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International Journal of Current Pharmaceutical Research Academic Sciences Vol 5, Issue 4, 2013 Research Article
POTENTIOMETRIC CARBON PASTE ISEs FOR DETERMINATION OF FLUOXETINE
HYDROCHLORIDE IN PHARMACEUTICAL PREPARATIONS
EMAD M. HUSSIEN, NAHLA S. ISMAIL AND FATMA M. ABDEL-GAWAD
National Organization for Drug Control and Research, Egypt. Email: [email protected]
Received: 01 July 2013, Revised and Accepted: 28 July 2013
ABSTRACT
Carbon paste ion selective electrodes for fluoxetine hydrochloride (FXCl) were prepared and characterized in terms of composition, response time and usable pH range. The electrodes were applied to assay of FXCl in the drug substance and pharmaceutical product. The electrodes are based on fluoxetinium-phosphomolebdate (FX-PM) or fluoxetinium-tetraphenylborate (FX-TPB) as an ion exchanger dissolved in dioctylphthalate (DOP) as pasting liquid. The electrodes showed a sub-Nernestian slope of 52.0 mV/decade over the concentration ranges from 3 x 10-5 to 1 x 10-2 mol/L and a near-Nernestian slope of 56.5 mV/decade over the concentration range from 4 x 10-5 to 10-2 mol/L for (FX-PM) and (FX-TPB) based electrodes, respectively. The electrodes exhibited good selectivity for fluoxetine cations with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The proposed electrodes offer the advantages of simplicity, accuracy and applicability to turbid solution Keywords: Fluoxetine hydrochloride; Carbon paste ion selective electrodes; Potentiometric determination, Prozac capsule.
Preparation of the ion exchangers
Fluoxetine hydrochloride (FXCl) ((±)-N-methyl-3-phenyl-3-[(α,α,α- The FX-TPB ion pair was prepared by mixing 100 ml of 10-2 mol/L trifluoro-p-tolyl)-oxy]propyl-amine hydrochloride) (Scheme 1) is a solution of FXCl with 100 ml of 10-2 mol/L solution of NaTPB. The selective serotonin reuptake inhibitor (SSRI) antidepressant drug, precipitate was filtered, washed thoroughly with bidistelled water, which has been widely prescribed for treatment of depression [1] and dried at room temperature and some other important disorders [2]. Fluoxetine overdoses may lead to seizures, rapid heartbeat and in worst cases to suicidal The FX-PM ion-associate was prepared by the addition of one volume of 10-2 mol/L phosphomolybdic acid to three volumes of 10-2 mol/L fluoxetine hydrochloride solution. The precipitate was filtered, washed with bidistelled water and allowed to dry at room temperature. Preparation of the electrodes
A Teflon holder (12 cm length) with a hole at one end (7 mm diameter, 3.5 mm deep) was as the electrode body. Electrical contact with carbon paste was made with a stainless-steel rod through the center of the holder. This rod can move up and down by screw movement. Modified carbon paste was prepared by mixing FX-PM or FX-TPB with DOP using 5 ml of THF. THF was Several analytical methods for the determination of fluoxetine in allowed to evaporate at room temperature. Carbon powder was pharmaceutical preparation have been developed such as then added and intimate homogenization was achieved by chromatography [3-6], spectrophotometry [7-9], voltammetry [10, careful mixing in a mortar. The paste was packed into the hole of 11]. These method are either expensive or use undesirable solvent the electrode body. The carbon paste was smoothed onto paper until it had a shiny appearance and was used directly for Previously, we reported on the construction of plastic membrane ion selective electrodes for fluoxetine [12]. A favorable characteristic of ion selective electrodes is the speed, electivity and ease of Electrochemical system
performing the assay. Herein, we extend this approach by the construction, potentiometric characterization, and analytical Potentiometric measurements were carried out with HI 9321 application of fluoxetine-selective carbon paste electrodes. The microprocessor pH meter. A saturated Ag/AgCl electrode was used proposed electrodes have the advantage of easy preparation and as an external reference electrode. The internal reference electrode generation of new active surface. The electrodes are based on the was a coated wire Ag/AgCl electrode. phosphomolebdate as ion-exchangers and dioctylphthalate (DOP) as The electrochemical system is represented as follows: Stainless steel/modified carbon paste/test solution//KCl salt
MATERIALS AND METHODS
Materials and reagents
Construction of calibration graph
Fluoxetine hydrochloride drug substance was obtained from Amriya The calibration graph for each electrode was constructed using Company (Alexandria, Egypt). Prozac capsules were from Eli-Lilly solutions of different concentrations of fluoxetine hydrochloride Company (Lilly France S.A.S., France). Sodium tetraphenylborate covering the concentration range from 10-6 to 10-2 mol/L. The cell (Na-TPB) and phosphomolybdic acid (PMA) were obtained from potential was recorded for each solution at constant stirring at room Fluka. Carbon powder and dioctylphthalate (DOP) were purchased temperature and plotted against log [FXCl]. The slope of the from Aldrich. Tetrahydrofurane (THF) was purchased from Lab- calibration graph was calculated using Nernestain equation.
Scan Analytical Science. All reagents were of chemically pure grades and bidistilled water was used throughout. Hussien et al.
Int J Curr Pharm Res, Vol 5, Issue 4, 18-22
Where: R is the gas constant, F is the Faraday equivalent and z is the Stock sample solution of Prozac capsules was prepared into 100- charge of the analyte. The term E°ISE is a constant which is the sum of mL measuring flask by dissolving an amount of the capsule all invariants in the system. powder (taken from average of 20 capsules), equivalent to 345.0 mg fluoxetine hydrochloride, in 50.0 ml bidistilled water. The Selectivity
solution was sonicated for 5 min and completed to mark with Potentiometric selectivity coefficient Kpot bidistilled water. The filtrate and washings were collected into a i,j for different inorganic and organic cations were evaluated using the separate solution method 100-ml standard volumetric flask and diluted to mark with (SSM) [13] and matched potential method (MPM) [14]. In the SSM bidistilled water. the EMF value (Ei and Ej) of the electrode in pure solution of each of An Aliquot of analyte solution containing 6.90, 10.35, and 17.25 mg the primary and the interfering ion, of equal concentration, are used for calculating the selectivity coefficient. The selectivity coefficient of drug was pipette into a 100-mL beaker, and the solution was diluted to 50 mL with bidistilled water. The solution was titrated i,j is calculated using Nickolsky-Eisenman equation. with 10-2 mol/L Na-TPB solution using the proposed electrodes. The volume of the titrant at the end point was obtained using the differential method. In the matched potential method the concentration of fluoxetine RESULTS AND DISCUSSION
hydrochloride solution was increased from ai = 1 × 10−6 mol/L Composition and characteristics of the electrodes
(reference solution) to a'i = 1 × 10−3 mol/L, and the change in potential (∆E) was recorded. Then, small amounts of a solution of an interfering Preliminary experiments showed that carbon paste electrodes, ion of concentration aj ( from 1 × 10−2 to 1 × 10−3 mol/L) was added to a which are free from ion-associate modifier have no response toward new 1 × 10−6 mol/L reference fluoxetine hydrochloride solution until the fluoxetine. Consequently, the ion associates fluoxetinium- same potential change (∆E) is achieved. The selectivity coefficient was phsphomolebdate (FX-PM), fluoxetinium-phosphotungestate (FX- calculated using the following equation: fluoxetinium-renicate tetraphenylborate (FX-TPB) were prepared and investigated as modifiers for the paste. FX-PTA was practically insoluble in the pasting liquid (DOP), and FX-RC was soluble in water, therefore, these ion-associates were not useful as modifiers and were excluded. The ion-associates, FX-TPB and FX-PM, were used for the preparation of modified carbon paste electrodes. The effect of varying the composition of the paste on the response of the Potentiometric determination of fluoxetine hydrochloride in
electrodes toward fluoxetine was investigated in terms of linear the drug substance and in prozac capsules
range, slope and detection limit. It was observed that the sensitivity Stock solution of fluoxetine hydrochloride drug substance was and linearity depend significantly on the amount (w/w %) of the prepared into 100.0 mL measuring flask by dissolving 345.0 mg modifier in the paste. Table 1 summarizes the effect of varying the fluoxetine hydrochloride drug substance in 50 mL bidistilled water composition of the paste on the response of FX- PMA and FX-TPB and diluting to mark with bidistilled water. based electrodes. Table 1: Effect of changing the composition on the response of the electrodes at room temperature
Electrode
Composition % (w/w)
Slope (mV/decade)
Detection
Ion-pair
range (mol/L)
limit (mol/L)
3.0 x 10-5 - 1.0 x 10-2 3.0 x 10-5 - 1.0 x 10-2 3.0 x 10-5 - 1.0 x 10-2 8.0 x 10-4 - 1.0 x 10-2 1.0 x 10-4 - 1.0 x 10-2 1.0 x 10-5 - 1.0 x 10-2 4.0 x 10-5 - 1.0 x 10-2 1.0 x 10-4 - 1.0 x 10-2 1.0 x 10-4 - 1.0 x 10-2 a Relative standard deviation (four preparations) A carbon paste electrode containing 5.0% FX-PM, 47.5% carbon Response time
powder and 47.5% DOP, showed a sub-Nernestian slope of 52.0±0.68 mV/decade with a linear response in the concentration The dynamic response time of the proposed electrodes was range from 3.0 x 10-5 to 1.0 x 10-2 mol/L and a detection limit of 3.0 x studied under stirring by measuring the time required to achieve a 10-5 mol/L. Whereas, a carbon paste modified with FX-TPB (5.0% steady state potential (within ± 1 mV) after successive immersion FX-TPB, 47.5% carbon powder and 47.5% DOP), exhibited a near of the electrode in a series of fluoxetine hydrochloride solutions Nernestian response of 56.5±0.36 mV/decade. The linear range and from 1.0 x 10-6 to 1.0 x 10-2 mol/L, each having a 10-fold increase the lower detection limit were 4.0 x 10-5 to 1.0 x 10-2 mol/L and 1.0 x in concentration. A small potential drift (2 mV/min.) was observed 10-5, respectively. The calibration curves of FX-PM and FX-TPB for the FX-PM based carbon paste electrode at lower modified carbon paste electrodes are shown in Figure 1. concentrations of fluoxetine hydrochloride, 10-6 and 10-5 mol/L. The cell potential remained constant (within ± 1 mV) for about 5 Calibration of the electrodes at different time intervals over four minutes at 10-4 and 10-3 mol/L. A drift in the cell potential of 1.4 weeks showed that the electrodes retained their sensitivity to mV/min was observed again when the electrode was immersed in fluoxetine for 10 days and 16 days for FX-PM and FX-TPB electrodes, 10-2 mol/L. Contrary to the FX-PM electrode, the FX-TPB electrode respectively. Afterwards, the slopes were decrease gradually to showed a small potential drift of 0.6 mV/min when the electrode reach 42 mV and 48 mV/decade for FX-PM and FX-TPB electrodes, was immersed in 10-6 mol/L. The cell potential was steady within ±1 mV at 10-5 mol/L and up to 10-2 mol/L fluoxetine hydrochloride

Hussien et al.
Int J Curr Pharm Res, Vol 5, Issue 4, 18-22
solution. Figure 2 shows the potential time response of FX-PM and independent of the pH in the range from 4 to 7 for 10-3 mol/L FX-TPB based carbon paste electrodes. fluoxetine hydrochloride solution. At higher pH (pH >7), the potential reading changes slightly due to the conversion of Effect of pH
fluoxetine hydrochloride (pKa = 8.7) to the fluoxetine base. Further In order to check the dependence of the potential of the electrodes addition of NaOH (at pH >8.7) lead to a dramatic change in the on the pH of the solution, potential-pH curves were constructed. The potential of the electrodes due to further depletion of fluoxetine pH of 10-3 mol/L fluoxetine hydrochloride solution was altered by hydrochloride and diffusion of OH- into the surface of the electrode. the addition of small volumes of 0.1 mol/L NaOH or 0.1 mol/L HCl. Interference from H+ at lower pH (pH <4) was observed for both shows that the potential of the electrodes is practically Fig. 1: Calibration curve of a) FX-PM and b) FX-TPB carbon paste electrodes.
Fig. 1: Typical potential-time plot for the response of a) FX-PM and b) FX-TPB carbon paste electrodes.
Fig. 2: Effect of pH change of 10-3 mol/L FXCl solution using a) FX-PM and b) Na-TPB based carbon paste electrodes.

Hussien et al.
Int J Curr Pharm Res, Vol 5, Issue 4, 18-22
Effect of interference
presence of high concentration of the interfering ions without fear of interference. The interference of some common inorganic cations, sugars and amino acids was investigated using the separate and matched potential method [13, 14]; the two methods were recommended by the IUPAC in 1976 and 1995, respectively. The MPM was recommended as a method that gives analytically relevant practical selectivity coefficient values and overcome the limitation of the SSM. In case of MPM, the selectivity coefficient was calculated using the concentration of the interfering ion that induces a cell potential change of ≥10 mV. The selectivity coefficient were not calculated for interfering ions which induced a cell potential change of <10 mV. The selectivity coefficients are summarized in Table 2. Due to the very small values of kMPMi,j they are tabulated as the negative logarithm –log kMPMi,j Practical calibration curves showed that there is small interference from Al3+, Fe3+ and Ce4+ at high concentration (figure 4). The selectivity coefficient values obtained by the MPM confirms a small interference from Al3+, Fe3+ and Ce4+ at high concentration whereas the SSM showed that the electrodes are extremely selective to FX ions for Al3+, Fe3+ and Ce4+, which is practically not correct. Fig. 4: Ecell-logc curves for determing the MPM selectivity
coefficient of FX-PM carbon paste electrodes for FXCl against
The selectivity coefficient values recorded in Table 2 indicate that Al3+, Fe3+ and Cr4+. The initial reference solution of FXCl was 1 x
the electrode can be used for determination of fluoxetine in 10-6 mol/L.
Table 2: Selectivity factor values
for FX- selective PVC membrane.
Interferent
Analytical application
recovery obtained was within ± 2% for the drug substance and Prozac capsule, respectively. The relative standard deviation was ≤2.0%, The proposed electrodes were proved useful for the assay of indicate reasonable repeatability and reproducibility of the proposed fluoxetine in the drug substance and pharmaceutical product by methods. The accuracy and precision of the assay of fluoxetine potentiometric titration using tetraphenylborate as a titrant. The end hydrochloride in the drug substance and in Prozac capsule using the point was determined by the first derivative method. The accuracy and proposed electrodes are summarized in Table 3. Figure 5 shows the precision were tested at three different concentration levels (6.90- potentiometric titration curves of FXCl with Na-TPB using the FX-PM 17.25 mg/50 mL), five samples were used at each level. The mean and FX-TPB electrodes. Table 3: Accuracy and precision for quantification of fluoxetine hydrochloride in the drug substance and Prozac capsule using FX-PM and
FX-TPB carbon paste electrodes.
Fluoxetine
Found ± SD
Recovery
Found ± SD
Recovery
Reported
(mg/50 ml)
(mg/50 ml)
(mg/50 ml)
method [8]
Mean ± standard deviation of five determinations.

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To compare the proposed methods to a reference method, stability and applicability over a wide pH range. The carbon paste fluoxetine in capsules was assayed by spectrophotometry using electrode has the advantage of being easy to prepare and 2,3-dichloro-5,6-dicyano-p-penzoquinone (DDQ) [8]. Statistical regeneration of the active surface. comparison using Student's t- and F-ratio tests at 95% confidence level, the calculated t- and F- values did not exceed the critical REFERENCES
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