Development of a fluorescent chelating ligand for scandium ion having a Schiff base moiety

Article abstract of DOI:10.1016/j.saa.2012.01.014

A fluorescent ligand, 1-(2-hydroxy-3-methoxybenzaldehyde)-4- aminosalicylhydrazone (HMB-ASH), was newly designed and synthesized, and its fluorescence characteristics for metal ions were investigated in the pH range 3.0-10.5 (at a difference of 0.5 for each metal). After testing 31 different metal ions, it was found that HMB-ASH was able to emit fluorescence intensely at 512 nm with an excitation wavelength of 353 nm in the presence of Sc ³⁺, one of the rare earth metals, at pH values around 3.5 and 8.0. The other metal ions hardly showed fluorescence with HMB-ASH. The fluorescence was more intense at pH 8.0, and the detection limit of Sc³⁺ in a buffer solution (pH 8.0) was approximately 18.8 nmol L^-1 (0.85 ppb).

Full text of DOI:10.1016/j.saa.2012.01.014

Spectrochimica Acta Part A 90 (2012) 72–77
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Development of a fluorescent chelating ligand for scandium ion having a Schiff
base moiety
Hiroshi Yamada, Masahito Kojo, Tomomi Nakahara, Kumi Murakami, Takashi Kakima, Hideaki Ichiba,
Takehiko Yajima, Takeshi Fukushima∗
Department of Analytical Chemistry, Faculty of Pharmaceutical Sciences, Toho University, 2-2-1 Miyama, Funabashi-shi, Chiba 274-8510, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A
fluorescent ligand, 1-(2-hydroxy-3-methoxybenzaldehyde)-4-aminosalicylhydrazone (HMB-ASH),
Received 28 September 2011
Received in revised form 5 January 2012
Accepted 8 January 2012
was newly designed and synthesized, and its fluorescence characteristics for metal ions were investigated
in the pH range 3.0–10.5 (at a difference of 0.5 for each metal).
After testing 31 different metal ions, it was found that HMB-ASH was able to emit fluorescence intensely
at 512 nm with an excitation wavelength of 353 nm in the presence of Sc3+, one of the rare earth metals,
at pH values around 3.5 and 8.0. The other metal ions hardly showed fluorescence with HMB-ASH. The
fluorescence was more intense at pH 8.0, and the detection limit of Sc3+ in a buffer solution (pH 8.0) was
approximately 18.8 nmol L−1 (0.85 ppb).
Keywords:
Metal-ion complex
Ligand
Fluorescence
Scandium ion
© 2012 Elsevier B.V. All rights reserved.
Rare earth metal
1-(2-Hydroxy-3-methoxybenzaldehyde)-4-
aminosalicylhydrazone
1. Introduction
base [8–10]. Thus, in this paper, we report the fluorescence
properties of a new fluorescent chelating ligand, 1-(2-hydroxy-3-
For the sensitive detection of trace metal ions in environmen-
tal samples, a number of fluorescent chelating ligands have been
developed [1,2]. Owing to the industrial significance of metal ions,
especially those of rare earth metals, the development of a superior
ligand for selectively chelating the metal ion is required.
Recently, we developed a fluorescent chelating ligand having
two Schiff base moieties, 2,4-[bis-(2, 4-dihydroxybenzylidene)]-
dihydrazinoquinazoline (DBHQ) [3,4] and 2,4-[bis-(2-hydroxy-3-
methoxybenzylidene)]-dihydrazinoquinazoline (HBQZ) [5]. DBHQ
and HBQZ can chelate gallium ions (Ga3+) and zinc ions (Zn2+),
respectively, to emit fluorescence. However, both ligands have
a small amount of intrinsic fluorescence because they possess a
quinazoline moiety. To obtain a good chelating ligand, the intrinsic
fluorescence originating from the ligand itself should preferably be
minimal.
methoxybenzaldehyde)-4-aminosalicylhydrazone (HMB-ASH), in
the presence of Sc3+
2. Experimental
2.1. Chemicals
.
4-Aminosalicylic acid and 80% hydrazine monohydrate were
bought from Tokyo Chemical Industries Co., Ltd. (Tokyo, Japan).
o-Vanillin was purchased from Kanto Chemical Co., Ltd. (Tokyo,
Japan). Ethanol (EtOH, 99.0%) was obtained from Japan Alcohol
Trading Co., Ltd. (Chiba, Japan) and was used after distillation.
Water was used after purification using an Autopure WR600G sys-
tem (Yamato Scientific Co., Ltd., Tokyo, Japan). Divalent or trivalent
ions tested in this study, which were purchased from Wako Pure
Chemicals Co., Ltd. (Osaka, Japan) in the form of salts with either
NO3−, SO42−, or Cl− ions, were of atomic absorption grade.
In order to reduce the intrinsic fluorescence emitted from
the ligand itself, aromatic groups other than quinazoline should
be selected. Therefore, in the present study, 4-aminosalicylate
(p-aminosalicylate), which is capable of chelating metal ions
[6,7], was employed and connected to an o-vanillin moiety,
which has also been used for chelating reagents via a Schiff
2.2. Apparatus
Excitation and fluorescence spectra were measured by using the
spectrofluorometer FP-6300 (Jasco Corporation, Tokyo, Japan) with
slit widths of 10 nm. All fluorescence and absorption data were
obtained in a temperature-controlled room (25 ◦C). NMR spectra
were measured by using a JEOL ECP1 spectrometer (JEOL Ltd.,
∗
Corresponding author. Tel.: +81 47 472 1504; fax: +81 47 472 1504.
E-mail address: t-fukushima@phar.toho-u.ac.jp (T. Fukushima).
1386-1425/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2012.01.014

H. Yamada et al. / Spectrochimica Acta Part A 90 (2012) 72–77
73
Tokyo, Japan) (500 MHz for 1H and 13C) with tetramethylsilane as
2.6. Effect of coexisting ions on the fluorescence intensity
an internal standard. The infrared spectrum was obtained using an
FT/IR-4100 spectrometer (Jasco). The mass spectrum was measured
using a JMS 600H spectrometer (JEOL Ltd., Tokyo, Japan).
In a test tube, 22.2 ␮mol L−1 (1.0 ppm) Sc3+ ions (50 ␮L) were
added to 100 mmol L−1 ammonia buffer (pH 8.0) (50 ␮L) and
100 ␮M HMB-ASH (50 ␮L), and then, the tested ions (11.1 ␮M
(0.5 eq.), 22.2 ␮M (1.0 eq.), 111 ␮M (5.0 eq.), 222 ␮M (10 eq.),
1,110 ␮M (50 eq.), and 2,220 ␮M (100 eq.)) were added and treated
in a similar manner as described above. An error within 5.0% of
the measured fluorescence intensity was considered tolerable.
To achieve masking of the 22.2, 44.4, 66.6, and 111 ␮mol L−1 Fe
3+ ions, 4.44 mM (200 eq. to Sc3+ ion) potassium thiocyanate (KSCN)
(50 ␮L) was added and treated in a similar manner as described
above (n = 3).
2.3. Synthesis of HMB-ASH
4-Aminosalicylic acid (10.0 g, 65 mmol) was dissolved in MeOH
(200 mL) and was refluxed in the presence of 10 mL concentrated
sulfuric acid for 4 h. After the reaction, the solution was concen-
trated to approximately 20 mL and was neutralized by adding
a 10% NaHCO3 aqueous solution. The crude crystal was filtered
and recrystallized from MeOH/H2O (1/1) to obtain methyl 4-
aminosalicylate (yield 65.7%).
Methyl 4-aminosalicylate (4.0 g, 23 mmol) was added to 80%
hydrazine monohydrate (12 mL), and the mixture was refluxed
for 90 min. After evaporation, the residue was added to distilled
H2O to obtain a crude crystal. The crude crystal was recrystal-
lized from EtOH to obtain 4-aminosalicyl hydrazide (yield 78.4%).
Subsequently, 4-aminosalicyl hydrazide (0.5 g, 3.0 mmol) in EtOH
(100 mL) was made to react with o-vanillin (0.45 g, 3.0 mmol)
for 2 h in a water bath at 100 ◦C. After cooling to room tem-
perature, the precipitate was collected by filtration and was
recrystallized from MeOH to obtain the final product, HMB-ASH
(yield 82.5%).
2.7. Binding ratio of Sc3+ to HMB-ASH
Molar ratio method: Fifty microliters of ammonia buffer (pH 8.0)
was added to 50 ␮L of varying concentrations (2.22, 6.67, 11.12,
15.57, 22.2, and 33.4 ␮mol L−1) of Sc3+, followed by the addition
of 50 ␮L of a 20 ␮mol L−1 solution of HMB-ASH in DMSO, and the
solution mixture was treated in a manner similar to that described
above. Next, 50 ␮L of ammonia buffer (pH 8.0) was added to 50 ␮L
of 22.2 ␮mol L−1 Sc3+, followed by the addition of 50 ␮L of varying
concentrations (10, 15, 30, 40, and 60 ␮mol L−1) of HMB-ASH in
DMSO, and the solution mixture was treated in a manner similar
to that described above (n = 3). The binding ratio was obtained by
using the molar ratio method; that is, the fluorescence intensities
were plotted against the molar ratios of Sc3+ to HMB-ASH, and the
molar ratio of HMB-ASH coordinated to Sc3+ was stoichiometrically
determined from the plots.
Continuous variation method: Fifty microliters of ammonia buffer
(pH 8.0) was added to 10, 20, 30, 40, 50, 60, 70, 80, and 90 ␮L of
22.2 ␮mol L−1 Sc3+, followed by the addition of 90, 80, 70, 60, 50, 40,
30, 20, and 10 ␮L of a 20 ␮mol L−1 solution of HMB-ASH in DMSO,
and the solution mixture was treated in a manner similar to that
described above (n = 3). The fluorescence intensity of each solution
was measured at 512 nm at an excitation wavelength of 353 nm.
The binding ratio was obtained by using the continuous vari-
ation method; that is, the fluorescence intensities were plotted
against the ratio [Sc3+]/([Sc3+] + [HMB-ASH]) or the ratio [HMB-
ASH]/([Sc3+] + [HMB-ASH]). Thereby, the molar ratio of HMB-ASH
coordinated to Sc3+ was stoichiometrically determined from the
plots.
FAB-MS: m/z 302 (M+H)+; Anal. Calcd. for C15H15O4N3: C, 59.80;
H, 5.02; N, 13.95. Found: C, 60.02; H, 4.89; N, 13.77. 1H NMR
(DMSO-d6) ı (ppm): 12.27 (s,1H), 11.67 (s,1H), 11.00 (s,1H), 8.55
(s,1H), 7.59 (d,1H), 7.06 (d,1H), 6.96 (d,1H), 6.80 (t,1H), 6.09 (d,1H),
5.99 (s,2H), 4.32 (s, 3H). 13C NMR (DMSO-d6) ı (ppm): 166.31,
162.33, 163.33, 155.25, 148.42, 148.02, 147.63, 129.44, 121.42,
119.46, 114.31, 106.41, 101.88, 99.86, 56.34. FT-IR (solid phase)
(cm−1): 3352 (vOH), 1595 (vC N), 1249, 1200 (vAr O). Melting point:
252–254 ◦C.
2.4. Screening assay of binding metal ions to HMB-ASH
Each metal ion (Li+, Ag+, K+, Na+, Mg2+, Ca2+, Sr2+, Ba2+, Co2+
Be2+, Zn2+, Hg2+, Ni2+, Cu2+, Cd2+, Ti2+, Mn2+, Fe3+, Ga3+, Al3+
,
,
In3+, Pb2+, Sn2+, Tl3+, Ce3+, Bi3+, Sb3+, Sc3+, Y3+, Ge4+, and Zr4+
)
was examined to determine whether it could be coordinated by
HMB-ASH to emit fluorescence. Each solution containing 100 ␮L
of the selected metal ion (1000 ppm), 100 ␮L of a 100 ␮mol L−1
solution of HMB-ASH in DMSO, and 100 ␮L of a buffer solution
with varying pH values (pH 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5,
8.0, 8.5, 9.0, 9.5, 10.0, and 10.5) was placed in a glass test tube.
The buffer solutions of pH 3.0–5.0, 5.5–7.5, and 7.5–9.0 were pre-
pared from 100 mmol L−1 CH3CO2Na CH3CO2H, CH3CO2H NH3,
and NH4Cl NH3, respectively. In a dark room, ultraviolet light
from a D2 lamp was irradiated on each test tube. The sample
emitting intense fluorescence was concluded to be the solu-
tion that contained the fluorescent complex of HMB-ASH. In this
experiment, the fluorescent emission was evaluated by visual
assessment.
2.8. Binding constant
The apparent binding constant of HMB-ASH with Sc3+ was cal-
culated using the modified Benesi–Hildebrand equation reported
by Roy et al. [11]:
ꢀFmax
ꢀF
1
K[C]
= 1 +
(1)
where ꢀF and ꢀFmax are equal to F − F0 and Fmax − F0, respectively.
F0, F, and Fmax are the fluorescence intensities of HMB-ASH (20 ␮M),
HMB-ASH with a test concentration of Sc3+ (2.22, 6.67, 11.12, 15.6,
22.2, and 33.4 ␮mol L−1), and HMB-ASH with the maximum con-
centration (33.4 ␮mol L−1) of Sc3+, respectively. K and [C] are the
apparent binding constant and test concentration of Sc3+, respec-
tively. ꢀFmax/ꢀF was plotted against 1/[C], and the value of K was
obtained from the slope of the obtained line.
2.5. Influence of pH and the excitation and emission spectra
In a polypropylene test tube, 50 ␮L of each pH buffer solu-
tion (100 mmol L−1 CH3CO2Na CH3CO2H, CH3CO2H NH3, and
NH4Cl NH3) was serially added to 50 ␮L of 44.4 ␮mol L−1 Sc3+
[Sc(NO3)3] in H2O and 50 ␮L of a 100 ␮mol L−1 solution of HMB-
ASH in DMSO, and the resultant solution mixture was left to stand
for 10 min at room temperature. Then, the solution was diluted 10-
fold with distilled EtOH, and its spectrum was measured by using
a spectrofluorescence photometer, FP-6300 (Jasco).
2.9. Calibration curve and detection limit
A calibration curve was constructed by plotting the values
of F − F0 against Sc3+ concentration. Fifty microliters of the Sc3+
solution (2.22, 4.44, 11.1, 15.5, 22.2, and 44.4 ␮mol L−1) was

74
H. Yamada et al. / Spectrochimica Acta Part A 90 (2012) 72–77
Fig. 1. Synthetic pathway of HMB-ASH.
added to 50 ␮L of a 100 ␮mol L−1 HMB-ASH solution and 50 ␮L
of 100 mmol L−1 ammonia buffer (pH 8.0) (n = 3). The subsequent
procedure was the same as that in the previous treatment.
The detection limit (DL) was determined by the obtained cali-
bration curve using the following equation:
results showed that Sc3+ ions coordinated with HMB-ASH to emit
intense fluorescence upon irradiation from a D2 lamp. Previously,
Tang and his colleagues reported a fluorescent ligand, salicylalde-
hyde salicyloylhydrazone (SASH), and the chemical structure of
SASH is quite similar to that of HMB-ASH, with the exception
that HMB-ASH bears 3-methoxy and aromatic 4-amino groups
attached to both phenyl moieties (Fig. 2). It has been reported
ꢁ
DL = 3.3
,
(2)
s
that SASH (Fig. 2(b)) exhibits fluorescence in the presence of Al3+
,
where ꢁ and s are the standard deviation of 22.2 nmol L−1 Sc3+ and
slope of the calibration curve, respectively (n = 5).
Sc3+, and In3+ [12–14]. However, the structurally similar com-
pound, HMB-ASH, showed fluorescence in the presence of only
Sc3+
.
2.10. Application to environmental water samples
In polypropylene test tubes, 1.0 ppm (22.2 ␮mol L−1) Sc3+ solu-
tions in a river water sample, taken from Shinkawa (Chiba, Japan),
and a tap water sample (Chiba, Japan) were prepared. These sam-
ples were subjected to a solid-phase extraction (SPE) procedure.
Four hundred microliters of these sample solutions were loaded on
an anion exchange cartridge, MonospinTM SAX (GL Sciences Inc.,
Tokyo, Japan), and were centrifuged at 1800 × g for 30 min. This
procedure was repeated twice. Fifty microliters of the obtained fil-
trate was serially added to 50 ␮L of 100 mmol L−1 ammonia buffer
(pH 8.0) and 100 ␮mol L−1 HMB-ASH, and the solution mixture was
treated in a similar manner as described in Section 2.5. In contrast,
50 ␮L of river and tap water samples was directly added to 50 ␮L
of 100 mmol L−1 ammonia buffer (pH 8.0) and 100 ␮mol L−1 HMB-
ASH (without SPE). The recovery of Sc3+ (%) was calculated by using
the following equation:
3.2. Influence of pH and the fluorescence spectrum
Fig. 3 (a) shows the excitation and emission spectra of the
HMB-ASH–Sc3+ complex obtained at pH 8.0. As shown in Fig. 3(a),
the optimum wavelengths for the excitation and emission were
353 and 512 nm, respectively. The level of intense fluorescence
exhibited by HMB-ASH in the presence of Sc3+ was approximately
30 times that exhibited by HMB-ASH alone, suggesting that the
formation of the HMB-ASH–Sc3+ complex certainly enhanced the
fluorescence.
With regard to the optimum pH for the measurement, it was
found that the fluorescence was intense in both weakly acidic (pH
3.5) and basic (pH 8.0) regions (Fig. 3(b)) and that the fluorescence
was more intense in the basic pH region than in the acidic pH region.
Among the organic solvents used for the dilution and fluorescence
measurement of the HMB-ASH–Sc3+ complex, EtOH gave the most
intense fluorescence (data not shown); therefore, EtOH was used
for further study.
Ftest − Fblank
Recovery (%) =
× 100,
(3)
Fstd − Fblank
where Fstd and Fblank are the fluorescence intensities in the presence
and absence of 1.0 ppm Sc3+ in the distilled H2O, respectively, and
Ftest is the fluorescence intensity of the 1.0 ppm Sc3+ solutions in
the environmental water samples.
3. Results and discussion
3.1. Synthesis and fluorescence property of HMB-ASH
HMB-ASH was designed and synthesized as shown in Fig. 1.
4-Aminosalicylic acid was first esterified to the methylester, and
subsequently, a hydrazine group was introduced to the ester
moiety. Next, an o-vaniline moiety was covalently bound to the
hydrazine group to form a Schiff base moiety. Elemental analysis,
FAB-MS, 1H NMR, and 13C NMR data showed that HMB-ASH was
successfully synthesized. Next, to identify a metal ion that could
coordinate with HMB-ASH to emit fluorescence, 31 types of metal
ions (1000 ppm) in different pH-buffered solutions were tested. The
Fig. 2. Chemical structures of HMB-ASH (a) and SASH [11–13] (b).

H. Yamada et al. / Spectrochimica Acta Part A 90 (2012) 72–77
75
Table 1
Effect of coexisting ions on the detection of 22.2 ␮M Sc3+ using 50 ␮M HMB-ASH at pH 8.0 and 3.5 (tolerable error: 5%).
Tolerance ratio (m/m)
Coexisting ions (pH 8.0)
−
H2BO3
>100
50
10
5
Al3+
Ni2+
In3+
Ga3+
Fe3+
Mn2+
Ca2+
Mg2+
Ba2+
Co2+
Sr2+
Zn2+
Pb2+
Cd2+
Hg2+
Br−
F−
Cl−
Hg2+
2
1
0.5
–
Tolerance ratio (m/m)
Coexisting ions (pH 3.5)
−
H2BO3
>100
50
10
5
Al3+
Sr2+
Cd2+
Ni2+
Mn2+
Ca2+
Pb2+
Hg2+
Br−
Cl−
Co2+
In3+
Fe3+
F−
2
1
0.5
Zn2+
–
Ga3+
Ba2+
Tolerance ratio (m/m) was expressed as a ratio of the tested ion (mol) to the Sc3+ ion (mol).
3.4. Binding ratio of HMB-ASH to Sc3+ and the binding constant
3.3. Coexisting ions
Table 1 shows the effect of ions on the fluorescence intensity
of the HMB-ASH–Sc3+ complex at pH 8.0 and 3.5. A difference was
observed in the effect of coexisting ions on the fluorescence inten-
sity at pH 3.5 and 8.0. Overall, very few ions interfered with the
fluorescence of the HMB-ASH–Sc3+ complex at pH 8.0. In the case
of SASH, trivalent cations such as Al3+, In3+, and Ga3+ interfered
with the SASH–Sc3+ complex [13]. However, these trivalent cations
could hardly influence the fluorescence in the case of the HMB-
ASH–Sc3+ complex. As shown in Table 1, among the tested ions,
Fe3+ intensively interfered with the fluorescence intensity of the
HMB-ASH–Sc3+ complex (pH 8.0). In order to prevent the inter-
Fig. 5(a) and (b) shows the plots of the fluorescence intensity
against the molar ratio of Sc3+ to HMB-ASH (a) and of HMB-ASH
to Sc3+ (b). Both plots (a) and (b) indicate that HMB-ASH could
bind to Sc3+ at a molar ratio of 1:1. In addition, the continuous
variation method (Job plot, Fig. 5(c) and (d)) also indicated the
binding of HMB-ASH to Sc3+ at the 1:1 ratio. Therefore, similar to
the SASH–Sc3+ [12] or SASH–In3+ complex [14], it was found that
HMB-ASH could bind to Sc3+ at a molar ratio of 1:1. The binding
association constant K was determined by the Benesi–Hildebrand
method, and log K was found to be approximately 5.4. This log K
value was considered to be sufficient for the fluorescence detection
of Sc3+ in the application samples.
ference by Fe3+, 44.4 mmol L−1 (200 eq. to Sc3+) thiocyanate ions
(SCN−) were added, which resulted in the masking of Fe3+ to form
a soluble complex, Fe(SCN)2+ or Fe(SCN)63−. The masking effect of
Fe3+ by SCN− was clearly observed until the experiment reached
5 eq. of Fe3+ to Sc3+ (Fig. 4).
3.5. Calibration curve and the detection limit
Fig. 6 shows a calibration curve for Sc3+ ions using the present
fluorescent ligand, HMB-ASH. A linear calibration curve was
obtained for the Sc3+ ions in the concentration range 22.2–444 nM
(r2 = 0.998) (Fig. 6). The precision, given by the relative standard
deviation (RSD) as a percentage, was in the range 2.22–11.8% (n = 3).
The detection limit of Sc3+ in the buffer (pH 8.0) was approximately
18.8 nmol L−1
.
Fig. 4. Masking effect of 44.4 mmol L−1 thiocyanate ions on the fluorescence inten-
sity of the HMB-ASH–Sc3+ complex in the presence of 22.2 ␮mol L−1 (1 eq.) to
111 ␮mol L−1 (5 eq.) Fe3+. Filled and open columns represent results obtained with
and without the thiocyanate ion, respectively. The mean value of the fluorescence
intensity in the presence of 22.2 ␮mol L−1 (1 eq.) Fe3+ was designated as 100. Each
column represents mean SD (n = 5).
Fig. 3. Excitation and emission spectra of HMB-ASH in the presence (solid line)
and absence (dotted line) of Sc3+ at pH 8.0 (a). Fluorescence intensity of the HMB-
ASH–Sc3+ complex at 512 nm (ex. 353 nm) as a function of pH (b).

76
H. Yamada et al. / Spectrochimica Acta Part A 90 (2012) 72–77
Fig. 5. Binding ratio of HMB-ASH to Sc3+ by molar ratio (a and b) and continuous variation (c and d) methods.
Table 2
3.6. Preliminary application to an environmental sample
Recovery of 1.0 ppm (22.2 ␮M) Sc3+ from tap and river water samples by the pro-
posed method with or without the solid-phase extraction (SPE) procedurea (n = 3).
Scandium is a rare earth metal and has been used for developing
industrial materials such as alloys and manufacturing devices such
as halide light bulbs [15]. Therefore, wastewater containing Sc3+
ions might be discharged from factories into natural water bod-
ies; consequently, environmental water might be contaminated
by Sc3+ ions. Steps should therefore be taken to prevent this con-
tamination. The proposed method was used to test tap and river
water samples for Sc3+ ions. No Sc3+ was detected in the tap and
river samples by using the present method (data not shown). Next,
1.0 ppm (22.2 ␮M) Sc3+ solutions containing tap and river water
samples were artificially prepared, and the recovery of Sc3+ was
examined. When the tap and river water samples were directly
used without SPE, Sc3+ was not sufficiently recovered (Table 2). In
contrast, the recovery of Sc3+ from these water samples remarkably
improved after SPE using an anion-exchange cartridge. Considering
this result, an anion found in the environment, such as F−, might
interfere with the detection of Sc3+ because F− was shown to inter-
fere with the fluorescence of the HMB-ASH–Sc3+ complex (Table 1).
Thus, the proposed method will be useful for Sc3+ detection in
environmental water samples after SPE using an anion-exchange
cartridge.
Recovery (%)
Tap water
Without SPE
With SPE
62.3 2.37
95.1 5.89
River water
Without SPE
With SPE
63.2 2.31
103 1.90
a
Solid-phase extraction with MonospinTM SAX.
4. Conclusion
A fluorescent chelating ligand, HMB-ASH, was newly designed
and synthesized. HMB-ASH exhibited selective fluorescence with
the Sc3+ ion. Thus, the selective and sensitive determination
of Sc3+ ions was achieved by using HMB-ASH as a fluorescent
ligand.
Acknowledgements
The authors thank Dr. Y. Ohshima, Dr. M. Fujii, and Prof. K. Kato of
Toho University for their kind advice on the measurement of NMR
and IR spectra of HMB-ASH. Thanks are also due to Miss Miyuki
Takeshima and Miss Haruyo Shibata of Toho University for their
technical assistance with this research.
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represents mean SD (n = 5).

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