Full text of DOI:10.1002/jccs.200100105

JournaloftheChineseChemicalSociety, 2001, 48, 733-738
733
Characteristics of Lar iat Crown Ether-Copper(II) Ion-Selective Elec trodes
Chia-Ching Su (
), Chuen-Her Ueng (
) and Lilian Kao Liu* (
)
DepartmentofChemistry,NationalTaiwanNormalUniversity,Taipei,Taiwan116,R.O.C.
An ion-selective elec trode us ing ionophore 2 -picolyl sym-dibenzo-16-crown-5 ether as mem brane car-
rier, so dium tetraphenylborate (NaTPB) as an an ion ex cluder, and 2-nitrophenyl-octyl ether (NOPE) as the
plasticingsolventmediatorhasbeensuccessfullydeveloped.Thiselectrodeexhibitsalinearresponsewitha
-
5
-1
-1
-1
slopeof42mV/decadeinconcentrationrangingfrom10 molL to 10 molL , slightly larger than the 30 mV
ex pected from the one-to-one com plex. The rea son for the super-Nernstain slope is the par tial dimmerforma-
tioninsidethemembraneoftheelectrode, becausethisdimmer[Cu(C25
H
27NO
6
)
2
(H
2
O)
2
] 2ClO , has been iso-
4
latedandconfirmedbysinglecrystalX-raycrystallography.Thedetectionlimitforthecop per(II) ion was es-
-
6
-1
ti mated to be 1 10 molL . Elec trodes com posed of other plasticing sol vent me di a tors such as tris(2-
ethylhexyl) phos phate (TOP), bis (2-ethylhexyl) sebacate (DOS) and dibutyl phthalate (DBP) were also in-
ves ti gated. Sta bil ity con stants (logKs) of the two to one and the one to one 2-picolylsym-dibenzo-16-crown-5
ether-Cu(II)complexeshavebeendeterminedbypotentiometrictitrationinmethanol.
INTRODUCTION
The first ion-selective elec trodes (ISEs) based on bulk
beenusedascopperpotentiometricsensors.Inordertoobtain
better se lec tiv ity, mem brane elec trodes based on macro-
2
2,23
24
cyclic polyethers
and polymethyldiene with ni tro gen
mem branes con tain ing an ion car rier were in tro duced more
than 30 years ago; many pa pers on ISEs have been pub lished
andoxygenatomsintheligandtoformastablecomplexwith
cop per have been de vel oped. To the best of our knowl edge,
cop per (II)-ISE us ing lar iat crown ethers as inophores have
neverbeenreported.
1
,2
since then. ISEs to day have be come one of the most im por-
tant groups of chem i cal sen sors, be cause they use rel a tively
in ex pen sive potentiometric dervices, yet give fast and re pro-
ducibleresponseswhichareusefulinprovidingdetermina-
tionofmanyionicspeciesinreal-lifemonitoring. ISEsbased
onionophore-impregnatedpolymermembranes(typically,
plasticized poly vi nyl chlo ride (PVC)) are now com monly
EXPERIMENTAL SECTION
Reagents
3
-6
em ployed in a va ri ety of anal y ses. In the area of mem-
brane-based ISEs, spe cial em pha sis has been placed on the
compositionofthemembranephaseandonthedevelopment
of new ionophores, aim ing at en hanc ing the potentiometric
responseandspecialcharacteristicsoftheISEs.
Re agent grades of o-nitrophenyl octyl ether (NPOE),
tris(2-ethyl-hexyl) phos phate (TOP), bis(2-ethylhexyl) seba-
cate (DOS), di-butyl phthalate (DBP), so dium tetra phenyl-
borate (NaTPB), PVC and Cu(ClO
4
2
) were pur chased from
Aldrich. Po tas sium tetrakis(4-chlorophenyl) bo rate (KTCPB)
was ob tained from Fluka. Re agent grades of meth a nol and
tetra-ethyl-ammonium perchloroate (TEAF) were pur chased
from Merck and used with out fur ther pu ri fi ca tion. 2-Picolyl
sym-dibenzo-16-crown-5 ether was syn the sized and used af-
ter recrystallization from chlo ro form-hexane (2:1) and vac-
uumdriedbeforeuse.
The sta ble sol u ble form of cop per, namely Cu(II) is
toxicatelevatedconcentration.Itsreactivityandbiological
up take are largely in flu enced by the free ion con cen tra tion
that is con trolled by the ex tent of cop per complexation with
ligands.Ofthemanyanalyticalmethodsavailableforthede-
terminationofcopper, oneusingdirectpotentiometrywitha
Cu-ion-selective elec trode has en abled the in situmea sure-
mentofthefreecopper(II)concentrationwithoutperturbing
Membranes, Cell AssemblyandApparatus
7
thenaturalspeciation. In view of this fact, re search ers in the
PVC (50 mg), plasticizer (100 mg), the lar iat crown
ether (25.0 mg), NaTPB or KCTPB (1.0 mg) were dis solved
in 1.5 mL of THF. Af ter com plete dis so lu tion of all the com-
po nents and thor ough mix ing, a Py rex tube [4 mm (id.) 20
cm] was dipped into the re sult ing so lu tion for a few min utes
so that a mem brane of about 0.3 0.5 mm in thick ness was
speciation field have at tempted to de velop sen sors for its de-
terminationwithhighselectivity.
Forcopperdetermination,solidmembraneelectrodes
8
-11
12
13,14
basedoncoppersulfide, tungstenoxide, ionexchangers
1
5-21
andcopper(II)complexes
as electroactive ma te rial have

734 J. Chin. Chem. Soc., Vol. 48, No. 4, 2001
Su et al.
formed.Thenthetubewasfilledwithinternalfillingsolution
of 1 10 Mcopper(II)perchlorate.
(m, 1H, 5 po si tion H of Py), 7.67 (m, 2H, 3 and 4 po si tion H of
Py), 8.55 (d, 3J= 4.4 Hz, 1H, 6 po si tion H of Py).
-3
PotentialMeasurements
Synthesis of Cu(II) and Lar iatCrown Complex
All emf mea sure ments were car ried out with a Keithley
4 2
The com plex of2 with Cu(ClO ) was pre pared by heat-
6
17 pro gram ma ble electrometer (Ohio, U.S.A.) at a con stant
ing [Cu(ClO (H O) ] (0.463 g, 1.25 mmol) and 2 (1.093 g,
4
)
2
2
6
temperatureof25 Cwiththefollowingassembly:
2.5 mmol) in meth a nol (25 mL) un der re flux for 0.5 h. Sin gle
crystalssuitableforX-raydeterminationwereobtainedfrom
recrystallization with eth a nol and slow evap o ra tion. Anal:
-
3
AgCl Ag 1
10 M Cu(ClO
SO
4
)
2
PVC-ionophore
SO (satd.)
membrane testsolution Hg Hg
2
4
K
2
4
Calc. (found) for C50
2 2
H58Cl CuN O22: C, 51.18 (51.07); H,
4
.98 (5.08); N, 2.39 (2.31).
Theresponsetimewasrecordedwhenastablepotential
changed within 1 to 2 mV) was achieved.
(
RESULTS AND DISCUSSION
Potentiometric Method
Potentiometric ex per i ments were car ried out with a
Keithley 617 programmable electrometer. The reference
Func tional groups of side arm lar iat ethers are key com-
po nents for the for ma tion of metal-crown ether com plexes
andformolecularrecognitioninsupramolecularchemistry.
Switch able pyridylmethyl (2 -picolyl) side arms on diazo-
2
+
elec trode used in all ti tra tions was a Cu/Cu elec trode. The
two half-cells were sep a rated by a salt bridge con tain ing 0.1
M TEAF. The stability constants of the copper(II)-lariat
crown ether com plexes were de ter mined by potentiometric
2
6,27
28,29
crownethers
and dioxocylam
wererecentlyreported.
On the other hand, our in ves ti ga tion in syn the sis of switch-
able C-privot lar iat ethers as heavy metal car ri ers led to the
successful preparation of two Pb(II) complexes with the
2 -methoxyethyl and the benzyl side arms in sym-dibenzo-
2
+
-3
ti tra tion of the re spec tive Cu so lu tion (1 10 M) with a
methanolic so lu tion of this spe cific lar iat crown ether. The
ionic strength was kept at I = 0.1 M by ad di tion of TEAF.
Mea sure ment was made af ter each ad di tion of a micropipet
vol ume of titrant. The ti tra tion was con sid ered sta ble when
the me ter read ing re mained con stant (within 1 to 2 mV) for at
least 30s. All ex per i ments were per formed at a con stant tem-
peratureof25 C 1 C.
3
0,31
16-crown-5etherseries.
In search ing for the stron ger co-
ordinatingfunctionalgroup,anewC-pivotlariatcrownether
con tain ing the pyridylmethyl side arm was syn the sized. Be-
causeofitshighselectivityandsensitivitytocopper(II)ions,
ion se lec tive elec trodes (ISEs) based on this ionophore were
con structed. We re port herein the syn the sis of this new iono-
phore, the as so ci ated X-ray sin gle crys tal struc ture of its
Cu(II) complex and the potential characteristics of this
Synthesis of Lar iatCrown Ether
Hydroxy-sym dibenzo-16-crown-5 ether 1 wassynthe-
2
5
2+
sized ac cord ing to the lit er a ture pro ce dures. 2 -picoyl
sym- dibenzo-16-crown-5 ether was pre pared as fol lows: An
amount of 1.73 g (5 mmol) of hydroxy-sym dibenzo-16-
crown-5 ether 1 was dis solved in 50 mL of an hy drous THF.
Then, 0.8g(20mmol)ofNaHwasaddedundernitrogen. The
re ac tion was heated to re flux for 30-40 min utes. Af ter ad di-
tion of 2-picolyl chlo ride hy dro chlo ride (5 mmol), the mix-
ture was heated (un der re flux) for six hours. The ex cess NaH
was then de stroyed and the re ac tion mix ture was vac uum
driedandrecrystalized(2:1chloroform-hexane).Thedesired
prod uct2 was ob tained in 85% (1.86 g) yield. m.p. 122.0
Cu -ISE.
Al though in the two lead (II) com plexes of the same
3
0,31
C-pivot lar iat ether se ries
both the 2 -methoxyethyl and
thebenzylsidearmswerefoundtocooperatewiththeringox-
ygenatomsincationbindingbypushingthelead(II)ioninto
the crown ring cav ity, the newly pre pared 2 -picoyl Cu(II)
com plex is quite dif fer ent be cause the ox y gen at oms in the
crown ether ring do not co or di nate with the Cu(II) ion. Co or-
dinationwascompletedbytwosidearmnitrogenatoms, two
bridged head oxygens and two wa ter mol e cules. The ge om e-
try around the metal is a dis torted octahedron with se lected
bond lengths and an gles shown in Fig. 1. Two per chlor ate an-
1
23.0 C. El e men tal anal y sis: Calc. (found) for C25
H
27NO ;
6
1
C, 68.62 (68.68); H, 6.22 (6.33), N, 3.20 (3.19), H NMR
CDCl 3.92 (m, 4H, OCH CH OCH CH O), 4.15 (m, 4H,
OCH CH OCH CH O), 4.29 (m, 3H, OCH
8.8 Hz, J = 3.4 Hz, 2H, OCH CH), 5.01 (s, 2H, CH
.86 (m, 4H, benzo group), 6.97 (m, 4H, benzo group), 7.19
ions also ex ist in the lat tice as the coun ter ions. The Cu-OH
2
(
3
)
2
2
2
2
bond lengths are shorter than the other Cu-O bonds ow ing to
the stron ger aqua ligand and the steric hin drance of crown
ether. From the fact that the ionic ra dius of Cu(II) is smaller
than Pb(II) and the plumb atom sits in side the crown ring for
2
2
2
2
2
2
CH), 4.40 (dd, J
Py),
3
=
2
2
6

Lar iat Crown Cu2+ ISE
J. Chin. Chem. Soc., Vol. 48, No. 4, 2001 735
3
1
R
Pb(II) benzyl-sym-dibenzo-16-crown-5 ether com plex, the
coordinationwiththesidechainfortheCu(II)complexinthe
pres ent case might be at trib uted to the cav ity size of the par-
ent crown ring which is too large for the cop per atom, the
strongercoordinationabilitytowardCu(II)fromthepyridine
ni tro gen, and the ex tra strength aris ing from hy dro gen bond-
ingbetweenthetwoaqualigandsandthetwocrownmoieties.
The re sponse char ac ter is tics of the cop per ISEs based
on lar iat crown ether are shown in Fig. 2. These fig ures re veal
O
O
O
O
O
M
that the po ten tial ( E)-pM(-loga ) plots ap proach the ex-
O
pected lin ear re sponse with fixed slopes. The emfs were mea-
sured at 25 C. Thebestresultistoexhibitalinearresponseto
1
. R=H
-5
cop per(II) ions in the con cen tra tion range from 1.0 10 -
-
1
1
.0 10 M with a slope of 42 mV per de cay of ac tiv ity,
2
. R=
N
slightly larger than the 30 mV ex pected from the one-to-one
com plex. To un der stand the or i gin of this super-Nernstain
slope, one can pro pose the si mul ta neous for ma tion of a dim-
(
a)
2
+
+
+
2 3
mer of L Cu and mono mer LCu and (LCuNO ) in side the
mem brane of the elec trode. Sim i lar re sults have been re-
ported for var i ous elec trodes, re sult ing from dif fer ent phe-
3
2-34
nomena.
We have iso lated and char ac ter ized the cor re-
sponding diaquabis(2 -picolyl-sym-dibenzo-16-crown-5 ether)
cop per(II) diperchlorate as men tioned above. Fur ther more,
+
+
+
both the LCu , the [LCuNO
3
] and [L Cu] com plexes were
2
clearly vis i ble with the cor rected iso to pic ra tio in the FAB
spec trum ob tained sim ply by the mix ing of this ligand with
Cu(NO
3
2
) in m-nitrobenzylalcohol. There fore, for ma tion of
the one to one Cu(II) 2 -picoly sym-dibenzo-16-crown-5
ether com plex in side the PVC mem brane and in the meth-
(
b)
Fig. 1. (a) The mo lec u lar struc tures ofsym-diben-
zo-16-crown-5 ether 1 and 2; (b) ORTEP
draw ing of the mo lec u lar struc ture of [Cu-
(C
25
H
27NO
6
)
2
(H
2
O)
2
4
] 2ClO with se lected bond
lengths (Å) and angle ( ): Cu-O(1) 2.376(5),
Cu-O(7) 1.962(4), Cu-O(8) 1.970(5), Cu-N(1)
1
9
7
.986(6), Cu-N(1 ) 1.970(5); O(1)-Cu-O(7)
2.6(2), O(1)-Cu-O(8) 94.4(2), O(1)-Cu-N(1)
4.8(23), O(1)-Cu-N(1 ) 101.7(2), O(7)-Cu-
Fig. 2. Po ten tial re sponses of var i ous plasticizers for
the 2 -picolyl sym-dibenzo-16-crown-5 ether
copper-selectivemembraneelectrode.
O(8) 86.7(2), O(7)-Cu-N(1) 92.3(2), O(7)-Cu-
N(1 ) 165.7(2), O(8)-Cu-N(1) 169.1(2), O(8)-
Cu-N(1 ) 91.1(2), N(1)-Cu-N(1 ) 92.6(2).

736 J. Chin. Chem. Soc., Vol. 48, No. 4, 2001
Su et al.
anolicsolutionisreasonable. Formationofaonetoonecom-
plexwiththenitrogenatomofpyridinesidearmcoordinateto
thecenterCu(II)ioninthelariatethercavityinvolvesconsid-
er able steric hin drance. Be cause in the sin gle crys tal of the
Pb(II) benzyl sym-dibenzo-16-crown-5 ether com plex that
intheemfmeasurements.
The se lec tiv ity of the cop per ion-selective elec trode
wasinvestigatedbypotentialmeasurementsinsolutionscon-
tainingafixedconcentrationofCu (1.0 10 M) and var i-
2
+
-3
2
+
ous amounts of the tran si tion metal ion (M ) by us ing equa-
3
1
38-39
we iso lated be fore, the phenyl group points out ward to
avoid crowd ed ness. It is rea son able to as sume that the bulki-
ness of the pyridine ring is about the same as the phenyl ring.
So it is the steric hin drance not the cav ity size which pro hib its
the iso la tion of the one to one com plex in the solid state. For
the lar iat’s cav ity in the com plex is more flex i ble than that of
the par ent crown ether and can ad just to an op ti mum size for
eachcation.
tion (1).
E2-E1/b
10
= 1 + KCu,M a’/a
(1)
1
where E is the po ten tial of a known vol ume of the so lu tion
2
+
containingCu cationatanactivityacu and E isthepotential
2
of the cop per so lu tion when a known vol ume of the in ter fer-
ing cat ion has been added. Ac cord ing to this equa tion KCu,M
can be evaluated from the slope of the graph of 10
E2-E1/b
Effectsofvariationinamountsofthelariatcrownether
(
wt%) for cop per-selective PVC mem brane elec trodes are
againsta’.Sincethechemicalsusedinourexperimentsareof
thehighestgradeinpurityavailable,theconcentrationofthe
tar get sub strates and interferents are pre sum ably equal to
theiractivitiesinourconcentrationrange.Theselectivityco-
listedinTable1. Thebestperformancewasobservedwiththe
membranehavingthecompositionoftheionophore2 -picoyl
sym-dibenzo-16-crown-5 ether-PVC-STPB-NPOE in the ra-
2
+
2+
tio of 25:50:1:100. This Cu -selectiveelectrodeappearsto
be more sen si tive than the com mer cial Cu -selectiveelec-
trode in emf mea sure ment. The po ten tial change is E = 28
mV, while our Cu -selectiveelectrodeis E = 36 mV for the
same amounts of change in Cu concentration(i.e.4.2 10
efficientsforCu rel a tive to the ion M in the PVC mem brane
2
+
elec trode based on this lar iat crown ether are listed in Ta ble 2.
-
4
2+
2+
2+
2+
2+
The pres ence of 1.0 10 M Cd , Co , Ni , Zn and Pb
2
+
divalenttransitionmetalionsinsolutiondonotsignificantly
2
+
-4
2+
af fect the se lec tiv ity of this cop per elec trode when the Cu
-
3
-3
to 4.2 10 M).TheresponsecharacteristicsofcopperISEs
based on 2 -picoyl sym-dibenzo-16-crown-5 ether with dif-
fer ent sol vent me di a tors NPOE, DOS, TOP and DBP are
shown in Fig. 2. These mem brane elec trodes all show lin ear
concentrationinsolutionis1.0 10 M (Fig. 3).
Potentiometric ti tra tions were per formed to mea sure
thecomplexationbehaviorsoftheLCE2with Cu(II) di rectly
in meth a nol. Using the ex per i men tal setup de scribed in a re-
-
5
39
-3
relationshipsintheconcentrationrangesof1.0 10 - 1.0
4 2
centpublication, a Cu(ClO ) so lu tion (1 10 M) is ti-
-
1
-4
-1
-4
-1
-4
1
-
0 , 1.0 10 - 1.0 10 , 1.0 10 - 1.0 10 and 1.0 10
trated with a so lu tion con tain ing the ligand (0.1 M) and an in-
ert elec tro lyte TEAF at a con stant ion strength of 0.1 M. To
calculatethestabilityconstant(Ks),amethanolsolutionof1
-
1
1.0 10 M with a slope of 42, 25, 22 and 28 mV per de cade
of ac tiv ity, re spec tively. The ad di tion of NaTPB re sults in a
largeimprovementintheresponseslope,becauseNaTPBcan
increasetheelectricalconductivityandthesensitivityofthe
-
3
10 M Cu(ClO
4
2
) wastitratedslowlywithamethanolsolu-
tion of the ionophore (0.1 M); upon ad di tion of the ligand the
cell potential decreases systematically. This behavior is
3
6-37
membraneelectrode.
used in stead of NaTPB for the Cu-LCE 2 mem brane elec-
trode, no dif fer ence was found be tween NaTPB and KTCPB
When an ion ex cluder KTCPB was
2
+
causedbya de crease inthe concentra tionofthe free Cu due
to the com plex for ma tion. The sta bil ity con stant Ks for the
Table 1. Optimization of Membrane Ingredients
Elecltrode No
Composition of membrane (Wt)
Working
concentration
range
Slope
(mV/decade
of activity)
Respone
time
s
Crown
ether
PVC
NaTPB
NPOE
M
-
1
-5
-5
-5
-5
-5
-5
1
2
3
4
5
6
5 mg
10 mg
15 mg
20 mg
25 mg
30 mg
50 mg
50 mg
50 mg
50 mg
50 mg
50 mg
1 mg
1 mg
1 mg
1 mg
1 mg
1 mg
100 mg
100 mg
100 mg
100 mg
100 mg
100 mg
1.0 10 -1.0 10
14.6
24.5
38.7
39.9
42
50
50
50
50
50
50
-
1
1.0 10 -1.0 10
-
1
1.0 10 -1.0 10
-
1
1.0 10 -1.0 10
-
1
1.0 10 -1.0 10
-
1
1.0 10 -1.0 10
33.2

Lar iat Crown Cu2+ ISE
J. Chin. Chem. Soc., Vol. 48, No. 4, 2001 737
n+
Table 2. Selectivity Coefficients of Various Interfering Ions (M )
logKs = 5.75 for the 1:1 com plex in meth a nol at 25 C.
AlthoughboththegasphaseevidenceobtainedbyFAB
massspectrometryandthesolutionphaseevidenceobtained
by ISE stud ies re veal the pre dom i nant pres ence of the one to
one 2 -picolyl sym-dibenzo-16-crown-5 ether-Cu(II) com-
plex, the iso lated form in solid state is the two to one com plex
men tioned above. This pre sum ably is due to the un usual sta-
bil ity aris ing from the hy dro gen bond ing be tween the two
aqua lig ands which holds the crown moi eties to gether be-
cause hy dro gen bond ing is very im por tant in na ture as in or-
ganizingaregularbiochemicalstructuresuchasthe -helix
in pro tein. Thus the char ac ter iza tion of the diaquabis(2 -
picolyl sym-dibenzo-16-crown-5 ether) copper(II) diper-
chloratereportedinthisstudyoffersasimpleexampleforthe
pos si bil ity of de sign ing a supramolecule to mimic en zyme
function.
for This Copper-selective Membrane Electrode
n+
M
Kcu,M
2
2
+
+
-1
-1
-1
-1
-2
Cd
Co
Zn
Ni
Pb
1.4 × 10
1.7 × 10
1.7 × 10
1.0 × 10
9.1 × 10
2
+
2+
2
+
1
:2 com plex is cal cu lated as logKs = 8.99, and for the 1:1
com plex logKs = 5.75 in meth a nol at 25 C.
CONCLUSION
It is well known that the sen si tiv ity and se lec tiv ity of
the ion-selective elec trodes de pend not only on the na ture of
ionophoreused, butalsosignificantlyonthemembranecom-
positionandthepropertiesoftheplasticizer. Inthisstudy, the
best per for mance was ob served with the mem brane hav ing
the com po si tion of the ionophore 2 -picolyl sym-dibenzo-
ACKNOWLEDGEMENTS
The au thors thank the Na tional Sci ence Coun cil of the
Re pub lic of China (Tai wan) for its fi nan cial sup port (NSC
1
6- crown-5 ether-PVC-STPB-NPOE in the ra tio of 25:50:
8
9-2113-003-022).
1
1
:100. This elec trode is use ful in the con cen tra tion ranges of
-
5
-1
.0 10 - 10 M with lin ear re sponse of slopes of 42 mV per
2
+
decade.ThisCu -selectiveelectrodeappearstobemoresen-
Received January 3, 2001.
2
+
si tive than the com mer cial Cu -se lec tive elec trode in emf
mea sure ment. The de tec tion limit for this cop per(II) ion was
es ti mated as 1 10 molL . A fast re sponse time of 50s,
and a good reproducibility over a pe riod of three months were
also ob served. The new lar iat crown ether re ported in this
study is a new ISE ma te rial that can make the mea sure ments
Key Words
-
6
-1
Lariat crown ether; PVC membrane; ISE;
Stability constant.
2
+
of Cu moreeffectiveandconvenient.Thestabilityconstant
Ks for the 1:2 com plex is cal cu lated as logKs = 8.99, and
NOTES AND REFERENCES
Crys tal data: C50
H58Cl
2
CuN O22,Molecularweight=
2
1
2
1
173.45, Blue crys tals, Monoclinic, space group C 2/c, a =
1.332(3), b = 14.218(7), c = 36.21(2) Å, = 91.60(3), V =
0978(8) Å , z = 4, D = 1.420 g/cm , Mu = 2.15 mm , Data
C
3
3
-1
collectionwascarriedoutonaNoniusCAD-4diffractometer
usinggraphite-monchromedCu-K ra di a tion at 25 C. A to-
tal 8072 re flec tions with I 2 (I) were used in the re fine-
ment.Includedreflectionsare5071. Full-matrixleast-squares
refinementledtoconvergencewithR=0.071andwR=0.072
with a good ness-of-fit of 2.858.
1. Bakker, E.; Bühlmann, P.; Pretsch, E. Chem. Rev. 1997,
Fig. 3. Selectivitymeasurementsforvariousionswith
the 2 -picolyl sym-dibenzo-16-crown-5 ether
copperion-selectivemembraneelectrode.
3083andreferencescitedtherein.
2. Bühlmann, P.; Pretsch, E.; Bakker, E. Chem. Rev. 1998,
98, 1593.

738 J. Chin. Chem. Soc., Vol. 48, No. 4, 2001
Su et al.
3
. Ar nold, M. E.; Meyerhoff, M. E. Crit. Rev. Anal. Chem.
988, 20, 149.
. Moody, G. J.; Saad, B. B.; Thomas, J. D. R. Sel.Electrode
Rev. 1988, 10, 71.
. Meyerhoff, M. E.; Opdycke, W. N. Adv. Clin. Chem.
986, 25, 1.
. Morf, P. W. E.; Oesch, U.; Ammann, D.; Pretsch, E.;
Shmon, W. Anal. Chem. Acta 1996, 180, 299.
Fukunaga, Y. Analst 1988, 113, 45.
1
23. Brzozka, Z. Chem. Anal. (War saw)1990, 35, 415.
24. Jain, K. A.; Gupta, V. K.; Sahoo, B. B.; Singh, L. P. Anal.
Proc. 1995, 32, 99.
25. (a) Kyba, E. P.; Helgeson, R. C.; Madan, K.; Gokel, G.
W.; Tarroeski, T. L.; Moore, S. S.; Cram, D. J. J. Am.
Chem. Soc. 1977, 99, 2564. (b) Heo, G. S.; artsch, R. A.;
Schlobohm, L. L.; Lee, J. G. J. Org. Chem. 1981, 46,
3574.
4
5
1
6
7. Neshkov, M. T.; Kirkova, A. A.; Cattrall, R. W.; Gregorio,
C. G.; Bond, A. M. Anal. Chim. Acta 1998, 362, 221.
26. Tsukube, H.; Yamashita, K.; Iwachido, T.; Zenki, M. Tet-
rahedronLett. 1988, 569.
27. Tsukube, H.; Yamashita, K.; Iwachids, T.; Zenki, M. J.
Org. Chem. 1991, 56, 268.
8
. Kouljenovic, J.; Martinac, V.; Radic, N. Anal. Chim. Acta
990, 231, 137.
. Stankovic, S. M.; Javanovic, V. M.; Javanovic, M. S. J.
1
9
Serb. Chem. Soc. 1990, 55, 125.
0. Neshkova, M. Anal. Chim. Acta 1993, 273, 255.
28. Kimura, E.; Shionoga, M.; Okamoto, M.; Nada, H. J. Am.
Chem. Soc. 1988, 110, 3679.
1
1
1. De Marco, R.; Mackey, D. J.; Zirino, A. Electroanalysis
29. Bu, X. H.; An, D. L.; Cao, X. C.; Zhang, R. H.; Clif ford,
T.; Kimura, E. J. Chem. Soc. Dal ton Trans. 1998, 2247.
30. Liu, L. K.; Lin, C.-S.; Young, D.-S.; Shyu, W.-J.; Ueng,
C.-H. J. Chem. Soc. Chem. Comm. 1996, 1255.
31. Lin, C.-S.; Liu, L. K.; Ueng, C.-H. Acta cryst. 1997, C53,
574.
1
997, 9, 330.
1
2. Chen, Z.; Al ex an der, P. W. Electroanalysis 1997, 9, 141.
3. Awasthi, S. P.; Thambi, T. C.; Sunderesan, M. J.
Electrochem. Soc. 1990, 39, 34.
1
14. Jain, A. K.; Singh, P.; Singh, L. P. Ind. J. Chem. 1994,
3
3A, 272.
32. Peyre, V.; Baillet, S.; Letellier, P. Anal. Chem. 2000, 72,
2377.
1
5. Ren, K. Talanta 1989, 36, 767.
16. Kamata, S.; Murata, H.; Kubo, Y.; Bhale, A. Anlyst 1989,
33. Egorov, V. V.; Borisenko, N. D.; Rakhmank ko, E. M. J.
1
14, 1029.
Anal. Chem. 1998, 53,855(P.750Englishtranslation).
34. Ceresa, A.; Pretsch, E.; Bakker, E. Anal. Chem. 2000, 72,
2050.
1
1
1
2
2
2
7. Askerov, G. A.; Chyragov, F. M.; Gambrov, D. G.;
Ayubova, A. M. Zh. Anal. Khim. 1992, 47, 337.
8. Nagashima, K.; Guo, J.; Hobo, T. Bunseki Kagaku 1992,
35. Sakai, T. S. K.; Tsubomura, T. SupramolecularChem.
1996, 7, 157.
4
1, 153.
9. Sun, C. Q.; Sun, Y. P.; Zhang, Y.; Xu, H. D.; Shen, J. C.
Anal. Chim. Acta 1995, 312, 207.
36. Si mon, W. Anal. Lett. 1974, 7, 9.
37. Boles, J. H.; Buck, R. P. Anal. Chem. 1973, 45, 2057.
38. Gokel, G. W. Chem. Soc. Rev. 1992, 21,39andreferences
cited therein.
39. Su, C. C.; Chang, M. C.; Liu, L. Kao Anal. Chim. Acta
2001, 432, 261.
0. Pleniceanu, M.; Preda, M.; Huresam, N.; Simoiu, L.
Anal. Lett. 1996, 29, 1485.
1. Xia, S. X.; Xio, D.; Yu, R. Q. Fensi Huaxue, Anal. Abstr.
1
995, 3D41.
2. Kamata, S.; Yamasaki, K.; Higo, M.; Bhale, A.;