This document describes a method using the H-point standard addition method (HPSAM) for the simultaneous determination of semicarbazide and hydrazine. The method is based on the reduction of Cu2+ to Cu+ by semicarbazide and hydrazine in the presence of neocuproine, followed by complex formation between Cu+ and neocuproine, producing a colored complex. The difference in the rates of reduction allows for the simultaneous analysis of both analytes. The method was able to determine semicarbazide in the range of 0.5-3.75 mg/ml and hydrazine in the range of 0.5-5 mg/ml in synthetic mixtures with different

1. Indirect simultaneous kinetic determination of semicarbazide
and hydrazine in micellar media by H-point standard addition
method
A. Safavi a,
1, H. Abdollahi b
, F. Sedaghatpour a
, M.R. Hormozi Nezhad a
a
Department of Chemistry, College of Sciences, Shiraz University, Shiraz 71454, Iran
b
Department of Chemistry, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
Received 28 May 2002; received in revised form 6 August 2002; accepted 23 August 2002
Abstract
H-point standard addition method (HPSAM) is suggested as a simple and selective method for the determination of
semicarbazide and hydrazine. The reduction of Cu2'
to Cu'
by semicarbazide and hydrazine in the presence of
neocuproine (Nc) and the subsequent complex formation between Cu'
and Nc produced a sensitive spectro-
photometric method for indirect determination of semicarbazide and hydrazine. The difference in the rate of reduction
of Cu2'
with semicarbazide and hydrazine in cationic micellar media is the basis of this method. Semicarbazide can be
determined in the range of 0.5Á/3.75 mg ml(1
with satisfactory accuracy and precision in the presence of excess
hydrazine. The proposed method was successfully applied to the simultaneous determination of semicarbazide (0.5Á/
3.75 mg ml(1
) and hydrazine (0.5Á/5 mg ml(1
) and also to the selective determination of semicarbazide in the presence
of hydrazine in several synthetic mixtures containing different concentration ratios of semicarbazide and hydrazine.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Semicarbazide; Hydrazine; Determination; HPSAM
1. Introduction
Hydrazine compounds are an important family
of organic compounds. Their separation and
detection have been of considerable analytical
interest for their wide applications in the chemical
industry and pharmacology [1]. Semicarbazide is a
poison and may be fatal if swallowed. Hydrazine is
a strong reducing agent used as an oxygen
scavenger for corrosion control in boilers and
hot-water heating systems [2]. It is also employed
as a starting material for many derivatives such as
foaming agents for plastics, antioxidants, polymer,
pesticides, plant-growth regulators and pharma-
ceuticals. Moreover, hydrazine, as well as its salts
and methyl and dimethyl derivatives, is used as
rocket fuel, gas generator and explosives. Hydra-
zine is volatile and toxic and is readily absorbed by
oral, dermal or inhalation routes of exposure [3].
Different methods for the determination of hy-
1 Corresponding author. Tel.: '/98-711-2284822; fax: '/98-
711-6305881
E-mail address: safavi@chem.susc.ac.ir (A. Safavi).
Talanta 59 (2003) 147Á/153
www.elsevier.com/locate/talanta
0039-9140/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 3 9 - 9 1 4 0 ( 0 2 ) 0 0 4 6 5 - 4

2. drazines have been described in the literature.
Spectrophotometric methods have been used to
analyze dilute hydrazine solutions using p-di-
methylaminobenzaldehyde [4], vanillin [5], salicy-
laldehyde [6] and silver-gelatin [7]. Optical
chemical sensors for determination of hydrazine
have also been described [8,9]. Flow-injection
method with spectrophotometric [10], fluorimetric
[11] and chemiluminiscence [12] detection have
also been developed for determination of hydra-
zine.
The formation of a chargeÁ/transfer complex
between Cu'
and neocuproine (Nc) (2,9-dimethyl-
1,10-phenantheroline) is the basis of the existing
spectrophotometric method for the indirect deter-
mination of reducing agents [13].
Campins-Falco et al. established the fundamen-
tals of the H-point standard additions method
(HPSAM) to kinetic data for the simultaneous
determination of binary mixtures or the calcula-
tion of analyte concentration completely free from
bias error [14]. In this method, simultaneous
analysis of two components is possible based on
the difference between the rates of the reaction of
the two components with a common reagent. Two
variants of the method are proposed; one is
applied when the reaction of one component is
faster than that of the other or the latter does not
take place at all [14,15]; the other is used when the
rate constant of two components are time-depen-
dent [14]. Under the assumption that only one of
the species, X, evolves with time, the variables to
be fixed are two times t1 and t2 at which the species
Y does not evolve with time or over the range
between these two times. The absorbance of X at a
given wavelength l and two times t1 and t2 will be
measured, while those of Y under the same
conditions will be measured as equal because Y
is not changing in the time domain of analysis. In a
mixture containing X and Y, standard addition of
X is performed at two times t1 and t2. The intersect
of the two straight lines of the standard addition
plots obtained at times t1 and t2 is known as H
point with characteristics of ((/CX, AY), where
(CX ) is the concentration of X and AY is the
analytical signal of species Y. This analytical
signal will enable calculation of concentration of
Y from a calibration curve.
In this work, the first variant of the H-point
standard addition method is suggested as a simple
and selective method for the determination of
semicarbazide in the presence of hydrazine. This
method is based on the difference in the rate of
reduction of Cu2'
with semicarbazide and hydra-
zine and complex formation of Cu'
with Nc in
cationic micellar media. The absorbance of the
colored Cu'
complex with Nc is then monitored
for indirect determination of semicarbazide and
hydrazine.
2. Experimental
2.1. Apparatus
The absorbance measurements as a function of
time, at a fixed wavelength were made with a
Shimadzu UV-1601PC spectrophotometer at-
tached to a Pentium 200 MHz computer. Mea-
surements of pH were made with a Metrohm 691
pH-meter using a combined glass electrode.
2.2. Reagents
All chemicals used were of analytical reagent
grade. Triply distilled water was used throughout.
An ethanolic stock solution of Nc, 3)/10(2
M
was prepared by dissolving 0.1629 g of Nc (Fluka)
in ethanol and diluting to 25 ml with the same
solvent. Copper stock solution, 0.1 M, was pre-
pared by dissolving 0.604 g of Cu(NO3)2.3H2O in
water and diluting to 25 ml. AceticÁ/acetate buffer
(pH0/5) was prepared by using acetic acid (1 M)
and sodium hydroxide (1 M) solution [16]. A stock
solution of cetyltrimethyl ammonium bromide
(CTAB) (0.1 M) was prepared by dissolving
0.9111 g of CTAB (Merck) in water and diluting
to 25 ml. A stock solution of semicarbazide was
prepared by dissolving 0.0125 g of semicarbazide
(Merck) in water and diluting to 25 ml. Hydrazine
stock solution (500 mg ml(1
) was prepared by
dissolving 0.0125 g of NH2NH2.2HCl (Merck) in
water and diluting to 25 ml.
A. Safavi et al. / Talanta 59 (2003) 147Á/153148

3. 2.3. Procedure
Stock Nc solution (1 ml), 1 ml of stock Cu2'
solution, 1 ml of buffer solution and 0.6 ml of
stock CTAB solution and appropriate volumes of
semicarbazide and hydrazine containing 2.5Á/18.75
mg semicarbazide and 2.5Á/25 mg hydrazine were
added to a 5 ml volumetric flask and made up to
the mark with water. For each measurement, :/2
ml of the above solution was transferred to the
spectrophotometric cell and the variation of the
absorbance versus time was recorded immediately.
The absorbance was measured at 450 nm with 1 s
time intervals for each sample. Simultaneous
determination of semicarbazide and hydrazine
with HPSAM was performed by measuring the
absorbances at 60 and 220 s after initiation of the
reaction.
3. Results and discussion
3.1. Principles of the method
The Cu2'
Á/Nc systems allows the spectrophoto-
metric determination of a reducing agent, Ared,
provided that the redox reaction:
n Cu2'
'2n Nc'Ared 0 n [Cu(Nc)2]'
'Aox
is complete with the formation of an equivalent
amount of [Cu(Nc)2]'
with respect to the n-
electron reductant, Ared. Copper (II) is a strong
oxidizing agent only when its reduction product,
Cu'
, is stabilized by a strong complex-forming
ligand, e.g. Nc. The standard potential of the
Cu2'
Á/Cu'
couple (0.17 V) is shifted to more
positive values by preferential complexation of
Cu'
. The stronger the reductant, the more
quantitative will be the reduction of Cu2'
with
the subsequent formation of [Cu(Nc)2]'
[13].
The reduction of Cu2'
to Cu'
by semicarba-
zide and hydrazine in the presence of Nc and
subsequent complex formation between resulted
Cu'
and Nc produce sensitive spectrophotometric
spectrum for indirect determination of semicarba-
zide and hydrazine.
Difference in kinetic behavior of two analytes
accompanied with mathematical treatment of data
using HPSAM permits simultaneous analysis of
two important hydrazine compounds, such as
semicarbazide and hydrazine. Fig. 1 shows that
the reduction of Cu2'
by semicarbazide and
hydrazine has a kinetic behavior and the absor-
bance at 450 nm changes with time during the first
few minutes from initiation of the reaction.
3.2. Effect of operational parameters
Selectivity is one of the most important require-
ments of any analytical method. Employing sui-
table experimental conditions and using desirable
mathematical algorithms can improve selectivity.
The kinetics behavior of most chemical species in
some chemical reactions can be controlled by
changing the microenvironment of reaction.
3.2.1. Effect of pH
The sensitivity and rate of reduction and com-
plex formation are dependent on pH of the
medium. Thus, the effect of pH was studied. pH
5 was selected as optimum pH. As shown in Fig. 1,
under optimum pH conditions the kinetic behavior
of the system is not completely suitable for
applying the first variant of HPSAM.
3.2.2. Effect of surfactants
Micelles change the effective microenvironment
around dissolved solutes and as a consequence
their physicochemical properties, such as rate
constant, spectral profile etc., can be affected.
Fig. 1. Kinetic curves for 5 mg ml(1
of semicarbazide and 5 mg
ml(1
of hydrazine at pH0/5 in the absence of CTAB.
A. Safavi et al. / Talanta 59 (2003) 147Á/153 149

4. The fact that micelles can accelerate reactions has
been increasingly exploited in the last few years to
improve the features of both catalytic [17Á/19] and
non-catalytic [20] kinetics methods [21]. Micelles
can alter reaction kinetics through their rate,
control pathways, change reaction mechanisms
and/or the observed rate constant ratio of two or
more species interacting with a common reagent.
Because micelles can affect the kinetics of reac-
tions; the effects of micelles on the system was
studied under optimum pH. Cetyltrimethyl am-
monium bromide (CTAB) as a cationic surfactant,
sodium dodecyl sulfate (SDS) as an anionic
surfactant and Triton X-100 as a nonionic surfac-
tant were selected. CTAB was found as the best
surfactant for HPSAM. It was observed that
CTAB increases the rates of both semicarbazide
and hydrazine reactions. This rate enhancement
might be due to the increased reactant concentra-
tions in the micellar pseudo-phase [22]. The
increased rates of reactions in the presence of
CTAB is in such a way that the rate of hydrazine
reaction becomes very fast while that of semicar-
bazide is not as fast as the reaction of hydrazine
(Fig. 2). This is a suitable condition for HPSAM
since the reaction of hydrazine is complete in the
time domain of analysis while that of semicarba-
zide is still in progress.
3.3. Analytical performance and figures of merit
Fig. 2 shows the possible applicability of
HPSAM to the simultaneous analysis of semicar-
bazide and hydrazine by the proposed system. As
shown when semicarbazide is selected as the
analyte, it is possible to select several pairs of
time where they present the same absorbance for
hydrazine species. As shown previously by Cam-
pins-Falco et al. [14], the higher the value for slope
increment, the lower the error for analyte concen-
tration. So, only the time pair that gave the
greatest slope increment and at which the change
in absorbance related to hydrazine concentration
was negligible was selected. For this reason, the
time pair of 60Á/220 s was employed for obtaining
Fig. 2. Kinetic curves for 5 mg ml(1
of semicarbazide and 5 mg
ml(1
of hydrazine at pH0/5 in the presence of CTAB.
Fig. 3. Plot of H-point standard addition method for simulta-
neous determination of semicarbazide (1.25 mg ml(1
) and
hydrazine (1.25 mg ml(1
) at different selected time pairs.
Fig. 4. Plot of H-point standard addition method for fixed
hydrazine concentration (1.25 mg ml(1
) and different concen-
trations of semicarbazide.
A. Safavi et al. / Talanta 59 (2003) 147Á/153150

5. the highest accuracy. Fig. 3 shows several H-point
standard addition calibration lines constructed at
some possible selected time pairs. It is observed
that the 60Á/220 s time pair shows the greatest
slope increment.
According to the theory of HPSAM at H-point
((/CX, AY ), CX (concentration of semicarbazide
at H-point) is independent from the concentration
of hydrazine (Fig. 4) and so Ay (the absorbance
value at H point, in this case the absorbance of
hydrazine) is also independent from the concen-
tration of semicarbazide (Fig. 5). The value of AH
enables calculation of the concentration of hydra-
zine from a calibration curve constructed from
ordinate of several HPSA plots with various
concentrations of hydrazine species.
For the determination of semicarbazide in the
presence of hydrazine, the absorbance increment
as the analytical signal was used. The application
of the HPSAM in the DAt 1(t2(/Cadded variant
yields the concentration of semicarbazide directly
from the graph [14]. However, in order to ensure
the absence of constant or proportional error from
the calculated concentration, all the possible
DAt1(t 2(/Cadded lines for semicarbazide should
intersect at the same point, namely that corre-
sponding to the unknown concentration, CH, as
this would indicate that the time evaluation of the
matrix would be a horizontal line. Fig. 6 and Table
1 show the results obtained from employing this
version of HPSAM on a mixture of semicarbazide
and hydrazine. The results obtained by this
procedure were in good agreement with the actual
concentrations.
Under optimum conditions, several synthetic
mixed samples with different concentration ratios
of semicarbazide and hydrazine (1:1, 1:2, 1:10,
1:2.4) were analyzed by using the suggested
method. As can be seen from Table 2, the accuracy
and precision of the results are all satisfactory.
Fig. 5. Plot of H-point standard addition method for fixed
semicarbazide concentration (1.25 mg ml(1
) and different
concentrations of hydrazine.
Fig. 6. DA versus added semicarbazide concentration at
different time intervals at 450 nm for a synthetic mixture
containing 1.25 mg ml(1
of semicarbazide and hydrazine.
Table 1
Application of signal increment version of HPSAM in a synthetic mixture containing semicarbazide (1.25 mg ml(1
) and hydrazine
(1.25 mg ml(1
)
Time interval (s)
55Á/512 65Á/220 60Á/210 80Á/210
Found semicarbazide conc. (mg ml(1
) 1.27 1.22 1.24 1.26
Recovery (%) 101.6 97.6 99.2 100.8
Relative standard deviation (%) (n0/4) 1.6 1.5 1.4 1.6
A. Safavi et al. / Talanta 59 (2003) 147Á/153 151

6. Limit of detection was calculated as LOD0/3SCH,
where SCH is the S.D. of several (n0/4) replicate
measurements of zero concentration of analyte
with HPSAM. The corresponding value obtained
for semicarbazide was 0.03 mg ml(1
. In addition,
for showing the applicability of the method,
environmental samples were spiked with semicar-
bazide and hydrazine and the proposed method
was applied to the determination of the analyte.
The results are shown in Table 3. As can be seen,
the results are all satisfactory. Semicarbazide and
hydrazine can be determined in the range 0.5Á/3.75
and 0.5Á/5 mg ml(1
with satisfactory accuracy and
precision.
3.4. Effect of interferences
The effect of hydrazine compounds, phenylhy-
drazine, dinitrophenylhydrazine and isoniazide
was studied. They showed a kinetic behavior the
same as hydrazine and thus interfere with the
determination of hydrazine. Table 4 shows the
results obtained for the analysis of semicarbazide
and hydrazine in the presence of dinitrophenylhy-
drazine. As is obvious, the presence of dinitrophe-
nylhydrazine does not affect the determination of
semicarbazide, but seriously interferes with the
determination of hydrazine.
Table 2
Results of several experiments for the analysis of semicarbazide and hydrazine mixtures
AÁ/C equation r Present (mg ml(1
) Found (mg ml(1
)
Semicarbazide Hydrazine Semicarbazide Hydrazine
A600/0.0755x'/1.315 0.985 0.50 5.00 0.43 5.07
A2200/0.2131x'/1.3746 0.997
A600/0.0474x'/0.8027 0.993 1.50 3.00 1.26 2.99
A2200/0.1099x'/0.8816 0.999
A600/0.0723x'/0.4263 0.997 1.25 1.25 1.26 1.36
A2200/0.159x'/0.5357 0.994
A600/0.0755x'/1.315 0.995 1.50 3.75 1.50 3.55
A2200/0.2131x'/1.3746 0.992
Table 3
Determination of semicarbazide and hydrazine in real sample
Sample Concentration (mg ml(1
)
Spiked Found
Semicarbazide Hydrazine Semicarbazide Hydrazine
River Water 2.50 1.50 2.529/0.02 1.469/0.01
River Water 2.00 2.50 2.109/0.07 2.309/0.06
River Water 1.00 1.50 1.029/0.07 1.369/0.03
Table 4
Results of experiment for the analysis of a semicarbazide and
hydrazine mixture in the presence of dinitrophenylhydrazine
(1.25 mg ml(1
)
Present (mg ml(1
) Found (mg ml(1
)
Semicarbazide Hydrazine Semicarbazide Hydrazine
1.25 1.25 1.24 3.10
A. Safavi et al. / Talanta 59 (2003) 147Á/153152

7. Acknowledgements
The authors gratefully acknowledge the support
of this work by Shiraz University Research
Council.
References
[1] W.-C. Yang, A.-M. Yu, Y.-Q. Dai, H.-Y. Chen, Anal.
Lett. 33 (15) (2000) 3343.
[2] H.W. Schessl, in: K. Othmer (Ed.), Encyclopedia of
Chemical Technology, vol. 13, 4th ed, Wiley/Interscience,
New York, 1995, p. 560.
[3] J.M. Pingarron, I. Ortiz Hernandez, A. Gonzalez-Cortes,
P. Yanez-Sedeno, Anal. Chim. Acta 439 (2001) 281.
[4] G.W. Watt, J.D. Chrisp, Anal. Chem. 24 (1952) 2006.
[5] S. Amlathe, V.K. Gupta, Analyst 113 (1988) 801.
[6] L.C. Bailey, T. Medwick, Anal. Chim. Acta 35 (1966) 330.
[7] T. Pal, D.S. Maity, A. Ganguly, Analyst 111 (1986) 1413.
[8] C. Gojon, B. Dureault, N. Hovnanian, C. Guizard, J. Sol-
Gel Sci. Technol. 14 (1999) 163.
[9] P. Ortega Barrales, A. Molina Diaz, M.I. Pascual Reguera,
L.F. Capitan Vallvey, Anal. Chim. Acta 353 (1997) 115.
[10] A.A. Ensafi, B. Naderi, Microchem. J. 56 (1997) 269.
[11] A.A. Ensafi, B. Rezaei, Talanta 47 (1998) 645.
[12] A. Safavi, M.R. Baezzat, Anal. Chim. Acta 358 (1988) 121.
[13] E. Tutem, R. Apak, F. Baykut, Analyst 116 (1991) 89.
[14] F. Bosch Reig, P. Campins Falco, A. Sevillano Cabeza, R.
Herreaz Hernandez, C. Molins Legua, Anal. Chem. 63
(1991) 2424.
[15] A. Safavi, H. Abdollahi, F. Sedaghatpour, S. Zeinali,
Anal. Chim. Acta 409 (2000) 275.
[16] J. Lurie, Handbook of Analytical Chemistry (English
translation), Mir, Moscow, 1975.
[17] M.L. Lunar, S. Rubio, D. Pe´rez-Bendito, Anal. Chim.
Acta 237 (1990) 207.
[18] D. Sicilia, S. Rubio, D. Pe´rez-Bendito, Talanta 38 (1991)
1147.
[19] D. Sicilia, S. Rubio, D. Pe´rez-Bendito, Anal. Chem. 64
(1992) 1490.
[20] E. Athanasiou-Malaki, M.A. Koupparis, Anal. Chim.
Acta 219 (1989) 295.
[21] D. Sicilia, S. Rubio, D. Pe´rez-Bendito, Anal. Chim. Acta
284 (1993) 149.
[22] D. Pe´rez-Bendito, S. Rubio, Trends Anal. Chem. 12 (1993)
9.
A. Safavi et al. / Talanta 59 (2003) 147Á/153 153