Stability-indicating spectrofluorimetric method for the assay of ziprasidone in capsules

Article abstract of DOI:10.1007/s10895-011-0855-x

A simple, rapid and highly sensitive spectrofluorimetric method was developed for determination of ziprasidone hydrochloride (ZPS) in capsules. The method is based on measuring the native fluorescence of ZPS in acetate buffer of pH 4.5 at 398 nm after excitation at 315 nm. The fluorescence-concentration plot was rectilinear over the range of 0.05-0.80 μg mL^-1 with a lower detection limit (LOD) of 6.0 ng mL^-1 and quantification limit (LOQ) of 20.0 ng mL^-1. The method was fully validated and successfully applied to the determination of ZPS in its capsules with average percentage recovery of 99.7±1.4. The method was extended to stability study of ZPS. The drug was exposed to acidic, alkaline, oxidative and photolytic degradation according to ICH guidelines. Moreover, the method was utilized to investigate the kinetics of the alkaline, acidic and oxidative degradation of the drug. A proposal for the degradation pathways was postulated. Springer Science+Business Media, LLC 2009.

Full text of DOI:10.1007/s10895-011-0855-x

J Fluoresc (2011) 21:1659–1667
DOI 10.1007/s10895-011-0855-x
ORIGINAL PAPER
Stability-Indicating Spectrofluorimetric Method
for the Assay of Ziprasidone in Capsules
Mohamed I. Walash & Fathalla Belal & Nahed El-Enany &
Manal Eid & Rania N. El-Shaheny
Received: 30 October 2010 /Accepted: 1 February 2011 /Published online: 16 February 2011
#
Springer Science+Business Media, LLC 2011
Abstract A simple, rapid and highly sensitive spectrofluori-
metric method was developed for determination of ziprasi-
done hydrochloride (ZPS) in capsules. The method is based
on measuring the native fluorescence of ZPS in acetate buffer
of pH 4.5 at 398 nm after excitation at 315 nm. The
fluorescence-concentration plot was rectilinear over the range
of 0.05–0.80 μg mL−1 with a lower detection limit (LOD) of
6.0 ng mL−1 and quantification limit (LOQ) of
20.0 ng mL−1. The method was fully validated and
successfully applied to the determination of ZPS in its
capsules with average percentage recovery of 99.7 1.4. The
method was extended to stability study of ZPS. The drug
was exposed to acidic, alkaline, oxidative and photolytic
degradation according to ICH guidelines. Moreover, the
method was utilized to investigate the kinetics of the
alkaline, acidic and oxidative degradation of the drug. A
proposal for the degradation pathways was postulated.
receptors as well as dopamine (D2) receptors. It is used for
the treatment of schizophrenia and in acute manic or mixed
episodes associated with bipolar disorder [1].
Literature survey revealed that several analytical methods
were reported for the determination of ZPS in biological
matrices, including; liquid chromatography-tandem mass
spectrometry [2–5], liquid chromatography/UV detection
[6], liquid chromatography/fluorescence detection [7]. Mean-
while, some analytical methods have been reported for the
determination of ZPS in raw material and pharmaceutical
formulations including; TLC densitometry [8], HPLC/UV
detection [8–10], capillary zone electrophoresis [11] and
spectrophotometric methods [12, 13].
To the best of our knowledge, up till now nothing has been
published concerning the specrofluorimetric determination of
ZPS. Therefore, the current study was aimed to develop and
validate a simple, rapid and sensitive spectrofluorimetric
methodology for the determination of ZPS utilizing its native
fluorescence. The proposed method was fully validated
according to ICH guidelines, and successfully applied for
the determination of the drug in its capsules.
.
.
.
Keywords Ziprasidone Spectrofluorimetry Capsules
Stability-indicating
The parent drug stability guidelines issued by the Interna-
tional Conference on Harmonization (ICH) [14] requires that,
analytical test procedure should indicate stability. Therefore,
the present study was extended to establish the inherent
stability of ZPS under different stress conditions such as,
alkaline, acidic, oxidative and photolytic conditions.
Introduction
Ziprasidone, (ZPS, Fig. 1), 5-{2-[4-(1,2-Benzisothiazol-3-
yl)-1- piperazinyl]ethyl}-6-chloro-2-indolinone, is an
indole-like heterocyclic antipsychotic agent. Ziprasidone is
an atypical antipsychotic drug reported to have affinity for
adrenergic (α1), histamine (H1), and serotonin (5-HT2)
Experimental
:
:
:
:
M. I. Walash F. Belal N. El-Enany M. Eid (*)
R. N. El-Shaheny
Department of Analytical Chemistry, Faculty of Pharmacy,
University of Mansoura,
35516, Mansoura, Egypt
e-mail: manal_eid@yahoo.com
Apparatus
–
The fluorescence spectra and measurements were
recorded using a Perkin-Elmer model LS 45 lumines-

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J Fluoresc (2011) 21:1659–1667
H
N
Cl
–
–
Acetate buffer solutions (0.2 M), covering the pH range
of 3.6–5.6, were prepared by mixing appropriate volumes
of 0.2 M sodium acetate trihydrate and 0.2 M acetic acid
and adjusting the pH using a pH-Meter.
Borate buffer solutions (0.2 M), covering the pH range
of 6.5–9.5, were prepared by mixing appropriate
volumes of 0.2 M boric acid and 0.2 M NaOH and
adjusting the pH using a pH-Meter.
HCl
O
N
N
OH2
N
S
Fig. 1 Chemical structure of ziprasidone hydrochloride monohydrate
(ZPS)
Stock and Standard Solutions
A stock solution containing100 μg mL−l of ZPS was
prepared in methanol. This solution was further diluted with
the same solvent to obtain a standard solution containing
5 μg mL−l of ZPS. The solutions were stable for 2 weeks
when kept in the refrigerator and protected from light.
cence Spectrometer (UK), equipped with a 150 W
Xenon arc lamp, grating excitation and emission
monochromators and a PerkinElmer recorder. Slit
widths for both monochromators were set at 10 nm.
A 1-cm quartz cell was used.
–
–
Hanna pH-Meter (Romania) was used for pH adjustments.
CAMAG UV-lamp (S/N 29000), dual wavelength
(254/366), 2×8 W (Muttenz, Switzerland) was used
in the photo-stability study.
General Procedures
–
Construction of calibration graph
Accurately measured volumes of the standard
solution of ZPS were transferred into a series of
10 mL volumetric flasks to give final concentrations
of 0.05–0.80 μg mL−1. 2 mL of 0.2 M acetate buffer
solution of pH 4.5 were added; the solutions were
completed to the volume with distilled water and mixed
well. The fluorescence intensities were measured at
398 nm after excitation at 315 nm. The relative
fluorescence intensities were plotted versus the final
concentration of the drug (μg mL−1) to get the
calibration graph; alternatively, the corresponding
regression equation was derived.
Materials and Reagents
All reagents used were of Analytical Reagent Grade, and
distilled water was used through out the study:
–
Ziprasidone hydrochloride monohydrate pure sample
was obtained from Pfizer Co. through Drug Control
Center, Riyadh, Saudi Arabia, and was used as
received. Its purity was found to be 99.47% according
to the comparison method [13].
–
–
Zeldox® capsules, batch # 910024732, labeled to contain
60 mg ziprasidone hydrochloride monohydrate/capsule,
product of Heinrich Mack Nachf, Germany, a subsidiary
of Pfizer Inc., was purchased from local pharmacy.
β-cyclodextrin (β-CD) and hydroxy propyl-β-
cyclodextrin (HP-β-CD) (Merck, Germany), 0.5%
aqueous solutions were prepared in hot distilled water.
Tween-80 (Adwic Co., Egypt), 0.5% aqueous solution
was prepared.
–
Procedure for capsules
The contents of ten capsules were emptied, mixed
well and pulverized. An accurately weighed quantity of
the powder equivalent to 10.0 mg of ZPS was
transferred into 100 mL volumetric flask and sonicated
with 80 mL of methanol for 30 min. The volume was
completed with methanol and the solution was filtered.
The solution was diluted with methanol to obtain a
standard solution containing 5 μg mL−l of ZPS. The
procedure described under “Construction of calibration
graph” was followed. The nominal content of the
capsules was calculated using the calibration graph or
the corresponding regression equation.
–
–
Sodium dodecyl sulfate (SDS, 95%) and cetyltrimethyl
ammonium bromide (CTAB, 99%) (Winlab, UK),
0.5% aqueous solutions were prepared.
–
–
Sodium acetate trihydrate (0.2 M solution), sodium
hydroxide (0.2 and 0.5 M solutions), boric acid (0.2 M
solution) (BDH, UK).
Hydrochloric acid (2 M solution), hydrogen peroxide
(6% w/v solution), dimethyl formamide (DMF) (BDH,
UK).
–
Procedures for stability studies
&
Alkaline and acidic degradation
Aliquots of ZPS stock solution (containing 100.0 μg)
were transferred into two series of small conical flasks;
5 mL of 0.5 M NaOH or 2.0 M HCl solutions were
added. The solutions were heated in a boiling water
bath for different time intervals (15–75 and 5–25 min
–
–
Methanol (Sigma, Germany).
Dimethyl sulfoxide (DMSO) and n-propanol (Riedel-
deHäen, Germany).

J Fluoresc (2011) 21:1659–1667
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for alkaline and acidic degradation, respectively). At
the specified time, the contents of each flask were
cooled; neutralized to pH 7 with either 0.5 M HCl or
2.0 M NaOH, respectively. The solutions were then
quantitatively transferred into 25 mL volumetric
flasks and completed to volume with methanol.
1.0 mL of the resulting solutions was then transferred
into 10 mL volumetric flasks and the procedure
described under “Construction of calibration graph”
was performed.
the inherent stability of ZPS under different stress conditions
according to ICH guidelines [14].
–
Fluorescence spectra and characteristics of ZPS
Ziprasidone was found to exhibit an intense native
fluorescence in aqueous acetate buffer solution of
pH 4.5 at 398 nm after excitation at 315 nm (Fig. 2).
It is clear that, ZPS exhibits two excitation wavelengths
of 237 and 315 nm. This is justified in theory by the
light absorption promoting electron from the ground
electronic state to two excited states [15]. A wavelength
of 315 nm was selected as the optimum excitation
wavelength since it gave the sharpest emission spec-
trum with best reproducibility and linearity. Fluores-
cence scan analysis showed best combination at 315
and 398 nm as excitation and emission wavelengths,
respectively.
&
Oxidative degradation
Aliquots of ZPS stock solution (containing 100.0 μg)
were transferred into a series of small conical flasks;
5 mL of 6% (w/v) H2O2 solution were added and the
solutions were heated in a thermostatically controlled
water bath at different temperature settings (50–80 °C)
for different time intervals (10–50 min). At the specified
time, the contents of each flask were cooled; the
solutions were then quantitatively transferred into
25 mL volumetric flasks and completed to volume with
methanol. 1.0 mL of the resulting solutions was
transferred into 10 mL volumetric flasks and completed
as under “Construction of calibration graph”
–
Study of Experimental Parameters
&
Effect of pH
The influence of pH on the native fluorescence
intensity of ZPS was studied using 0.01 M HCl
(pH=2.0) and different types of buffer solutions
covering the pH range of 3.6–9.5. It was found that,
the maximum and constant relative fluorescence inten-
sity (RFI) was achieved over the pH range of 3.6–5.6,
so that; pH 4.5 was chosen as the optimum pH value.
Increasing the pH value more than pH 5.6 caused
gradual decrease of the RFI of ZPS (Fig. 3).
&
Photolytic degradation
Aliquots of ZPS stock solution (containing 100.0 μg)
were transferred into a series of 25 mL volumetric
flasks and diluted to the volume with either methanol,
water, or methanol/water mixture (50:50, v/v). The
solutions were exposed to UV-lamp at a wavelength of
254 nm at a distance of 15 cm placed in a wooden
cabinet for 24 h. At the specified time, the flasks were
removed from the UV-lamp cabinet. 1.0 mL of the
solutions was then transferred into 10 mL volumetric
flasks and the procedure described under “Construction
of calibration graph” was followed.
&
Effect of different organized media
The influence of different surfactants and macro-
molecules on the native fluorescence intensity of ZPS
was studied; hopefully, a significant increase in the
fluorescence intensity could be achieved. Different
surfactants such as anionic surfactant (SDS), cationic
surfactant (CTAB), non-ionic surfactant (tween-80), and
different macromolecules such as β-CD, HP-β-CD and
methyl cellulose (1 mL of 0.5% aqueous solution of
each) were investigated. It was found that, methyl
cellulose did not affect the fluorescence intensity of
ZPS. On the other hand, β-CD, HP-β-CD, CTAB, SDS
and tween-80 caused a significant decrease in the
fluorescence intensity of ZPS. Therefore, no surfactant
was used throughout this study.
Results and Discussion
The ultraviolet spectrum of aqueous buffered solution of
ZPS at pH 4.5 exhibits two absorption maxima at 237 and
315 nm, with a specific absorbance [A1%, 1cm] of 1,000 and
144, respectively. As a consequence, poor sensitivity will
be achieved by conventional spectrophotometric measure-
ments. This problem is highly aggravated when it is needed
to determine the drug especially in pharmaceutical prepa-
rations. This fact led us to investigate the native fluores-
cence behavior of ZPS in an attempt to develop a sensitive,
simple and reliable method for its determination. Different
experimental parameters affecting the fluorescence intensity
of ZPS were carefully studied and optimized. Such factors
were changed individually, where others kept constant.
Furthermore, the developed method was applied to establish
&
Effect of diluting solvent
Dilution with different solvents such as water,
methanol, acetonitrile, n-propanol, DMF and DMSO
were studied. Water was the best solvent for dilution
since it gave the highest RFI and the lowest blank
reading with reproducible results. A distinct and
sharp decrease of the fluorescence intensity was
observed upon using methanol, acetonitrile and n-
propanol for dilution; this may be attributed to
change in the medium polarity that may result in

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J Fluoresc (2011) 21:1659–1667
Fig. 2 Flurescence spectra of:
(A, A′): Acetate buffer of
pH 4.5. (B, B′): ZPS (0.4 μg
mL−1) in acetate buffer of
pH 4.5. Where: (A, B) are the
excitation spectra. (A′, B′) are
the emission spectra
620.0
600
550
500
450
400
350
300
250
200
150
100
50
B
B`
A
A`
0.0
220.0 240 260 280 300 320 340 360 380 400 420 440 460 480 500 520 540 560 580 600.5
nm
Wavelength, nm
some sort of physical interaction between these
solvents and the excited singlet state of the drug
molecules. On the other hand, DMF and DMSO
greatly quenched the fluorescence of ZPS (Fig. 4),
since they initiated intersystem crossing process
(similar to heavy atom effect) [16].
molecules [17]. Therefore, the study was carried out at
room temperature (25 °C).
Validation of the Method
The validity of the proposed method was tested using the
following criterion: linearity, sensitivity, limit of detection,
limit of quantitation, specificity, accuracy, precision and
robustness according to ICH recommendations [18].
&
&
Effect of time
The effect of time on the RFI of ZPS was also
studied. It was found that the fluorescence intensity was
immediately developed and remained stable for more
than 2 hours.
&
Linearity and range
Effect of temperature
Assessment of linearity of the assay method was
performed by analyzing seven sets (standard calibration
curve). Adopting the previous procedure, a linear
regression equation was obtained. The regression plot
showed a linear dependence of RFI on drug concentra-
tion over the range of 0.05–0.80 μg mL−1. Statistical
evaluation of the regression data for ZPS regarding
Another factor that affects the fluorescence intensity
is temperature. The effect of temperature was studied in
the range of 40–100 °C using a thermostatically
controlled water bath. It was found that increasing the
temperature resulted in a gradual decrease in the RFI.
This effect can be attributed to higher internal conver-
sion as the temperature increases, facilitating non-
radiative deactivation of excited singlet state and
increase of the loss of energy via collision with solvent
350
300
250
200
150
100
50
500
400
300
200
100
0
0
DMF
DMSO acetonitrile methanol n-propanol
water
0
2
4
6
8
10
Type of Solvent
pH
Fig. 3 Effect of pH on RFI of ZPS (0.4 μg mL−1
Fig. 4 Effect of the type of diluting solvent on RFI of ZPS (0.4 μg
)
mL−1) in aqueous acetate buffer of pH 4.5

J Fluoresc (2011) 21:1659–1667
1663
Table 1 Performance data for the proposed spectrofluorimetric
method for determination of ZPS
high accuracy and high precision of the method,
respectively.
&
Limit of quantification (LOQ) and limit of detection
(LOD):
The limit of quantification (LOQ) and limit of
detection (LOD) were determined according to ICH
Q2 (R1) recommendations [18]. The results are
summarized in Table 1.
Parameter
Results
0.05–0.80
Concentration range (μg mL−1
Limit of detection (LOD) (ng mL−1
Limit of quantification (LOQ) (ng mL−1
)
)
6.0
)
20.0
Correlation coefficient(r)
0.9999
Slope
Intercept
Sy/x
743.0
20.2
3.1
LOQ and LOD were calculated according to the
following equations:
LOQ ¼ 10Sa=b
LOD ¼ 3:3Sa=b
Sa
1.5
Sb
4.7
% RSD
% Error
1.4
0.5
Where, Sa is the standard deviation of the intercept of
regression line and b is the slope of the regression line.
Where:
Sy/x Standard deviation of the residuals
Sb Standard deviation of the slope
% Error=% RSD/√n
&
Sensitivity:
The sensitivity of the assay is defined as the change
in response with the change in the concentration of the
drug. The proposed method is highly sensitive since a
high change in response is achieved with the small
change in concentration as indicated by the high value
of the slope (Table 1).
Sa Standard deviation of the intercept
standard deviation of the residual (Sy/x), standard
deviation of the intercept (Sa) and standard deviation
of the slope (Sb) is given in Table 1 [19]. The small
values of the figures point out to low scattering of the
points around the calibration curve, thus, indicating the
&
Accuracy:
The accuracy of the proposed method is defined as
the similarity of the results obtained by this method to
Table 2 Assay of ZPS in pure sample and commercial capsules using the proposed and comparison methods
Parameter
Proposed method
Comparison method [13]
Conc. taken (μg mL−1) Conc. found (μg mL−1) %Recovery
Conc. taken (μg mL−1) % Recovery
Pure form
0.05
0.10
0.20
0.30
0.40
0.60
0.80
0.051
0.099
0.199
0.306
0.396
0.597
0.804
102.00
5.0
8.0
98.60
100.40
99.40
99.00
99.50
10.0
102.00
99.00
99.50
100.50
x ꢀ S:D:
100.1 1.4
1.438(2.365)*
5.563(19.3)*
101.0
99.5 0.9
t
F
Zeldox® capsules (60 mg ZPS/Cap.)
0.10
0.30
0.60
0.101
0.295
0.589
5.0
8.0
98.7
98.4
99.4
98.1
10.0
101.2
x ꢀ S:D:
99.7 1.4
1.619(19.0)*
2.582(2.776)*
99.8 1.3
t
F
Each result is the average of three separate determinations
*Values between brackets are the tabulated t and F values, at p=0.05[19]

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J Fluoresc (2011) 21:1659–1667
Table 3 Precision data for the proposed method of determination of
Table 4 Results of the degradation study of ZPS under different stress
ZPS in pure form
conditions
Conc. (μg mL−1
)
% Recoverya
% RSD
% Error
Degradation condition
Reaction rate
Half life time
(t1/2, min)
constant (K, min−1
)
Intraday precision
Alkaline degradation
(0.5 M NaOH, 100 °C)
Acidic degradation
(2.0 M HCl, 100 °C)
Oxidative degradation
(6% H2O2, 80 °C)
0.025
0.019
0.035
28
37
20
0.10
98.60 1.4
97.71 1.4
99.96 1.0
1.4
1.4
1.0
0.8
0.8
0.6
0.30
0.60
Interday precision
0.10
0.30
0.60
100.2 1.2
101.2 0.8
98.6 0.9
1.2
0.8
0.9
0.7
0.5
0.5
&
Precision:
The intra-day precision was evaluated through
replicate analysis of different concentrations of the drug
in pure form within the specific working concentration
range. Each sample was analyzed three successive
times. The results are summarized in Table 3.
Similarly, the inter-day precision was evaluated
through replicate analysis of the three different concen-
trations on three successive days. The results obtained
are abridged also in Table 3.
The data presented in Table 3 indicate high accuracy
and precision of the developed method. The high value
of the average percentage recovery and the small value
of% RSD indicate the high accuracy and precision,
respectively.
a Each result is the average of three separate determinations
the true values. To test the validity of the method it was
applied to the determination of pure samples of ZPS
over the range of 0.05–0.80 μg mL−1. The results
obtained were in good agreement with those obtained
using the comparison spectrophotometric method [13].
Using the student t-test and the variance ratio F-test
revealed no significant difference between the perfor-
mance of the two methods regarding the accuracy and
precision, respectively (Table 2).
&
Robustness:
a
The robustness of the proposed method was demon-
strated by the constancy of RFI with the deliberated
minor changes in the experimental parameters such as
pH, 4.5 0.5, volume of buffer, 2.0 0.5 mL. These
minor changes that may take place during the experi-
mental operation did not greatly affect the fluorescence
intensity of ZPS.
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
25
50
75
100
0.9
0.8
0.7
0.6
Time (min)
b
0.40
0.35
0.30
0.25
0.20
0.15
0.5
0.4
0.3
0.2
0.1
0
80
70
60
10
20
30
0
10
20
30
50
40
50
Time (min)
Time (min)
Fig. 5 a Effect of boiling time with NaOH (0.5 M) on ZPS
(0.4 μg mL−1). b Effect of boiling time with HCl (2.0 M) on ZPS
Fig. 6 Three-dimensional plot showing the effect of heating time with
H2O2 solution (6% w/v) on ZPS (0.4 μg mL−1) at different heating
temperatures
(0.4 μg mL−1
)

J Fluoresc (2011) 21:1659–1667
1665
-1.25
-1.50
-1.75
-2.00
-2.25
-2.50
nents did not interfere with the proposed method
(Table 2). This was revealed by carrying out the same
experiment using placebo capsule and omitting the
drug.
Results of Stability Studies and Degradation Kinetics
The alkaline treatment of ZPS with 0.5 M NaOH was
accompanied by a gradual decrease in the fluorescence
intensity. The alkaline degradation of ZPS was found to be
time dependent (Fig. 5a). Upon boiling with 0.5 M NaOH
for 75 min, about 78% degradation of the original sample
occurred. The apparent first order degradation rate constant
and half-life time were calculated (Table 4).
Considerable degradation was also observed in ZPS
sample under acidic stress condition. The acidic degrada-
tion of ZPS was found to be time dependent (Fig. 5b), after
boiling with 2.0 M HCl solution for 40 min, about 56% of
the original drug sample was degraded. The apparent first
2.7
2.8
2.9
1/T (×10-3)
3.0
3.1
3.2
3.3
Fig. 7 Arrhenius plot for the oxidative degradation of ZPS in 6% (w/v)
H2O2
&
Specificity:
The specificity of the proposed procedure was
proven by its ability to determine ZPS in its capsules
confirming that, there was no interference by common
excipients and additives; such as lactose, pregelatinized
starch and magnesium stearate. These matrix compo-
Scheme 1 Proposal for the
degradation pathways of ZPS
H
N
Cl
O
N
N
H2O2
N
or UV light
S
H
Cl
N
O
O
N
N
ZPS
N
NaOH
or
S
HCl
H2N
Cl
O
N
HO
N
N
S

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J Fluoresc (2011) 21:1659–1667
order rate constant and half-life time were also calculated
(Table 4).
composed of chloroform: methanol: glacial acetic acid (75:
5: 4.5 mL, v/v); visualized under UV lamp at 254 nm [8],
revealed that;
Degradation of ZPS under oxidative stress conditions was
also studied. The oxidative degradation of ZPS was found to be
temperature and time dependent. Figure 6 is a three
dimensional plot showing the effect of different heating times
(10–50 min) with H2O2 solution (6%, w/v) at different
heating temperatures (50–80 °C). The apparent first order
degradation rate constant and half-life times were also
calculated (Table 4). By plotting log Kobs values versus 1/T,
Arrhenius plot was obtained (Fig. 7). The activation energy,
Ea, was calculated and was found to be 10.0 K. Cal.mol−1.
Arrhenius equation was derived and it was found to be:
–
Under oxidative and photolytic conditions, one spot was
obtained in each case corresponding to the same degrada-
tion product with characteristic Rf value of 0.1. These
results indicate that the degradation followed the same
pathway under oxidative and photolytic conditions.
Acidic and alkaline degradation of ZPS yield the same
degradation product that’s retained on the base line,
indicating that the degradation pathways are the same
under acidic and alkaline conditions.
–
–
–
The Rf value of the intact ZPS drug substance is 0.75.
The spot of the higher Rf value (0.1) is corresponding
to the degradation product of less polarity (sulphoxide
derivative), while the degradation product that
remained on the base line is more polar due to the free
amino and carboxylic groups resulted from cleavage of
the indole ring.
Log K ¼ 4:515 ꢁ ð2:16=TÞ
The effect of UV-light on the stability of ZPS was also
studied by exposing ZPS solutions in different solvents
(methanol, water, methanol/water mixture, 50/50, v/v) to
the UV-light at 254 nm. It was found that a significant
decrease in the RFI of ZPS was observed upon exposure of
aqueous solution of the drug to UV-light for 24 h (31%
degradation), on the other hand, mild degradation was
observed in methanolic solution of ZPS (only 9% degrada-
tion of the original sample) when irradiated for the same
period. This can be explained by the fact that, polar
solvents tend to increase the degradation of drug molecules
that produce degradates which are more polar than the
original drug, and non-polar solvents enhance the degrada-
tion of polar compounds that produce less polar degradates
[20]. This could be a possible explanation for the decreased
stability of the drug solutions containing water, where, it is
expected that, the photolytic degradation of ZPS proceeds
through photo-oxidation of the sulfur atom yielding the
corresponding sulphoxide derivative of ZPS which is more
polar than the parent drug itself. This proposal is based on
previous reports concerned with the photodegradation of
organosulfur compounds, proving that the photodegrada-
tion of sulfur containing compounds proceeds via sulph-
oxide formation [21].
The main pathway of H2O2 degradation is proposed to
proceed via oxidative degradation with the formation of the
corresponding sulphoxide derivative.
Alkaline and acidic degradation of ZPS occurred
significantly at boiling temperature, where, at lower
temperatures the degradation is mild. The alkaline and
acidic treatments of ZPS are expected to cause cleavage of
the indole ring resulting in decrease of the native
fluoresecence intensity of the drug.
TLC fractionation of the hydrolysates obtained follow-
ing the exposure of ZPS to alkaline, acidic, oxidative and
photolytic degradation, utilizing silica gel sheets 60 F254
(5 cm×10 cm with 0.2 mm thickness), run with solvent
A proposal for the possible degradation pathways of ZPS
is presented in Scheme 1.
Applications of the Proposed Method to the Determination
of ZPS in Capsules
The proposed method was successfully applied to the assay
of ZPS in commercial capsules. The average percent
recoveries of different concentrations were based on the
average of three replicate determinations. The results shown
in Table 2 are in good agreement with those obtained with
the comparison spectrophotometric method [13].
Conclusion
The developed spectrofluorimetric method provided a
reliable, reproducible and specific assay for ZPS in
pharmaceutical preparations. The method is sensitive
enough to detect as low as 6 ng mL−1 of ZPS. Based on
problems encountered from post publications, the present
study has served to develop a simple, satisfactory, rapid,
and fully validated assay method of ZPS in pharmaceutical
preparations.
References
1. Sweetman SC (2009) “Martindale: the complete drug reference”,
36th edn. The Pharmaceutical Press, London, pp 1036–1037
2. Zhang G, Terry AV Jr, Bartlett MG (2008) Determination of the
lipophilic antipsychotic drug ziprasidone in rat plasma and brain
tissue using liquid chromatography–tandem mass spectrometry.
Biomed Chromatogr 22:770–778

J Fluoresc (2011) 21:1659–1667
1667
3. Zhang G, Terry AV Jr, Bartlett MG (2007) Sensitive liquid
chromatography/tandem mass spectrometry method for the
simultaneous determination of olanzapine, risperidone, 9-
hydroxyrisperidone, clozapine, haloperidol and ziprasidone in
rat brain tissue. J Chromatogr B 858:276–281
4. Zhang G, Terry AV Jr, Bartlett MG (2007) Liquid chromatogra-
phy/tandem mass spectrometry method for the simultaneous
determination of olanzapine, risperidone, 9-hydroxyrisperidone,
clozapine, haloperidol and ziprasidone in rat plasma. Rapid
Commun Mass Spectrom 21:920–928
5. Al-Dirbashi OY, Aboul-Enein HY, Al-Odaib A, Jacob M, Rashed
MS (2006) Rapid liquid chromatography–tandem mass spectrom-
etry method for quantification of ziprasidone in human plasma.
Biomed Chromatogr 20:365–368
6. Zhang G, Terry AV Jr, Bartlett MG (2007) Simultaneous
determination of five antipsychotic drugs in rat plasma by high
performance liquid chromatography with ultraviolet detection. J
Chromatogr B 856:20–28
11. Cecilia F, Leopold K, Augusta RM, Ernst K (2008) Determination
of ziprasidone in pharmaceutical formulations by capillary zone
electrophoresis. J Pharm Biomed Anal 46:471–476
12. Srinubabu G, Rani BS, Rao JVLVNS (2006) Spectrophotometric
determination of Ziprasidone in pharmaceutical formulations. E J
Chem 3:9–12
13. Anand kumar Y, Anitha M, Hemanth A, Srinivas S (2010)
Development of rapid UV spectrophotometric method for the
estimation of ziprasidone hydrochloride in bulk and formulations.
Digest Journal of Nanomaterials and Biostructures 5:279–283
14. ICH, Q1A (R2), Stability Testing of New Drug Substances and
Products, International Conference on Harmonization, Geneva, 2003.
15. Ohannesian L, Streeter AJ (2002) “Handbook of Pharmaceutical
Analysis”, Marcel Dekker, Inc. USA, Electronic version.
16. Skoog DA, Holler FJ, Crouch SR (2007) Principles of instrumen-
tal analysis, 6th edn. Thomson, Belmont, p 406
17. Skoog DA, West DM, Holler FJ, Crouch SR (2004) “Fundamen-
tals of analytical chemistry”, 8th edn. Saunders College Publish-
ing, Philadelphia, p 1003
18. ICH, Q2 (R1), Validation of analytical procedures: text and
methodology, International Conference on Harmonization, Gene-
va, 2005.
19. Miller JN, Miller JC (2005) “Statistics and Chemometrics for
Analytical Chemistry”, 5th Ed., Pearson Education Limited:
Harlow, England, pp. 39–73, 107–149, 256.
20. Aulton ME (Ed.) (2002) “Pharmaceutics—the science of dosage
form design” 2nd Ed., Churchill Livingstone, Toronto, pp. 129–
132.
7. Suckow RF, Fein M, Corell CU, Cooper TB (2004) Determination
of Plasma ziprasidone using liquid chromatography with fluores-
cence detection. J Chromatogr B 799:201–208
8. El-Sherif ZA, El-Zeany B, El-Houssini OM, Rashed MS, Aboul-
Enein HY (2004) Stability indicating reversed-phase high-
performance liquid chromatographic and thin layer densitometric
methods for the determination of ziprasidone in bulk powder and
in pharmaceutical formulations. Biomed Chromatogr 18:143–149
9. Rani BS, Reddy PV (2006) Estimation of Ziprasidone Hydro-
chloride monohydrate in bulk and capsules by reversed phase
HPLC. E J Chem 3:169–172
21. Alvaro M, Carbonell E, García H (2004) Photocatalytic
degradation of sulphur-containing aromatic compounds in the
presence of zeolite-bound 2, 4, 6-triphenylpyrylium and 2, 4,
6-triphenylthiapyrylium. Appl Catal B Environ 51:195–202
10. Prasanthi NL, Rao NR (2010) High performance liquid chro-
matographic estimation of ziprasidone in pharmaceutical dosage
forms. Int J Pharm Pharm Sci 2:120–122