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Electroreduction and Quantication of Furazolidoneand Furaltadone in Different Media
Mahmoud Khodari, H. Salah El-Din, and Gaber A. M. Mersal
Chemistry Department, Faculty of Science, South Valley University, Qena, Egypt
Abstract. Adsorptive cathodic stripping voltammetry
was used for the determination of furazolidone (FZ)
and furaltadone (FD) in borax and phosphate buffers,
respectively, using HMDE as working electrode. The
inuence of different factors upon the peak current
response such as accumulation potential, scan rate,
preconcentration time, pH and other variables was
studied.
Furazolidone and furaltadone showed an adsorption
character on HMDE in presence of borax and
phosphate buffers, respectively. A single cathodic peak
at 0.36 V in borax (pH 9.5) was observed for FZ,while FD gave a cathodic peak at 0.32 V in phosphatebuffer (pH 8.5).
The calibration graph showed a linear behavior over
the range 3 1099 108 mol dm3 for furazoli-done. In the case of FD, concentrations from 3 109
to 2 107 moldm3 gave a linear relationship withthe peak current. A detection limit of 2 109 moldm3 and 1 109 mol dm3 was obtained for fura-zolidone and furaltadone, respectively. This method
was applied to determine these drugs in pharmaceutical
formulations, urine and serum samples.
Key words: Cathodic stripping voltammetry; furazoldone; fural-
tadone; biological samples; pharmaceutical formulations.
Furazolidone (FZ), [3-(5-nitrofurfurylideneamino)-2-
oxazolidone], furaltadone (FD), 5-morpholinyl
methyl-3-(5-nitro-furfurylideneamino)-2-oxazolidone
and other nitrofuran derivatives are highly effective
chemotherapeutic drugs, well known as antibacterial
agents, have been used for the treatment of gastro-
intestinal infections. The use of most nitrofurans is
strictly regulated in many countries [1]. Spectro-
photometric, conductimetric, gas and liquid chroma-
tographic methods have been used for the
determination of these drugs. The electrochemical
behavior of furazolidone was studied using polaro-
graphy. It was determined in urine [2], tablets [3, 4],
and water [5]. Also the polarographic behavior of
furaltadone has been studied [68]. The dc polaro-
graphic analysis of FD in oral suspensions and tablets
[810], milk and urine [11] was reported. Partial least
squares methods in the analysis by differential pulse
polarography have been used for the resolution of
ternary mixtures of nitrofurantoin, furazolidone and
furaltadone [12] and the simultaneous determination
of FZ and FD [13].
The electrochemical and bacterial effect of FZ and
its metal complexes was investigated by Narad et al.
[14]. Morales et al. [15] have studied the mechanism of
the electroreduction of FZ, while FD was investigated
by Galeano Diaz et al. [11]. No attention has been
given to the stripping voltammetric behavior of these
compounds. So in the present work the cathodic
stripping voltammetric method was reported to study
the adsorptive character of both FZ and FD using
HMDE. Owing to the high sensitivity of stripping
analysis methods [16], it was tried to determine the
mentioned drugs in different media (water, urine and
serum). The optimum conditions for the determination
of these compounds in pharmaceutical formulations,
urine and serum samples were studied. ADSV was
reported as a valid method for the determination of
some antibacterial drugs [17, 18].
Mikrochim. Acta 135, 917 (2000)
To whom correspondence should be addressed
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Experimental
Apparatus and Chemicals
Cathodic stripping and cyclic voltammetric measurements were
performed using the EG&G PAR Model 263 polarographic
analyzer with 250/270 research electrochemistry software version
4.0. A cell model 303A static mercury drop electrode (SMDE) wasconnected to the potentiostat, a hanging mercury drop electrode
(HMDE) was used as a working electrode, silver/silver chloride
(saturated KCl) as a reference electrode and a platinum wire as an
auxiliary one.
Furazolidone (FZ) and furaltadone (FD) were obtained from
Sigma and were used without further purication; all other
chemicals used were either AR grade from BDH or general
reagent grade from Merck. Stock solutions of 1 103 moldm3
FZ and FD were prepared daily by dissolving the required amount
of each drug in DMF and stored in the dark at 4 C, the other
solutions containing various concentrations of FZ or FD were
obtained by dilution with bidistilled water.
Stripping Voltammetric Procedure
10 mL of supporting electrolyte containing the examined drug was
placed into the voltammetric cell. The solution was deoxygenated
for 8 min. with a stream of pure nitrogen before recording the
voltammograms. After deaeration, a hanging mercury drop was
formed, the selected deposition potential was applied with stirring
for a given time interval, while the accumulation of the analyte at
the electrode proceeded. After a rest period of 15 s, the potential
was scanned to the negative direction.
Assay Procedure for Applications
Interferences Studies. The voltammograms of the examined drug
in presence of suitable concentrations of some metal ions or someamino acids were recorded by the method described above in order
to study their possible interferences and its inuence on the peak
current response of the drug.
Analysis of Pharmaceutical Formulations. An oral suspension
(containing a nominal 16.66 mg furazolidone per 5 mL), has been
shaken for 30min and 5 mL were transferred into 100 mL
calibrated ask and diluted to the mark with DMF. Then the ask
was shaken for another 30 min. After the solution was ltered, a
dilute solution was prepared from either the ltered solution or the
unltered one.
Ten tablets (each containing 50mg of FZ) were pulverized
and mixed, two samples of an approximate concentration of
1 103 mol dm3 FZ weighed, dissolved in DMF, transferredinto two 100 mL calibrated asks are diluted to the mark with DMF.
Then the ask were shaken for 30 min. One of the two samples was
ltered. Two diluted solutions were prepared, one from the ltered
solution and the other from the unltered one.
Urine Treatment. The urine sample was ltered and the pH was
adjusted to the required value by the selected buffer.
Serum Treatment. One mL human serum was diluted to 10 mL by
the selected buffer and the required pH was adjusted by sodium
hydroxide.
Results and Discussions
Furazolidone (FZ)
Cyclic Voltammetry and Reversibility Studies of FZ.
Cyclic voltammetry of furazolidone (FZ) in a borax
buffer (pH 9.5) showed only a single cathodic peak dueto the reduction of the nitro group. The cathodic peak
current sharply decreased in the second and third cycles
in the repetitive cyclic voltammogams. The preliminary
results showed that the peak response is highly affected
by preconcentration time. Fig. 1 shows typical voltam-
mograms of FZ with and without preconcentration.
The cathodic peak current was examined with res-
pect to the experimental conditions and other variables.
Effect of Supporting Electrolytes and pH Values. The
adsorptive peak current of FZ has been strongly
affected by the type of supporting electrolyte. To study
the adsorptive behavior of FZ, different supporting
electrolytes including sodium nitrate, sodium acetate,
sodium perchlorate, potassium chloride, sodium borate,
potassium phosphate, Britton-Robinson (B.R.) and
borax buffers were examined. The adsorption character
of FZ on HMDE appeared in borax, sodium citrate and
B.R. buffers, whereas the other supporting electrolytes
did not show this behavior. Borax buffer was recom-
mended to complete these studies where FZ showed the
highest peak current and the best peak shape.
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The effect of pH of borax on the peak current of FZ
was examined from 6 to 11, FZ showed a small peak
current at lower pH values, then the peak current raised
with increasing the pH values with a maximum at pH
9.5 (Fig. 2a), hence borax buffer (pH 9.5) was selected
for further investigations.
The effect of the ionic strength of supporting elec-
trolyte was examined at pH 9.5 over the range 0.001
0.05 M. The peak current increases with increasing
borax concentration with a maximum at 0.005 M, so
borax buffer (0.005M) was selected for subsequent
work.
Effect of Accumulation Potential and Scan Rate. The
cathodic peak current of FZ was studied with respect to
the variation of accumulation potential (Eacc). A
deposition potential ranging from 0.05 to 0.26 Vwas examined. The peak current of FZ increased with a
maximum at 0.22V (Fig. 2b), so this value wasselected for further studies.
By varying the scan rate values from 50 to 400m
Vs1 for 3 108 mol dm3 FZ, the peak current
increases linearly with raising the scan rate where the
peak potential shifts to more negative values. At higher
scan rate values, the peak current shape was distorted.
For subsequent work 100 mV s1 was selected. On
plotting log i vs. log v (v scan rate), a straight linewas obtained with a slope of 1.054 and a correlation
coefcient, r 0:990. A slope of 1.00 is expected forideal reaction of surface species [19].
Effect of Accumulation Time and Reproducibility. The
FZ peak current increased with the accumulation time,
proving the adsorption characters of the studied
compound. The resulting peak current multiplied by
about 3 times after 7 second accumulation time. The
peak current of FZ was studied using variable deposi-
tion times (230 s). The results showed a linear relation
between the accumulation time and the peak height of
FZ up to 20 s. For 3 108 mol dm3 FZ, a deviationfrom the linearity was observed at accumulation time
after 18, 15, 12 and 7 s for 5 108, 1 107,2 107, and 4 107 mol dm3 FZ, respectively.This behaviour may be due to surface saturation.
The high sensitivity of adsorptive voltammetry is
accompanied by the good reproducibility of the results.
This can be attributed to the reproducible area and self-
cleaning control provided by the PARC 263 potentio-
stat (using a new drop of reproducible area in each
run). The reproducibility of the results was determined
by ten successive measurements of 9 108 mol dm3
FZ at an accumulation potential 0.22 V, scan rate
100mVs1 and preconcentration time 15 s. The mean
peak current is 77.4nA with a relative standard
deviation of 1.43%.
Analytical Applications, Calibration Curves and
Detection Limit. The effect of concentration of FZ on
the peak current was investigated at different pre-
concentration times (030 s) at Eacc 0:22 V, thepeak current of FZ was increased by increasing its
concentration. Table 1 shows the regression data for the
relation between ip and [FZ]. From the correlation
coefcients one can observe that the linear relationship
is the best one to t the results in comparison with
other regression models.
A lower detection limit of 2 109 mol dm3 FZwas experimentally obtained in borax buffer (pH 9.5)
after a 20 s preconcentration time, 100 mV s1 scan rate
and 0.22 V accumulation potential. This resultindicates the higher sensitivity of ADSV compared
with a detection limit of 1:24 105 [2] and1:77 106 mol dm3 [13] with d.p.p. technique.Chronopotentiometry gives a detection limit of
Fig. 1. Typical cathodic stripping voltammograms of 4 107 moldm
3FZ in borax buffer (pH 9.5) at 0.2 V accumulation time, a
scan rate of 100mV s1. (a) Zero pre-concentration time; (b) 7 s
preconcentration time
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1:0 106 mol dm3 [20]. This means that ADSVgives a value better than the other techniques by about
one thousand time.
Effect of Interferences. 1.) Effect of some metal ions.
The effect of co-existing metal ions (whether electro-
active or not) was examined by introducing different
concentrations of some metal ions to the voltammetric
cell and recording the corresponding voltammogram
using the conditions selected above. It was observed
that 1 108 moldm3 Cu(II) ion decreased the peakcurrent of 5 107 mol dm3 FZ by about 31.4%,while the other concentrations have no effect on the
peak response. Addition of 5 107 mol dm3 ofZn(II) ion to 5 107 moldm3 of FZ decreased thepeak current by about 7.7%, and also addition of a
Fig. 2. Dependence of the peak current on (a) pH values, (b) deposition potential for 1 107 mol dm3 FZ in borax buffer (pH 9.5)
tacc 15 s, scan rate 100 mV s1
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concentration of 1 108, 1 107 and 5 107 moldm3 Ni(II) ion decreased the peak current by about
6.1, 27.4 and 31.3%, respectively. Addition of Ca(II)
and Al(III) with a concentration ranging from 1 108
to 5 106 mol dm3 has no effect on the peak re-sponse. The results could be attributed to the competi-
tion between the metal ions and the studied compound
for the electrode surface or due to the complex for-
mation between FZ and the added metal ion.
2.) Effect of some amino acids, urea and gelatin. The
effect of some amino acids was also studied, where the
addition of 5 107 moldm3 glycine and L-leucinedecreased the peak current of FZ by about 5.0 and
6.5%, respectively. Also the addition of 1 108 and1 107 mol dm3 aspartic acid decreased the peakcurrent response of 5 107 mol dm3 of FZ byabout 18.7 and 22.7%, respectively. Addition of
1 107 mol dm3 of urea decreased the peak currentby about 15.4%, and a concentration of 5 107 moldm3 decreased the peak current of FZ by about
21.6%, while the addition of 5 107 moldm3 L-valine decreased the peak current of FZ by about 20%.
These results could be attributed to the occupation of
the drop surface by the added compounds.
The addition of the surfactant (gelatin) has a great
effect on the peak current response of FZ. This effect
was examined by adding ratios of 0.000001 to 0.01%.
It was observed that 0.000005, 0.00005 and 0.005%,
decreased the peak current response of 5 107 moldm
3 FZ by about 8.8, 11.8 and 31.9%, respectively.
But the presence of 0.01% gelatin suppressed com-
pletely the peak current.
Applications. From the present study, FZ can be
successfully determined in borax buffer (pH 9.5), scan
rate 100 mV s1 and 0.22 V accumulation potential.
To study the efciency of this method, FZ was
determined in both pharmaceutical formulations (sus-
pensions and tablets) and in biological samples (urine
and serum).
Determination of FZ in pharmaceutical formulations
(suspension and tablets).
Standard addition method was used to determine this
drug in ltered and unltered solution of both sus-
pension and tablets by the above conditions. Table 2
shows the assay results for FZ in pharmaceutical
formulations (tablets and suspension).
Determination of FZ in biological samples
Determination of FZ in urine sample
Urine samples were treated by the method men-
tioned above. Voltammograms were recorded in
presence of different FZ concentrations at 5 s and
0.22 V accumulation potential. A well dened catho-dic peak appeared for 1 107 mol dm3 FZ; the peakcurrent increased by increasing FZ concentrations
(Fig. 3b) and a linear behavior was observed for a
concentration range from 1 107 to 1 105 moldm3 FZ r 0:994). Determination of FZ in serum samples
By applying of the optimum conditions,
2 107 moldm3 FZ was determined in serumsamples. Also a linear behavior was observed for the
concentration range 2 107 1 105 mol dm3
with a correlation coefcient r 0:997. Fig 3a shows
Table 1. Characteristics of the calibration curves using different
accumulation times
Regression
modes
Accumulation
time(s)
[Furazolidone]
mol dm3Correlation
coefcient
Linear 5 3 1093 107 0.997i A Bt 15 1 1093 107 0.973
Power 5 3 109
3 107
0.889i A tB 15 1 1093 107 0.949Exponential 5 3 1093 107 0.895i A eBt 15 1 1093 107 0.820Logarithmic 5 3 1093 107 0.676ln i A B lnt 15 1 1093 107 0.791
Table 2. Assay results of FZ in pharmaceutical formulations
Drug Furakin M tablet Fudizol suspension
In lteredtablet soln.
In unlteredtablet soln.
In ltered oralsuspension soln.
In unltered oralsuspension soln.
Mean [mg] 49.075 51.93 16.415 15.08
Recovery (%) 98.15 103.86 98.53 90.52
Each tablet contains 50 mg of FZ. Each 5 mL of an oral suspension contains 16.66 mg of FZ.
Electroreduction and Quantication of Furazolidone and Furaltadone in Different Media 13
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typical voltammograms for different concentrations of
FZ in serum samples.
Furaltadone (FD)
Cyclic Voltammetry and Reversibility Studies of FD.
From cyclic voltammograms FD showed a single
cathodic peak at 0.32V in phosphate buffer(pH 8.5). This peak arises from the reduction ofthe nitro group. The cyclic voltammogram illustrates
the irreversible behavior of the reduction process.
The resulting cathodic stripping voltammetric peak
current which increased with time was used for the
determination of FD. It depends on supporting electro-
lyte, pH value and other experimental parameters.
Effect of Supporting Electrolytes and pH Value. The
effect of the supporting electrolyte on the peak current
was studied using sodium nitrate, sodium acetate,
sodium perchlorate, potassium chloride, sodium borate,
Britton-Robinson (B.R.), borax and sodium phosphate.
The results showed that sodium phosphate gave the
highest peak current, while in the other supporting
electrolytes, FD did not show any adsorption behavior.
The effect of pH on the peak response was investigated
over the range from 5 to 12. FD showed only one
cathodic peak in the tested range; the current increased
by raising the solution pH with a maximum at 8.5; this
value was selected to complete this study. The effect of
supporting electrolyte concentration has been also
investigated using a concentration range from 0.001
to 0.2 M where 0.05 M gave the highest peak current.
From the above results, FD can be determined
successfully in phosphate buffer (0.05 M, pH 8.5).
Effect of Accumulation Potential and Scan Rate. The
effect of accumulation potential (Eacc) on the peak
current was studied over the range 0.0 to 0.22 V, thepeak current of FD increased by shifting the accumula-
tion potential towards more negative values with a
maximum at 0.17 V, so this potential was selected forsubsequent work (Fig. 4). The effect of scan rate on the
peak current response of FD was also examined from
20 to 350 mV s1. The peak current was enhanced with
Fig. 3. Cathodic stripping voltammograms and the effect of different FZ concentrations on the peak current of FZ in (a) Serum samples: i
9 107, ii 3 106, iii 5 106, iv 7 106, v 9 106, vi 1 105. (b) Urine: i Zero, ii 4 107, iii 1 106, iv 3 106, v7 106, vi 1 105
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increasing scan rate till 250 mV s1. For higher values
the peak response was not clear, and also at higher
deposition times, the higher scan rate gave distorted
peak. So a scan rate of 100 mV/s was selected for
further studies. On plotting log ip against log v scan rate
from 50250 mV s1
, a linear relation was obtained
with r 0:997 and a slope of 0.958 was obtained. Aslope of 1.00 is expected for an ideal reaction surface
[19].
Effect of Accumulation Time and Reproducibility. The
cathodic stripping voltammograms for 1 107 mol
dm3 FD were recorded at different accumulation
times ranging from 1 to 60 s, where the peak current
increased by increasing the accumulation time. The
in uence of accumulation time at different FD con-
centrations (3 109 to 3 107 mol dm3) wasinvestigated. The peak current increased by increasing
the accumulation time till 30 s with the concentration
range from 3 109 to 1 108 mol dm3, On plot-ting the peak current vs. the square root of accumula-
tion time a straight line was obtained with a correlation
coefcient of 0.991 and a slope of 16.281 for
5 108 mol dm3 FD.The high sensitivity of stripping analysis was proved
by the good reproducibility of the results. This was
examined by eight successive measurements of
5 108 mol dm3 FD at 0.17 V accumulationpotential and 15s accumulation time. A relative
standard deviation of 1.93% was obtained.
Calibration Cures, Linearity and Detection Limit.
Figure 5 shows the cathodic voltammograms of FD at
different concentrations. The peak current increased
with increasing concentration. The relation between
the peak current and [FD] at three accumulation times
was examined. FD showed a linear region
up to 3 109 3 107, 3 109 9 108 and3 109 3 108 mol dm3 FD for accumulationtimes of 5, 10 and 15 s, respectively.
A detection limit of 1 109 mol dm3 FD wasobtained using the following conditions: phosphate
buffer (pH 8.5); 20s accumulation time; Eacc 0:17V vs. Ag/AgCl; scan rate 100mV s1. Theother reported values are 1:85 106 mol dm3 [13].1:
25 107 mol dm3 [11] and 1:
75 106 mol dm3
[10], Table 3 indicates the reported detection limis, the
conditions used and the applied techniques.
Effect of Interferences of Some Metal Ions, Amino
Acids and Gelatin. The inuence of some metal ions
on the cathodic peak current of FD was examined in a
wide range of concentrations in phosphate buffer
(pH 8.5), tacc 15s, Eacc 0:17V and 100mVs1 scan rate. The addition of 5 109 and1 107 mol dm3 Pb(II) to 5 108 mol dm3 FD
Fig. 4. Effect of the deposition potential on the peak current and
peak potential of 1 107 mol dm3 furaltadone (FD), inphosphate (8.5), scan rate 100 mV s1, Eacc 0:17 V
Fig. 5. Typical voltammograms of different FD concentrations;
scan rate 100mV s1, Eacc 0:17 V, phosphate buffer (pH8.5), and preconcentration time10 s a blank, b 7 109, c9 108, d 2 107, e 3 107
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reduced the peak current response of FD by about
11.7 and 27.9% respectively, while the addition of
1 108 and 1 106 mol dm3 UO22 reduced thepeak current response by about 5.9 and 20.5% res-
pectively. A concentration of 5 108 mol dm3
Zn(II) and Ca(II) ions reduced the peak current by
about 10.1 and 12.7%, respectively, while with a
concentration ranging from 1 109 to 1 106 moldm3 Cu(II), Ni(II), Cr(III), Mn(II), Mg(II), Al(III),
Co(II), Ba(II), Sr(II) and Fe(III) do not show any
in uence on the FD peak current. The presence of
1 105 mol dm3 L-valine reduces the FD peakcurrent by about 6.9%. But no effect was observed
after the addition of one thousand fold of glycine,
aspartic acid or L-leucine to the voltammetric cell.
The effect of some surfactants such as gelatin on the
peak current of FD was also investigated by adding
ratios of 0.00001 to 0.005%. The results showed a
depression of FD current by about 13.1 and 56.4 for
0.00001% and 0.0001% gelatin concentration, respec-
tively, while a concentration of more than 0.001%
gelatin suppressed completely the peak current of FD.
Table 3. Comparison between the detection limits for furaltadone in the present work and the other previous ones
Technique Supporting
electrolyte
Working
electrode
Reference
electrode
Ep or
E1/2
Detection
limit
Reference
D. P. P. B.R (pH 6.8) Ag/AgCl 0:23 1:85 106 13D. P. P. universal
buffer
DME SCE 1:25 107 11
D. P. P. universal buffer DME SCE 1:
75 106
10Cathodic
stripping
voltammetry
phosphate
buffer pH8.5HMDE Ag/AgCl 0:32 1 109 present work
Fig. 6. Cathodic stripping voltammograms of 1 107 mol dm3 FD in the three different media, at 0.17V accumulation potential, 5 saccumulation time and a scan rate of 100 mV s1. (a) Twice distilled water, (b) urine, (c) serum samples
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Applications on Biological Samples. Determination of
FD in urine samples. By applying the above selected
optimum conditions, FD has been determined in urine
after treated as described above. A detection limit of
1 108 mol dm3 FD was obtained after 5 s accumu-lation time. Different voltammograms were recorded
in presence of different FD concentrations. The peak
current increased by increasing [FD] and a linear
relationship between ip and [FD] was obtained over the
range 1 108 1 107 mol dm3 (r 0:999).Determination of FD in serum samples. FD was
determined in serum samples with a detection limit of
3 107 mol dm3 after 5 s accumulation time. Theeffect of [FD] was studied. The peak current increased
with increasing FD concentration and showed a linear
relation over the range 3 1071 105 mol dm3
(r 0:998).Figure 6 shows typical voltammograms for
3 107 mol dm3 FD in bidistilled water, urine andserum after 5 s preconcentration time, 0.22 V accu-mulation potential and a scan rate of 100 mV s
1. From
the gure one can observe that the peak current is
reduced by about 40% in urine and 70% in serum
compared to the obtained value in bidistilled water.
These results are due to the presence of organic matters
in urine and to the different constituents present in
serum.
Conclusion
Cathodic stripping voltammetry was achieved in borax
and phosphate buffer for the determination of furazo-
lidone and furaltadone in pure forms with a lower limit
of detection of 2 109 and 1 109 mol dm3 forFZ and FD, respectively. This method gives good
results for the determination of these drugs in
pharmaceutical formulations, urine and serum samples.
The suggested procedures offer a high repeatability and
can be used in routine analysis.
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Electroreduction and Quantication of Furazolidone and Furaltadone in Different Media 17