1.5%; MCPF:
1.0 ꢂ 10ꢁ4 mol Lꢁ1; pH 3.3, Reference: MCPF-Os(VIII) solution.