American Journal of Anal yt ical Chemistry, 2011, 2, 223-234
doi:10.4236/ajac.2011.22027 Published Online May 2011 (http://www.SciRP.org/journal/ajac)
Determination of the Antiretroviral Drug Zidovudine in
Diluted Alkaline Electrolyte by Adsorptive Stripping
Voltammetry at the Mercury Film Electrode
Arnaldo Aguiar Castro1,2, Ricardo Queiroz Aucélio1, Nicolás Adrián Rey1, Eliane Monsores Miguel1,
Percio Augusto Mardini Farias1
1Department of Chemistry, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, Brazil
2Fac. Química, Química Analítica, Universidad de La Habana, Havana, Cuba
Received October 7, 2010; revised November 4, 2010; accepted December 28, 2010
Abstract
This paper describes a stripping method for the determination of zidovudine at the submicromolar concentra-
tion levels. This method is based on the controlled adsorptive accumulation of zidovudine at the thin-film
mercury electrode, followed by a linear-sweep stripping voltammetry measurement of the surface species.
Optimal experimental conditions include a NaOH solution of 2.0 × 10–3 mol·L–1 (supporting electrolyte), an
accumulation potential of –0.30 V and a scan rate of 100 mV·s–1. The response of zidovudine is linear over
the concentration range 0.01 - 0.08 ppm. After an accumulation time of 5 minutes, the detection limit was
found to be 0.67 ppb (2.5 × 10–9 mol·L–1). More convenient methods to measure zidovudine concentration in
the presence of the didanosine, acyclovir, nevirapine, lamivudine, and efavirenz, were also investigated. The
presence of zidovudine together with ATP or ssDNA demonstrates the utility of this method.
Keywords: Zidovudine Determination, Antiviral Drugs, Ssdna, Thin-Film Mercury Electrode, Stripping
Voltammetry
1. Introduction
Zidovudine (Figure 1) or azidothymidine (AZT) (also
called ZDV), is a nucleoside analog reverse transcriptase
inhibitor (NRTI), a type of antiretroviral drug. It is also
sold under the names Retrovir and Retrovis, and as an
ingredient in Combivir and Trizivir. It is an analog of
thymidine. It was used as the first approved treatment for
HIV. AZT does not destroy the HIV infection, but only
delays the progression of the disease and the replication
of virus, even at very high doses. During prolonged AZT
treatment, HIV has the ability to increase its resistance to
AZT by mutating its reverse transcriptase. In order to
slow down the process of developing resistance, physic-
cians generally recommend that AZT be given in com-
bination with another reverse transcriptase inhibitor and
an antiretroviral from another group, such as a protease
inhibitor or a non-nucleoside reverse transcriptase in-
hibitor [1-8].
Several methods have been discovered for the quanti-
tative determination of zidovudine including chromatog-
N
–
═
N
+
═
N
Figure 1. Structure of zidovudine (AZT); [1-[(2R,4S,5S)-4-
azido-5-(hydroxymethyl)oxolan-2-yl]-5-methyl-1,2,3,4-tetra
hydropyrimidine-2,4-dione].

A. A. CASTRO ET AL. 224
raphy [9-15], fluorescence polarization immunoassay
[16], using diamond paste based immunosensor [17],
fluorescence spectroscopy [18] and voltammetry [19-24].
With the recent advancements in properties of the ad-
sorptive stripping voltammetry, new methodologies have
been developed for adenine, thymine, guanine, ATP, and
DNA determinations employing alkaline solution with
lower ionic strength as the supporting electrolyte [25-28].
Using this alkaline electrolyte, the present work found a
new stripping voltammetric procedure to trace the detec-
tion of zidovudine based on its adsorption at the thin film
mercury electrode. The advantages, instrumental pa-
rameters, and possible limitations of this procedure will
be explained in this paper. Furthermore, the effects of a
wide range of potentially interfering compounds such as
didanosine, acyclovir, nevirapine, lamivudine, efavirenz,
some metal ions, and ATP or ssDNA are examined.
2. Experimental
2.1. Apparatus
Linear-sweep stripping voltammograms were obtained
with an EG&G PAR model 384-B Polarographic Ana-
lyser (Princeton Applied Research, Princeton, NJ, USA),
equipped with an external cell and a Houston Ametek-
DMP-40 series digital plotter. The working electrode
was a glassy carbon electrode (GCE, 3.0 mm diameter,
BAS-Bioanalytical Systems, Inc., West Lafayette, Indi-
ana 47906, USA) containing thin-film mercury, an Ag/
AgCl reference electrode with vicor tip and a platinum
auxiliary electrode. A magnetic stirrer and stirring bar
(Nalgene Cat. No. 6600 - 0010, Rochester, NY, USA)
provided convective transport during the process of ac-
cumulation.
2.2. Forming Thin-Film Mercury Electrode
The thin mercury film was formed in a 10–2 mol·L–1
Hg(NO3)2 solution, prepared by the dissolving 0.4 g of
mercury (II) nitrate into 100 mL of an acidified Milli-Q
water (5% of HNO3). A glassy carbon electrode (GCE,
BAS) was first polished with alumina (PK-4, BAS) and
then mounted with the help of a Teflon holder in a volt-
ammetric cell provided with an Ag/AgCl reference elec-
trode, a platinum auxiliary electrode, 1 mL of mercury
(II) nitrate solution, 1 mL of 10–1 mol·L–1 potassium ni-
trate solution and 8 mL of purified water. The solution
was purged with nitrogen for 240 s in order to eliminate
the oxygen that was present initially. Mercury plating
was carried over for 5 min at a cell of –0.9 V. After
checking that the electrode was plated properly, the set
of electrodes was rinsed with water and a new clean cell
containing the analyte solution was fitted.
2.3. Reagents
Water purified in a Milli-Q purification system (Milli-
pore, Billerica, MA, USA) was used for all dilutions and
sample preparations. All chemicals were of the analytical
reagent grade. Zidovudine standard was used as it was
received by the FarManguinhos – FIOCRUZ (Fundação
Oswaldo Cruz – RJ). Stock solutions of 1000 ppm were
prepared by dissolving 50 mg of the target reagent zi-
dovudine into 5 mL of 2 mol·L–1 NaOH, 5 mL of ethylic
alcohol and water until a volume of 50 mL was reached.
Diluted zidovudine solutions of 100 or 10 ppm were pre-
pared daily by dissolving 5 mL of 1000 or 100 ppm zi-
dovudine into water until a volume of 50 mL was
reached. Stock solutions of other HIV drugs were pre-
pared using the same procedure described for zidovudine.
The didanosine and aciclovir stock solutions were pre-
pared without using along with ethylic alcohol. A 1000
ppm copper, other metal stock solutions (atomic absorp-
tion standard solution, Sigma-Aldrich Brasil Ltda.), were
used and diluted as required for standard additions. Stock
solutions of 1000 ppm of adenosine 5’-tripho- sphate and
disodium salt hydrate (ATP) were prepared by dissolving
10 mg of the target reagent into 2 mL of diluted perchlo-
ric acid (10–1 mol·L–1). The subsequent solution was
heated at 70˚C for 30 seconds. After being heated, the
sample was cooled down and diluted with water to a
volume of 10 mL. Single-stranded calf thymus DNA
(Cat. No. D-8899; Lot 43H67951) was used as it was
received from Sigma. A 500 g DNA/mL stock solution
(around 5 mg/10 mL; lyophilized powder containing
63% DNA) was prepared according to the ATP proce-
dure. The final solution was stored at 4oC.
2.4. Procedure
A known volume (10 mL) of the supporting electrolyte
solution (2.0 × 10–3 mol·L–1 sodium hydroxide (with 1%
v/v of ethylic alcohol)) was added to the voltammetric
cell and degassed with nitrogen for 8 min (and for 60
seconds before each adsorptive stripping cycle). First, the
condition potential (usually –0.9 V) was applied to the
electrode for a set amount of time (usually 60 s). After-
wards, the initial potential (–0.30 V) was applied to the
electrode for a set amount of time (usually 90 s). The so-
lution was stirred slowly throughout this time. The stir-
ring was then stopped, and after 30 s, the voltammogram
was recorded by applying a negative-going potential scan.
The scan (at 100 mV·s–1) was stopped at –1.10 V, and the
adsorptive stripping cycle was repeated using the same
thin-film mercury. After the background stripping volt-

A. A. CASTRO ET AL. 225
ammograms were obtained, aliquots of the zidovudine
standards were introduced. The entire procedure was
automated, as controlled by 384-B Polarographic Ana-
lyser. Throughout this operation, nitrogen was passed
over the surface of the solution. All data were obtained at
room temperature (25˚C).
3. Results and Discussion
3.1. Parameters Affecting the Adsorptive
Stripping Behavior
Figure 2 compares the differential-pulse, linear-scan and
linear-sweep adsorptive stripping voltammograms using
0.10 ppm zidovudine in a 2.0 × 10–3 mol·L–1 NaOH solu-
tion (with 1% v/v of ethylic alcohol) after 90 seconds of
preconcentration, stirring at –0.30 V. A mercury film
was used as a work electrode. After an equilibrium time
of 30 s, the differential pulse (A) and linear (B) or cyclic
cathodic voltammogram (C) was recorded at 50 (A) and
100 (B,C) mV·s–1, respectively. Both scan modes offer
excellent signal-to-background characteristics. Linear scans,
however, offer a higher current peak and a greater speed,
and are recommended for the determination of zi-
dovudine. The linear-sweep stripping mode yields a
well- defined peak, with half-width (b½) of 80 mV. The
zidovudine cyclic cathodic peak (Ip) appears at –0.68V
(Ep). No anodic peak was observed in the first scan.
Figure 3 shows the linear-sweep adsorptive voltam-
mogram for 0.1 ppm of zidovudine in a 2.0 × 10–3 mol·L–1
NaOH solution (with 1% v/v of ethylic alcohol), using a
pre-concentration time of 60 s, while being stirred how-
ever, at –0.15 (A) and –0.30 (B) V. After an equilibrium
time of 30 s, the linear-sweep voltammogram was re-
corded at 100 mV·s–1. With accumulation potential at
–0.15 V, the zidovudine cyclic voltammogram showed
two peaks at –0.28 and –0.62 V. Only a single, well- de-
fined, higher cathodic peak (Ip) with half-width (b½) of 80
mV peak appears at –0.68 V(Ep). This occurs when the
accumulation potential used was of –0.30 V. This accu-
mulation potential was used throughout this study.
Other chemicals and instrumental parameters such as
the supporting electrolyte, the pH level, the accumulation
time, and the scan rate (which directly affects the zi-
dovudine adsorptive stripping peak response) were also
optimized. The adsorption properties of the zidovudine
vary depending on the composition of the supporting
electrolyte. Various electrolytes, e.g. Briton-Robinson,
(a) (b) (c)
Figure 2. Differential-pulse (a), linear-scan (b) and linear-sweep adsorptive (c) voltammograms of 0.10 ppm zidovudine in 2.0 ×
10–3 mol·L–1 NaOH (with 1% v/v of ethylic alcohol). Condition time, 60 s at –0.90 V; accumulation time, 90 s at –0.30 V with
stirring; amplitude pulse, 50 mV (a); scan rate, 50(a) and 100(b,c) mV·s–1; thin-film mercury electrode (5 min at –0.9 V).

A. A. CASTRO ET AL. 226
(a) (b)
Figure 3. Linear-sweep adsorptive voltammogram of a 0.10 ppm zidovudine solution in 2.0 × 10–3 mol·L–1 NaOH (with 1% v/v
of ethylic alcohol). Condition time, 60 s at –0.90 V; accumulation time, 60 s at –0.15 (a) and –0.30 (b) V with stirring; scan rate,
100 mV·s–1; thin-film mercury electrode (5 min at –0.9 V).
phosphate and NaOH solution, were determined to be
suitable media for the adsorptive stripping measurement
of zidovudine. The best results (with respect to signal en-
hancement and reproducibility) were obtained using the
NaOH electrolyte. The alkaline medium was employed
throughout this study. The adsorptive stripping signal of
zidovudine depends on the sample pH.
Figure 4 shows the dependence of the zidovudine
peak current on the solution’s pH (from 2 to 11). No re-
sponse to zidovudine was observed in solutions more
acidic than pH 6. Increasing the pH level from 6.5 to 11
resulted in rapid increase in the zidovudine peak current.
However, the stability of the zidovudine peak in aqueous
solutions decreased when the pH was above 11. Because
of this, a pH of approximately 11 was used to satisfy the
sensitivity and stability requirements throughout the ex-
periment.
Figure 5 shows a detailed study of the effect of the
accumulation potential (from +0.05 to –0.30 V) on the
stripping zidovudine voltammograms. Parameters like
the potential peak (Ep), the half-width (b½) and the cur-
rent peak (Ip) were also observed. The first zidovudine
peak at approximately 0.28 V is closer than the other
HIV drugs’ peaks, which were previously analyzed as
possible interferences to ziduvudine determination. The
second peak, at –0.68 V, is in agreement with the peak
observed in Figure 3(b), which shows a very welled-
fined peak with best half-width/ background resolution.
The accumulation potential at –0.30 V was then confirm-
ed as ideal and used throughout this study.
Figure 6 shows a study of the effect of the scan rate at
10 (a) and 200 mV·s–1 (b) on the zidovudine stripping
voltammograms. With a scan rate of 200 mV·s–1, the
peak current for a 0.10 ppm zidovudine solution was
about 30.5 times larger than the corresponding peak ob-
tained with 10 mV·s–1 response. However, this gain in
sensitivevity is accompanied by broadening peaks. The
peak current (Ip) for the surface-adsorbed zidovudine is
directly proportional to the scan rate (υ). A plot of Ip vs υ
was linear (correlation coefficient, 0.998), with a slope of
235.3, over the 10 - 100 mV·s–1 range. Overall, a scan
rate of 100 mV·s–1 would be the best solution when con-
sidering the sensitivity, resolution and speed require-
ments.
Figure 7 shows the dependence of the linear cyclic
current peak along with the pre-concentration time. The
peak increases linearly with time and then levels off.
Such time-dependent profiles represent the corresponding

A. A. CASTRO ET AL.227
(a) (b)
Figure 4. Effect of pH (A-7; B-11) on the linear-sweep adsorptive stripping voltammograms of 0.05 ppm zidovudine. Condi-
tions: time, 60 s at –0.90 V; accumulation time, 90 s at –0.30 V; scan rate, 100 mV·s–1; equilibrium time, 30 s; thin-film mercury
electrode (5 min at –0.9 V). Also shown is the resulting current peak versus pH plot.
absorption isotherms since the peak current depends on
the amount adsorbed. With 90 s of pre-concentration, the
peak current for a 0.10 ppm zidovudine solution was
about 13.3 times larger than the corresponding peak ob-
tained with a direct (0 s) response. The resulting plot of
peak current vs. accumulation time (0 - 60 s) is linear
(slope 240.8 nA·s–1 and correlation coefficient, 0.993).
3.2. Quantitative Utility
The effect of the pre-concentration associated with the
adsorption process yields a significantly lower detection
limit compared to the corresponding solution measure-
ments. A detection limit of 0.67 ppb (2.5 × 10–9 mol·L–1)
was estimated from quantifying 0.01 ppm after a 5-min
accumulation (S/N = 2). Thus, 6.7 ng was detected in the
10 mL of solution used. The reproducibility was esti-
mated by was taking ten successive measurements of a
stirred 0.04 ppm zidovudine solution (other conditions:
supporting electrolyte, 2.0 × 10–3 mol·L–1 NaOH (with
1% v/v of ethylic alcohol); condition time, 60 s at –0.9 V;
accumulation time, 90 s at –0.3 V; final potential, –1.1 V;
scan rate, 100 mV·s–1; equilibrium time, 30 s and thin-
film mercury electrode). The mean peak current was
5503 nA with a range of 5407 - 5593 nA and a relative
standard deviation. The Ep and the b1/2 remained the
same at –0.68 V and 80 mV, respectively. Figure 8 dis-
plays voltammograms for increasing zidovudine concen-
tration (A –0.02 and B –0.08 ppm) after 90 s of accumu-
lation. Well-defined stripping peaks (at –0.68 V) were

A. A. CASTRO ET AL. 228
Figure 5. Effect of accumulation potential on the linear-sweep adsorptive stripping voltammograms of 0.10 ppm zidovudine
solution in 2.0 × 10–3·mol·L–1 NaOH (with 1% v/v of ethylic alcohol). Conditions: time, 60 s at –0.90 V; accumulation time, 60;
scan rate, 100 mV·s–1; equilibrium time, 30 s; thin-film mercury electrode (5 min at –0.9 V). (A) Accumulation potential versus
potential zidovudine peak, (B) versus half-width of zidovudine peak and (C) versus current zidovudine peak. (a) Zidovudine
first peak and (b) second zidovudine peak.

A. A. CASTRO ET AL.229
(a) (b)
Figure 6. Effect of scan rate on the linear-sweep voltammograms of 0.10 ppm zidovudine in 2.0 × 10–3 mol·L–1 NaOH (with 1%
v/v of ethylic alcohol). Accumulation time, 90 s at –0.30 V. Final potential, –1.1 V. The (a) and (b) curves are relative to scan
rate of 10 and 200 mV·s–1, respectively. Conditions: time, 60 s at –0.90 V; equilibrium time, 30 s; thin-film mercury electrode (5
min at –0.9 V). Also shown is the resulting current peak versus scan rate plot.
(a) (b)
Figure 7. Effects of accumulation time at –0.30V on the linear-sweep adsorptive stripping voltammograms of 0.10 ppm of zi-
dovudine in 2.0 × 10–3 mol·L–1 NaOH (with 1% v/v of ethylic alcohol). The (a) and (b) curves are relative to accumulation times
of 5 and 90 s, respectively. Condition time, 60s at –0.90 V; scan rate, 100 mV·s–1, equilibrium time, 30 s; thin-film mercury
electrode (5 min at –0.9 V). Also shown is the resulting current peak versus accumulation time plot.

A. A. CASTRO ET AL. 230
(a) (b)
Figure 8. Linear-sweep adsorptive stripping voltammograms obtained after increasing the zidovudine concentration in a solu-
tion of 2.0 × 10–3 mol·L–1 NaOH(with 1% v/v of ethylic alcohol). The (a) and (b) curves are relative to 0.02 and 0.08 ppm of
zidovudine concentration, respectively. Accumulation time, 90 s at –0.30 V. Condition time, 60 s at –0.9 V. Scan rate, 100
mV·s–1. Final potential at –1.1 V. Equilibrium time, 30 s. Thin-film mercury electrode (5 min at –0.9 V). Also shown is the re-
sulting calibration curve plot.
observed between the 0.01 and the 0.06 zidovudine con-
centration ranges. The plot of peak current versus con-
centration that resulted is linear (slope 119014 nA/ppm;
correlation coefficient, 0.998). This linearity prevails as
long as linear isotherm conditions (low surface coverage)
continue to exist. Table 1 shows a summary of the opti-
mized conditions for zidovudine determination by linear
cyclic adsorptive stripping voltammetry at the mercury
film electrode.
Practical applications of the linear-sweep adsorptive
stripping analyses may be interfered with by the presence
of metal ions and/or surface active compounds. With
respect to the surface reaction, double layer changes or
direct interactions deriving from these substances may
inhibit or aid in the accumulation of the analyte. Meas-
urements of 0.05 ppm zidovudine (other conditions:
supporting electrolyte, 2.0 × 10–3 mol·L–1 NaOH (with
1% v/v of ethylic alcohol) ; condition time, 60s at –0.9 V;
accumulation time, 90 s at –0.30 V; final potential, –1.1
V; scan rate, 100 mV·s–1; equilibrium time, 30 s and
thin-film mercury electrode) were not affected by the
addition of up to 0.03 ppm of lead (II); up to 0.05 ppm of
cobalt (II); up to 0.06 ppm of nickel (II) and up to 0.10
ppm of iron (III) or copper (II) or cadmium (II) or zinc
(II). Preliminary studies were developed for the dete
mination of zidovudine in the presence of other antiret-
roviral drugs for the treatment of human immunodefi-
ciency virus (HIV): didanosine, acyclovir, nevirapine

A. A. CASTRO ET AL.231
Table 1. Optimized conditions for zidovudine determination
by linear cyclic adsorptive stripping voltammetry at the
mercury film electrode.
Parameters Optimized conditions
Thin-film mercury electrode 5 minutes at –0.9 V
Zidovudine concentration range 0.01 - 0.08 ppm
Electrolyte 2.0 × 10–3 mol·L–1 NaOH
Scan mode Linear cyclic
Initial potential –0.3V
Final potential –1.1 V
Scan rate 100 mV·s–1
Condition potential –0.9 V
Condition time 60 seconds
Accumulation potential –0.3 V
Accumulation time 90 seconds
Equilibrium time 30 seconds
and lamivudine. Measurements of 0.05 ppm zidovudine
(other conditions: supporting electrolyte, 2.0 × 10–3 mol·L–1
NaOH (with 1% v/v of ethylic alcohol); condition time, 60s
at –0.9 V; accumulation time, 90 s at –0.30 V; final poten-
tial, –1.1 V; scan rate, 100 mV·s–1; equilibrium time, 30 s
and thin-film mercury electrode) were not affected by the
addition of up to 0.06 ppm of lamivudine or up to 0.10 ppm
of acyclovir, nevirapine, didanosine or efavirenz.
Figure 9 illustrates the method’s suitability for the
determination of zidovudine through linear-sweep ad-
sorptive stripping voltammetry in a synthetic sample
containing several antiretroviral drugs (efavirenz, nevi-
rapine, didanosine, lamivudine, zidovudine and acyclovir;
all with 2.0 ppm of concentration). Four successive
standard additions to the sample resulted in well-shaped
adsorptive stripping peaks. The zidovudine peak in the
original sample (curve A) can, therefore, be quantified
(a) (b) (c)
Figure 9. Illustration of zidovudine determination in a synthetic sample contain several antiretroviral drugs (efavirenz, nevi-
rapine, didanosine, lamivudine, zidovudine and acyclovir; all with 2 ppm of concentration) by linear-sweep adsorptive strip-
ping voltammetry. Supporting electrolyte, 10 mL of 2.0 × 10–3 mol·L–1 NaOH. (a) addition of 150 μL of synthetic sample; (b)
(0.05 ppm) and (c) (0.20 ppm) addition of standard zidovudine. Condition time, 60s at –0.9 V. Accumulation time, 90 s at –0.40
V. Potential final, –0.9 V. Scan rate, 100 mV·s–1. Equilibrium time, 30 s. Thin-film mercury electrode (5 min at –0.9 V).

A. A. CASTRO ET AL. 232
based on the resulting standard addition plot (also show
in Figure 9). Because of the inherent sensitivity of this
method, short (90 s) accumulation times should be used.
Five consecutive analyses of the sample yielded an av-
erage value of 2.7 ppm with a standard deviation of 0.5
ppm, in “relative” agreement with the zidovudine value
(2.0 ppm). Preliminary studies were also developed for
the determination of zidovudine in the presence of
ssDNA and ATP. The current measurements of 0.05 ppm
of zidovudine (other conditions: supporting electrolyte,
2.0 × 10–3 mol·L–1 NaOH (with 1% v/v of ethylic alco-
hol); condition time, 60 s at –0.9 V; accumulation time,
90 s at –0.30 V; final potential, –1.1 V; scan rate, 100
mV·s–1; equilibrium time, 30 s and thin-film mercury
electrode) were not affected by the addition of up to 0.10
ppm of ATP or 0.06 ppm of ssDNA.
The Figure 10 shows the linear cyclic adsorptive
stripping voltammograms of 0.05 ppm zidovudine in the
presence of copper II ions and ssDNA (0.10 ppm) using
an accumulation time of 90 s at –0.15 (A) and –0.30 (B)
V (other conditions: supporting electrolyte, 2.0 × 10–3
mol·L–1 NaOH (with 1% v/v of ethylic alcohol); condi-
tion time, 60 s at –0.9 V; final potential, –1.2 V; scan
rate, 100 mV·s–1; equilibrium time, 30 s and thin-film
mercury electrode). When the accumulation potential
was applied to the –0.15 V (prior to the scan) the zi-
dovudine peak appears at –0.35 V and the ssDNA peak
at –0.78 V, but at –0.30 V the ziduvudine peak appears at
–0.63 V and the ssDNA at –0.79 V. Without the present
copper II ions, the ssDNA current peak does not appear
efficiently. The zidovudine and ssDNA current peaks
increase with higher accumulation times. A small peak of
the copper (II) ion was also observed in the anodic scan
at –0.40 V.
4. Conclusions
This paper has thoroughly described an effective means
for the determination of trace levels of zidovudine. The
use of the simple and diluted alkaline electrolytes provided
a sensitive and selective adsorptive stripping voltam-
metric method for zidovudine determination. This ap-
proach is rapid, yields a high sensitivity, and is largely
unaffected by a large number of commonly presented
antiretroviral drugs for the treatment of human immuno-
deficiency virus (HIV), such as didanosine, acyclovir,
nevirapine and lamivudine. The zidovudine peak is sepa-
rated by 0.43 V with the ssDNA stripping peaks. In par-
ticular, this approach offers similar efficiency in com-
parison to electrochemistry [24] and chromatographic
methods. Additionally, further studies using diluted alka-
line solution as the supporting electrolyte and film mer-
cury electrode modified in situ by metallic ions can be
(a)
(b)
Figure 10. Linear-sweep adsorptive stripping voltammo-
gram of zidovudine (0.05 ppm) in the presence of copper II
ions and DNA (0.10 ppm) in a solution of 2.0 × 10–3 mol·L–1
NaOH (with 1% v/v of ethylic alcohol). Accumulation time,
90 s at –0.15 (a) and –0.30 (b) V. Condition time, 60 s at –0.9
V. Scan rate, 100 mV·s–1. Final potential at –1.2 V. Equilib-
rium time, 30 s. Thin-film mercury electrode (5 min at –0.9
V).
used to detect other drugs and DNA-intercalating dyes,
as well as amino-acids, peptides and protein determina-
tions.
5. Acknowledgements
The authors gratefully acknowledge the CAPES-Brazil
and MES-Cuba for their support of this work. In addition,
we thank Dr. Katia Cristina Leandro of Fundação Oswal-
do Cruz for generously supplying the sample of zidovu-
dine.

A. A. CASTRO ET AL.233
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