INTRODUCTION:
Cefepime,(6R,7R)-7-{[(2Z)-2-(2-amino-1,3-thiazol-4-yl)-2-(methoxyimino)acetyl]amino}-3-[(1-methyl-pyrrolidinium-1-yl)methyl]-8-oxo-5-thia-1-azabicyclo
[4.2.0]oct-2-ene-2-carboxylate.Cefepime like all Cephalosporins,
it inhibits bacterial growth by
interfering with a specific step in bacterial cell wall synthesis[1]. The
fourth generation cephalosporins are active mainly
against gram-positive bacteria and to a relative extent against gram-negative organisms[2].
Several
methods have been developed for determination of cefepime,
including spectrophotometric methds[3-10],
high-performance liquid chromatography (HPLC) [11 - 21], capillary zone electrophoresis [22], electro chemical methods [23,24].
Captopril, 1 - [(2S)- 3 - mercapto -2 -methylpropionyl]-L-proline, (CPT)
is an angiotensin-converting enzyme inhibitor, which reduces peripheral
resistance end lowers blood pressure. It is extensively used for the treatment
of hypertension and congestive failure [25]. several
methods have been developed for its determination, including spectrophotometric
methds[26-35], spectroflurometry
[36 - 39], high-performance liquid chromatography (HPLC) [40 - 44], Electro
chemical methods [45-50].
NBD - Cl
has been reported as fluorogenic reagent for
determination of amines [51].and for spectrophotometric determination of many
compounds [52-55]. Thiocompounds were reported to form
intensely coloured products in an alkaline medium
with NBD Cl which could be used for their
colorimetric determination [56].
On the basis of the
aforementioned reasons,it
was thought to develop a quantitative spectrophotometric method for determination
of cefepime and captopril. the
developed method is based on the alkaline hydrolysis of the studied drugs and
subsequent reactions of the resulting hydrolysates
with NBD-Cl as a chromogenic
reagent which could be used for their analysis
in pure forms and in pharmaceutical formulations.
EXPERIMENTAL:
Apparatus:
·
Labomed®Spectro UV-VIS Double Beam
(UVD-2950) Spectrophotometer with matched 1 cm quartz cells connected to
windows compatible computer using UV Win 5 Software v5.0.5 (U.S.A).
·
Thermostatically controlled
Water bath (WISD laboratory instruments, Korea).
MATERIALS
AND REAGENTS:
·
All solvents and
reagents were of analytical grade and double distilled water was used
throughout the work.
·
Cefepime
(Adwia), and Captopril
(EIPICO) Standard solutions 100 µg.ml-1 of cefepime
and 10 µg.ml-1 of captopril was prepared by dissolving each
pure drug in 100
ml bidistilled
water.
·
4-Chloro 7 nitrobenzofurazan NBD-C1 (Flukachemice
AG Switzerland) freshly prepared 3x 10-3 M equivalent to 0. 060 % w/
v in acetone.
·
Sodium hydroxide
(El Nasr Chemical Co. Cairo Egypt) 0.5M aqueous solution.
·
HCl
(El-Nasr Chemicals, Egypt) was concentrated HCl
(36%).
Pharmaceutical preparations:
The following available vial and tablet preparations
were analyzed
·
Pimfast®
vials labeled to contain 1000 mg cefepime per
vial. Batch No. 120224 (Rameda, Egypt).
·
Capotril®
tablets labeled to contain 25 mg captopril
per tablet. Batch No. 1041 (Eipico, Egypt).
General Procedure:
Accurately measured one
milliliter aliquot volume of the standard or sample solutions was transferred
into 10-ml volumetric flask. 5 ml of 0.5 M NaOH were
added and the flask was heated in water bath at 1000C for 30 min,
cooled to room temperature and completed to volume with double distilled water.
One milliliter of the resulting drug hydrolysate was
pipette into 10mL volumetric flask 1.0 ml (in case of cefepime)
or 1.2 ml (in case of captoril) of 3x10-3 M NBD-C1 was added followed
by 1ml of concentrated HC1 The resulting solution was mixed well and the flask
was completed to volume with ethanol .The absorbance was measured at 401 nm
against reagent blank treated similarly.
RESULTS
AND DISCUSSION:
Thiocompounds were previously reported to produce sulphide ions upon alkaline degradation and it was found to
be one of their major degradation products [57-58]. NBD-Cl is an active halide derivative, which was considered as
a likely target for good nucleophils, under alkaline
conditions, such as amines, amino acids and thiocompounds[55-56].
In the proposed method, sulphide ions were allowed to react with NBD-Cl via SN2 mechanism. The high nucleophilicity of sulphide ions,
the presence of Cl- anion as a good leaving group at
position 4 in addition to the presence of nitro group as an electron
withdrawing group at position 7 of the
aromatic ring in NBD-Cl result in replacement of Cl- anion with the
attaching sulphide ions which in turn lead to the
formation of a yellow – coloured chromophore
(λ max at 401nm).the reaction product is stable in strong acidic medium, moreover acidification could minimize
possible competition between the generated sulphide nucleophile and excess OH- which may lead to decrease in chromogen formed. The proposed reaction mechanism is given
in figure 1.
The production of sulphide ions was confirmed by carrying out specific
qualitative tests such as dilute hydrochloric acid, cadmium acetate, sodium nitroprusside and methylene blue
tests [59].It
was also confirmed by comparing λ max of the formed chromogen
with that obtained after applying the developed method to sodium sulphide and the same results were obtained.
Since the developed method
depends on the formation of coloured product by the
interaction of NDB-C1 with sulphide ions resulted
from the alkaline degradation of the drugs so optimization studies were carried
out extensively to find the optimum conditions for the alkaline degradation and
subsequently the optimum yield of sulphide ions and
the maximum stability of the chromogen formed.
Absorption spectra:
the absorption spectrum of
NBD-C1 and the interaction coloured product of cefepime and captopril hydrolysates
with NBD-C1 shows absorption maximum at 340 nm and 401 nm respectively
Fig.2.
Fig.2. Absorption spectrum of NBD-Cl (a), reaction product of captopril(b) and cefepime (c) with NBD-Cl after
hydrolysis by NaOH at 401 nm.
Effect of NaOH concentration:
The influence of sodium
hydroxide concentration on producing the maximum absorption intensity was
investigated using 0.1-1.0M NaOH keeping other
factors constant. Maximum absorption readings were obtained upon using 0.5M NaOH above this concentration and up to 1M NaOH the absorbance remains constant. So this concentration
was selected for further work Fig.3.
Fig.3. Effect of NaOH
concentration on the absorbance of the reaction coloured
product at 401 nm
Effect of hydrolysis time:
Theeffect of hydrolysis time on the absorption intensity was
studied using different heating times in water bath at 1000C
starting from 10 min until 1 hours and the reaction was carried out as usual.
The obtained absorbance readings were plotted against hydrolysis time. The
maximum absorption intensity was attained after 30 min and remained stable for
at least 100min. 30 minutes hydrolysis time was used in all subsequent
experiments in case of cefepime. In case of captopril
it attained after 10 minutes at room temperature as shown in Figs.4.
Fig.4. Effect of
hydrolysis time on the absorbance of the reaction colored product at 401 nm.
Effect of NBD-C1 concentration:
The volume of 3x 10 -3 NBD-C1for the maximum colour development was varied in the range of 0.2 – 1.8 ml
It was found that 1 ml and 1.2 ml of
NBD-C1 Was the most suitable volume for determination of cefepime
and captopril respectively, as shown in Fig.5. Owing to the presence of labile
chloride a daily fresh solution is recommended.
Fig.5. Effect of 3 X 10—3 M
NBD-CI volume the absorbance of the reaction colored product at 401 nm.
Effect of type and concentration of acid:
Different
acids such as sulphuric, hydrochloric, percloric, nitric and acetic acids were tested to detrmine the most suitable acid for the reaction. 1 ml of
concentrated HCl was selected in this study as it
gave the highest absorbance readings with cefepime
(table 1).
Table(1).Effect of different acids on the absorbance readings of the reaction coloured product of cefepimea
with NBD Cl.
|
Absorbance b
|
Acid (1ml)
|
|
0.377
|
sulphuric
acid
|
|
0.404
|
hydrochloric acid
|
|
0.366
|
percloric
acid
|
|
0.316
|
nitric acid
|
|
0.196
|
acetic acid
|
aCefepime concentration used is 60 ug/ml.
b
Average of three determinations.
The effect of HCl volume on the absorption intensity was studied using
different volumes. It was found that 1 ml of HCl gave
the highest absorbance readings as showen in
fig.6.
Fig. 6.Effect of HCI volume on the
absorbance of the reaction colored product at 401 nm.
Effect of reaction time:
The reaction between the
investigated drug hydrolysates and NBD-Cl was very rapid and the interaction colored product can
survive befor dilution unchanged for at least 1 hour.
However, measurements were carried out instantaneously fig.7.
Fig. 7.Effect of time after addition of the reagent on the absorbance of the
reaction colored product at 401 nm.
Effect of diluting solvent:
Different solvents were
tested in order to select the most appropriate solvent for optimum color
development. The results dos not show any shifts in
the position of the maximum absorption peak. The absorption intensities were
slightly influenced. Ethanol gave the highest absorbance readings and the most
reproducible results as shown in table 2.
Table (2).Effect of diluting
solvent on wavelength and the absorbance readings of the reaction coloured product of cefepime and
captopril with NBD Cl.
|
 Drug
Solvent
|
Cefepime
(ug.ml-1)
|
Captopril
(ug.ml-1)
|
|
|
λ max
|
Aa
|
λ max
|
Aa
|
|
Acetone
|
400
|
0.413
|
400
|
0.738
|
|
Methanol
|
400
|
0.432
|
400
|
0.768
|
|
Ethanol
|
401
|
0.486
|
401
|
0.797
|
|
water
|
401
|
0.323
|
401
|
0.722
|
a
Average of three determinations.
Stability of the reaction coloured
product:
Stability time was obtained
by following the absorbance readings of the developed reaction product for 24
hours at room temperature (25± 5)0C.It was found that the produced
color was stable for 24 hours for the two drugs.
Effect of temperature:
The effect of temperature on
the absorption intensity was studied using different temperatures in a water
bath ranged from to starting from 250C until 1000C and
the reaction was carried out as usual. The obtained absorbance readings were
plotted against temperature. The maximum absorption intensity was attained at
1000C in case of cefepime and (25± 5)
0C in case of captopril as shown in Figs.8.
Fig.8. Effect of temperature on the
absorbance of the reaction colored product at 401 nm.
Method validation:
The developed methods were
validated according to international conference on harmonization guidelines [60].The linearity range of absorbance as a function of
drug concentration (Table 3) provides good indication about sensitivity of
reagents used. Calibration curves have correlation coefficients (r) 0.999
indicating good linearity. The accuracy of the methods was determined by
investigating the recovery of drugs at concentration levels covering the
specified range (three replicates of each concentration). The results showed
excellent recoveries (table 4). Also, the Limit of detection (L.D.), Limit of quantitation (L.Q.), Sandell’s
sensitivity (S.S.) and Molar absorbitivity were
calculated. The small values of SD and %
RSD point to high precision of the proposed method. Intra-day precision was
evaluated by calculating standard deviation (SD) of five replicate
determinations using the same solution containing pure drugs (table 7). The SD
values revealed the high precision of the methods For inter - day
reproducibility on a day - to - day basis, a series was run, in which the
standard drug solutions were analyzed each for five days (table 7). The effect
of the presence of common excipients such as starch,
talc, lactose and glucose was studied. It was found that no interference was
introduced by any of them indicated high selectivity. Robustness was examined by evaluating the
influence of small variation of method variables including; NaOH
concentration, NBD-Cl concentration, heating
temperature and heating time on the method suitability and sensitivity. (table 8) shows that
none of these variables significantly affects the performance of the method
which indicates robustness of the proposed method.
Table(3). Analytical parameters for the determination of cefepime and captopril by NBD-Cl.
|
Methyl orange
(60µg/ml)
|
PARAMETERS
|
|
Captopril
|
Cefepime
|
|
|
401
|
401
|
λmax, nm
|
|
1
|
1.2
|
Volume of NBD-Cl, ml
|
|
1
|
1
|
Volume of HCL, ml
|
|
5
|
5
|
Volume of NaOH (.5 M) , ml
|
|
10
|
25
|
Time of
hydrolysis min.
|
|
25(±5)
|
85
|
Temperature 0
C
|
|
2
|
2
|
Time after NBD-Cl addition, min
|
|
2-24
|
8- 120
|
Beer's law
limits, µg/ml
|
|
y=0.035x+ 0.100
|
y=0.003x+0.161
|
Regression
equation
|
|
0.999
|
0.999
|
Correlation
Coefficient
|
y =
a + bx,
where y is the absorbance, a is
the intercept, b is the slope and x is the concentration in
µg/ml.
Table (4).Results of the analysis for the determination of cefepime
and captopril using NBD-Cl method.
|
Parameters
|
NBD-Cl
|
|
Cefepime*
|
Captopril*
|
|
Taken µg/ml
|
Found µg/ml
|
Recovery %
|
Taken µg/ml
|
Found µg/ml
|
Recovery %
|
|
|
8
|
8
|
100
|
2
|
2.028
|
101.43
|
|
|
20
|
20.25
|
101.25
|
4
|
3.94
|
98.57
|
|
|
40
|
40.75
|
101.88
|
8
|
7.857
|
98.21
|
|
|
60
|
61
|
101.67
|
12
|
12.23
|
101.9
|
|
|
80
|
79.75
|
99.68
|
16
|
15.74
|
98.39
|
|
|
100
|
100
|
100
|
20
|
20.4
|
102
|
|
|
120
|
117.75
|
98.12
|
24
|
23.8
|
99.17
|
|
Mean
|
|
|
100.37
|
|
|
99.95
|
|
±SD
|
|
|
1.32
|
|
|
1.74
|
|
±RSD
|
|
|
1.32
|
|
|
1.74
|
|
±SE
|
|
|
0.44
|
|
|
0.615
|
|
Variance
|
|
|
1.750
|
|
|
3.0268
|
|
Slope
|
|
|
0.004
|
|
|
0.035
|
|
L.D.
|
|
|
2.439
|
|
|
0.589
|
|
L.Q.
|
|
|
8.12
|
|
|
1.96
|
|
S.S.
|
|
|
0.0432
|
|
|
0.01799
|
|
ε
|
|
|
4614.0821
|
|
|
11089.3
|
*Average
of three independent procedures.
Table
(5).Statistical analysis of results obtained by the
proposed methods applied on cefepime (pimfast®) vials compared with reference method.
|
Parameters
|
Proposed
method
|
Reported method[6].
|
|
N
|
5
|
5
|
|
Mean Recovery
|
99.653
|
98.656
|
|
±SD
|
1.381
|
1.221
|
|
±RSD
|
1.385
|
1.24
|
|
±SE
|
0.6173
|
0.432
|
|
Variance
|
1.9049
|
1.494
|
|
Student-t
|
1.2(2.57)a
|
|
|
F-test
|
1.28(6.256)b
|
|
a and b are the Theoretical Student t-values and
F-ratios at p=0.05.
Table
(6).Statistical analysis of results obtained by the
proposed methods applied on captopril (capotril®)tablets compared with reference method.
|
Parameters
|
Proposed
method
|
Reported method[28].
|
|
N
|
5
|
5
|
|
Mean Recovery
|
99.947
|
98.53
|
|
±SD
|
1.3365
|
1.215
|
|
±RSD
|
1.337
|
1.233
|
|
±SE
|
0.597
|
0.429
|
|
Variance
|
1.786
|
1.475
|
|
Student-t
|
1.75(2.57)a
|
|
|
F-test
|
1.2(6.256)b
|
|
a and b are the
Theoretical Student t-values and F-ratios at p=0.05.
Applications:
Some Pharmaceutical
formulations containing stated drugs have been successfully analyzed by the
proposed methods. Excipients did not show
interference indicating high specificity. Results obtained were compared to
those obtained by applying reported reference methods using aqoues NaOH by ultraviolet
spectroscopy in case of cefepime[6] and the reaction with
4-chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) in the
presence of sodium tetraborate in absolute methanol
in case of captopril [28].where Student’s t-test and F-test were performed
for comparison. Results are shown in ( tables 5,6) where the calculated t and F
values were less than tabulated values which in turn indicate that there is no
significant difference between proposed methods and reference ones relative to
precision and accuracy.
Table
(7).Results of the intraday and interday precision
for the determination of cefepime and captopril using NBD-Cl method.
|
Intraday and interday precision
|
|
drug
|
Intraday
|
Interday
|
|
Mean of recovery ±SD
|
RSD
|
Mean of recovery ±SD
|
RSD
|
|
Cefepime
|
100.1±0.477
|
0.476
|
99.56±0.98
|
0.98
|
|
Captopril
|
101.4±0.476
|
0.469
|
100.19±1.21
|
1.21
|
Table (8). Results of the robustness for the determination of cefepime,
and captopril using
NBD-Cl method.
|
Parameters
|
Cefepime
|
Parameters
|
Captopril
|
|
mean
of recovery ±SD
|
mean
of recovery ±SD
|
|
No
variation
|
99.68±1.32
|
No variation
|
101.9±1.73
|
|
NaOH
|
|
NaOH
|
|
|
0.45M
|
98.125±1.56
|
0.45M
|
98.09±1.6
|
|
0.55M
|
100.9±1.29
|
0.55M
|
101.9±1.73
|
|
NBD.Cl
|
|
NBD.Cl
|
|
|
2.8x
10-3
|
99.06±1.40
|
3.4x 10-3
|
98.8±1.54
|
|
3.2x
10-3
|
100.32±1.36
|
3.8x 10-3
|
101.19±1.62
|
|
temp.
|
|
|
|
|
75̊ ˚C
|
98.12±1.56
|
|
|
|
85̊ ˚C
|
100.3±1.28
|
|
|
|
time
|
|
time
|
|
|
25min.
|
101.5±1.35
|
8min.
|
98.57±1.56
|
|
35min.
|
98.4±1.5
|
12min.
|
99.76±1.51
|
CONCLUSION:
Spectrophotometry is simple
and inexpensive. The proposed methods require sodium hydroxide and hydrochloric
acid and NBD-Cl as reagents which are readily
available, no pH adjustment is required and the procedures do not involve any
critical reaction conditions or tedious sample preparation. Morever,
methods are simple, moderately fast, accurate, adequately sensitive and free
from interference by common additives and excipients
which make it as choice for routine quality control analysis. The recovery %
obtained by the proposed methods is between 98.12% and 101.8%, within the
acceptance level of 95% to 105%. The present methods are superior to the
reference method with respect to both sensitivity and selectivity. The methods
have been successfully applied for the analysis of marketed cefepime
vials and captopril tablets.
REFERENCES:
1.
B.G. Katzung, Basic and Clinical Pharmacology, 8th ed., McGraw-
Hill, Boston, MA, pp. 755 and 766(2001).
2.
P.C. Van Krimpen, W.P. Van Bennekom, A. Bult, Pharm. Weekbl. [Sci.]. 9
(1987) 1-23.V. Rodenas, A. Parra, J.
Garcia-Villanova, M. Dolores-Gomez, J. Pharm. Biomed. Anal. 13, 1095-1099(1995).
3.
Rabindra K. Nanda, Dipak A. Navathar, Amol A. Kulkarni, Subodh S. Patil, International Journal of ChemTech
Research Vol.4, No.1, pp 152-156, Jan-Mar 2012.
4.
Dave Vimal M, Hirpara Kinjal P,
Shital Faldu
JPSBR: Volume 2, Issue 2, 58-62( 2012).
5.
Satyajeet Singh, Mohd. Riyaz, Vinit Raj and Ashish Kumar, International Journal of Pharmacy and
Integrated Life Sciences, Vol. 1-I4, PG149-158( 2013).
6.
C. Rambabu, C.A. Jyothirmayee, K.
Naga Raju, Int J Pharm PharmSci, Vol 4, Suppl 1, 417-418.
7.
Brijesh Patel, Japan Patel, Kaushal Parmar, Manish Patel, 2IJPI’s Journal of Analytical
Chemistry, Vol 1: (2011).
8.
Chafle D. M. Der PharmaChemica, 5(2):127-132(2013).
9.
Navin K. Khare, Rabindra K. Nanda, Raymond M. Lawrence, Dipak
A. Navathar, International Journal of Institutional
Pharmacy and Life Sciences 2(2): March-April 2012.
10.
F.C. Maddox, J.T.
Stewart, J. Liq. Chromatogr. Relat.
Technol.22, 2807-2813(1999).
11.
P. N. Patel, U. D.
Patel, SH. K. Bhavsar and A. M. Thaker
1735-2657/10/91-7-10 Iranian Journal of Pharmacology & Therapeutics IJPT
9,7-10(2010).
12.
V. Das Gupta, PhD,
J. Maswoswe, R. E. Bailey, International Journal of
Pharmaceutical Compounding, Vol.1 No.6 November/December 1997.
13.
Deanna Hurum, Brian De Borba, and Jeff
Rohrer, dionex corporation the
application notebook–lcgc0209_sec2_48.pgs February 2009.
14.
Harshal Kanubhai Trivedi,
Nayan Kshtri, Mukesh C. Patel, Sci. Pharm;
81: 151–165(. 2013).
15.
Y.L. Chang, M.H.
Chou, M.F. Lin, C.F. Chen, T.H. Tsai, J. Chromatogr.
A 914, 77-82(2001).
16.
N. Cherti, J.M. Kinowski, J.Y. Lefrant, F. Bressolle, J. Chromatogr. B: Biomed. Appl. 754, 377-386(2001).
17.
I.N. Valassis, M. Parissi-Poulou, P. Macheras, J. Chromatogr. B:
Biomed. Appl. 721, 249-255(1999).
18.
B. Calahorra, M.A. Campanero, B. Sadaba, J.R. Azanza, Biomed. Chromatogr. 13, 272-275(1999).
19.
H. Elkhaili, L. Linger, FI. Monteil,
F. Jhel, J. Chromatogr. B:
Biomed. Appl. 690, 181-188(1997).
20.
F.J.J. Palacios,
M.C. Mochon, J.C.J, Sanchez, M.A.B. Lopez, A.G.
Perez, Chromatographia 62, 355-361(2005).
21.
Y.R. Chen, S.J.
Lin, Y.W. Chou, H.L. Wu, S.H. Chen,J. Sep. Sci. 28,
2173-2179(2005).
22.
F.J. Jimenez
Palacios, M. Callejon Mochon,
J.C. Jimenez Sanchez, J. Herrera Carranza, Electroanalysis
(N. Y.) 12, 296-300(2000).
23. S.A. Ozkan, B. Uslu, P. Zuman, Anal. Chim. Acta 457, 265-274(2002).
24. Jasek, W, ed. (2007). Austria-Codex (in German). Vienna: Österreichischer Apothekerverlag.
ISBN 978-3-85200-181-4.
25. Basavaiah, K. and Nagegowda,
P., J. Iran. Chem. Soci., 1, 106-114 (2004).
26. Basavaiah, K. and Nagegowda,
P., Oxid. Commun, 27, 203-210 (2004).
27. Rim Haggag, Saied Belal, Rasha
Shaalan, Sci Pharm; 76: 33–48( 2008).
28. Hosseinimehr, S.J., Ebrahimi, P., Hassani, N., Mirzabeigi, P. and Amini, M., Boll. Chim.
Farm, 143, 249-251 (2004).
29. Nafisur, R., Manisha, S. and Nasrul, H., IL Farmaco, 60,
569-74 (2005).
30. Shama, S.A., Amin, A.E.S. and Omara,
H., J. Quant. Spectrosc. Radiat.
Transfer, 102, 261-268 (2006).
31. Sharma, M., Koty, A.,
Srivastava, M. and Srivastava, A., J. Chin. Chem. Soc., 54, 1419-1432 (2007).
32. Belal, S.F., Haggag, R.S. and Shaalan,
R.A.A., J. food drug anal., 16, 26-33 (2008).
33. Gao, L.X., Wu, L.L.AndLi,
Q.M
., Anal. Chim. Acta, 626, 174-179 (2008).
34.
Wang, L., Yang, X.F. and Zhao, M., J. Fluoresc., 19, 593-599 (2009).
35.
Li,
Y.H., Zhang, A.H., Du, J.X. and Lu, J.R., Anal. Lett., 36, 871-879 (2003).
36.
Ivashkiv, E., J.
Pharm. Sci., 73, 1427-1430 (2006).
37.
Wang,
S.L., Wang,
M. andLi,
Q.M., Chin.Chem. Lett., 20, 88-91 (2009).
38.
El-Didamony, A.M., J. Chin.
Chem. Soc., 56, 755-762 (2009).
39.
Liu,
Y.C., Wu,
H.L., Kou,
H.S., Chen,
S.H. and Wu,
S.M. Anal. Lett., 28, 1465-1481 (1995).
40.
Bald,
E., Sypniewski, S., Drzewoski, J. and Stepien,
M., J. Chromatogr., B-Biomed. Appl., 681, 283-289
(1996).
41.
Liu,
C., Liu,
S., Chen,
H. andXie,
X., Chin. J. Chromatogr., 16, 82-83 (1998).
42.
Amini, M., Zarghi, A. and Vatanpour,
H., Pharm. ActaHelv., 73, 303-306 (1999).
43.
Tache, F., Farca,
A., Medvedovici, A. and David, V., J. Pharm. Biomed. Anal., 28, 549-557 (2002).
44.
Parham,
H. Zargar, B., Talanta, 65,
776-780 (2005).
45.
Pérez-Ruiz, T., Martínez-Lozano, C. and Galera,
R., Pharm. Anal., 27, 2310-2316 (2006).
46.
Ziyatdinova, G.K., Budnikov, G.K. and Pogorel'tsev,
V.I., J. Anal. Chem., 61,
798-800 (2006).
47.
Lourencao, B.C., Marcolino, L.H. and Fatibello-Filho, O., Quimica.
Nova. 31, 349-352 (2008).
48.
Rezaei, B. and Damiri, S., Sens. Actuators B, 134, 324-331 (2008).
49.
Karimi-Maleh, H., Ensafi, A.A. and Allafchian,
A.R., J. Solid State Electrochem., Published on line
(2009).
50.
K. Omai, T. Toyo'oka, H. Miyano, Analyst 109, 1365-1372(1984).
51.
A. Onal, S.E. Kepekci, A. Oztunc, J.AOAC Int.
88, 490- 495(2005).
52.
R.O. Olojo, R.H. Xia, J.J. Abramson, Anal. Biochem.
339, 338-344(2005).
53.
A.A. El-Emam, S.H. Hansen, M.A. Moustafa, S.M. El-Ashry D.T. El-Sherbiny, J. Pharm. Biomed. Anal. 34, 35-44(2004).
54.
N. El-Enany, F.Belal,
M. Rizk, Chem. Anal. (Warsaw, Pol.) 49,
261-269(2004).
55.
H.F. Askal, O.H. Abdelmaged, P.Y. Kashaba, Egypt
J. Anal. Chem. 4, 89-103(1995).
56.
M.A. Abdalla, A.G. Fogg, J.G. Baber, C. Burgess, Analyst 108, 53-57(1983).
57.
N. Grekas, A.C. Calokerinos, Analyst 115, 613-616(1990).
58.
G. Svehla, Vogel's Textbook of
Macro and Semi-Micro Qualitative Inorganic Analysis, 5lh ed., The
Chaucer Press, Great Britain,
pp. 308-310,331 and 342(1979).
59.
Guidance for Industry: Q2B of Analytical Procedures;
Methodology: International Conference on Harmonization (ICH). Nov. (1996).