Dysprosium(III) ion-selective electrochemical sensor based on 6-hydrazino-1,5-diphenyl-6,7-dihydropyrazolo-[3,4-d]pyrimidine-4(5H)-imine

Article abstract of DOI:10.1135/cccc20071189

A Dy(III) ion-selective electrode based on 6-hydrazino-1,5-diphenyl-6,7- dihydropyrazolo-[3,4-d]pyrimidine-4(5H)-imine (HDDPI) as an excellent sensing material was developed. The sensor exhibits a Nernstian behavior (a slope of 19.6 ± 0.3 mV per decade) o

Full text of DOI:10.1135/cccc20071189

Dysprosium(III) Ion-Selective Electrochemical Sensor
1189
DYSPROSIUM(III) ION-SELECTIVE ELECTROCHEMICAL SENSOR
BASED ON 6-HYDRAZINO-1,5-DIPHENYL-6,7-DIHYDROPYRAZOLO-
[3,4-d]PYRIMIDINE-4(5H)-IMINE
b,c
a2
Hassan Ali ZAMANIa1,*, Mohammad Reza GANJALI and Nasim SEIFI
a
Department of Applied Chemistry, Quchan branch, Islamic Azad University, Quchan, Iran;
1
2
e-mail: haszamani@yahoo.com, nseifi2006@yahoo.com
Center of Excellence in Electrochemistry, University of Tehran, Tehran, Iran
Endocrine & Metabolism Research Center, Tehran University of Medical Sciences, Tehran, Iran;
e-mail: ganjali@gmail.com
b
c
Received Septem ber 9, 2006
Accepted Decem ber 12, 2006
A Dy(III) ion -selective electrode based on 6-h ydrazin o-1,5-diph en yl-6,7-dih ydropyrazolo-
[3,4-d]pyrim idin e-4(5H)-im in e (HDDPI) as an excellen t sen sin g m aterial was developed. Th e
sen sor exh ibits a Nern stian beh avior (a slope of 19.6 ± 0.3 m V per decade) over a wide con -
cen tration ran ge (from 1.0 × 10–1 to 8.0 × 10–7 M Dy) with a detection lim it of 4.2 × 10–7 M.
Th e sen sor respon se is in depen den t of pH of th e solution in th e pH ran ge 3.5–8.3. Th e sen -
sor possesses th e advan tages of sh ort con dition in g tim e, fast respon se tim e (<10 s) an d in
particular, good selectivity an d sen sitivity to th e dysprosium ion in th e presen ce of a variety
of cation s, in cludin g alkali, alkalin e earth , tran sition an d h eavy m etal ion s. Th e sen sor also
sh owed a great en h an cem en t in selectivity coefficien ts for dysprosium ion s, in com parison
with th e form erly m en tion ed dysprosium sen sors. Th e electrode can be used for at least 10
weeks with out an y con siderable divergen ce in th e poten tials. Th e proposed electrode was
successfully used as an in dicator electrode in poten tiom etric titration of Dy(III) ion s with
EDTA. Th e m em bran e sen sor was also used in th e determ in ation of con cen tration of F– ion s
in som e m outh wash in g solution s an d in th e Dy3+ recovery from solution .
Keyw ord s: Poten tiom etry; Dysprosium sen sors; ISEs; 6-Hydrazin o-1,5-diph en yl-6,7-dih ydro-
pyrazolo[3,4-d]pyrim idin e-4(5H)-im in e; Metal ion s com plexation .
At presen t, an alysis an d determ in ation of lan th an ides con sist of essen tial
issues, on th e groun ds th at lan th an ides sh ow sim ilar ch em ical an d ph ysical
properties. For th e determ in ation of each on e of th em , first separation
alon g with purification , an d even som etim es precon cen tration , are n eces-
sary steps1. Dysprosium is on e of th e lan th an ides widely used as a fluores-
cen ce an d m agn etic m aterial, m agn etic m aterial as well as in th e field of life
scien ce. As already m en tion ed, th e difficulty degree of th e lan th an ides de-
term in ation is h igh . Th erefore, a sen sitive an d selective m eth od is required
in order to gain a precise result. Several m eth ods h ave been used for th e
Dy3+ determ in ation like spectrom etry2–5, in ductively coupled plasm a6,7
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206
© 2007 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20071189

1190
Zamani, Ganjali, Seifi:
(ICP), ch rom atograph y8,9, electroch em istry10,11, reson an ce ligh t scatterin g12
(RLS) an d capillary zon e electroph oresis coupled with cloud poin t extrac-
tion 13. Despite th e fact th at th ese m eth ods are precise an d sen sitive, th ey
are also expen sive an d tim e-con sum in g. An oth er m eth od for th e determ i-
n ation of th is elem en t is th e ion selective electrode (ISE) for Dy(III) poten -
tiom etric titration . Th e ISEs work fast an d th ey are easily prepared with out
an y special or expen sive equipm en t.
We h ave curren tly developed som e ISEs for th e poten tiom etric determ i-
n ation of lan th an ides, wh ere polym eric m em bran es were prepared with in -
creasin gly selective ion oph ores, sen sin g an alyte selectively. Th e ISEs
in clude in particular; terbium (III)14, ytterbium (III)15, sam arium (III)16, lan -
th an um (III)17, cerium (III)18 an d gadolin ium (III)19 sen sors. Neverth eless,
th ere is on ly a lim ited n um ber of reports con cern in g th e developm en t of
h igh ly selective ion oph ores for dysprosium in literature20–22
.
Th is study describes an oth er ion selective sen sor for Dy(III) poten tio-
m etric determ in ation based on 6-h ydrazin o-1,5-diph en yl-6,7-dih ydro-
pyrazolo[3,4-d]pyrim idin e-4(5H)-im in e (HDDPI), as a n ovel n eutral ion o-
ph ore (Sch em e 1, com poun d 3). Th ree n oticeable ben efits dem on strated
by th is sen sor are th e fast respon se tim e, low detection lim it an d also great
selectivity.
NH
NH
Ph
Ph
S
MeI
N
N
N
N
N
N
Ph
KOH
N
H
SMe
N
H
Ph
1
2
NH2NH2
NH
N
Ph
N
N
Ph
N
H
NHNH2
3
SCHEME 1
Gen eral procedure for th e HDDPI syn th esis
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Dysprosium(III) Ion-Selective Electrochemical Sensor
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EXPERIMENTAL
Reagen ts
Merck Ch em ical an d th e Aldrich Co. were th e suppliers of th e n itrate an d ch loride salts of
all cation s an d th e reagen t grades of 2-n itroph en yl octyl eth er (NPOE), dibutyl ph th alate
(DBP), n itroben zen e (NB), sodium tetraph en ylborate (NaTPB), tetrah ydrofuran (THF) an d
h igh -m olecular-weigh t PVC. All reagen ts were used with out an y m odification . Nitrates an d
ch lorides of th e em ployed cation s were of th e h igh est available purity. Th ey were vacuum -
dried over P2O5. Triply distilled deion ized water was used in experim en ts.
HDDPI Syn th esis
6-(Methylsulfonyl)-1,5-diphenyl-6,7-dihydropyrazolo[3,4-d]pyrimidine-4(5H)-imine
(2):
4-im in io-1,5-diph en yl-4,5-dih ydropyrazolo[3,4-d]pyrim idin e-6(7H)-th ion e (1; 5 m m ol) an d
m eth yl iodide (5 m m ol) were dissolved in EtOH (20 m l) an d H2O (15 m l), con tan in g KOH
(10 m m ol). Th e reaction m ixture was stirred at room tem perature for 5 h . Th en , th e crude
product was filtered off an d recrystallized from eth an ol to give com poun d 2 in 70% yield,
m .p. 162–163 °C. 1H NMR (DMSO-d6): 2.7 (S, 3 H, CH3); 7.2–8.1 (m , 11 H, arom .); 9.6 (s,
1 H, NH, exch an geable with D2O). MS, m/z: 333 (M+). For C18H15N5S (333.0) calculated:
64.84% C, 4.53% H, 21.01% N, 9.62% S; foun d: 64.87 C, 4.48 H, 20.97 N, 9.65% S.
6-Hydrazino-1,5-diphenyl-6,7-dihydropyrazolo[3,4-d]pyrimidine-4(5H)-imine (3): 6-(m eth yl-
sulfon yl)-1,5-diph en yl-6,7-dih ydropyrazolo[3,4-d]pyrim idin e-4(5H)-im in e (2; 1 m m ol) an d
h ydrazin e h ydrate were h eated at 60 °C in eth an ol (10 m l) for 8 h . Th en , th e precipitate
was filtered off an d recrystallized from eth an ol to give com poun d 3 in 62% yield, m .p.
221–223 °C. 1H NMR (DMSO-d6): 4.7 (s, 1 H, NH, exch an geable with D2O); 6.8–8.2 (m ,
11 H, arom .); 4.7 (s, 1 H, NH, exch an geable with D2O); 9.2 (s, 1 H, NH, exch an geable with
D2O). MS, m/z: 317 (M+). For C17H15N7 (317.4) calculated: 64.34% C, 4.76% H, 30.90% N;
foun d: 64.36% C, 4.72% H, 30.86% N.
Electrode Preparation
Th e PVC m em bran e preparation in volved blen din g of th e followin g com poun ds; 30 m g of
powdered PVC, 63 m g of NPOE an d 2 m g of NaTPB in 5 m l THF. To th is solution , 5 m g of
HDDPI was added an d m ixed well. Th en , th e resultin g m ixture was tran sferred in to a glass
dish of 2 cm in diam eter. A Pyrex tube (5 m m o.d.) was dipped in to th e m ixture for about 5 s,
leadin g to th e form ation of a tran sparen t m em bran e (about 0.3 m m in th ickn ess). After-
wards, th e tube was rem oved from th e m ixture, kept at room tem perature for at least 12 h
an d filled with an in tern al fillin g solution (1.0 × 10–3 M DyCl3). Even tually, th e electrode
was con dition ed for 24 h by soakin g in 1.0 × 10–2 M DyCl3 23–31. A silver/silver ch loride elec-
trode was used as an in tern al referen ce electrode.
Th e em f Measurem en ts
Th e equipm en t for th e electrom otive force (em f) m easurem en ts con sisted of: (i) Ag–AgCl|
in tern al solution , 1.0 × 10–3 M DyCl3|PVC m em bran e|sam ple solution |Hg–Hg2Cl2, KCl (sat.),
(ii) a Corn in g ion an alyzer with a 250 pH/m V m eter an d (iii) a double-jun ction saturated
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206

1192
Zamani, Ganjali, Seifi:
calom el electrode (SCE, Ph ilips) with th e ch am ber filled with an am m on ium n itrate solu-
tion . Th e poten tial m easurem en ts were perform ed at 25.0 °C.
Com plexation Study
Con ductivity m easurem en ts were carried out with a Metroh m 660 con ductivity m eter.
A dip-type con ductivity cell m ade of black platin um was used with a cell con stan t of
0.83 cm –1. In all m easurem en ts, th e cell was th erm ostatted at th e desired tem perature
25.0 °C, usin g a Ph ywe im m ersion th erm ostat.
In a typical experim en ts, 25 m l of a cation n itrate solution (1.0 × 10–4 M) was placed in a
water jacketed cell, equipped with a m agn etic stirrer an d con n ected to a water th erm ostat.
In order to keep th e electrolyte con cen tration con stan t durin g titration s, both th e startin g
solution an d th e titran t h ad th e sam e cation con cen tration . Th en , a kn own am oun t of th e
HDDPI (1.0 × 10–2 M) solution was added stepwise usin g a calibrated m icropipette. Th e solu-
tion con ductan ce was m easured after each addition . Th e HDDPI addition was con tin ued
un til th e desired HDDPI/cation m ole ratio was ach ieved. Th e 1:1 bin din g of th e cation s with
HDDPI can be expressed by th e followin g equilibrium :
Kf
→ n+
Mn+ + L
ML
.
(1)
→
Th e correspon din g equilibrium con stan t, Kf, is given by
[MLn +
]
f( MLn +
)
Kf
=
×
,
(2)
[Mn + ][L] f( M n + f(L )
)
wh ere [MLn+], [Mn+], [L] an d f represen t th e equilibrium m olar con cen tration of com plexes,
free cation , free HDDPI an d th e activity coefficien t of th e species in dicated, respectively. Un -
der th e dilution con dition s, th e activity coefficien t of th e un ch arged ligan d, f(L) can be rea-
son ably assum ed as un ity32. Th e use of Debye–Hückel lim itin g law for 1:1 electrolytes33
,
leads to th e con clusion th at f( M n + ≈ f( MLn + ) , so th e activity coefficien t in Eq. (2) is can celed
)
out. Th us, th e com plex form ation con stan t in term s of m olar con ductan ce Λ, can be ex-
pressed as34
:
[MLn +
]
(ΛM − Λobs
)
Kf
=
=
,
(3)
(4)
[Mn + ][L] (Λobs − ΛML )[L]
wh ere
C M (ΛM − Λobs
)
Kf = CL
−
.
(Λobs − ΛML
)
Here, ΛM is th e m olar con ductan ce of th e cation before th e HDDPI addition , ΛML th e m olar
con ductan ce of th e com plexed, Λobs th e m olar con ductan ce of th e solution durin g titration ,
CL th e an alytical con cen tration of th e added HDDPI an d CM th e an alytical con cen tration of
th e cation salt. Th e com plex form ation con stan t, Kf, an d th e m olar con ductan ce of th e com -
plex, ΛML, were obtain ed by com puter-fittin g Eqs (3) an d (4) to th e m olar con ductan ce-m ole
ratio data, usin g a n on lin ear least-squares program KINFIT 35
.
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Dysprosium(III) Ion-Selective Electrochemical Sensor
1193
RESULTS AND DISCUSSION
HDDPI Complexation with Some Cations in Acetonitrile
In prim ary experim en ts, th e in teraction of HDDPI (with seven n itrogen
don or atom s) with a n um ber of m etal ion s was in vestigated in an aceton i-
trile solution usin g th e con ductom etric m eth od. Th e associated results il-
lustrated th at th e ligan d/cation m ole ratio is 1 in all cases. Th e form ation
con stan ts (Kf) of th e resultin g 1:1 com plexes were evaluated by com puter-
fittin g th e m olar con ductan ce-m ole ratio data to th e appropriate equation s.
Th e results are sum m arized in Table I. Th e obtain ed form ation con stan ts
revealed th at HDDPI could be used as an excellen t ion carrier for th e con -
struction of a selective Dy(III) m em bran e sen sor.
TABLE I
Th e form ation con stan ts of HDDPI–Mn+ com plexes
Cation
log Kf
Cation
log Kf
Dy3+
Ce3+
La3+
Eu3+
Gd3+
Sm 3+
Nd3+
Cr3+
Fe3+
5.46 ± 0.08
2.93 ± 0.05
<2
Na+
K+
Ca2+
Sr2+
Co2+
Ni2+
Cd2+
Cu2+
Zn 2+
<2
<2
<2
3.56 ± 0.01
<2
<2
<2
<2
2.65 ± 0.11
<2
<2
2.83 ± 0.02
<2
2.14 ± 0.04
2.21 ± 0.07
Response of the HDDPI-Based Sensors to Dy(III) Ions
HDDPI was used as a n eutral ion carrier to prepare a n um ber of m em bran e
sen sors for som e m etal ion s. Th en , th eir poten tial respon ses were m easured
th e results are sh own in Figs 1a, 1b an d 1c. It can be seen th at th e HDDPI-
based m em brane displays a Nernstian response to the concentration of Dy(III)
ion s in a wide con cen tration ran ge.
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1194
Zamani, Ganjali, Seifi:
n+
pM
n+
pM
n+
pM
FIG. 1
Potential responses of various ion-selective electrodes based on HDDPI. a: ꢀ Dy, ᭹ Nd, × Eu, ء Gd,
᭝ Sm , | Ce, - La; b: ꢀ Dy, ᭝ Co, × Zn , ء Cu, ᭹ Cd, | Ni; c: ꢀ Dy, ᭿ Pb, × Na, ᭺ Mg, | Ca, - Fe, – Cr
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206

Dysprosium(III) Ion-Selective Electrochemical Sensor
1195
Membrane Composition Effect on the Potential Response of the
HDDPI-Based Dy(III) Sensor
Sin ce th e sen sitivity an d selectivity for a given ion oph ore depen d sign ifi-
can tly on th e m em bran e in gredien ts, th e n ature of th e solven t m ediator
an d th e additive36–46, th e in fluen ce of m em bran e com position on th e po-
ten tial respon se of th e Dy(III) sen sor was in vestigated. Th e data reported in
Table II dem on strate th at an ion oph ore am oun t in crease up to 5% in th e
presen ce of 2% NaTPB an d 63% polar solven t (NPOE) results in th e ach ieve-
m en t of th e optim um sen sitivity. Gen erally speakin g, th e presen ce of lipo-
ph ilic an ion s in a cation -selective m em bran e based on a n eutral carrier n ot
on ly dim in ish es th e oh m ic resistan ce an d en h an ces th e respon se beh avior
an d selectivity, but also, in cases wh ere th e extraction capability is poor,
in creases th e m em bran e electrode sen sitivity46–50. However, th e m em bran es
with th e com position 30% PVC, 5% HDDPI, 2% NaTPB an d 63% NPOE
sh ow a Nern stian poten tial respon se.
TABLE II
Optim ization of m em bran e com position (wt.%)
Sen sor
No.
Slope
m V/decade
Dyn am ic lin ear ran ge
m ol/l
PVC
Plasticizer
HDDPI NaTPB
1
2
3
4
5
6
7
8
30
30
30
30
30
30
30
30
NPOE,68
NPOE,66
NPOE,64
NPOE,63
NPOE,62
NPOE,62
NB,63
2
2
4
5
5
6
5
5
0
2
2
2
3
2
2
2
7.3 ± 0.4
4.3 × 10–2 – 1.0 × 10–4
5.0 × 10–1 – 1.0 × 10–5
1.0 × 10–1 – 2.5 × 10–6
1.0 × 10–1 – 8.0 × 10–7
1.0 × 10–1 – 1.0 × 10–6
1.0 × 10–1 – 1.0 × 10–6
1.0 × 10–1 – 1.0 × 10–6
1.0 × 10–1 – 5.0 × 10–6
12.5 ± 0.6
17.3 ± 0.7
19.6 ± 0.3
18.2 ± 0.5
17.9 ± 0.4
17.5 ± 0.6
16.7 ± 0.7
DBP,63
Calibration Graph and Statistical Data
Th e poten tial respon se of th e developed HDDPI-based sen sor (com position
No. 4) sh ows a lin ear respon se to th e con cen tration of Dy ion s in th e ran ge
8.0 × 10–7–1.0 × 10–1 M Dy (Fig. 2). Th e results m ay be sum m arized as fol-
lows. Th e calibration graph slope is 19.6 ± 0.3 m V per decade of th e Dy(III)
con cen tration . Th e detection lim it of th e sen sor, as determ in ed from th e
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206

1196
Zamani, Ganjali, Seifi:
intersection of the two extrapolated segm ents of the calibration graph, is 4.2 ×
10–7 M. Th e stan dard deviation of eigh t replicate m easurem en ts is ±0.4 m V.
It sh ould be n oted th at th e observed detection lim its are usually affected
by th e presen ce of oth er in terferin g ion s or im purities. So, if m etal buffers
are used to elim in ate such effects, wh ich lead to th e con tam in ation of very
dilute solution s, th e detection lim it can be en h an ced down to 10–10 M.
Recen tly, it was sh own th at th e lower detection lim it is n ot an in h eren t
property of ISEs, an d is determ in ed by a sm all flux of prim ary ion s from th e
organ ic sen sin g m em bran e in to its aqueous surface layer51–53. As a con se-
quen ce, a con stan t low activity, ailim , of th e prim ary ion (i) is m ain tain ed in
th is surface layer even wh en th e activity of (i) in th e sam ple, ai, is lower
th an ailim 54–56. Th is sm all flux of th e target ion s h as been successfully elim i-
n ated by ch oosin g an in tern al solution with a con stan t low activity of (i)
an d a h igh on e of an in terferin g ion (j)57–59
.
Origin ally, in tern al solution s with ion buffers (e.g., EDTA) were used for
th is purpose. Obviously, th is is n ot feasible with cation s such as alkali
m etal an d am m on ium ion s as well as m an y an ion s for wh ich n o appropri-
ate com plexin g agen ts are available. An oth er m eth od to avoid leach in g of
prim ary ion s from th e m em bran e in to th e sam ple m akes use of an exter-
n ally applied curren t th at gen erates a steady flux of cation s toward th e in -
n er com partm en t of th e ISE 60. Alth ough th is m eth od does n ot require an y
3+
pDy
FIG. 2
Calibration curve of th e dysprosium electrode based on HDDPI
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Dysprosium(III) Ion-Selective Electrochemical Sensor
1197
com plexin g reagen ts, it n eeds m ore soph isticated in strum en tation s an d
m easurem en t procedures an d is, th erefore less appropriate for routin e appli-
cation s.
Ion s leach in g from th e m em bran e in to th e sam ple n ot on ly in fluen ces
th e lower detection lim its of ISEs, but also bias th e selectivity coefficien ts
sin ce th ey m ay be poten tial determ in in g even if m easurem en ts are taken in
pure solution s of a stron gly discrim in ated ion 61–66. It was foun d th at th e
th us-obtain ed selectivity coefficien ts represen t upper lim its rath er th an true
(th erm odyn am ic) values, wh ich m ay be better by m an y orders of m agn itude
th an th ose determ in ed by con ven tion al m eth ods61.
Pretsch et al. added a cation -exch an ge resin to th e in tern al solution of
ISEs to keep th e prim ary ion activity at a con stan t low level. Th e results
sh owed th at th e lower detection lim it is im proved an d true selectivities are
obtain ed for a valin om ycin -based K+-ISE. Th e gen eral applicability of th e
m eth od is dem on strated by im provin g th e lower detection lim its of NH+4
,
Pb2+, Cd2+ an d Ca2+-ISEs 67. Mich alska et al. reduced th e detection lim it of
a con ductin g polym er (CP) poly(pyrrole)-based poten tiom etric ch loride-
selective electrode over th ree orders of m agn itude by applin g an odic cur-
ren t of den sity in th e ran ge of m icroam peres per cen tim eter squared68
.
In 2003, Pretsch et al. devised a n ew tech n ique for im provin g th e detec-
tion lim its of ISEs, by th e in corporation of liph oph ilic particles such as
silica gel 100 C18-reversed ph ase 40–63 µm (230–400 m esh ASTM) in to th e
sen sin g m em bran e of ion -selective m em bran e sen sors th at stron gly in flu-
en ces th e uptake of ion s from th e sam ple solution . Th e apparen t super-
Nern stian respon se of ISEs caused by a stron g flux of th e target ion s from
th e sam ple to th e in n er fillin g solution can be com pletely suppressed. Th e
m en tion ed effect open s up n ew possibilities for th e trace-level detection of
ion s. Figure 10 in ref.69 sh ows th e optical m icroscope im ages of th e two
sides of a typical ion -selective m em bran e sen sor with 16 wt.% of silica gel
focusin g on th e particles th rough th e tran sparen t m em bran e again sh ows
th at th ey are closely packed69
.
Life-Time Study
Th e stability an d life-tim e evaluation of th e recom m en ded m em bran e
sen sor required four electrodes. Th ey were tested for a period of 12 weeks,
durin g wh ich th e electrodes were used exten sively (on e h our per day)70,71
.
After 10 weeks, a sligh t gradual decrease in th e slopes (from 19.6 to 17.8 m V
per decade) was observed.
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1198
pH Effect on the Electrode Response
Zamani, Ganjali, Seifi:
For th e study of th e pH effect on th e sen sor perform an ce, th e poten tials
were determ in ed in th e pH ran ge 2.0–11.0 (pH was adjusted with con cen -
trated NaOH or HCl) at the concentration of the Dy(III) solution 1.0 × 10–3 M.
Th e resultin g data are depicted in Fig. 3. Eviden tly, th e poten tial respon se
of th e sen sor rem ain s con stan t in th e pH ran ge 3.5–8.3. At pH values lower
th an 3.5, a poten tial in crease was n oticed. Th is ph en om en on is attributed
to th e m em bran e respon se to h ydron ium ion (proton ation of n itrogen
atom s in acid m edia). At pH values greater th an 8.3, a poten tial decrease
took place, owin g to th e form ation of in soluble dysprosium h ydroxide.
Dynamic Response Time of the Dy(III) Sensor
Gen erally, dyn am ic respon se tim e is a sign ifican t param eter for an y ion -
selective electrode. In th is research , th e practical respon se tim e of th e rec-
om m en ded sen sor was recorded by ch an gin g th e dysprosium ion con cen -
tration in a series of solution s from 1.0 × 10–6 to 1.0 × 10–1 M. Th e presen ted
data in Fig. 4 illustrate th at th e sen sor reach es its equilibrium respon se
quickly (<10 s) in th e wh ole con cen tration ran ge.
pH
FIG. 3
Th e pH effect of test solution s (1.0 × 10–3 M) on th e poten tial respon se of th e dysprosium sen sor
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Dysprosium(III) Ion-Selective Electrochemical Sensor
1199
Dy(III) Electrode Selectivity
Th e in fluen ce of in terferin g ion s on th e respon se beh avior of an y ion -
selective sen sor is usually described in term s of selectivity coefficien ts, Ksel.
In th is work, selectivity coefficien ts were determ in ed by th e m atch ed po-
ten tial m eth od (MPM)72–76. Accordin g to th is m eth od, a specified activity
(con cen tration ) of prim ary ion s (A, 5.0 × 10–5 M Dy ion s) is added to a refer-
en ce solution (1.0 × 10–6 M Dy) an d th e poten tial is m easured. In a separate
experim en t, in terferin g ion s (B, 1.0 × 10–1 M) are successively added to an
iden tical referen ce solution , un til th e m easured poten tial m atch es th e on e
obtain ed before th e prim ary ion s addition . Th e m atch ed poten tial m eth od
selectivity coefficien t, KMPM, is th en given by th e ratio of activities (con -
cen tration ) of th e resultin g prim ary ion to th ose of in terferin g ion KMPM
aA/aB.
=
Th e resultin g poten tiom etric selectivity coefficien ts values are sum m a-
rized in Table III. For all diverse ion s, th e selectivity coefficien ts of th e elec-
trode are of th e order of 1.0 × 10–3 or sm aller, in dicatin g th at th ey would
n ot sign ifican tly disturb th e fun ction of th e Dy(III) selective m em bran e
sen sor. Table III also sh ows th e selectivity coefficien t of th e m em bran e
with out ion oph ore. In th e absen ce of th e ion oph ore in th e m em bran e th e
t, s
FIG. 4
Dyn am ic respon se tim e of th e dysprosium electrode for step ch an ges in th e Dy3+ con cen tra-
tion (in M): A 1.0 × 10–6, B 1.0 × 10–5, C 1.0 × 10–4, D 1.0 × 10–3, E 1.0 × 10–2, F 1.0 × 10–1
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206

1200
Zamani, Ganjali, Seifi:
selectivity coefficien ts are very h igh , wh ich is due to th e ability of th e in ter-
ferin g ion s to extract from aqueous solution in to th e organ ic layer by in ter-
action with th e additive. It is also worth n oticin g th at th e Dy(III) sen sor
respon se was foun d to be in sen sitive to th e n ature of th e used an ion s.
TABLE III
Selectivity coefficien ts of various in terferin g ion s for th e m em bran e (sen sor No. 4)
K MPM
3 +
K MPM
3 +
Ion s
K MPM
3 +
K MPM
3 +
, B
a
a
Ion s
Dy
, B
Dy
, B
Dy
, B
Dy
Eu3+
Nd3+
Sm 3+
Gd3+
La3+
Ce3+
Cr3+
Fe3+
7.3 × 10–1
8.5 × 10–1
6.0 × 10–1
4.0 × 10–1
4.8 × 10–1
6.0 × 10–1
5.3 × 10–1
4.7 × 10–1
4.1 × 10–1
1.3 × 10–3
2.7 × 10–4
1.0 × 10–3
1.0 × 10–5
2.8 × 10–4
1.0 × 10–4
7.3 × 10–4
6.4 × 10–4
2.3 × 10–4
Cd2+
Cu2+
Zn 2+
Ni2+
Pb2+
Na+
1.2 × 10–1
1.3 × 10–1
3.5 × 10–1
2.2 × 10–1
2.1 × 10–1
1.3 × 10–2
2.1 × 10–2
2.2 × 10–1
3.5 × 10–1
5.6 × 10–4
6.2 × 10–4
2.9 × 10–4
1.0 × 10–4
5.8 × 10–4
2.5 × 10–4
2.1 × 10–4
1.6 × 10–4
1.5 × 10–4
K+
Mg2+
Ca2+
Co2+
a
Th e selectivity coefficien ts for th e m em bran e with out ion oph ore.
Furth erm ore, Table IV com pares th e selectivity coefficien ts of th e Dy(III)
sen sor with th ose of th e best form erly Dy(III) electrodes in th e litera-
ture20–22. From th e reported data in Table IV, it is in stan tly clear th at th e
con cen tration ran ge, respon se tim e, detection lim it of th e proposed elec-
trode an d also selectivity coefficien ts of th e sen sor are superior to th ose
foun d by oth er research ers.
Analytical Application
Th e developed Dy3+ ion -selective electrode was foun d to work well un der
laboratory con dition s. It was used as an in dicator electrode in th e titration
of 1.0 × 10–4 M dysprosium ion s solution with a stan dard 1.0 × 10–2 M EDTA.
Th e resultin g titration curve is sh own in Fig. 5. Eviden tly, th e sen sor is ca-
pable of m on itorin g th e dysprosium ion am oun t.
Th is electrode was also effectively used in th e direct dysprosium detec-
tion in tap water an d river water. Th e 10.0 m l wastewater was taken an d di-
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206

Dysprosium(III) Ion-Selective Electrochemical Sensor
1201
TABLE IV
Com parison of selectivity coefficien ts (MPM), lin earity ran ge, detection lim it an d respon se
tim e of th e Dy(III) electrode an d th e previously reported Dy(III) PVC-m em bran e sen sors
Ion
Ref.20
Ref.21
Ref.22
Th is work
Eu3+
Nd3+
Sm 3+
Gd3+
La3+
Ce3+
Cr3+
Fe3+
Co2+
Cd2+
Cu2+
Zn 2+
Ni2+
Pb2+
Na+
4.0 × 10–4
–
–
1.3 × 10–3
2.7 × 10–4
1.0 × 10–3
1.0 × 10–5
2.8 × 10–4
1.0 × 10–4
7.3 × 10–4
6.4 × 10–4
2.3 × 10–4
5.6 × 10–4
6.2 × 10–4
2.9 × 10–4
1.0 × 10–4
5.8 × 10–4
2.5 × 10–4
2.1 × 10–4
1.6 × 10–4
1.5 × 10–4
<10
3.5 × 10–4
–
–
2.0 × 10–4
2.1 × 10–2
–
1.0 × 10–5
2.5 × 10–2
–
3.0 × 10–4
1.7 × 10–2
–
1.5 × 10–4
1.8 × 10–2
–
–
–
–
–
–
–
–
3.9 × 10–3
–
–
–
–
1.5 × 10–5
6.3 × 10–3
–
–
–
–
–
4.1 × 10–3
2.99 × 10–4
–
8.0 × 10–4
5.0 × 10–3
2.0 × 10–3
–
2.99 × 10–4
2.17 × 10–4
3.13 × 10–4
2.17 × 10–4
~10
K+
–
–
Mg2+
Ca2+
3.0 × 10–5
–
–
–
Respon se <20
tim e, s
<20
Lin earity 1.0×10–6–1.0×10–2 1.0×10–5–1.0×10–1 8.0×10–6–1.0×10–1 8.0×10–7–1.0×10–1
ran ge,
m ol/l
Lim it of
detection ,
m ol/l
8.0 × 10–7
6.0 × 10–6
2.0 × 10–6
4.2 × 10–7
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206

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Zamani, Ganjali, Seifi:
luted with distilled water in a 25.0 m l volum etric flask. Th e poten tial of
th is solution was m easured by th e proposed sen sors. Th e resultin g data are
sum m arized in Table V. It was foun d th at th e accuracy of dysprosium de-
tection in differen t solution sam ples is alm ost quan titative.
Furth erm ore, th e electrode was used in th e poten tiom etric determ in ation
of fluoride ion s in two m outh wash sam ples. 1.0 g of each sam ple was taken
an d diluted with distilled water in a 100 m l flask an d titrated with a Dy3+
solution (1.0 × 10–3 M) an d th e results of triplicate m easurem en ts are sum -
TABLE V
Dy(III) determ in ation in tap water an d river water with th e recom m en ded electrode
Sam ple
Added, m g/m l
Foun da, m g/m l
Recovery, %
River water
0.3
0.5
0.35 ± 0.03
0.54 ± 0.04
116.6
108
Tap water
0.3
0.5
0.34 ± 0.02
0.54 ± 0.03
103.3
108
a
Results of th ree m easurem en ts.
V
, µl
EDTA
FIG. 5
Poten tiom etric titration curve of 25.0 m l 1.0 × 10–4 M Dy3+ with 1.0 × 10–2 M EDTA
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206

Dysprosium(III) Ion-Selective Electrochemical Sensor
1203
m arized in Table VI. Th e m easurem en t prin ciple for th e determ in ation of
fluoride ion s is based on th e m on itorin g of th e Dy3+ ion con cen tration . At
th e begin n in g of th e titration , th e con cen tration of th e Dy3+ is zero. By ad-
dition of Dy3+ to th e solution con tain in g F– ion s, th e in soluble TbF3 is
form ed an d th e poten tial durin g th e titration rem ain s alm ost con stan t.
Th is is due to th e form ation of in soluble DyF3 an d ch an ges in th e poten tial
are belon gs to th e Ksp of DyF3. After total F– ion s con verted to DyF3, by ad-
dition of Dy3+ ion s, th e poten tial of th e solution will ch an ge sh arply. Th e
begin n in g poin t of sh arp ch an ges is th e en d poin t of titration . As it is seen ,
th ere is a satisfactory agreem en t am on g th e declared fluoride con ten t an d
th e determ in ed values by th e sen sor an d com m ercial solid fluoride. Th e as-
sociated data from triplicate m easurem en ts are displayed in Table VI. It is
clear th at th ere is a satisfactory agreem en t between th e declared fluoride
con ten t an d th e values determ in ed by th e com m ercial solid fluoride sen sor
an d th e proposed electrode.
TABLE VI
Determ in ation of fluoride ion s in m outh wash solution s
Com m ercial Fluo-
ride
ISE, m g/m l
Mouth wash
Man ufactures
Labeled
m g/m l
Foun da
m g/m l
Aquafresh , Bren tford, U.K.
Eurodon t, DuroDon t Gm bH
1.35
1.45
(1.37 ± 0.04)b
(1.48 ± 0.03)b
(1.33 ± 0.02)b
(1.44 ± 0.02)b
a
b
ISE with proposed Dy3+ sen sor. Based on th ree m easurem en ts.
CONCLUSION
Th is research dem on strated th at ISEs, con structed on 6-h ydrazin o-1,5-di-
ph en yl-6,7-dih ydropyrazolo[3,4-d]pyrim idin e-4(5H)-im in e (HDDPI), exh ib-
ited dysprosium selectivity with low in terferen ce of com m on alkali,
alkalin e earth , tran sition an d h eavy m etal ion s. Th e recom m en ded sen sor
displayed a sh ort respon se tim e (<10 s) an d its poten tial respon ses were
pH-in depen den t in th e ran ge of pH 3.5–8.3. Moreover, it was successfully
used as an in dicator electrode in th e cadm ium ion titration with EDTA as
well as in th e dysprosium ion detection in solution .
The authors gratefully acknowledge the financial support from the Research Council of the Quchan
University.
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1189–1206

1204
Zamani, Ganjali, Seifi:
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