Polarographic behavior and determination of 1,1-dimethyl-3-phenyltriazene

Article abstract of DOI:10.1135/cccc20071229

Polarographic behavior of the genotoxic substance 1,1-dimethyl-3- phenyltriazene was investigated and optimum conditions were found for its determination by sampled direct current polarography and differential pulse polarography at a static mercury drop electrode in the concentration range from 1 × 10^-4 to 1 × 10^-7 mol l^-1. It was established that for reduction of the triazene group four electrons are required resulting in the formation of amino and hydrazo compound. The resulting products were identified, and the reduction pathway was proposed.

Full text of DOI:10.1135/cccc20071229

1
,1-Dimethyl-3-phenyltriazene
1229
POLAROGRAPHIC BEHAVIOR AND DETERMINATION OF
,1-DIMETHYL-3-PHENYLTRIAZENE
1
Ljubiša M. IGNJATOVIĆ *, Jiří BAREK , Jiří ZIMA and Dragan A. MARKOVIĆa2
a1,
b1
b2
a
Faculty of Physical Chemistry, University of Belgrade, P.O. Box 137,
1
2
1
1 001 Belgrade, Serbia; e-mail: ljignjatovic@ffh.bg.ac.yu, skiper@isp.b92.net
Charles University Prague, Faculty of Science, Department of Analytical Chemistry,
UNESCO Laboratory of Environmental Electrochemistry, Hlavova 2030, 128 43 Prague 2,
b
1
2
Czech Republic; e-mail: barek@natur.cuni.cz, zima@natur.cuni.cz
Received Novem ber 22, 2006
Accepted April 6, 2007
Polarograph ic beh avior of th e gen otoxic substan ce 1,1-dim eth yl-3-ph en yltriazen e was in ves-
tigated an d optim um con dition s were foun d for its determ in ation by sam pled direct curren t
polarograph y an d differen tial pulse polarograph y at a static m ercury drop electrode in th e
–
4
–7
–1
con cen tration ran ge from 1 × 10 to 1 × 10 m ol l . It was establish ed th at for reduction
of th e triazen e group four electron s are required resultin g in th e form ation of am in o an d
h ydrazo com poun d. Th e resultin g products were iden tified, an d th e reduction path way was
proposed.
Keyw ord s: Triazen es; Polarograph y; Electroreduction s; Reduction m ech an ism ; Carcin ogen s.
1
,1-Dim eth yl-3-ph en yltriazen e an d its o-, m- an d p-substituted derivatives
1
,2
ran k am on g gen otoxic substan ces th at also exh ibit can cerostatic activity
.
Th erefore, th ere is an in creasin g dem an d for sen sitive an alytical m eth ods
for th e determ in ation of th ese substan ces.
Th ey can be determ in ed spectroph otom etrically in th e ultraviolet region 3
an d also via th eir protolysis followed by azo couplin g of th e aren ediazo-
n ium salt form ed with N-eth yl-1-n aph th ylam in e to form an azo dye, wh ich
4
can be determ in ed ph otom etrically in th e visible region .
5
Con siderin g th e fact th at triazen e group is polarograph ically active , di-
rect curren t polarograph y h as been used to study 1,1-dim eth yl-3-ph en yl-
6
4
triazen e an d its derivatives . More sen sitive tech n iques, such as differen tial
7
–9
9–11
pulse polarograph y
an d adsorptive strippin g voltam m etry
h ave been
used for th e determ in ation of variously substituted derivatives of 1,1-di-
m eth yl-3-ph en yltriazen e.
In th e presen t paper, an attem pt was m ade to im prove th e sen sitivity of
polarograph ic determ in ation of 1,1-dim eth yl-3-ph en yltriazen e by sam pled
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243
©
2007 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc20071229

1
230
Ignjatović, Barek, Zima, Marković:
direct curren t polarograph y (SDCP) an d differen tial pulse polarograph y
DPP) at a static m ercury drop electrode (SMDE). On th e basis of polarog-
(
raph ic, coulom etric, spectroph otom etric an d ch rom atograph ic m easure-
m en ts, th e m ech an ism of th e electroch em ical reduction of th e triazen e was
in vestigated an d th e correspon din g reduction sch em e was postulated.
EXPERIMENTAL
Reagen ts
Th e purity of th e prepared 1,1-dim eth yl-3-ph en yltriazen e12 was ch ecked by th in -layer
ch rom atograph y, HPLC an d elem en tal an alysis. A stock stan dard solution of th is substan ce
–
3
–1
(
1 × 10 m ol l ) was prepared by dissolvin g a precisely weigh ed am oun t of th e substan ce in
–
4
–1
m eth an ol (an alytical-reagen t grade, Fluka). A m ore dilute solution (1 × 10 m ol l ) was pre-
pared by dilution of th e stock solution with m eth an ol. All solution s were stored in th e dark.
Spectroph otom etric study of th e stability of th e stock solution s dem on strated th at th e stock
stan dard solution was stable for at least two m on th s, wh ile th e m ore dilute solution was
prepared weekly.
Britton –Robin son (BR) buffers were prepared in th e usual way (i.e., by m ixin g a solution
–
1
of 0.04 m ol l orth oph osph oric acid, acetic acid an d boric acid with th e appropriate
–
1
am oun t of 0.2 m ol l sodium h ydroxide solution ). All th e ch em icals used were of an alytical-
reagen t grade, obtain ed from Merck.
Deion ized water, produced by an Ultra Clear basic SG Water apparatus (SG Wasser-
aufbereitun g Gm bH, Germ an y) was used in all experim en ts.
Apparatus
Polarograph ic m easurem en ts were carried out usin g a PA 4 polarograph ic an alyzer with
an SMDE 1 static m ercury drop electrode (both from Laboratorn í přístroje, Prah a, Czech
Republic). Th e capillary em ployed h ad an in tern al diam eter of 0.136 m m ; th e m axim um
drop size, obtain ed by open in g th e electrom agn etic valve for 160 m s, was used. Th e th ree-
electrode system was com pleted with a platin um rod auxiliary electrode an d a saturated cal-
om el referen ce electrode (SCE), to wh ich all th e poten tials are referred to. Th e m easure-
–
1
m en ts were perform ed at a sweep rate of 5 m V s an d an SMDE drop tim e of 1 s. A pulse
am plitude of –100 m V was em ployed in DPP.
Th e lin ear scan voltam m etric an d cyclic voltam m etric (LSV an d CV) m easurem en ts were
perform ed usin g th e sam e apparatus an d referen ce an d auxiliary electrodes. For th is purpose,
SMDE 1 electrode was used in th e h an gin g m ercury drop electrode m ode (HMDE) with th e
sam e drop size.
Con stan t-poten tial coulom etric (CPC) m easurem en ts were perform ed usin g a PAR 173
poten tiostat with a PAR 179 digital coulom eter (Both from Prin ceton Applied Research ,
U.S.A.). Th e m ercury pool was used as th e cath ode, with an SCE as referen ce an d platin um
gauze as coun ter electrode. Th e cath odic an d an odic com partm en ts were separated with a
sin tered glass diaph ragm .
Spectroph otom etric m easurem en ts were carried out on a Varian Cary 17D UV/VIS
spectroph otom eter (Varian In c., U.S.A.) in 10-m m quartz cuvettes.
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1
,1-Dimethyl-3-phenyltriazene
1231
HPLC m easurem en ts were perform ed in an isocratic system con sistin g of a m odel 2250
serial dual piston pum p, 4110 VarioTh erm colum n th erm ostat, DG-1310 solven t degasser
an d Lam bda 1010 UV-VIS spectroph otom etric detector with a flow cell optical path len gth
of 10 m m an d volum e 10 µl (all from Bisch off Ch rom atograph y Gm bH, Germ an y).
A Rh eodyn e 7725i sam ple in jector with 10 µl sam ple loop (Rh eodyn e LLC, U.S.A.) was used.
Th e reversed-ph ase colum n Pron toSil C18 AQ with th e pore size 200 Å an d particle size of
5
µm was used (Bisch off Ch rom atograph y Gm bH, Germ an y). As suitable m obile ph ase, a
–
1
m ixture of aqueous 0.1 m ol l sodium acetate with m eth an ol (6 + 4) was used; th e flow rate
was 0.3 m l m in –1. Th e UV detection was perform ed at 278 as well as at 230 n m .
A Metroh m 744 pH m eter (Metroh m Ltd., Switzerlan d) equipped with a com bin ed glass
pH electrode an d tem perature sen sor was used for pH m easurem en ts.
Procedures
Mixed BR buffer–m eth an ol m edium was used as th e supportin g electrolyte in order to en -
sure th e solubility of th e in vestigated substan ce. Th e actual pH of th e BR buffer–m eth an ol
m ixture (1 + 1) was m easured with a com bin ed pH electrode calibrated usin g acetate, borate
1
3
an d ph osph ate buffers in 50% m eth an ol . Th e pH value of th e BR buffer–m eth an ol m ixture
con tain in g 10 vol.% of m eth an ol was m easured with a pH electrode calibrated usin g aque-
1
4
ous buffers
.
A 10-m l aliquot of an appropriate supportin g electrolyte solution was placed in a voltam -
m etric cell an d deaerated for 5 m in with n itrogen . Th e voltam m etric cell was flush ed with
n itrogen passed successively th rough a solution of ch rom ium (II) ion s in dilute h ydroch loric
acid con tain in g h eavily am algam ated zin c gran ules, distilled water, m olecular sieves an d,
fin ally, th rough a solution h avin g th e sam e solven t an d supportin g electrolyte com position
as th e test solution . After recordin g th e baselin e, th e required am oun ts of th e stock solution
of th e in vestigated substan ce were added an d th e polarogram s or voltam m ogram s were re-
corded.
Th e calibration curves were m easured in triplicate an d evaluated by th e least-square lin ear
regression m eth od. Th e determ in ation lim it was calculated as ten tim es th e stan dard devia-
tion for ten determ in ation s of th e an alyte at a con cen tration correspon din g to th e lowest
1
5
poin t of th e appropriate calibration graph
.
In th e coulom etric determ in ation of th e n um ber of electron s exch an ged, 20 m l of th e
supportin g electrolyte were placed in th e coulom etric cell an d bubbled with n itrogen , with
sim ultan eous in itiation of pre-electrolysis at a selected con stan t poten tial. After about
2
0 m in , wh en th e residual curren t value dropped below 0.1 m A an d n o lon ger ch an ged, th e
circuit param eters were adjusted for autom atic residual curren t com pen sation . An aliquot of
th e stock solution of th e tested substan ce was th en added an d reduction was carried out at a
con stan t poten tial with con stan t stirrin g an d bubblin g with n itrogen . Th e electrolysis was
term in ated wh en th e curren t decreased to th e residual value an d th e passed ch arge was de-
term in ed by electron ic in tegration . Th e reduction was also followed spectroph otom etrically,
polarograph ically an d ch rom atograph ically. In th e m easurem en ts, th e sam ples were taken
prior to start of th e coulom etric reduction an d after reduction of 25, 50, 75 an d 100% of th e
triazen e.
All th e m easurem en ts were perform ed at laboratory tem perature (20 ± 1 °C).
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
232
Ignjatović, Barek, Zima, Marković:
RESULTS AND DISCUSSION
Effect of pH on the Polarographic Behavior of
1
,1-Dimethyl-3-phenyltriazene
With in th e in vestigated ran ge of pH values of th e supprotin g electrolyte,
,1-dim eth yl-3-ph en yltriazen e (DPT) yields on e polarograph ic wave (Fig. 1),
1
i.e. on e differen tial pulse polarograph ic peak (Fig. 2). Half-wave poten tial
E1/2 an d th e poten tial of DPP peak E sh ift towards n egative values with in -
p
creasin g pH of th e supportin g electrolyte, th e resultin g E1/2–pH an d E –pH
p
depen den ces h avin g asym ptotic ch aracter (Fig. 3). Th ose two ch aracteristic
poten tials differ, at th e given pH, by 50 m V, wh ich correspon ds to th e h alf
am plitude of th e superim posed pulse. Th e fact th at E1/2 an d E sh ift towards
p
n egative values with in creasin g pH in dicates th at proton s are in volved in
1
6
th e reduction process .
At pH > 7.0, th e sam pled DC polarograph ic waves an d DPP peaks de-
crease with in creasin g pH an d th ey com pletely disappear at pH > 11.0. At
pH < 5.5, th e curren t of polarograph ic waves decreases with tim e. Th e ob-
served tim e depen den ce of polarograph ic curren ts is associated with
1
7
h ydrolytic decom position of th e in vestigated substan ce .
Th e lin ear depen den ce of n atural logarith m of lim itin g curren t ln I on
1
tim e in buffered acid m edium in dicates th at th is h ydrolysis is a first-order
FIG. 1
Selected sam pled DC polarogram s of DPT (4 × 10 m ol l–1) in m ixed BR buffer–m eth an ol (1:1)
–5
m edium at pH 2.80 (1), 4.10 (2), 5.00 (3), 5.90 (4), 6.50 (5), 8.01 (6) an d 9.30 (7)
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
,1-Dimethyl-3-phenyltriazene
1233
FIG. 2
DP polarogram s of DPT (4 × 10 m ol l–1) in m ixed BR buffer–m eth an ol (1:1) m edium at pH
–
5
4
.10 (1), 5.90 (2), 6.50 (3), 8.01 (4) an d 8.70 (5)
FIG. 3
Th e in fluen ce of pH of th e supportin g electrolyte on th e h alf-wave poten tial E1/2 (1), DPP peak
–
5
–1
poten tial E (2), th e lim itin g curren t I (3) an d DPP peak curren t I (4) of DPT (4 × 10 m ol l
)
p
l
p
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
234
Ignjatović, Barek, Zima, Marković:
pseudom on om olecular reaction . Durin g th e decom position of DPT, n o n ew
polarograph ically active species appear, wh ich en ables a con tin ual SDC
polarograph ic m on itorin g of th is process. At pH 4.1, th e rate con stan t of
–2
–1
DPT hydrolysis, at the tem perature 20 °C, am ounts to 4.27 × 10 m in , while
th e activation en ergy determ in ed on th e basis of th e depen den ce ln k =
–
1
–1
f(T ), with in th e tem perature ran ge 10–40 °C, am oun ts to 87 ± 1 kJ m ol .
It can be seen from Fig. 4a th at in BR buffer with 50% m eth an ol (pH 4.1)
DPT yields 3 in ten sive absorption ban ds at λ = 304 n m (log ε = 4.076), λ =
1
2
2
82 n m (log ε = 4.102) an d λ = 222 n m (log ε = 3.954), wh ich is in accor-
3
3
,4
dan ce with th e m easurem en ts in eth an ol as a solven t . Durin g th e h ydro-
lytic reaction , absorption of th e 304 n m ban d decreased. Con siderin g th at
th is ban d is due to π–π* electron ic tran sition of th e triazen e groupin g, th e
decrease in its in ten sity in dicates th e disappearan ce of th is ch rom oph ore,
i.e. of th e triazen e groupin g. Th e π–π* absorption ban d at 282 n m sh ifts
durin g th e h ydrolysis of DPT towards lower wavelen gth s, occupyin g th e po-
sition at λ ′ = 270 n m 30 m in after th e begin n in g of th e reaction , with loga-
2
rith m of m olar absorption coefficien t log ε = 3.954. Th e absorption ban d of
DPT at λ = 282 n m is a con sequen ce of th e π–π* electron ic tran sition of π
2
electron s of arom atic rin g, addition ally stabilized by delocalization with
π electron s of th e triazen e bon din g. Th e h ypsoch rom ic sh ift of th is ban d
FIG. 4
UV spectroph otom etric m on itorin g of DPT (1 × 10 m ol l–1) degradation , pH 4.10. a Mon i-
torin g th e reaction at room tem perature; b 6 h after th e begin n in g of th e reaction : product of
DPT decom position (1), ph en ol (2)
–4
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
,1-Dimethyl-3-phenyltriazene
1235
of 12 n m , in dicates discon tin uation of th e addition al stabilization by de-
localization , i.e. it is on e m ore in dication of triazen e bon din g break. Th e
product of DPT h ydrolysis recorded 6 h after th e begin n in g of th e reaction
displays a ban d at 270 n m (log ε = 3.236). UV absorption spectrum of
ph en ol, recorded un der th e sam e con dition s, also yields a ban d at 270 n m
(
log ε = 3.236) wh ich im plies th at on e of th e reaction products is ph en ol.
On th e basis of th e obtain ed results an d of th e beh aviour of sim ilar com -
1
7
poun ds , it m ay be con cluded th at th e DPT h ydrolysis in th e used buffer
m edium proceeds as acid-catalyzed, with a com plex rate con stan t ktot
k k /k an d accordin g to th e reaction sch em e sh own in Fig. 5.
=
2
1
–1
At pH values above 9.5, E1/2 an d E do n ot ch an ge. Th e obtain ed de-
p
1
8
pen den ces m ay be approxim ated by tan gen ts in tersectin g at pH 9.5,
wh ich is th e experim en tally (polarograph ically) determ in ed pK value of
a
DPT. At pH values below pK = 9.5, DPT exists in th e acid form , wh ile at pH
a
of th e supportin g electrolyte h igh er th an 9.5, its con jugated alkalin e form
predom in ates in th e solution .
Th e n on typical SDC polarogram s of DPT obtain ed in th e pH ran ge of th e
supportin g electrolyte 8.0–11.0 are associated with th e presen ce of m eth a-
n ol an d with its in fluen ce on th e prelim in ary proton ation of electroactive
species. Th e fact th at, with in th is pH ran ge, th e slope of th e E1/2–pH de-
pen den ce does n ot correspon d to th e relation dE/dpH = –2.303mRT/αn F
a
1
9
in dicates th at a substan ce adsorbed on th e electrode surface is subjected
to proton ation prior to th e electrode reduction . With in creasin g m eth an ol
con ten t, th e rate of th e precedin g proton ation reaction decreased for two
reason s: due to a lower con stan t rate of proton ation an d due to a decreased
adsorption of th e in vestigated triazen e. Th e observed decrease in th e lim it-
in g curren t (an d th e curren t beyon d th e DP polarograph ic peak) in th e re-
gion aroun d –1.6 V at pH > 7.5 is associated with th e decrease in th e rate of
surface proton ation as a con sequen ce of desorption of th e in vestigated sub-
CH3
CH3
CH3
k1
N
N
N
+
H
N
N
+
HN
k-1
CH3
k2
N
N
+
H2O
OH
+ N2 + H2
FIG. 5
Th e reaction sch em e of 1,1-dim eth yl-3-ph en yltriazen e decom position in acidic m edium
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
236
Ignjatović, Barek, Zima, Marković:
stan ce at poten tials m uch m ore n egative th an th e poten tial of electrocapil-
lary m axim um , wh ere m axim al adsorption of un ch arged m olecules of th e
in vestigated substan ce is expected20
.
The Electrode Reduction Mechanism
From th e logarith m ic an alysis of SDC polarogram s it follows th at th e elec-
trode process is irreversible. Th e irreversible ch aracter of th e electrode re-
duction of DPT is also con firm ed by cyclic voltam m etric m easurem en ts
usin g th e h an gin g m ercury drop as th e workin g electrode; n o an odic peak
was obtain ed at an y pH value of th e supportin g electrolyte an d at an y po-
larization rate of th e workin g electrode (Fig. 6), wh ich in dicates th at th e
products of DPT reduction are n ot oxidized at th e m ercury electrode. Th e
absen ce of an odic peak is on e of th e m ain criteria for th e establish m en t of
2
1
electrode process irreversibility . At pH 6.5, th e poten tial of cath odic CV
peak sh ifts towards m ore n egative values with in creasin g scan rate, wh ich
also con firm s th e irreversible ch aracter of th e electrode process.
Th e values of αna for DPT electroch em ical reduction in crease with in -
creasin g pH of th e supportin g electrolyte to 5.9 an d 7.1, an d decrease after-
wards, wh ich leads to th e con clusion th at th e coefficien t of electron
tran sition th rough th e en ergy barrier of double electric layer is th e h igh est
FIG. 6
Linear voltam m ogram s of DPT (4 × 10 m ol l–1, pH 6.50) at various polarization rates (in m V s–1):
–
5
1
0 (1), 20 (2) an d 50 (3)
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
,1-Dimethyl-3-phenyltriazene
1237
at pH 6.5 (αn = 1.13). Th e values of αn can also be determ in ed from th e
a
a
depen den ce of DPT CV peak poten tial E (in m V) on th e logarith m of po-
p
–
1
22
ten tial scan rate v (in m V s ) of th e workin g electrode . Th e experim en -
tally obtain ed straigh t-lin e depen den ce (r = 0.9981) m ay be represen ted by
th e equation
–
Ep = 1146 + 0.019 log v .
On th e basis of th e slope of th e straigh t lin e th e value of αn = 1.12 is cal-
a
culated for pH 6.5, wh ich is in quite good correlation with th e results ob-
tain ed from sam pled DC polarograph ic m easurem en ts.
Voltam m etric reduction of DPT is con trolled by th e diffusion of electro-
active species as th e slowest step in th e electroch em ical process. Th e diffu-
sion n ature of th e voltam m etric peak of DPT is con firm ed on th e basis of
2
2
lin ear depen den ce of CV peak curren t I on th e square root of polariza-
p
1
/2
tion rate v : a lin ear depen den ce log I = f(log v) with r = 0.9991, with th e
p
slope of 0.495 was obtain ed.
On th e basis of th e calculated an d cited values of αn (1.12 at pH 6.5),
a
takin g also in to con sideration th at 4 electron s participate in th e reduction
process (wh ich will be explain ed bellow), th e value of th e diffusion coef-
–
5
2
–1
ficien t of DPT in th e given m edium was calculated 1.25 × 10 cm s . Th is
value is in good agreem en t with th e value of th e diffusion coefficien t cal-
culated accordin g to th e Ilkovic equation (for diffusion -con trolled four-
electron process) 1.20 × 10–5 cm s .
2
–1
Th e n um ber of electron s participatin g in th e DPT reduction on m ercury
electrode was determ in ed by coulom etry at a con stan t poten tial of –1.300 V,
wh ich correspon ds to th e lim itin g curren t of th e polarograph ic wave of th e
in vestigated substan ce. By coulom etric an alysis it was establish ed th at
electrode reduction takes place with th e participation of 4 electron s per on e
m olecule of DPT. Lim itin g curren ts of SDC polarograph ic waves lin early de-
creased with in creasin g of th e percen tage of reduced substan ce recalculated
for th e n um ber of electron s, n, per on e m olecule of DPT (Fig. 7), wh ich in -
2
3
dicates th at th ere is n o oth er secon dary process con sum in g th e ch arge
an d th e result sh owin g th e participation of 4 electron s per on e DPT m ole-
cule can be con sidered as reliable.
UV absorption spectrum of DPT at pH 6.5 (Fig. 8, curve 1) yields th ree in -
ten sive absorption ban ds with th e followin g param eters: λ = 306 n m (log ε =
1
3
.980), λ = 282 n m (log ε = 3.957) an d λ = 222 n m (log ε = 3.854). Th e
2 3
product of DPT electrolysis (Fig. 8, curve 2) h as two absorption m axim a
with λ = 278 n m (log ε = 3.041) an d λ = 229 n m (log ε = 3.833). Durin g
1
2
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
238
Ignjatović, Barek, Zima, Marković:
FIG. 7
SDC polarogram s of DPT (1 × 10 m ol l–1, pH 6.50) after passage of ch arge correspon din g to n =
–
4
0
(1), 2 (2), 3 (3) an d 4 (4)
FIG. 8
UV absorption spectra: DPT (1), product of DPT electrolysis (2), an ilin e (3) an d
ph en ylh ydrazin e (4). Solven t: BR buffer–m eth an ol (1:1) pH 6.50; con cen tration of th e m ea-
–
4
–1
sured substan ces 1 × 10 m ol l
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
,1-Dimethyl-3-phenyltriazene
1239
electrolysis, th e absorption ban d of DPT at 306 n m disappears, wh ich is a
con sequen ce of reduction of th e triazen e double bon d as a ch rom oph ore.
Th e obtain ed UV absorption spectrum of th e product of DPT reduction is
sim ilar to th e spectra of an ilin e an d ph en ylh ydrazin e (Fig. 8, curves 3 an d
4
). Th e ch aracteristics of an ilin e an d ph en ylh ydrazin e spectra in th e pH 6.5
buffer are as follows: an ilin e h as two absorption m axim a at λ = 280 n m
1
(
log ε = 3.000) an d λ = 227 n m (log ε = 3.839), ph en ylh ydrazin e h as also
2
two absorption m axim a at λ = 276 n m (log ε = 3.173) an d λ = 232 n m
1
2
(
log ε = 3.900). It is clear th at it is n ot possible to iden tify th e DPT electroly-
sis products with certain ty on ly on th e basis of UV absorption spectra. For
th at reason , addition al HPLC m easurem en ts were carried out yieldin g ch ro-
m atogram s of DPT electrolysis product (Fig. 9, ch rom atogram d) an d th e
m ixture of an ilin e an d ph en ylh ydrazin e at various con cen tration s (Fig. 9,
ch rom atogram s a–c). UV detector was adjusted to th e wavelen gth 278 n m ,
so it could detect all th e substan ces of in terest. An ilin e in th e obtain ed
ch rom atogram s yields a peak with th e reten tion tim e 5.9 m in , an d ph en yl-
FIG. 9
Liquid ch rom atogram s of an ilin e an d ph en ylh ydrazin e at th e followin g con cen tration s (in
–
1
–4
–4
–4
m ol l ): 1 × 10 (a), 2 × 10 (b), 3 × 10 (c) an d ch rom atogram of electrolysis product of DPT
–
4
with in itial con cen tration 5 × 10 (d)
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
240
Ignjatović, Barek, Zima, Marković:
h ydrazin e 10.8 m in . In th e ch rom atogram of th e electrolysis product (Fig. 9,
ch rom atogram d), both an ilin e an d ph en ylh ydrazin e appear. On th e basis
of calibration curve of an ilin e an d ph en ylh ydrazin e, given as th e depen d-
en ce of th e peak area on th e con cen tration , it was foun d th at th e relative
ratio of an ilin e an d ph en ylh ydrazin e in th e electrolysis product is 55:45.
Con siderin g th at th e slope of th e E1/2–pH depen den ce at pH 6.5 (Fig. 3)
am oun ts to 0.056 V per pH un it an d th at th e total n um ber of exch an ged
electron s, wh ich was obtain ed coulom etrically, n = 4, on th e basis of th e
equation dE/dpH = –2.303mRT/αn F, it is foun d th at th e total n um ber of
a
proton s participatin g in th e electroch em ical DPT reduction at th e given pH
value of th e supportin g electrolyte am oun ts to m = 3.8 ± 0.3.
On th e basis of th e presen ted results it can be con cluded th at 1,1-di-
m eth yl-3-ph en yltriazen e is reduced on m ercury electrode accordin g to th e
sch em e sh own in Fig. 10.
Analytical Utilization of Polarographic Behavior of
1
,1-Dimethyl-3-phenyltriazene
Th e supportin g electrolyte foun d to be m ost suitable is a m ixture of BR
buffer an d m eth an ol with pH 6.50. In Figs 1 an d 2 it can be seen th at DPT
is stable en ough at th e above pH an d th at it yields well defin ed an d easily
evaluated polarograph ic curves, with th e h igh est curren t values for th e
given con cen tration . Usin g buffers con tain in g 50 vol.% m eth an ol, lin ear
calibration depen den ces for SDC an d DP polarograph ic determ in ation s of
th e in vestigated substan ce were obtain ed with in th e con cen tration ran ge
–
6
–4
–1
1
× 10 –1 × 10 m ol l .
Th e sen sitivity of th e polarograph ic determ in ation of th e in vestigated
substan ce is in creased by five-fold dilution of BR buffer an d decreasin g th e
m eth an ol con ten t to 10 vol.%, wh ile pH values of th e resultin g solution s
CH3
NH2
+
H2N
N
CH3
CH3
CH3
N
N
N
+
4 H
+ 4 e
CH3
CH3
NH NH2
+
HN
FIG. 10
Th e sch em e of polarograph ic reduction of 1,1-dim eth yl-3-ph en yltriazen e
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
,1-Dimethyl-3-phenyltriazene
1241
are m ain tain ed un ch an ged. Th us, th e con cen tration s of th e im purities pres-
en t in th e supportin g electrolyte origin atin g from im purities in th e ch em i-
cals used for th e electrolyte preparation decreased, wh ich leads to sm ooth er
supportin g electrolyte polarograph ic curves an d an in crease in th e determ i-
n ation sen sitivity. Th e m eth an ol con ten t decrease in polarograph ed solu-
tion s leads to a sh ift of h alf-wave poten tials an d DP peak poten tials toward
m ore positive values an d it also in creases th e reversibility of th e electrode
process an d th us it in creases determ in ation sen sitivity. Th e use of th e last
m en tion ed m edium as th e supportin g electrolyte en abled DP polarograph ic
–
7
–1
determ in ation s in th e con cen tration ran ge (1–10) × 10 m ol l , as is pre-
sen ted in th e Fig. 11.
Th e param eters of calibration straigh t lin es – th e slope A an d its stan dard
deviation S(A), th e in tercept B an d its stan dard deviation S(B), th e deviation
of th e experim en tal poin ts from th e calculated straigh t lin e SI,C an d th e cor-
relation coefficien t r with th e calculated lim its of determ in ation LOD for
th e above-described polarograph ic m easurem en ts – are given in Table I. Th e
values of DPP peak poten tial E are also given .
p
Th e possibility to furth er in crease th e sen sitivity of th e determ in ation
usin g differen tial pulse voltam m etry an d adsorptive strippin g voltam m etry
at a h an gin g m ercury drop electrode is un der in vestigation .
FIG. 11
DP polarogram s of DPT in five-fold diluted BR buffer–m eth an ol (9:1) m edium , pH 6.50;
–
1
–7
–7
–7
–7
–7
con cen tration (in m ol l ): 1 × 10 (1), 2 × 10 (2), 4 × 10 (3), 6 × 10 (4), 8 × 10 (5) an d
–
7
1
0 × 10 (6)
Collect. Czech. Chem. Commun. 2007, Vol. 72, No. 9, pp. 1229–1243

1
242
Ignjatović, Barek, Zima, Marković:
TABLE I
Param eters of calibration straigh t lin es an d th e values of DPP peak poten tial for polarog-
raph ic determ in ation of 1,1-dim eth yl-3-ph en yltriazen e
C
m ol l
Ep
V
A/S(A)a
m A l m ol
B/S(B)b
n A
SI,Cc
n A
LOD
m ol l
Meth od
r
–
1
–1
–1
SDCd
SDCd
SDCe
DPPd
DPPd
DPPe
DPPe
(1–10)×10–5
(1–10)×10–6
(1–10)×10–6
(1–10)×10–5
(1–10)×10–6
(1–10)×10–6
(1–10)×10–7
–
10.0/0.2
10.3/0.2
11.3/0.4
16.9/0.2
18.1/0.3
22.2/0.9
24.3/0.5
36/10
5/1
15
1
0.9992
0.9993
0.9976
0.9998
0.9997
0.9970
0.9994
–
1×10–6
8×10–7
–
10/2
3
–1.130
–1.130
–1.060
–1.055
22/10
–1/1
12.5
2
8×10–7
1×10–7
10/5
6
–0.6/0.3
0.3
a
Slope/stan dard deviation . b In tercept/stan dard deviation . Deviation of th e experim en tal
c
poin ts from th e calculated straigh t lin e. BR buffer–m eth an ol (1:1) m edium , pH 6.50. e Five
d
tim es diluted BR buffer–m eth an ol (9:1) m edium , pH 6.50.
This research was supported by the Ministry of Education, Youth and Sports of the Czech Republic
(
project No. LC 06035 and MSM 0021620857) and by the Ministry of Science and Environmental
Protection of Serbia (project 142047).
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