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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.

10 M. Khodari et al.

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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

Electroreduction and Quantication of Furazolidone and Furaltadone in Different Media 11

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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.


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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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Received December 15, 1998, Revision February 4, 2000.


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