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ORIGINAL ARTICLE
Kinetic spectrophotometric method for the determination
of some fourth generation fluoroquinolones in bulk and
in pharmaceutical formulations
Akram M. El-Didamony *, Mona O. Abo-Elsoad
Chemistry Department, Faculty of Science, Zagazig University, Zagazig 44519, Egypt
Received 29 December 2012; revised 21 September 2013; accepted 8 October 2013
KEYWORDS
Kinetic spectrophotometric;
Potassium permanganate;
Gemifloxacin;
Gatifloxacin;
Dosage forms
Abstract A kinetic spectrophotometric method for accurate and sensitive determination of gemi-
floxacin (GMFX) and gatifloxacin (GTFX) has been described. The method is based on the reac-
tion of the studied drugs with potassium permanganate in the presence of sodium hydroxide to form
a water-soluble green product which shows maximum absorbance at 604 nm. The determination of
GMFX and GTFX drugs by rate constant, fixed-concentration, and fixed time methods was feasi-
ble with the calibration equations obtained but the fixed time method had been found to be more
applicable. The concentration of the selected drugs is calculated using the calibration equation for
the fixed time method. The absorbance–concentration plot is linear over the range of 4–36 lgmL
1
and 4–40 lgmL
1
with correlation coefficient of 0.9998 and 0.9991, for GMFX and GTFX, respec-
tively. The molar absorptivity, Sandell sensitivity, detection and quantification limits were also cal-
culated. The different experimental parameters affecting the development and stability of the color
were carefully studied and optimized. The intra- and inter-day RSD values indicated the ruggedness
of the method. The proposed method has been successfully applied to pharmaceutical formulations
of each drug. Statistical comparison of the results with a well established reported method showed
excellent agreement and proved that there is no significant difference in the accuracy and precision.
ª2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.
1. Introduction
Fluoroquinolones, as a group, have shown excellent activity
against the most frequently occurring gram-positive and -neg-
ative ocular pathogens [1,2,3,4,5]. Earlier generation fluoro-
quinolones, such as ciprofloxacin and ofloxacin, have
been used widely to treat various pathogenic conditions.
However, the development of a resistant strain against these
fluoroquinolones has been reported [6,7]. Gemifloxacin and
gatifloxacin are fourth-generation fluoroquinolones, possess
an improved antibacterial spectrum, particularly against resis-
*Corresponding author. Tel.: +20 002052276476.
E-mail address: ak_eldidamony@yahoo.com (A.M. El-Didamony).
Peer review under responsibility of King Saud University.
Production and hosting by Elsevier
Journal of Saudi Chemical Society (2013) xxx, xxx–xxx
King Saud University
Journal of Saudi Chemical Society
www.ksu.edu.sa
www.sciencedirect.com
Please cite this article in press as: A.M. El-Didamony, M.O. Abo-Elsoad, Kinetic spectrophotometric method for the determination of some fourth generation
fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
1319-6103 ª2013 Production and hosting by Elsevier B.V. on behalf of King Saud University.
http://dx.doi.org/10.1016/j.jscs.2013.10.003
tant staphylococcus and streptococcus pathogens, compared
with older fluoroquinolones [8,9].
Gemifloxacin (GMFX) (R,S)-7(3-aminomethyl-4-syn-
methoxyimino-1-pyrrolidinyl)-1-cyclopropyl-6-fluro-1, 4 dihy-
dro-4-oxo-1, 2 naphthyridine-3-carboxylic acid (Fig. 1a) [10].
Gemifloxacin is an antibacterial compound with enhanced
affinity for bacterial topoisomerase IV and is being used for
the treatment of respiratory and urinary tract infections. The
compound has a broad spectrum of activity against gram-po-
sitive and gram-negative bacteria. Gemifloxacin mesylate is
not official in any pharmacopoeia.
Literature survey revealed that few analytical methods have
been reported for the estimation of GMFX in pharmaceutical
preparations or human plasma by visible spectrophotometry
[11,12], capillary electrophoresis [13], high performance liquid
chromatography–tandem mass spectrometry [14,15], and
microchip electrophoresis [16]. These methods were related
with some major drawbacks such as having inadequate sensi-
tivity, being time-consuming, tedious, and dedicated to sophis-
ticated and requiring expensive instruments.
Gatifloxacin (GTFX) (1-cyclopropyl-6-fluoro-1,4-dihydro-8-
methoxyl-7-(3-methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic
acid), (Fig. 1b) [17]. It is widely used in the treatment of urinary
tract infection, acute bacterial sinusitis, community acquired pneu-
monia, and acute bacterial exacerbation of chronic bronchitis [18].
Gatifloxacin is an antibacterial drug having selective antimicrobial
activity against streptococcus pneumoniae and penicillin-resistant
pneumococci. It is also active against anaerobic pathogen, bacte-
roides fragilis, and mouth anaerobes [19]. It is available in the tablet
form and not official in any pharmacopoeia.
Several techniques have been proposed for the quantifica-
tion of GTFX in pure, pharmaceutical dosage forms and in
biological fluids by titrimetry (Marona et al., 2003), voltamme-
try [20,21], chromatography [22,23,24,25,26,27], capillary elec-
trophoresis [28], atomic absorption spectrometry [29],
chemiluminescence [30], fluorimetry, [31]; and [32] and spectro-
photometry [29,33,34,35,36]. The titrimetry is insensitive and
time consuming. The voltammetric, chromatographic, electro-
phoretic, atomic absorption spectrometric and chemilumino-
metric methods utilized dedicated and/or expensive
instruments that are not available in most quality control lab-
oratories’ analytical technique. Spectrophotometry is consid-
ered the most convenient analytical technique, because of its
inherent simplicity, low cost, and wide availability in most
quality control laboratories [37]. However, few spectrophoto-
metric methods were reported for the determination of GTFX
in its pharmaceutical dosage forms [29,33,34,35,36]. These
methods were associated with some major drawbacks such as
decreased selectivity due to measurement in ultraviolet region,
[33] and/or decreased simplicity of the assay procedure e.g. te-
dious precipitation, [29] or liquid–liquid extraction steps are
based on the formation of ion-pair complex [36].
The kinetic spectrophotometric method offers an easy, less
time consuming, sensitive analysis, by using simple and avail-
able reagents, which are able to be used for routine determina-
tions of drug substances. Therefore kinetic spectrophotometric
analysis is one of the major interests of analytical pharmacy.
This work represents the first attempt at assaying gemifloxacin
(GMFX) and gatifloxacin (GTFX) in pharmaceutical prepara-
tions by the use of the kinetic spectrophotometric method. The
method is based on oxidizing the drugs with alkaline potas-
sium permanganate. The reaction is followed up spectrophoto-
metrically and the rate of change of absorbance at 604 nm is
measured. The fixed time method is adopted after full investi-
gation and understanding of the kinetics of the reaction. The
proposed method is simple, accurate and sensitive.
2. Experimental
2.1. Apparatus
All the absorbance spectral measurements were made using
spectroscan 80 D double-beam UV/Vis spectrophotometer
(Biotech Engineering Ltd., UK), with a wavelength range of
190–1100 nm, spectral bandwidth 2.0 nm, with 10 mm
matched quartz cells. A water bath shaker was used to control
the heating temperature for color development.
2.2. Reagents and solutions
All chemicals and reagents used were of analytical grade. High
purity double distilled water was used throughout.
i. Standard stock solutions of GMFX and GTFX containing
200 lgmL
1
were prepared separately in distilled water.
GMFX and GTFX were kindly supplied from the Egyptian
International Pharmaceutical Industries Company (EIPI-
CO), Egypt. Samples of adrenergic blocker drugs were gen-
erously supplied by their respective manufacturers and were
used without further purification. The stock and working
standard solutions must be freshly prepared.
ii. Commercial dosage forms of GMFX (320 mg/tablet
Floxgurad, product of Al-Debeiky Pharma, Al-Obour
City, Egypt) and GTFX (Tymer, sterile ophthalmic
solution 0.3% produced by JamJoom Pharmaceuticals,
Jeddah, Saudi Arabia).
Figure 1 Chemical structure of (a) gemifloxacin and (b)
gatifloxacin.
2 A.M. El-Didamony, M.O. Abo-Elsoad
Please cite this article in press as: A.M. El-Didamony, M.O. Abo-Elsoad, Kinetic spectrophotometric method for the determination of some fourth generation
fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
iii. Potassium manganate (Merck, Germany), 5 ·10
3
M
aqueous solutions, should be freshly prepared and its
molarity was checked titrimetrically.
iv. NaOH (BDH, UK), 1.0 M aqueous solution was pre-
pared by dissolving 4.0 g of the chemical in 100 mL of
water.
2.3. General recommended procedure
Accurate volumes of GMFX or GTFX working solution over
the concentration range of 4–36 lgmL
1
and 4–40 lgmL
1
,
respectively were transferred into a series of 10 mL standard
flasks. To each flask 1.5 mL of 1.0 M sodium hydroxide fol-
lowed by 2.0 mL of 5 ·10
3
M potassium permanganate was
added. Complete to volume with water and mix well. After
mixing, the reaction mixture was transferred to a thermostati-
cally controlled water bath adjusted to 70 ± 2 Cor
50 ± 2 C, at fixed time of 15 min for GMFX and GTFX,
respectively. Cool and then, measure the absorbance of solu-
tions at 604 nm against reagent blank treated similarly. Con-
struct the calibration graph by plotting the final
concentration of the drug against the absorbance values, mea-
sured at a fixed time of 15 min. Alternatively, derive the corre-
sponding regression equation.
2.4. Procedures for pharmaceutical formulations
2.4.1. Procedure for the tablets
Ten tablets of floxguard each containing 320 mg of GMFX
were crushed, powdered, weighed out and the average weight
of one tablet was determined. An accurately weighed portion,
equivalent to 20 mg was dissolved in about 10 mL of distilled
water and any remaining residue was removed by filtration.
The filtered solution was then transferred into a 100 mL cali-
brated flask and diluted to 100 mL with water. The nominal
content of the tablet was assayed from the calibration curve.
2.4.2. Procedure for eye drops
The contents of five tymer samples (each 1.0 mL contains 3 mg
of GTFX) were mixed. A volume equivalent to 20 mg of
GTFX was transferred to a 100 mL volumetric flask and made
up to the mark with water. Suitable dilution was made to fit
the applicable concentration range and the above described
procedures were followed. The nominal content of the bottles
was calculated either from calibration graph or using the
regression equation.
3. Results and discussion
3.1. Optimization of parameters
The absorption spectrum of aqueous potassium permanganate
solution in alkaline medium exhibited an absorption band at
530 nm. The additions of any of the studied drugs to this solu-
tion produce a new characteristic band at 604 nm (Fig. 2). This
band is due to the formation of manganate ion, which resulted
from the oxidation of GMFX by potassium permanganate in
alkaline medium. The intensity of the color increases with
time; therefore a kinetically based method was developed for
the determination of GMFX and GTFX in their pharmaceuti-
cal formulations. The various experimental factors affecting
the development and stability of the reaction product were
studied and optimized. Such factors which were changed indi-
vidually, include concentration of the reagents (KMnO
4
and
NaOH), order of addition of reagents, temperature, time of
heating and buffer solutions.
3.1.1. Effect of KMnO
4
concentration
Potassium permanganate oxidizes GMFX and GTFX in the
presence of sodium hydroxide to form the green product
resulting from the reduction of permanganate to manganate.
Different concentrations of potassium permanganate from
1·10
4
to 1.25 ·10
3
M were studied. The absorbance at
604 nm was measured at a fixed time of 15 min. The reaction
increased substantially with increasing the concentration of
KMnO
4
(Fig. 3). Maximum absorbance was obtained when
2.0 mL of KMnO
4
solution was used (the concentration in
the final assay solution was 1.0 ·10
3
M). Further increase
in the concentration had no effect on the reaction.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
450 500 550 600 650 70
0
Wavelength, nm
Absorbance
a
b
Figure 2 Absorption spectrum of GMFX (36 lgmL
1
) after
reaction with KMnO
4
(1 ·10
3
M): (a) manganate ions and (b)
reagent blank.
0
0.2
0.4
0.6
0.8
1
1.2
0.2 0.7 1.2 1.7 2.2
Absorbance
mLadded of 5×10-3 M KMnO4
GMFX
GTFX
Figure 3 Effect of the volume of 5 ·10
3
M KMnO
4
on the
reaction of GMFX (36 lgmL
1
) and GTFX (40 lgmL
1
) with
alkaline potassium permanganate. The reactions were carried out
at room temperature (25 ± 2 C).
spectrophotometric determination of GMFX and GTFX 3
Please cite this article in press as: A.M. El-Didamony, M.O. Abo-Elsoad, Kinetic spectrophotometric method for the determination of some fourth generation
fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
3.1.2. Effect of NaOH concentration
NaOH concentration on the reaction rate was studied using
0.2–3.0 mL of 1.0 M NaOH. It was found that increasing the
volume of 1.0 M NaOH, would increase the absorbance of
the reaction product up to 1.0 mL. It was also observed that
there was no significant difference in the absorbance of reac-
tant solutions at NaOH concentrations above 1.0 mL, while
decreasing NaOH concentration resulted in lower absorbance
values. Therefore, 1.5 mL of 1.0 M NaOH was found to be
the most suitable concentration for maximum absorbance
(Fig. 4). The effect of different Na salt buffers, particularly
acetate, borate, carbonate, oxalate and phosphate, was investi-
gated. No effect was observed when 0.01 M of these buffers
was added to a solution.
3.1.3. Effect of time
To study the effect of time, a fixed concentration of the studied
drugs (36 lgmL
1
) was made to react with 2.0 mL of
5·10
3
M KMnO
4
solution; absorbance readings were re-
corded at different times in the range of 2.0–40 min. The oxi-
dation reaction was completed in 35 min and the color was
stable up to 60 min in the presence of the reaction product(s)
(Fig. 5).
3.1.4. Effect of temperature
Preliminary test proved that a complete color formation was
achieved by heating the resulting solution in a thermostati-
cally-controlled water bath. Different temperature settings
were used with constant heating time. Increasing temperature
of the water bath was found to produce a proportional in-
crease in absorbance (Fig. 6). So, trials have been done to carry
out the reaction at higher temperatures but unwanted chemical
changes e.g. precipitation of manganese (II) dioxide might oc-
cur. To avoid this and for the sake of good results, the opti-
mum temperature of 70 ± 2 C and 50 ± 2 C was selected
for the determination of GMFX and GTFX, respectively.
The time of heating is an essential part of the experiment. Dif-
ferent time intervals were tested to ascertain the time after
which the solution attains its highest absorbance. It was found
that heating for 15 min gave the highest absorbance readings
for each drug. Excessive heating time did not produce a signif-
icant increase in absorbance readings (Fig. 7).
3.1.5. Order of addition
The experimental parameters were fixed, and further experi-
ments were performed to test the influence of the order of
the addition of reactants. It was found that the order (KMnO
4
,
NaOH and drug), results in maximum absorbance. Addition
orders, other than those described in the procedure, gave lower
results.
0.4
0.6
0.8
1
1.2
1.4
0 0.5 1 1.5 2 2.5 3
Absorbance
mL added of 1.0 M NaOH
GMFX
GTFX
Figure 4 Effect of the volume of 1.0 M NaOH on the reaction of
GMFX (36 lgmL
1
) and GTFX (40 lgmL
1
) with alkaline
potassium permanganate. The reactions were carried out at room
temperature (25 ± 2 C).
0.3
0.5
0.7
0.9
1.1
5 10152025303540
Absorbance
Time, min
GMFX
GTFX
Figure 5 Effect of time on the reaction of GMFX (36 lgmL
1
)
and GTFX (40 lgmL
1
) with alkaline potassium permanganate.
The reactions were carried out at room temperature (25 ± 2 C).
0.5
0.7
0.9
1.1
1.3
1.5
25 40 55 70 85 100
Absorbance
Temp.,oC
GMFX
GTFX
Figure 6 Effect of temperature on the reaction of GMFX
(36 lgmL
1
) and GTFX (40 lgmL
1
) with alkaline potassium
permanganate.
0.9
1
1.1
1.2
1.3
5101520253
0
Absorbance
Heating time, min
GMFX
GTFX
Figure 7 Effect of heating time on the reaction of GMFX
(36 lgmL
1
) and GTFX (40 lgmL
1
) with alkaline potassium
permanganate.
4 A.M. El-Didamony, M.O. Abo-Elsoad
Please cite this article in press as: A.M. El-Didamony, M.O. Abo-Elsoad, Kinetic spectrophotometric method for the determination of some fourth generation
fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
3.1.6. Stoichiometric ratio
The stoichiometric ratio between studied drugs and potassium
permanganate was determined by the limiting logarithmic
method, [38] by performing two sets of experiments. In the first
set, the concentration of drug was varied keeping a constant
concentration of KMnO
4
. In the second set of experiment,
concentration of drug was kept constant while varying the con-
centration of KMnO
4
. The logarithm of the absorbance was
plotted against the logarithm of the respective varied concen-
tration of drug or KMnO
4
(Figs. 8 and 9). The slopes of the
two straight lines were calculated and found to be unity in each
case. Thus, the stoichiometric ratio between each drug and
potassium permanganate was found to be 1:1.
3.2. Evaluation of the kinetic methods
The quantitative determination of GMFX and GTFX under
the optimized experimental conditions outlined above would
result in a pseudo-first order reaction with respect to their con-
centration where, KMnO
4
concentration was at least 30 times
the concentration of each drug, and NaOH concentration was
at least 600 times the initial concentration of each drug. How-
ever, the rates will be directly proportional to drug concentra-
tion in a pseudo-first order rate equation as follows:
Rate ¼K0þ½Cnð1Þ
Eq. (1) was the basis for several experiments, which were car-
ried out to obtain drug concentration. The rate constant, fixed-
concentration, and fixed time methods [39,40] were tried and
the most suitable analytical method was selected taking into
account the applicability, the sensitivity, the correlation coeffi-
cient (r), and the intercept. Taking logarithms of rates and con-
centrations (Table 1), the above equation becomes:
log K¼log DA=Dt¼log k0þnlog Cð2Þ
where Ais the absorbance, tis the time in seconds and Kis the
pseudo-first order rate constant. Regression of log (K) versus
log [C] gave the regression equations:
log K¼log DA=Dt¼0:2524 þ0:6389 log C;
r¼0:9971 for GMFX
log K¼log DA=Dt¼0:7526 þ0:8835 log C;
r¼0:9997 for GTFX
A straight line with slope values of (n1) was obtained con-
firming that the reaction was first order.
3.2.1. Fixed-time method
Reaction rates were determined for different concentrations of
the investigated drugs. At a preselected fixed time, which was
accurately determined, the absorbance was measured. Calibra-
tion graph of absorbance versus initial concentration of drugs
was established at fixed time of 2, 5, 7, 10, 13, 15, 20, 25 and
30 min (Figs. 10 and 11) with the regression equation assem-
bled in Table 2. It is clear that the slope increases with time
and the most acceptable values of the correlation coefficient
(r) and the intercept were obtained for a fixed time of
15 min, which was therefore chosen as the most suitable time
interval for measurement. The analytical parameters for the
determination of drugs in pure form by the fixed time method
are shown in Table 2. After optimizing the reaction conditions,
-1.4
-1
-0.6
-0.2
0.2
-4.8 -4.3 -3.8 -3.3
log A
log C
A
B
Figure 8 Limiting logarithmic plots for the molar ratio: (A) log
Avs. log [KMnO
4
], (B) log Avs. log [GMFX].
-0.8
-0.5
-0.2
0.1
-5 -4.5 -4 -3.5 -3 -2.5 -2
log A
log C
A
B
Figure 9 Limiting logarithmic plots for the molar ratio: (A) log
Avs. log [KMnO
4
]; (B) log Avs. log [GTFX].
Table 1 Relation between reaction rates and concentrations.
Drug log DA/Dtlog [drug] Regression equation, log DA/Dt= log k
-
+nlog CCorrelation coefficient (r)
GMFX 3.041 4.387 log DA/Dt=0.2524 + 0.6389 log C0.9971
2.886 4.289
2.762 4.211
2.674 4.143
2.638 4.086
3.380 4.371
3.100 4.274
GTFX 2.951 4.195 log DA/Dt=0.7526 + 0.8835 log C0.9997
2.848 4.128
2.758 4.070
spectrophotometric determination of GMFX and GTFX 5
Please cite this article in press as: A.M. El-Didamony, M.O. Abo-Elsoad, Kinetic spectrophotometric method for the determination of some fourth generation
fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
the fixed time method was applied to the determination of the
studied drugs in pure form over the concentration range of 4–
36 and 4–40 lgmL
1
for GMFX and GTFX, respectively.
3.2.2. Rate constant method
Graphs of log (absorbance) versus time for GMFX concentra-
tions in the range of 2.05 ·10
5
–1.02 ·10
4
M and GTFX
concentrations in the range of 2.12 ·10
5
–1.06 ·10
4
M were
plotted. Pseudo-first-order rate constants (K) corresponding to
different concentrations of the investigated drugs [C] were cal-
culated from the slopes multiplied by 2.303 (Table 3).
Regression of Kvalues versus [C] gave the equations:
K¼0:0011 þ5:533C;r¼0:9839 for GMFX
K¼0:00085 þ4:739C;r¼0:9821 for GTFX
where Ais the absorbance at 604 nm and Cis the molar con-
centration. The method suffered from poor linearity as indi-
cated from rvalue, therefore this method was excluded.
3.2.3. Fixed absorbance method
Reaction rates were determined for different concentrations of
the investigated drugs. A pre-selected absorbance value was
fixed (0.5 for both GMFX and GTFX) for different concentra-
tions of the studied drugs, in the range of 2.05 ·10
5
–
1.02 ·10
4
M for GMFX and 2.12 ·10
5
to 1.06 ·10
4
M
for GTFX and the time required for each concentration to
reach the preselected absorbance value was measured in sec-
onds. The reciprocal of time (1/t) versus drug concentrations
was plotted and the following equations were obtained by lin-
ear regression:
1=t¼0:00057 þ162:28C;r¼0:9960 for GMFX
1=t¼0:0044 þ131:57C;r¼0:9965 for GTFX
The concentration ranges giving the most satisfactory calibra-
tion graphs were limited, therefore this method was abandoned.
3.3. Linearity
The kinetic curves obtained at different concentrations of
GMFX or GTFX, under the optimized conditions, were
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 5 10 15 20 25 30
Time,min
Absorbance
a
b
c
d
e
Figure 10 Absorbance–time curves for the reaction between
GMFX and KMnO
4
in aqueous medium: 2.0 mL of 5 ·10
3
M
KMnO
4
and GMFX (a) 4.10 ·10
5
(b) 5.13 ·10
5
(c)
6.15 ·10
5
, (d) 7.18 ·10
5
and (e) 8.20 ·10
5
M.
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25 30
Time, min
Absorbance
a
b
c
d
e
Figure 11 Absorbance–time curves for the reaction between
GTFX and KMnO
4
in aqueous medium: 2.0 mL of 5 ·10
3
M
KMnO
4
and GTFX: (a) 4.25 ·10
5
, (b) 5.32 ·10
5
(c)
6.38 ·10
5
, (d) 7.44 ·10
5
and (e) 8.51 ·10
5
M.
Table 2 Regression equations for the studied drugs of different concentrations at different time intervals using the fixed time method.
Drug Time, min Regression equation
*
A=a+bC Correlation coefficient (r)
GMFX 2 0.1296 + 0.0322C0.9984
5 0.2135 + 0.03668C0.9959
7 0.2583 + 0.03803C0.9954
10 0.3197 + 0.04148C0.9916
13 0.4259 + 0.04173C0.9993
15 0.4764 + 0.04285C0.9998
20 0.4992 + 0.0429C0.9939
25 0.5400 + 0.0415C0.9894
30 0.5612 + 0.04083C0.9865
20.0210 + 0.03195C0.9995
5 0.0058 + 0.03605C0.9983
7 0.0244 + 0.0391C0.9985
GTFX 10 0.0366 + 0.0417C0.9974
13 0.0590 + 0.04325C0.9987
15 0.0616 + 0.0456C0.9991
20 0.0697 + 0.04678C0.9991
25 0.0777 + .04828C0.9990
30 0.0928 + 0.0483C0.9987
*
Ais the absorbance at 610 nm and Cis the concentration in lgmL
1
.
6 A.M. El-Didamony, M.O. Abo-Elsoad
Please cite this article in press as: A.M. El-Didamony, M.O. Abo-Elsoad, Kinetic spectrophotometric method for the determination of some fourth generation
fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
processed by the fixed-time method. Calibration graphs of
absorbance versus initial concentrations of GMFX or GTFX
were established at different fixed-time intervals. It was found
that the slopes increase with time and the most acceptable val-
ues of the correlation coefficient (r) and the intercept were ob-
tained at a fixed time of 15 min for both GMFX and GTFX
which were, therefore, chosen as the most suitable time inter-
vals for measurement. The calibration graphs were linear over
the concentration range of 2.05 ·10
5
–1.02 ·10
4
M for
GMFX and 2.12 ·10
5
–1.06 ·10
4
M for GTFX. Regression
analysis indicates linear relationships with negligible inter-
cepts. Table 4 presents the analytical parameters, molar
absorptivity and the results of the statistical analysis of the
experimental data: regression equations calculated from cali-
bration graphs along with standard deviation of the slope
(S
b
) and intercept (S
a
) on the ordinate and the standard devi-
ation of residuals (S
y/x
). The high values of the correlation
coefficients of regression equations indicate good linearity
and conformity to Beer’s law.
3.4. Accuracy and precision
The accuracy and precision of the proposed kinetic spectro-
photometric method were determined in terms of intermediate
precision (intra-day and inter-day). Three different concentra-
tions of the studied drugs were analyzed in five replicates
during the same day (intra-day precision) and for seven con-
secutive days (inter-day precision). The analytical results ob-
tained from the investigation are summarized in Table 5.
The percentage relative standard deviation (RSD%) for the re-
sults did not exceed 1.4% (Table 5), proving the high
Table 3 Values of Kcalculated from slopes of log Aversus tgraphs multiplied by 2.303 for different concentrations of the studied
drugs.
Drug [Drug] KRegression equation Correlation coefficient (r)
GMFX 2.05 ·10
5
9.442 ·10
4
K=0.0011 + 5.533C0.9839
4.10 ·10
5
8.728 ·10
4
6.15 ·10
5
6.701 ·10
4
8.20 ·10
5
6.125 ·10
4
1.02 ·10
4
5.066 ·10
4
2.12 ·10
5
7.622 ·10
4
4.25 ·10
5
6.310 ·10
4
GTFX 6.38 ·10
5
5.135 ·10
4
K=0.00085 + 4.739C0.9821
8.51 ·10
5
4.652 ·10
4
1.06 ·10
4
4.490 ·10
4
Table 4 Analytical parameters for the determination of
GMFX and GTFX in pure form using the fixed time method.
Parameters GMFX GTFX
k
max
, nm 610 610
Temperature, C 70±2 50±2
Heating time, min 15 15
Beer’s law limit, lgmL
1
4–36 4–40
Molar absorptivity, L mol
1
cm
1
1.21 ·10
4
1.18 ·10
4
Sandell’s sensitivity, ng cm
2
29.72 31.97
Correlation coefficient (r) 0.9998 0.9991
Regression equation
*
Slope (b) 0.0299 0.0312
Intercept (a) 0.2930 0.1482
S
y/x
8.36 ·10
3
1.85 ·10
3
SD of slope (S
b
) 1.22 ·10
3
2.72 ·10
4
SD of intercept (S
a
) 7.79 ·10
3
1.73 ·10
3
LOD, lgmL
1
0.0778 0.0778
LOQ, lgmL
1
0.2951 0.2591
*
Regression equation: A=a+bC, where Cis the concentration
of drug (lgmL
1
).
Table 5 Intra- and inter-day precision and accuracy of the reaction of GMFX and GTFX by the proposed kinetic spectrophotometric
method.
Frequency of analysis Drugs Taken, lgmL
1
Recovery, % RSD
a
,% Er
b
%SE
c
Intra GMFX 8 99.691 1.295 6.0 ·10
3
3.316 ·10
3
20 99.998 0.841 2.0 ·10
3
3.872 ·10
3
32 99.999 0.461 2.0 ·10
3
2.549 ·10
3
Enter 8 99.999 1.391 4.0 ·10
3
3.674 ·10
3
20 99.999 0.491 3.0 ·10
3
2.236 ·10
3
32 99.999 0.519 0.012 2.915 ·10
3
Intra GTFX 8 99.999 0.634 4.4 ·10
3
1.224 ·10
3
20 99.998 0.976 3.0 ·10
3
3.741 ·10
3
32 99.999 0.118 2.2 ·10
3
6.244 ·10
3
Enter 8 99.998 0.618 0.025 1.224 ·10
3
20 99.999 0.405 4.0 ·10
3
1.581 ·10
3
32 99.998 0.340 6.0 ·10
3
1.870 ·10
3
a
Relative standard deviation for five determinations.
b
Er, relative error.
c
Standard error.
spectrophotometric determination of GMFX and GTFX 7
Please cite this article in press as: A.M. El-Didamony, M.O. Abo-Elsoad, Kinetic spectrophotometric method for the determination of some fourth generation
fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
reproducibility of the results and the precision of the method.
This good level of precision was suitable for quality control
analysis of the studied drugs.
3.5. Analytical applications
The fixed-time method has been successfully applied to deter-
mine GMFX in tablets and GTFX in eye drops. The concen-
trations of each drug were calculated using the corresponding
regression equations at fixed time of 15 min for both GMFX
and GTFX. The results obtained are presented in Table 6. Sta-
tistical analysis of the results obtained by both the proposed
method and reported spectrophotometric methods, [11,12,36]
revealed no significant difference in the performance of the
two methods regarding accuracy and precision as revealed by
t-test and F-test, respectively (Table 6).
4. Conclusion
The proposed method can be easily applied to the determina-
tion of GMFX and GTFX in pure and dosage forms, which do
not require elaborate treatment of the analyte and tedious
extraction of the chromospheres produced. The proposed
method (fixed-time) is sensitive enough to enable determina-
tion of a lower amount of the drugs. These advantages encour-
age the application of the proposed method in routine quality
control of the investigated drugs in industrial laboratories. No
interference has been observed with excipients found in drug
formulations.
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Drug Formulations Nominal value Recovery
a
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GMFX Floxguard
b
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GTFX Tymer
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a
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8 A.M. El-Didamony, M.O. Abo-Elsoad
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fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
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spectrophotometric determination of GMFX and GTFX 9
Please cite this article in press as: A.M. El-Didamony, M.O. Abo-Elsoad, Kinetic spectrophotometric method for the determination of some fourth generation
fluoroquinolones in bulk and in pharmaceutical formulations, Journal of Saudi Chemical Society (2013), http://dx.doi.org/10.1016/j.jscs.2013.10.003
