American Journal of Anal yt ical Chemistry, 2011, 2, 174-181
doi:10.4236/ajac.2011.22020 Published Online May 2011 (http://www.SciRP.org/journal/ajac)
Copyright © 2011 SciRes. AJAC
Stripping Voltammetric Determination of Timolol Drug in
Pharmaceuticals and Biological Fluids
Ali F. Al-Ghamdi
Department of Chemistry, College of Science, Taibah University, Madinah, Saudi Arabia
E-mail: aghamdi@taibahu.edu.sa
Received March 13, 2011; revised April 29, 2011; accepted May 3, 2011
Abstract
A sensitive and reliable stripping voltammetric method was developed to determine timolol drug. This me-
thod is based on the adsorptive accumulation of the drug at a hanging mercury drop electrode (HMDE) and
then a negative sweep was initiated, which yield a well defined cathodic peak at –850 mV versus (Ag/AgCl)
silver reference electrode. To achieve high sensitivity, various experimental and instrumental variables were
investigated such as supporting electrolyte, pH, accumulation time and potential, scan rate, frequency, pulse
amplitude, convection rate and working electrode area. The monitored adsorptive current was directly pro-
portional to the concentration of timolol and it shows a linear response in the range from 1 × 10–7 to 1.5 ×
10–6 mol·l–1 of this drug (correlation coefficient = 0.998) and the detection limit (S/N = 3) is 1.26 × 10–9
mol·l–1 at an accumulation time of 30 sec. The developed adsorptive stripping voltammetry (AdSV) proce-
dure shows a good reproducibility, the relative standard deviation RSD% (n = 8) at a concentration level of 1
× 10–6 mol·l–1 of timolol was 0.13%, whereas the method accuracy was indicated via the mean recovery of
110% ± 1.414. Possible interferences by several substances usually present in the pharmaceutical formula-
tions have been also evaluated. The applicability of this approach was illustrated by the determination of the
drug in pharmaceutical preparation and biological fluids such as serum and urine.
Keywords: Stripping Voltammetry, HMDE, Timolol, Urine, Serum
1. Introduction
Of the most commonly used instrumental techniques,
electroanalytical approach is the one of choice, and
stripping voltammetric method has provoked particular
interest because it is currently the most sensitive and
widely used electrochemical technique. Its possibility of
applications cover many fields ranging from environment,
pharmaceutical and clinical to food and industrial
samples. Many of the adsorptive stripping voltammetric
(adsv) approach features such as sensitivity, selectivity,
simplicity and versatility attributed to the combination of
an effective preconcentartion step based on non-electro-
lytic adsorptive accumulation process with an advanced
measurement procedures such as differential pulse (DP)
or square wave (SW) [1-5]. Unlike conventional strip-
ping approaches (anodic and cathodic stripping voltam-
metry), which are based on an electrolytic nature of
preconcentration step, adsorptive stripping voltammetric
approach in contrast is based on adsorptive accumulation
of the analyte on the electrode at open circuit with no
charge transferred. Consequently, for a wide range of
surface-active organic and inorganic species, which can-
not be preconcentrated electroanalytically, the adsorption
approach allows these analytes to be interfacially accu-
mulated on the electrode and hence analysed. There have
been many reviews devoted to emphasize and illustrate
the wide spectrum and scope of adsorptive stripping vol--
tammetric applications and potentialities in the analysis of
metal ions [6,7] organic analytes [8,9] and pharma--
ceutical drugs and biomedical compounds, such as, the
anti-Inflammatory drug Lornoxicam, the antidepressant
drug sulpiride and Josamycin, a Macrolide Antibiotic
[10-14]. Timolol was the first beta (β) blocker to be used
as an anti-glaucoma agent and to date remains as the
standard because none of the newer β blockers were
found to be more effective. Timolol maleate is the generic
name for (Ocumol 0.5, Timolo 0.5%, 5 mg/ml- Riyadh,
Pharma-SA), an eye drop (ophthalmic solution) indicated
for the treatment of elevated intraocular pressure for
those patients with primary open-angle glaucoma and
ocular hypertension. Timolol maleate should be used
A. F. Al.-GHAMDI175
with care. It is important not to contaminate the solution,
because this can cause infection and/or inflammation in
the eye. If you are using more than one eye-drop me-
dication, administration of the drugs should be spaced at
least ten minutes apart to provide adequate time for
absorption. Timolol is soluble in distilled water, its mole-
cular weight is 316.421 g/mol and systematic IUPAC
name is (S)-1-(tert-butylamino)-3-[(4-morpholin-4-yl-1,
2,5-thiadiazol-3-yl)oxy]propan-2-ol[15,16]. The chemical
structure of this drug and the mechanism for the elec-
trochemical reduction process of its compound are
shown in Scheme 1 (The mechanism proposed of elec-
trochemical reduction for timolol drug). Timolol drug
has been analysed in pharmaceutical formulations and
biological samples by various analytical methods such as
spectrophotometric [17-19], chromatographic [20,21],
high performance liquid chromatography (HPLC) [22]
and differential pulse voltammetric [23]. However, to the
best of our knowledge, the square wave voltammetric
behavior of timolol and thus its square-wave adsorptive
stripping voltammetry (SW-adsv) have not been per-
formed and reported so far. Consequently, the aim of this
work was to develop more sensitive, reliable and simple
SW-adsv procedure for the determination of timolol drug
in biological media and pharmaceutical formulations.
2. Experimental
2.1. Apparatus
All adsorptive stripping measurements were carried out
with 797 VA computrace (Metrohm, Switzerland) in
connection with Dell computer and controlled by VA
computrace 2.0 control software. Stripping voltammo-
grams were obtained via a hp color laserjet CP1215
printer. A conventional three electrode system was used
in the hanging mercury drop electrode (HMDE) mode.
pH values were measured with Hanna instruments pH
211 (Romania made) pH meter. The labofuge 200 instru-
ment , Heraeus sepatech (Germany) was used for centri-
fuging of biological fluids to suite for stripping analysis.
Scheme 1. The mechanism proposed of electrochemical re-
duction for timolol drug.
2.2. Reagents
All chemicals used were of analytical reagent grade and
were used without further purification. Timolol stock
solution of 1 × 10–2 mol·l–1 were prepared by dissolving
the appropriate amount of this drug in distilled water in
10 ml volumetric flask. This stock solution was stored in
the dark and under refrigeration in order to minimize
decomposition. Standard solutions of this drug with lower
concentrations were prepared daily by diluting the stock
solution with distilled water. Britton-Robinson support-
ing buffer (pH 2, 0.04 M in each constituent) was pre-
pared by dissolving 2.47 g of boric acid in 500 ml dis-
tilled water containing 2.3 ml of glacial acetic acid and
then adding 2.7 ml of ortho-Phosphoric acid and diluting
to 1 L with distilled water. In addition, phosphate sup-
porting buffer (0.1 M NaH2PO4 and 0.1 M H3PO4) was
prepared by dissolving 12 g of NaH2PO4 and 6.78 g of
H3PO4 in 1000 ml distilled water. Acetate supporting
buffer (0.02 M in each constituent) was prepared by dis-
solving 1.68 g of sodium acetate in 500 ml distilled water
containing 1.12 ml of acetic acid and diluting to 1 L with
distilled water. Finally, carbonate supporting buffer (0.1
M in each constituent) was prepared by dissolving 10.6 g
of sodium carbonate and 8.4 g of sodium hydrogen car-
bonate in 1000 ml distilled water.
2.3. Procedure
The general procedure adopted for obtaining adsorptive
stripping voltammograms was as follows: A 10 ml ali-
quot of B-R supporting buffer (unless otherwise stated)
at the desired pH (e.g. 3.5) was pipetted into a clean and
dry voltammetric cell and the required standard solution
of timolol was added. The test solution was purged with
nitrogen for 5 minutes initially, while the solution was
stirred. The accumulation potential of –0.8 V vs. Ag/AgCl
was applied to a new mercury drop while the solution
was stirred for 30 seconds. Following the preconcentra-
tion period, the stripping was stopped and after 20 sec-
onds had elapsed, cathodic scans were carried out over
the range 0.0 to –1.2 V. All measurements were made at
room temperature.
3. Preliminary Observations
When the differential pulse polarographic behavior was
investigated for timolol drug in acetate buffer at pH 3.5,
a broad polarographic wave at Ep = –0.850 V was ob-
served and this obtained polarographic wave, as shown
in Figure 1 (Differential Pulse Polarographic of 5 × 10–5
mol·l–1 Timolol in pH 3.5 Acetate buffer, scan rate 25
mV·s–1), is probably due to the electrochemical reduction
Copyright © 2011 SciRes. AJAC
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176
Figure 1. Differential Pulse Polarographic of 5 × 10–5 mol·l–1
Timolol in pH 3.5 Acetate buffer, scan rate 25 mV·s–1.
of the double bond (–N=C) as shown in the previous
scheme1, which including a proposed mechanism for the
electrochemical reduction of this drug. This mechanism
suggesting that the electrochemical reaction is an irre-
versible process, an assumption which was confirmed by
cyclic voltammetric measurement at a scan rate of 50
mV–1 of timolol in acetate buffer (pH 3.5) as shown in
Figure 2 (Cyclic voltammogram of 5 × 10–5 mol·l–1 Ti-
molol in pH 3.5 Acetate buffer, scan rate 50 mV·s–1).
In order to obtain a voltammetric peak with better de-
finition and higher sensitivity, a HMDE was used to
study the adsorptive prosperities of timolol compound.
The AdSV behavior of the drug was investigated in var-
ious supporting electrolytes at different pH values. This
Drug compound yielded a well-developed and defined
AdSV peak corresponding to the electroactive –N=C at
peak potential of –0.85 V. A typical adsorptive stripping
voltammogram for 5 × 10–7 mol·l–1 timolol in acetate buf-
fer is shown in Figure 3 (SW-AdSV voltammogram
Figure 2. Cyclic voltammogram of 5 × 10–5 mol·l–1 Timolol
in pH 3.5 Acetate buffer, scan rate 50 mV·s–1.
Figure 3. SW-AdSV voltammogram of 5 × 10–7 mol·l–1 Ti-
molol in pH 3.5 Acetate buffer. Accumulation time 30 sec,
accumulation potential –0.8 V and scan rate 250 mV·s–1.
of 5 × 10–7 mol·l–1 Timolol in pH 3.5 Acetate buffer. Ac-
cumulation time 30 sec, accumulation potential –0.8 V
and scan rate 250 mV·s–1), which illustrates a well ob-
served electrochemical peak indicating a strong and rea-
dily adsorption process at the surface of the working
electrode.
3.1. Parameters Affecting the Adsorptive
Stripping Response
3.1.1. Effect of Supporting Electrolyte and pH
The nature and acidity of the supporting buffer are some
of the most important factors which strongly influence
the stability of the analyte and its cathodic reduction and
adsorption processes. Among the various investigated
buffers (B-R, acetate, carbonate and phosphate) the best
voltammetric signal in terms of sensitivity (peak height)
and resolution (peak shape) have been secured using
acetate buffer. In addition, when the AdSV peak current
was measured as a function of pH over 2-6 range, the
stripping voltammetric signal increased steadily over the
acidic region and the peak current reached its maximum
value at pH 3.5 which was selected as optimal value for
subsequent studies. It is noteworthy that when more than
3.5 acetate supporting electrolyte was used, timolol was
barely detectable and nearly no stripping voltammetric
signal was observed. The variation of AdSV peak current
with pH, obtained for 1 × 10–6 mol·l–1 Timolol drug con-
centration accumulated for 30 sec is exhibited in Figure
4 (Effect of pH on AdSV peak current of 1 × 10–6 M Ti-
molol at Acetate buffer).
3.1.2. Effect of Accumulation Time and Potential
Preconcentration of the analyzed drug on the surface of
the working electrode (HMDE) is one of the essential
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A. F. Al.-GHAMDI177
Figure 4. Effect of pH on AdSV peak current of 1 × 10–6 M
Timolol at Acetate buffer.
conditions for highly sensitive determinations. Variation
of the accumulation time over 0 - 150 sec period for 1 ×
10–6 mol·l–1 timolol drug solution at a preconcentration
potential of 0.0 V, showed a gradual enhancement for the
monitored peak current over the range 0 - 30 sec. The de-
pendence of peak current on accumulation time is pre-
sented in Figure 5 (Effect of accumulation time on AdSV
peak current of 1 × 10–6 M Timolol in pH 3.5 Acetate buf-
fer). The proportional relationship was nearly ob- served
up to 30 sec and then it became virtually curved and lev-
eled off owing to the saturation of the hanging mercury
drop by the analyte. For further experiments an accumula-
tion time of 30 sec was selected as optimal because it pro-
vided relatively high peak current with adequate practical
time. The variation of accumulation time did not produce
significant shifts in peak potential value.
In addition, as can be seen from Figure 6 (Effect of
accumulation potential on AdSV peak current of 1 × 10–6
M Timolol in pH 3.5 Acetate buffer and accumulation
time 30 sec), when the influence of accumulation poten-
tial on the monitored electrochemical response was ex-
amined over the –0.8 to +0.8 V range at 30 sec precon-
centration time, the peak current was directly reached its
maximum value at Ep = –0.8 V then it decreased sharply
after potential –0.8V. Thus, Eacc= 0.8 V will be adopted
as optimum operational value for the following works as
it ensured the highest AdSV signal.
Figure 5. Effect of accumulation time on AdSV peak cur-
rent of 1 × 10–6 M Timolol in pH 3.5 Acetate buffer.
Figure 6. Effect of accumulation potential on AdSV peak
current of 1 × 10–6 M Timolol in pH 3.5 Acetate buffer and
accumulation time 30 sec.
3.1.3. Effect of Scan Rat
The cathodic peak current of timolol drug was found to
be forthwith proportional to the scan rate, particularly at
low scan rate values, a phenomenon characterized for
adsorbed materials [24]. When the stripping voltammet-
ric peak current of 1 × 10–6 mol·l–1 timolol drug in pH 3.5
acetate buffer was measured over the range 10 - 300
mV/s, it was found that peak height was observed in the
scan rate 250 mV/s as it was shown in Figure 7 (Effect
of scan rate on AdSV peak current of 1 × 10–6 M Timolol
in pH 3.5 Acetate buffer, accumulation time 30 sec and
accumulation potential –0.8 V). However, after this
maximum value the peak current started to decrease di-
rectly with faster scan rate. Accordingly, 250 mV/s scan
rate value was adopted as optimum condition for further
investigations.
3.1.4. Effec t of Pulse Amplitude and Freq uency
In addition, the impact of varying the excitation wave
pulse amplitude on the voltammetric current intensity
was also evaluated. The effect of this operating variable
was studied over the rang 10 - 120 mV (see Figure 8:
Effect of pulse amplitude on the peak current of 1 × 10–6
M Timolol in pH 3.5 Acetate buffer, accumulation time
30 sec, accumulation potential –0.8 V and 250 mV/s scan
Figure 7. Effect of scan rate on AdSV peak current of 1 ×
10–6 M Timolol in pH 3.5 Acetate buffer, accumulation time
30 sec and accumulation potential -0.8 V.
Copyright © 2011 SciRes. AJAC
A. F. Al.-GHAMDI
178
Figure 8. Effect of pulse amplitude on the peak current of 1
× 10–6 M Timolol in pH 3.5 Acetate buffer, accumulation
time 30 sec, accumulation potential 0.8 V and 250 mV/s
scan rate.
rate) and it was concluded that in order to assure maxi-
mum peak current, 100 mV pulse amplitude was the ideal
choice for this operational parameter. Moreover, varying
the value of square wave frequency also plays an impor-
tant role for the measured signal of square wave- adsorp-
tive stripping voltammetric (SW-AdSV) approach. When
the voltammetric peak current of 1 × 10–6 mol·l–1 timolol
drug in acetate buffer pH 3.5 was measured over the
range 10 - 50 Hz, as in Figure 9 (Effect of frequency on
the peak current of 1 × 10–6 M Timolol in pH 3.5 Acetate
buffer, accumulation time 30 sec, accumulation potential
–0.8 V, Scan rate 250 mV/s and pulse amplitude 0.10 V),
it was found that peak height was observed at a low fre-
quency 10 - 15Hz only, after this value (15Hz) the peak
current started to decrease with increasing frequency. Ac-
cordingly, for farther work 15 Hz square wave frequency
value was adopted.
3.1.5. Effect of Instrumental Parameters
The monitored adsorptive stripping voltammetry (AdSV)
peak height could be further maximized by optimizing
other experimental factors that can affect the adsorption
Figure 9. Effect of frequency on the peak current of 1 × 10–6
M Timolol in pH 3.5 Acetate buffer, accumulation time 30
sec, accumulation potential –0.8 V, Scan rate 250 mV/s and
pulse amplitude 0.10 V.
process of the formed drug. The influence of both the
surface size of the mercury drop working electrode and
electrode convection rate was also evaluated. An increase
in the surface of the working electrode (over 0.15 - 0.60
mm2) yielded, as expected, a linear enhancement in the
analytical signal and did not affect the value of the strip-
ping voltammetric potential. In addition, an increase in
the stirring rate (raising it from 0.0 to 3000 rpm) yielded,
a linear enhancement in the analytical signal from 0.0 to
2000 rpm, after that it is decreased and did not affect the
value of the stripping voltammetric potential. Thus, for
optimal sensitivity, 0.60 mm2 drop size and 2000 rpm
stirring speed were chosen for subsequent practical
works (see Figures 10: Effect of electrode area on the
peak current of 1 × 10–6 M Timolol in pH 3.5 Acetate
buffer, accumulation time 30 sec, accumulation potential
–0.8 V, Scan rate 250 mV/s, pulse amplitude 0.10 V and
frequency 15 Hz, Figure 11: Effect of convection rate on
the peak current of 1 × 10–6 M Timolol in pH 3.5 Acetate
buffer, accumulation time 30 sec, accumulation potential
–0.8 V, Scan rate 250 mV/s, pulse amplitude 0.10 V,
frequency 15 Hz and drop size 0.6 mm2).
3.2. Analytical Performance (Method Validation)
Once the most ideal and suitable chemical conditions and
instrumental parameters for the adsorptive determination
were established, a calibration plot for the analyzed drug
was recorded to estimate the analytical characteristics of
the developed method.
3.2.1. Calib ra t i on Graph
Under the optimum conditions a very good linear corre-
lation was obtained between the monitored voltammetric
peak current and timolol concentration in the range 1 ×
10–7 - 1.5 × 10–6 mol·l–1, is constant in all measurements,
(see Figure 12: SW-AdSV voltammogram for Timolol
in acetate buffer, pH = 3.5, Tacc = 30 sec, Eacc = –0.80 V.
Figure 10. Effect of electrode area on the peak current of 1
× 10–6 M Timolol in pH 3.5 Acetate buffer, accumulation
time 30 sec, accumulation potential –0.8 V, Scan rate 250
mV/s, pulse amplitude 0.10V and freque nc y 15 Hz.
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A. F. Al.-GHAMDI179
Figure 11. Effect of convection rate on the peak current of 1
× 10–6 M Timolol in pH 3.5 Acetate buffer, accumulation
time 30 sec, accumulation potential –0.8 V, Scan rate 250
mV/s, pulse amplitude 0.10V, fre quency 15Hz and drop size
0.6 mm2.
Figure 12. SW-AdSV voltammogram for Timolol in acetate
buffer, pH = 3.5, Tacc =30 sec, Eacc = –0.80 V. Drug Conc.:-
(A = 1 × 10–7 M, B = 3 × 10–7 M, C = 5 × 10–7 M, D = 7 × 10–7
M, E = 1 × 10–6 M, F = 1.5 × 10–6 M). Drug Conc.:- (A = 1 ×
10–7 M, B = 3 × 10–7 M, C = 5 × 10–7 M, D = 7 × 10–7 M, E =
1 × 10–6 M, F = 1.5 × 10–6 M).
Least-square treatment of the calibration graph yielded
the following regression equation:
ip (nA) = 53.1 + 3.1 × 108 C (mol l–1) r = 0.998, n = 6.
where ip is the adsorptive stripping peak current, C is the
analysed drug concentration and r is the correlation coef-
ficient.
3.2.2. Detect i o n Li mi t
The lowest detectable concentration of this drug was
1.26 × 10–9 mol·l–1(0.4 ppb), which was estimated based
on the signal-to-noise ratio (S/N = 3) and this obtained
analytical sensitivity is very promising since it was
achieved after employing very short accumulation time
(30 s) comparing to that reported for the previous volt-
ammetric determination of timolol using differential pulse
voltammetry (DPV) technique which required 2.5 ppb
detection limit [23].
3.2.3. Reproducibility
The high sensitivity of adsorptive voltammetry is ac-
companied by very good reproducibility. This analytical
performance was evaluated from eight repeated meas-
urements of electrochemical signal of 1 × 10–6 mol·l–1 ti-
molol drug solution. The precision of the electrochemical
developed method in terms of the relative standard de-
viation (RSD%) was 0.13%.
3.2.4. Accuracy
The accuracy of the proposed method was checked by
calculating the recovery of known amount of timolol (5 ×
10–7 mol·l–1) solution added to acetate buffer solution and
analysed via the optimized stripping voltammetric pro-
cedure. The value of the recovery obtained by the stan-
dard addition method was 110% ± 1.414.
3.2.5. Stability
Under the optimum conditions, the stability of 1 × 10–6
mol·l–1 timolol solution was evaluated by monitoring the
changes in the height of adsorptive stripping voltammet-
ric (AdSV) peak over a period of 90 min. The electro-
analytical signal was gradually constant with time. The
acidic media (pH 3.5) of the acetate electrolyte solution
probably initiated a slow degradation process for the
drug.
3.3. Interference Studies
In order to evaluate the selectivity of the developed
AdSV procedure, the influence of various interferences
was examined. Considerable interference can be caused
by co-existing surface-active compounds capable of com-
peting with the analyte of interest for the adsorption site
on the electrode surface, resulting in decreased or in-
creased peak height. The competitive co-adsorption in-
terference was evaluated in the presence of various sub-
stance usually occur in the pharmaceutical eye-drops and
formulations. For these investigations, the interfering
species were added at different concentrations (one,
5-fold and 50-fold) higher than the concentration of ti-
molol (1 × 10–6 mol·l–1). The addition of starch at these
concentration levels caused the adsorptive stripping vol-
tammetric (AdSV) peak current to decrease by about 3%,
4% and 6%, respectively, of its original peak current.
Also the addition of 50-fold of sucrose in the test drug
solution (1 × 10–6 mol·l–1), caused the stripping voltam-
metric peak current to decrease by about 8%. Apparently,
Copyright © 2011 SciRes. AJAC
A. F. Al.-GHAMDI
180
these inhibition effects were caused by the working elec-
trode surface blockage due to adsorption of interferences.
In contrast, the addition of 50-fold of lactose in the drug
solution, caused the square wave adsorptive stripping
voltammetry (SW-AdSV) response of the drug to in-
crease by about 16%.
3.4. Practical Applications
The reliability of the proposed adsorptive stripping vol-
tammetry (AdSV) method for the determination of ti-
molol drug was investigated by assaying this drug in
some real samples. Following the developed electroana-
lytical procedure described above, timolol drug was ana-
lysed in pharmaceutical formulation. The timolol content
of commercially available eye drop (Ocumol 0.5, Ti-
molol 0.5%, 5 mg/ml) was determination directly by the
square wave adsorptive stripping voltammetry (SW-
AdSV) method after the required dissolving steps. Four
aliquots of the dissolved sample were diluted to the re-
quired concentration level and measured via the standard
additions approach. For these studies, results obtained
gave a recovery mean 80% with standard deviation of ±
2.94%. As can be seen from Table 1 (Analysis of Ti-
molol drug in its commercial eye drop).
In addition, the applicability of the stripping voltam-
metric procedure for the analysis of timolol drug in bio-
logical samples was also evaluated by estimating its re-
coveries from spiked human urine and serum samples. A
simple and fast pretreatment (clean-up) procedure, which
is in fact a slight modification of the sample preparation
method develop for the determination of some antagonist
drugs [25] was used. By adding a small amount of 5%
ZnSO4·7H2O solution, NaOH and methanol to the serum
sample and centrifuging the mixture, most of the inter-
fering substances (mainly proteins) were simply removed
and eliminated by precipitation. As can be extracted from
Table 2 (Analytical results for timolol drug recoveries
from urine and serum samples), this adsorptive stripping
voltammetric (AdSV) method (after appropriate dilution)
allowed the determination of timolol drug in urine and
Table 1. Analysis of Timolol drug in its commercial eye drop.
Found (mg) Recovery %
Labeled 3.85 77
Content 3.90 78
5 mg/ml 4.10 82
Timolol 4.15 83
Mean 80
Standard Deviation ±2.94
Table 2. Analytical results for timolol drug recoveries from
urine and serum samples.
Recovery%: Spiked Urine Spiked Serum
86 108
88 107
Added Timolol 85 109
5.0 × 107 mol·l1 89 106
Means 87 107.5
Standard Deviations±1.83 ±1.3
serum samples with mean recoveries 87% ± 1.83 and
107.5% ± kmi 1.3, respectively.
4. Conclusions
Voltammetric methods have proved to be very sensitive
for the determination of organic molecules, including
drugs and related molecules in pharmaceutical dosage
forms. These techniques have several advantages, in-
cluding that they are quick and reproducible, present low
limits of detection and quantification and have relatively
low cost compared with the more traditional techniques.
Moreover, they provide a better discrimination against
background currents.
In this study, a new, simple, selective, accurate and
precise SW-AdSV method developed for the determina-
tion of Timolol in pharmaceutical formulation. In this
study, all experimental and instrumental parameters were
optimized, as their values strongly affect the sensitivity
of the voltammetry. The peak current was investigated
using differential pulse polarography and cyclic voltam-
metry. The electrochemical reduction of Timolol is an
irreversible process controlled by adsorption under the
conditions described in this work. The proposed method
with the optimized parameters demonstrated a good lin-
ear relationship between the peak current and the Ti-
molol concentration for a wide range of concentration.
The applicability of the proposed procedure was tested
using a commercial pharmaceutical formulation of Ti-
molol. This drug was quantified in the pharmaceutical
preparation and biological fluids such as serum and urine,
and no pretreatment or time - consuming extraction was
required prior to the analysis. The results are in good
agreement with the labeled values. Accuracy and selec-
tivity of the developed method were demonstrated by
recovery studies. Reproducibility, stability, and interfer-
ences studies of this proposed method suggest that this
method could be used in quality control analysis, clinical
laboratories, and pharmacokinetic studies.
Copyright © 2011 SciRes. AJAC
A. F. Al.-GHAMDI
Copyright © 2011 SciRes. AJAC
181
5. Acknowledgements
I would like to thank Prof. Mohammed Hefnawy and
Prof. Mohammed Al-Omar at King Saud University for
their assistances.
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