uk journal of pharmaceutical and biosciences vol....

UK Journal of Pharmaceutical and Biosciences Vol. 2(6), 09-21, 2014 RESEARCH ARTICLE

New Two Sensors PVC- Membrane and Chemically Carbon Paste for Determination of Antidepressant Drug Escitalopram Oxalate in Bulk, Cipralex and Human Fluids Amal F. Khorshid*

Department of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, Nahda University, NUB, Beni-Sueff, 082-Egypt

Article Information

Received 22 September 2014

Received in revised form 25 Dec 2014

Accepted 27 Dec 2014

Abstract

Preparation and construction of a new polyvinyl chloride PVC-membrane and chemically

modified carbon paste (CMCP) sensors based on ion-pair exchanger escitalopram-silicotungstic

(Es-ST) (Sensor 1) and escitalopram-silicomolybdic (Es-SM) (Sensor 2). The effect of several

plasticizers and composition of ion-exchangers on the performance characteristics of the sensors

was studied. Sensors(1, 2) with 1% composition and dioctyl phthalate (DOP) as plasticizer in

PVC-membrane showed Nernstian slopes ranged from 57.5- 59.5 ±0.1 mV/decade over the

concentration ranged from 5.0 x 10-7-1.0 x 10

-2 M with the life span not less than two months and

pH 2.5-7.5 with a detection limit 0.1 nM. While in (CMCP) sensors (1, 2) exhibited with 3%

composition and tricresylphthalate (TCP) as binder an excellent Nernstian slopes 59.5, 60.5±0.5

mV/decade for 1 and 2 respectively and a wide concentration range from 1.0 x 10-7-1.0 x 10

-2 M

and pH 2.5-7.5 with a detection limit 0.5 nM. The sensors reflected high selectivity towards

different anions, cations, sugars and amino acids and was recommended by IUPAC. The

standard addition, the calibration curve and potentiometric titration methods were used for

determination escitalopram in its bulk powder, pharmaceutical tablets Cipralex, human

plasma/urine and monitoring profile for the tablet in vitro-dissolution rates. The recoveries were

excellent and with good agreement compared with British Pharmacopoeia.

Keywords:

Escitalopram Oxalate (Cipralex),

PVC-membrane,

Carbon-paste Sensor,

Potentiometry,

Vitro-dissolution rates,

British Pharmacopoeia

*Corresponding Author:

E-mail: [email protected]

Tel.: 01280875558

1 Introduction

Escitalopram Oxalate is an antidepressant drugwith a potent

selective serotonin reuptake inhibitor (SSRI) which is used for the

treatment of depression, generalized anxiety, social anxiety and

panic disorders. Escitalopram is a single isomer of the pure S-

enantiomer for the racemic phthalane bicyclic derivative of

citalopram. Escitalopram oxalate has a chemical structure S-(+)-1-

[3-(amino-dimethyl-)propyl]-1-(p-fluorophenyl)-5- oxalate of phthalan

carbonitrile as shown in Fig 1.

The empirical formula is C20H21FN2O.C2H2O4 with its weight 414.40.

Escitalopram oxalate is a white to slightly yellowish fine powder and

is freely soluble in methanol and (DMSO) dimethyl sulfoxide , soluble

in isotonic of saline solution, sparingly soluble in water and ethanol ,

insoluble in heptane with slightly soluble in ethyl acetate1,2

.

Literature survey showed several methods for the determination of

escitalopram including chromatographic HPLC3-6

, HPTLC7-10

, TLC11

,

spectrophotometric12-18

, fluorimetry19-20

, LC-MS21-24

, LC-MS/MS25

,

enantiomeric separation26

, CE27

and only one ISE method28

. A major

advantage of ISE is that it can be used very rapidly without having to

change range to measure samples with large batches covering wide

concentrations range. Achieving sufficient selectivity to measure, a

specific ion in the presence of others for the research29

. In addition, a

chemically modified sensor (CMEs) is one of the most important

electrochemical methods, which have been widely used as sensitive

and selectiveanalytical methods for the detection of the trace

amounts of biologically important compounds30,31

. CMEs have

important properties of their ability to enhance the selectivity in the

electroanalytical methods with respect for the potential and the

relatively selective interaction of the sensor mediator with the target

analyte in a coordination medium.

This work explains the formation and construction with potentiometric

characterization and analytical application of two types of ISSs for

the determination of escitalopram Oxalate. The first type based on

the formation of PVC- plastic membrane with ion-pair exchangers

escitalopram-silicotungstic (Es-ST) (Sensor 1) and escitalopram-

UK Journal of Pharmaceutical and Biosciences

Available at www.ukjpb.com ISSN: 2347-9442

Khorshid New two sensors pvc- membrane and chemically carbon paste

UK J Pharm & Biosci, 2014: 2(6); 10

silicomolybdic (Es-SM) (Sensor 2) and dioctyl phthalate (DOP) as

the best plasticizer, while the second type depends on the

construction of CMCPSs with the same ion-pair exchangers(Sensor

1 , 2) and tricresyl phthalate (TCP) as the best binder. The studying

in-vitro dissolution rate of bioavailability of poor water-soluble drug

escitalopram-oxalate that showed it is important in biopharmaceutical

quality of the product in its lifecycle. In addition, the analytical

determination of the drug in its pure state, tablets (Cipralex® 10

mg/tablet), biological fluids and the statistical treatments of the

results with respect to the official method and compared with sensors

previously reported28

.

NC

O

F

NCH3

CH3

C2H2O4

Fig 1 The chemical structure of Escitalopram Oxalate

2 Materials and Methods

2.1The Electrochemical system

The potentiometric measurements mode was carried out with a

Jenway 3510 digital pH/mV meter at 25±1 oC and Jenway 3505

digital pH/mV meter for measuring the ruggedness and pH. A

saturated calomel electrode (SCE) was used as an external

reference electrode. A techno circulator thermostat was used to

control the temperature of the test solution and for shaken the

samples. USP XXXII32

method was used to study the dissolution with

apparatus II33

, which was supplied in vitro dissolution testing for

controlled/modified-release preparations, and more uniform flow

profile. The equipment used is "SR8Plus", model CA USA Hanson

Research; with number "73-100-116" and the spectrophotometer

instrument UV-1800 Shimadzu (Japan).

2.2 Reagents and materials

All reagents used were chemically pure grade. Doubly distilled water

was used throughout all the experiments. Escitalopram Oxalate (Es-

Ox,M.wt = 414.40), and its pharmaceutical preparations (Cipralex®

10mg/tablet) were provided by H. Lundbeck Company, Cairo-

A.R.E.under License of Denmark. Silicotungstic acid (STA)

H4[SiW12O40], silicomolybdic acid (SMA) H4[SiMo12O40],

Dibutylphthalate (DBP), dioctylphthalate (DOP), tricresylphosphate

(TCP), tributylphosphate (TBP), graphite powder, poly (vinyl chloride)

(PVC) of high relative molecular weight, acetone, and

tetrahydrofuran (THF) were obtained from Aldrich.

0.5 M chloride solution for each of the following: Na+, K

+, NH4

+, Ca

2+,

Mg2+

, Ba2+

, Mn2+

, Zn2+

, Co2+

, Ni2+

, Cu2+

, Cd2+

, Pb2+

, Sr2+

, Cr3+

, Al3+

and Fe2+

solutions (1000 µg ml-1) , glucose anhydrous, lactose

monohydrate, maltose, urea, ascorbic acid, citric acid, L-threonine,

L-lysine, L-cystine, L-glycine, arginine, and L-alanine were prepared

and supplied from Aldrich. Silver nitrate and hydrochloric acid are

from local stores of NODCAR. Plasma was provided by VACSERA

(Giza, Egypt) and was used within 24 h while urine samples were

obtained from healthy volunteers.

2.3 Preparation and construction of plastic membrane sensors

Different compositions of membranes sensors were prepared. The

ion-exchangers were changed to cover the ranges of percentages

0.5-5% of each Es-ST, Es-SM. The membranes were prepared by

dissolving and mixing amounts of PVC and DOP in 5 ml THF as

solvent in Petri-dish (7.0 cm diameter) with the ion-exchangers Es-

ST or Es-SM. The total weight of constituents is fixed at 0.350 g. To

obtain uniform thickness, and homogenous the membranes were left

to dry freely in air (not less than 24 h).

For each composition, a membrane disk with 12 mm diameter was

punched from the large membrane and glued by a mixture of

(PVC+THF) to the polished end of a 2 cm long PVC plastic cap

attached by the same mixture to one end of a 10 cm glass tube

homemade sensor body. The sensors were filled with a mixture

solution of (10-1 M KCl and 10

-3M Es-Ox drug) as internal solution

and soaking in 10-3M Es-Ox drug solution. The electrochemical

system is represented as follows: Ag/AgCl/filling solution/PVC

membrane/test solution//SCE.

2.4 Preparation of carbon paste sensors

Fresh surfaces of the sensors wereprepared directly for

potentiometric measurements by wiped the surplus paste out and

squeezing more out of the paste. The exposed surface was polished

on a paper until the freshly surface showed shiny appearance.

Chemically modified carbon paste sensors were as previously

described30,31,34

.

2.5 Construction of the sensor calibration

A standard drug solutions were added to 50 ml doubly distilled water

to cover the concentration range 1.0x10-7

-1.0x10-2 M. Lower

Concentrations were prepared by appropriate dilutions. The sensor

and the reference sensor were immersed in the solution, and the emf

value was recorded at 25±l˚C, after each addition, the values were

plotted versus the negative logarithmic value of the drug

concentration (pDrug) and the resulting graph was used for



subsequent determination of unknown drug concentration from the

liner part of the curve (calibration curve method).

2.6 Effect of soaking on life span of the sensors and regeneration

The investigated conventional sensor (PVC membrane) was soaked

in 10-3 M Es-Ox drug solution at 25˚C. A calibration graph was

constructed for each sensor after different time intervals covering the

range from ½ h up to more than two months for each sensor. The

measurements were stopped when the slope of the calibration graph

deviated largely from Nernstian value and the sensor recovery

becomes out of range.

The sensor(s) regeneration was examined by freshly the reformation

of the ion-exchangers on the external gel layer of membrane. The

regeneration of the Es PVC membrane was achieved successfully by

soaking the exhausted sensor(s) for 24 h in a 1.0 x 10-2 M STA or

SMA solution, followed by soaking for 3 h in 1.0 x 10-2M Es-Oxdrug

solution.

2.7 Effect of pH on the sensor potential

The effect of pH on the test solution at different concentrations of the

Es-Ox (1.0x10-3, 1.0x10

-4 and 1.0x10

-5 M) on the potential values of

the sensor system was studied. For each concentration, 50 ml of the

drug solution were transferred to 100 ml measured cell, and the IS

sensor in conjunction with the calomel reference sensor, combined

with glass sensor were immersed in the same solution. The pH and

mV readings were recorded simultaneously. The pH for each

concentration was varied from 1.0-10.0 by adding very small

amounts of 2 M HCl and/or (0.1-1.0 M) NaOH solution. The pH-

values for each concentration were plotted against the mV-readings.

2.8 The selectivity of sensors

The matched potential method35,36

was recommended by IUPAC as a

method that gives analytically relevant practical selectivity coefficient

values. To study the selectivity coefficients of different interfering ion

for the IS sensors, a reference solution (aA) is added to the drug so

give a final concentration of (a-A), the change in potential (ΔΕ) is thus

measured. In addition, a reference solution containing the same

concentration (aA), the additional amount of the interference ion with

concentration not less than tenth times the concentration of the drug

that cause or reached the same change (ΔΕ) value so determined

(aj). The following equation is used to calculate the selectivity values

ofpot

JEs, zKlog :

Where: aA- is the initial concentration of drug, adrug is the activity of the

added drug, and aj is the activity of the added interfering ion

producing the same increase in potential.

2.9.1 Potentiometric determination of Es-Ox

The standard additions method was achieved by adding certain

volumes of standard drug solution to 50 ml water containing different

volumes of the Es-Ox drug in its pure state, pharmaceutical

preparation (tablets), and in human biological fluids plasma/urine

samples spiked with known volumes of the Es-Ox drug. The jump in

mV reading was recording for each increment and used to calculate

the concentration of the drug in sample solution using the following

equation [37]:

Vs Vx Cx = Cs (ـــــــــــــــ) (10

n (ΔΕ//S)(ــــــــــــــ -

-1

Vx+VS VS+Vx

Where Cx is the concentration to be calculated, Vx is the volume of

the original sample solution, Vs and Cs are the volume and

concentration of the standard solution added to the sample to be

analyzed, respectively, ΔΕ is the change in potential after addition of

certain volume of standard solution, and S is the slope of the

calibration graph.

2.9.2 Analysis of pharmaceutical preparation

20 tablets of (Cipralex® 10 mg/tablet) were powdered and weighed

(200-250 mg) portion from each was mixed with 50 ml doubly

distilled water, using the mechanical shaker for shaken in an about

30 min, filtered into a 100 ml volumetric flask and the solution was

filled to the mark with doubly distilled water and shaken. Different

known amounts of the solution (1.0-10 ml) were putted and

subjected to the potentiometric determination.

2.9.3 In spiked human plasma

Half ml drug of Es-Ox solution was taken from the concentration

1x10-3, 1x10

-4 and 1x10

-5 M in centrifugation shaking tubes 20-ml

stoppered and spiked with 4.5 ml plasma separately in each tube.

Adjusted the pH with phosphate buffer 6 then immersed the modified

sensor in conjunction with the calomel electrode taken the reading of

mV for each tube and washed with water between measurements.

From emf produced for each solution, the concentration of Es-Ox

drug was determined from the corresponding calibration and

standard addition methods.

2.9.4 In spiked human urine

Different quantities of the concentrations from 1.0x10-6 to 5.0x10

-4 M

Es-Ox drugs were putted in 100 ml volumetric flask spiked with five

ml urine and shaking for 5 min, then completed to the mark with

doubly redistilled water. A small addition of 0.01 M HCl (0.1– 2.0 ml)



was putted to adjust the pH from 4 to 5. The spiked urine was

determinedby the standard addition method for drug determination.

2.10 Content uniformity of Es tablets

Ten tablets of Cipralex® 10 mg/tablet was putted in 100 ml

measuring flask dissolved with doubly bidistilled water until 50 mL

mark then each sensor was immediately immersed in the sample

solution three times, washed between each individual measurement

with redistilled water to reach steady potential. Using the mean

potential from the calibration graph the content uniformity was

determined while for the spectrophotometric measurements by using

the standard solution employing UV absorbance λ max 240 nm.

2.11 Dissolution

In vitro release study, using USP XXXII32

apparatus II(paddle

method), one tablet of Cipralex® 10 mg/tablet was placed in gastric

media so the dissolution medium pH 1.2 (900 ml of 0.01 M HCl) was

maintained at 37±0.5˚C for 1 h.The revolution per minute dissolution

speed of the escitalopram tablet is measured at (90 rpm), close to

coated tablet with its physiological conditions. At intervals of time, the

potential values were recorded from the cell containing the

investigated sensor in conjunction with (SCE) reference sensor and

the amount of releasing was calculated from the calibration graph. In

the spectrophotometric measurements, five ml of the dissolution

solution were withdrawn then filtered and diluted with 0.01 M HCl

sothe concentration of samples was used in analyzed UV

spectrophotometer (1800, Shimadzu, Japan) and the absorbencies

were measured at λ max 240 nm. For drug release calculation the

calibration graph was used.

3 Results and Discussions

3.1 The Optimum composition of PVC membrane/ CMCPS

In plastic membrane sensors, the amount of the plasticizer should be

to the extent that produces a membrane of good physical properties

and at the same time plays efficiently its role as a solvent mediator

for the ion-exchanger(s) (lipophilic salts) [38].In this work, the ratio of

the plasticizer to polymer (PVC) was always 1:1 w/wand containing

one of the lipophilic salt, escitalopram-silicotungstic (Es-ST) (Sensor

1) and/or escitalopram-silicomolybdic (Es-SM) (Sensor 2).The

composition of each of these membranes or pastes was varied to

reach the optimum composition exhibiting the best performance

characteristics, (slope of calibration graph, concentration range and

reproducibility of the results) table 1.

Five plasticizers with differentpolarities, including DBP, TBP, TCP,

DOP and 2-NPPE was used to study the influence of the plasticizer

in PVC membrane or binder in CMCPs.The sensors in PVC

membrane containing DOP generally showed better potentiometric

responses, while in CMCPs TCP is the best, i.e. the sensitivity and

the linearity of the calibration plots. This is attributed to DOP in PVC

or TCP in CMCPs, as a low polarity mediator, for incorporation of the

highly lipophilesEs+ ion into the membrane prior or the paste binder

to its exchange with the soft ion-exchanger(s).

In addition among the different compositions studied1% composition

and dioctyl phthalate (DOP) as plasticizer in PVC-membrane showed

Nernstian slopes ranged from 57.5-59.5±0.1 mV/decade over the

concentration ranged from 5.0 x 10-7-1.0 x 10

-2 M with the life span

not less than two months and pH 2.5-7.5 with a detection limit 0.1

nM. While in (CMCP) sensors (1, 2) exhibited with 3%

compositionand tricresyl phthalate (TCP) as binder an excellent

Nernstian slopes 59.5, 60.5±0.5 mV/decade for 1 and 2 respectively

and a wide concentration range from 1.0 x 10-7

-1.0 x 10-2

M and pH

2.5-7.5 with a detection limit 0.5 nM.

3.2 Effect of soaking on life span and regeneration

In the PVC membrane, the effect of soaking on the performance

characteristics of the Es-sensors was studied for variable intervals of

time. Continuous soaking of the sensors for prelongated intervals of

time affected negatively their response to the drug cation. The

soaking has negative value effect may be due to the ion-

exchanger(s) leaching with plasticizer in the bathing solution that is

related to the diffusion rates and the distribution equilibria. The other

explanation can be attributed to the solvation by the water molecules

from the bulk solution into the surface of the membrane where the

lipophilic salts increase slow solvation, which leads to slowly leached

out with limiting the sensor life39

. As shown in table 2 and fig. 2.

After regeneration of the exhausted sensor characteristics (linear

concentration range, limit of detection, and slope 1x10-5-1x10

-2,

7.6x10-6 M and 38, 36 mV/decade for sensors1,2 respectively, were

changed to 1x10-5-1x10

-2, 3.5x10

-6 M and 55, 54 mV/decade for

sensors 1, 2 respectively. This can be attributed to the formation of

Es-ST or Es-SM after transferring the sensor from the drug to STA

and SMA solutions.

The effect of time on the performance of the CMCPS was studied by

measuring the slope at variable intervals of time starting from 30 min

reaching to 3 months. The results indicated that the life span (t), of

the sensors, in general, is more than those of the similar

conventional plastic membrane sensors. It is obvious that after

cutting and polishing the sensors surface, the slopes of the sensors

increase again as new sensor. The life span of the surface of the Es-

CMCPE sensor is at least or more than 90 days. As shown in table 2

3.3 Reproducibility of the Sensor

The repeatability examination for the potential reading of the Es-ST

sensor (1) and Es-SM sensor (2)/ PVC membrane was studied by

the subsequent measurements in 1.0 x 10-3 M Es-Ox solution then



followed by measuring the first set of at 1.0 x 10-4 M solution Es-Ox.

The standard deviation values for sensors are given in table 3 by

measuring emf for six replicate measurements. The obtained values

indicate the repeatability of the potential response of the sensors is

shown excellent results. In addition, the slope of the calibration graph

forEs-ST or Es-SM /CMCPS was nearly constant due to polishing

for any time taken days but starts to decrease gradually without

polishing so it consider as a new sensor with cutting and polishing to

the sensor. Table 3 exhibited the standard deviation values of

measuring emf for six replicate measurements obtained for each

type.

The dynamic response time40

was taken for any sensor by recording

the time required to achieve a steady-state potential (within ± 1 mV)

after subsequence immersions of the sensor in a series of Es- drug

solutions, each having a 10-fold increase in concentration from 1.0 x

10-7 to 1.0 x 10

-2 M. The practical response time was followed inEs-

Ox concentration up to be 10-fold.The sensors reached steady

potential differ in PVC than in CMCP where in CMCPS is less than

PVC. At the solution–paste interface, the kinetics of association–

dissociation of the ionophores with escitalopram ion is probably fast

exchange. The potential–time plot for the response of the sensor Es-

/PVC orCMCPs is shown in Fig. 3.

3.5 Effect of pH

The potential of the pH profile is obtained in the studying Es-

PVC/CMCPs and the responses of the sensors are constant over the

pH range 2.5–7.5. Inthat range the sensor can be safely used for the

determination of the Es-drug and there is no need to adjust the pH or

use buffer solution, as the drug solution is in the allowable or working

range of the pH of the sensors. It can be seen from Fig. 4 that at pH

values lower than the 2.5 pH ranges, the decrease of potential

readings can be related to interference of hydronium ion while at pH

values higher than pH 7.5 the formation of free base of escitalopram

at pH values higher than 7.5 decreases of the protonated species in

the test solutions leads to gradually decrease of the potential

readings.

3.6 Selectivity of the sensors

The sensors response towards different substances and ionic

species such as inorganic / organic cations, sugars, and amino acids

that may be present in the pharmaceutical preparations was

examined by MPM conditions for sensors 1, 2 in PVC and/ or CMCP

so the values of selectivity coefficients were used to evaluate of their

interference. The inorganic cations do not interfere due to their

mobility and permeability is difference both in PVC and/ or CMCP as

compared to escitalopram cation. For sugars and amino acids,the

high selectivity is related to the difference in polarity and lipophilic

nature of their molecules relative to escitalopram cation as shown in

table 4.

3.7 Validation of the proposed method

3.7.1 Linearity and detection limit (LOD)

The value of LOD for the proposed method is indicting the sensitivity

for detection the very small concentrations of Es reach to 0.1, 0.5nM

for PVC and/or CMCPS respectively. The correlation coefficient (r)

and other statistical parameters were listed in table 1.

3.7.2 Accuracy

The accuracy of the proposed PVC/CMCPS methods were

investigated by the determination of Es-Ox in its pharmaceutical

preparations without interfering from the co formulated adjuvant as

indicated by the mean recovery value of 99.75±0.08, 97.65±0.05

mV/decad for sensor 1, 2 in PVC and 99.87±0.04, 99.39±0.06

mV/decad for the investigated sensors 1, 2 in CMCP.

3.7.3 Precision

The relative standard deviation (% RDS) of the PVC/CMCPS

methods was tested by repeating the proposed method for analysis

of the investigated Es-Ox in intra-day (within the day) and inter-day

(consecutive days) to six replicates. The precision measured as

percentage of % RSD values obtained which are less than 2%,

indicating good precision.

3.8 Analytical applications

3.8.1 In PVC

For PVC sensors the analytical determination of the drug in its pure

state, tablets, and plasma/urine by the standard addition method,

calibration curve37

and potentiometric titration which are frequently

the most, applied in analytical application. The methodssuccessfully

were proved for the determination of escitalopram ions. The data

reflect the high validation for linearity, the investigated sensors for

determination of escitalopram ion and its statistical data treatments

in comparison with official methods1,2

. As shown in tables 5 and table

6.

3.8.2 In CMCP

The determination of Es shows that a wide concentration range of

the drug can be determined by the investigated sensors 1, 2 by

CMCP with high precision and accuracy. In addition, plasma/urine

samples the standard addition technique was applied to overcome

the matrix effects in these samples. Also, the response times of the

CMCP sensors are instant (within10 s), so the sensors are very

rapidly transferred back and forth between the biological human

samples and washed by the bi-distilled water between

measurements to protect the sensing component from adhering to



the surface of some matrix components. It is concluded that the

CMCP sensors can be applied successfully in vitro studies or for

clinical use. This confirms that limit of quantification (LOQ) and the

sensitivity are adequate for determination of escitalopram oxalate in

pharmacokinetic studies and the data are summarized in table 5.

Table 1 Composition and slope of calibration curves for Es- PVC membrane and CMCP sensors at 25.0±0.1˚C

Composition % (w/w) Slope

Es-ST PVC DOP C.R. (M) LOD (M) (mV/decade) R(s)

0.5 49.75 49.75 5.55 x 10-7- 1.0 x 10

-2 7.90 x 10

-7 58.5±0.1 ≤14

1.0* 49.50 49.50 5.00 x 10

-7- 1.0 x 10

-2 1.00 x 10

-8 59.5±0.1

* ≤12

3.0 48.50 48.50 6.35 x 10-7- 1.0 x 10

-2 7.90 x 10

-7 57.5±0.1 ≤14

5.0 47.50 47.50 7.45 x 10-7- 1.0 x 10

-2 7.90 x 10

-7 56.5±0.1 ≤15

7.0 46.50 46.50 7.79 x 10-7- 1.0 x 10

-2 7.90 x 10

-7 55.5±0.1 ≤15

Es-SM

0.5 49.75 49.75 6.25 x 10-7- 1.0 x 10

-2 7.90 x 10

-7 56.5±0.1 ≤14

1.0* 49.50 49.50 5.00 x 10

-7- 1.0 x 10

-2 1.25 x 10

-8 57.5±0.1

* ≤12

3.0 48.50 48.50 7.50 x 10-7- 1.0 x 10

-2 7.99 x 10

-7 56.5±0.1 ≤15

5.0 47.50 47.50 7.94 x 10-7- 1.0 x 10

-2 8.65 x 10

-7 55.5±0.1 ≤15

7.0 46.50 46.50 8.35 x 10-7- 1.0 x 10

-2 8.90 x 10

-7 54.5±0.1 ≤15

CMCPS

Composition % (w/w)

Es-ST graphite TCP C.R. (M) LOD (M) Slope R(s)

(mV/decade)

0.5 55.0 44.5 2.50 x 10-7-5.00 x 10

-3 6.50 x 10

-7 57.5±0.5 ≤8

1.0 55.0 44.0 5.00 x 10-7-1.00 x 10

-3 1.00 x 10

-7 58.5±0.5 ≤8

3.0* 55.0 42.0 1.00 x 10

-7-1.00 x10

-2 5.00 x 10

-8 60.5±0.5

* ≤5

5.0 55.0 40.0 5.00 x 10-7-1.00 x 10

-3 1.25 x 10

-7 57.5±0.5 ≤7

Es-SM TCP

0.5 55.0 44.5 7.99 x 10-7-5.00 x 10

-3 7.90 x 10

-7 56.8±0.5 ≤10

1.0 55.0 44.0 6.55 x 10-7-8.99 x 10

-3 5.50 x 10

-7 57.6±0.5 ≤7

3.0* 55.0 42.0 3.50 x 10

-7-1.00 x 10

-2 4.00 x 10

-8 59.5±0.5⃰ ≤5

5.0 55.0 40.0 7.50 x 10-7-7.31 x 10

-3 5.00 x 10

-7 57.0±0.5 ≤8

Continued Table 1: Response characteristics of the Es-ion exchangers at 95% confidence intervals, average of six replicates at

25.0±0.1 °C

Parameters

Sensors

PVC membrane CMCPS

Sensor 1

Es-ST

Sensor 2

Es-SM

Sensor 1

Es-ST

Sensor 2

Es-SM

Composition

(W/W %)

1 % Es-ST

+49.50 % PVC

+49.50 % DOP

1 % Es-SM +49.50 PVC

+49.50 DOP

3 % Es-ST

+ 55.0 % G

+ 42.0 % TCP

3 % Es-SM

+ 55.0 % G

+ 42.0 % TCP

Slope (mV/decade) 59.5±0.1 57.5±0.1 60.5±0.5 59.5±0.5

Correlation coefficient

(r) 0.998 0.997 0.999 0.998

LOD (M) 1.00 x 10-8 1.25 x 10

-8 5.00 x 10

-8 4.00 x 10

-8

Linear range (M) 5.0x10-7

-1.0x10-2

5.0x10-7-1.0x10

-2 1.0x10

-7-1.0x10

-2 3.5x10

-7-1.0x10

-2

Working pH range 2.5-7.5 2.5-7.5

Response time (s) ≤12-15s

≤5-10 s

Life span (days) 72 ds 66 ds 90 ds 90 ds

Recovery (%) ± S.D*

99.75±0.08 97.65±0.05 99.87±0.04 99.39±0.06

Robustness 99.88±0.02 99.27±0.05 99.87±0.08 99.70±0.05

Ruggedness 99.65±0.06 99.45±0.07 99.95±0.05 99.55±0.03

* Six replicates



Table 2 Effect of soaking on Es-PVC membrane sensor using 1.00x10-3

M Es-Ox at 25.0±1.0˚C

Soaking time Slope (mV/decade) Linear-range (M) Response time

Es-ST/ PVC (tresp). (s)

1/2 hr 59.5±0.1 5.00x10-7

-1.00x10-2

≤12

1 59.5±0.1 5.00x10-7

-1.00x10-2

≤12

7 59.5±0.1 1.00x10-7-1.00x10

-2 ≤20

14 59.5±0.1 5.00x10-6

-5.00x10-3

≤20

21 52.0±0.1 1.00x10-6

-5.00x10-3

≤20

28 48.5±0.1 5.00x10-5

-3.50x10-3

≤25

45 45.0±0.1 1.00x10-5

-2.50x10-3

≤25

60 42.5±0.1 5.00x10-4

-2.50x10-3

≤30

70 38.0±0.1 1.00x10-4

-1.25x10-3

≤30

Soaking time Slope (mV/decade) Linear-range (M) Response time

Es-SM/ PVC (tresp). (s)

1/2 hr 57.5±0.1 5.00x10-7

-1.00x10-2

≤12

1 57.5±0.1 5.00x10-7

-1.00x10-2

≤12

7 55.5±0.1 1.00x10-7-1.00x10

-2 ≤20

14 55.5±0.1 5.00x10-6-5.00x10

-3 ≤20

21 52.0±0.1 1.00x10-6

-5.00x10-3

≤20

28 48.5±0.1 5.00x10-5

-3.50x10-3

≤25

45 45.0±0.1 1.00x10-5

-2.50x10-3

≤30

60 42.5±0.1 5.00x10-4

-2.50x10-3

≤30

66 38.0±0.1 1.00x10-4

-1.25x10-3

≤30

Effect of soaking on Es-CMCPE using 1.00x10-3

M Es-Ox at 25.0±1.0˚C

Soaking Time Slope (mV/decade) Linear range (M) Response time

(tresp), (s)

CMCP Es-ST Es-SM

1/2 hr 59.5±0.1 57.5±0.1 5.00x10-7

-1.00x10-2

≤ 6

3 days 59.5±0.1 57.5±0.1 5.00x10-7

-1.00x10-2

≤ 6

10 days 59.5±0.1 57.5±0.1 1.00x10-7-1.00x10

-2 ≤ 7

15 days 58.5±0.1 57.5±0.1 5.00x10-7

-1.00x10-2

≤ 7

20 days 58.5±0.1 56.5±0.1 5.00x10-7

-1.00x10-2

≤ 8

35 days 57.5±0.1 56.5±0.1 1.00x10-6-1.00x10

-3 ≤ 8

50 days 57.5±0.1 56.5±0.1 5.00x10-6

-1.00x10-3

≤ 9

75 days 57.5±0.1 55.5±0.1 5.00x10-6

-1.00x10-3

≤ 9

85 days 57.5±0.1 55.5±0.1 1.00x10-6-1.00x10

-3 ≤ 10

90 days 57.5±0.1 55.5±0.1 5.00x10-6

-1.00x10-3

≤ 10



Table 3 Standard deviation values of measuring emf for six replicate measurements obtained for each type

Sensors Standard deviation S.D

1.0 x 10-4

1.0 x 10-3

Es- Sensors

(1) Es-ST/ PVC 0.23 0.42

(2) Es-SM/ PVC 0.54 0.76

(3) Es-ST/ CMCP 0.29 0.47

(4) Es-SM/ CMCP 0.33 0.55

Table 4 Selectivity coefficient values for pot

zJDrug,K log - Es-PVC/CMCPS

Sensor 2 Sensor 1 Sensor 2 Sensor 1

CMCP PVC CMCP PVC Interferent CMCP PVC CMCP PVC Interferent

4.22 4.10 4.28 4.12 Glucose

3.73 3.42 3.84 3.55 Na+

4.17 4.00 4.21 4.07 Lactose 3.30 3.15 3.49 3.27 K+

4.15 4.06 4.20 4.10 Maltose 3.80 3.82 3.92 3.64 NH4+

4.02 4.01 4.06 4.05 L-Lysine 3.79 3.87 3.83 3.90 Cu2+

4.10 4.06 4.15 4.08 L-cystine 3.71 3.50 3.87 3.67 Zn2+

4.03 4.01 4.07 4.01 L-Glycine 3.63 3.80 3.98 3.95 Co2+

4.14 4.03 4.16 4.06 L-Theronine 2.40 2.13 2.42 2.14 Fe2+

4.27 4.27 4.31 4.35 Urea 3.60 3.73 3.88 3.86 Fe3+

4.13 4.21 4.18 4.24 Ascorbic acid 3.59 3.68 3.69 3.79 Ni2+

4.15 4.01 4.17 4.05 Asparagine 3.66 3.69 3.68 3.75 Mn2+

4.05 4.21 4.36 4.18 L-arginine 3.83 3.77 3.89 3.84 Mg2+

4.32 4.26 4.42 4.53 L-proline 3.84 3.90 4.07 3.97 Cr3+

4.22 4.27 4.52 4.31 L-valine 3.94 3.89 4.25 4.12 Ba2+

Each value is the average of three determinations

Table 5 Determination of escitalopramoxalate in bulk solutions, tablet, plasma and urine applying the standard addition method and

potentiometric titrations in PVC membrane and CMCPS

Standard addition method

Bulk solutions

Potentiometric titration

Bulk solutions

Potentiometric titration

Cipralex® 10 mg/tablet

PVC CMCP PVC CMCP PVC CMCP

Taken

(mg)

R (%) R.S.D

%

R (%) R.S.D

%

Taken

(mg)

R (%) R.S.D

%

R (%) R.S.D

%

R (%) R.S.D.

%

R (%) R.S.D

%

Sensor 1 Es-ST Sensor 1 STA as titrant

2.07 98.7 0.66 99.7 0.74 12.43 99.8 0.62 99.9 0.48 101.7 0.44 101.9 0.48

4.14 98.4 0.58 99.8 0.62 20.72 99.6 0.47 99.7 0.52 101.8 0.52 101.7 0.59

6.21 98.8 0.49 99.4 0.60 29.01 99.7 0.79 99.8 0.70 101.5 0.60 101.4 0.67

8.28 98.1 0.82 98.9 0.45 41.44 98.4 0.93 99.6 0.43 101.9 0.48 101.7 0.71

Sensor 2 Es-SM Sensor 2 STA as titrant

2.07 98.7 0.46 99.4 0.26 6.21 99.1 0.54 99.7 0.52 101.6 0.57 101.4 0.43

4.14 98.6 0.59 99.6 0.65 8.28 99.3 0.33 99.0 0.47 102.0 0.48 101.3 0.69

6.21 98.5 0.66 99.3 0.39 12.43 99.0 0.43 99.6 0.79 101.8 0.53 101.0 0.47


Sensor 1

20.72

29.01

100.9

101.3

0.50

0.33

99.3

98.6

0.65

0.53

101.4

101.7

0.38

0.22

101.2

101.5

0.41

0.52

2.07 99.1 0.71 99.8 0.44

4.14 99.4 0.58 99.5 0.76 Sensor 1 SMA as titrant

6.21 98.8 0.56 99.0 0.93 6.21 100.1 0.32 100.5 0.83 100.7 0.59 101.4 0.39

Sensor 2 8.28 100.5 0.50 100.6 0.78 101.5 0.49 101.7 0.66

2.07 99.0 0.38 99.7 0.59 12.43 100.2 0.57 100.3 0.40 101.3 0.29 102.0 0.61

4.14 98.7 0.84 99.4 0.73 20.72 100.7 0.46 100.8 0.69 101.8 0.77 101.6 0.53

6.21 99.1 0.56 99.0 0.51 29.01 100.5 0.62 101.3 0.48 101.5 0.66 101.7 0.48

Spiked human plasma Sensor 1 41.44 101.4 0.74 101.8 0.67 101.9 0.80 101.2 0.42

2.07 98.1 0.88 98.9 0.42 Sensor 2 SMA as titrant

4.14 98.8 0.57 99.0 0.59 2.07 100.5 0.38 100.4 0.46 101.3 0.43 101.6 0.78

6.21 98.5 0.70 98.7 0.53 4.14 100.7 0.44 100.7 0.64 101.5 0.61 101.7 0.61

Spiked urine Sensor 1 8.28 100.4 0.37 101.0 0.36 101.7 0.71 101.9 0.63



Table 6 Statistical treatment of data obtained for the determination of escitalopram oxalate applying the standard addition method and

potentiometric titration by comparison with official methods and using PVC / CMCPs

X±S.E.: Recovery± standard error, F-tabulated is 6.39 at 95.0% confidence limit, t-tabulated is 3.143 at 99.0% confidence limit and 6 degrees of freedom

pEs

2468

E, m

V

50

100

150

200

250

300

350

400

450

2468

2468

2468

2468

2468

2468

2468

2468

Fig. 2 Calibration graphs obtained at 25 o C after soaking [1] Es-ST and [2] Es-SM PVC- membrane sensors for 1/2 hr (a), 1 d (b), 7 d (c), 14 d (d), 21 d (e),

28 d (f), 45 d (g), 60 d (h) and 70 days (i)

pEs

2468

E, m

V

50

100

150

200

250

300

350

400

2468

2468

2468

2468

2468

2468

2468

2468

(a)(b)

(c) (d)

(e)

(f)

(g)

(h)

(i)

(a) (b)

(c)

(d)

(e)(f)

(g)

(h) (i)

[1] [2] Es-SMEs-ST

Time, sec0 200 400 600

E, m

V

100

200

300

400

500

600

700

Es-ST /PVC

Es-ST /CMCPS

Es-SM /PVC

Es-SM /CMCP

Fig. 3 The response time-potential plot for Es-Ox

10-7

10-6

10-5

10-4

10-3

10-2

M

M

M

M

M

M

2.07 98.0 0.66 99.4 0.51 12.43 100.8 0.58 101.5 0.63 101.5 0.85 101.6 0.48

4.14 98.7 0.54 99.6 0.48 20.72 100.9 0.17 101.3 0.49 101.3 0.55 101.5 0.71

6.21 98.4 0.49 99.2 0.63 29.01 101.4 0.47 101.7 0.77 102.0 0.44 101.9 0.55

Standard addition method

Sample Official (1)

method

PVC CMCP

Sensor 1 Sensor 2 Sensor 1 Sensor 2

Bulk solutions

X±S.E. 98.5±0.2 98.7±0.3 98.4±0.1 99.2±0.6 98.5±0.1

F value 4.55 3.93 5.33 5.25

t value 2.78 2.57 4.61 3.44


X±S.E. 101.7±0.2 101.1±0.7 101.4±0.1 101.3±0.5 101.7±0.5

F value 4.98 5.63 4.70 6.35

t value 3.61 4.98 3.32 4.15

Potentiometric titrations

Bulk solutions

X±S.E. 98.5±0.2 99.4±0.2 99.5±0.1 99.7±1.0 99.8±0.4

F value 2.30 2.44 3.38 3.11

t value 2.45 2.22 2.78 2.50


X±S.E. 101.7±0.2 101.8±0.7 100.7±0.5 100.8±0.3 100.9±0.5

F value 3.13 2.35 3.45 4.66

t value 2.45 1.77 2.72 4.65

Spiked human plasma

X±S.E. 101.7±0.2

101.5±0.4 101.2±0.5 100.7±0.2 100.9±0.5

F value

3.66 3.55 3.05 3.68

t value

2.83 2.45 2.44 2.76

Spiked human urine

X±S.E. 101.7±0.2

101.5±0.8 101.7±0.5 101.0±0.6 101.4±0.5

F value

2.83 2.75 3.65 4.55

t value

2.66 2.67 2.12 2.94



pH0 2 4 6 8 10

E,

mV

50

100

150

200

250

300

350

400

Es-ST / (PVC)

0 2 4 6 8 10

0

100

200

300

400

500

Es-SM / (PVC)

E,

mV

pH

0 2 4 6 8 10

0

100

200

300

400

500

600

E,

mV

pH

Es-ST /CMCPs

0 2 4 6 8 10

0

100

200

300

400

500

E,

mV

pH

Es-SM /CMCPs

Fig. 4 Effect of pH on the potential response of Es-Ox for PVC and CMCP sensors

10-5

10-4

10-3

10-5

10-4

10-3

M

M

M

M

M

M

10-5

M

10-4

M

10-3

M

10-5

M

10-4

10-3

M

M

0 10 20 30 40 50 60 70

0

20

40

60

80

100

120

CMCP

Fig. 5 Dissolution profiles of 10 mg escitalopram tablets obtained by (A) potentiometric:

sensor Es-PVC/CMCPE, and (B) spectrophotometric measurements at 240 nm.

Time in min

Rel

ease

%

PVC

spectro

Statistical treatment of results

The recoveries of the results for Es applying the calibration curve,

standard additions method and the potentiometric titration were

evaluated statistically and were compared with the values obtained

with the (0fficial) pharmacopeia method by applying the F-tests41,42

.

The values obtained table 6 show that the determination methods

have a precision comparable to that of the pharmacopeia method.

However, the PVC/ CMCP methods are more practical regarding

time of analysis, consumption of solvents and sample pretreatment

requirements for spectrophotometric or chromatographic analysis of

escitalopram oxalate.

3.9 Robustness and ruggedness

The robustness method was examined by the replacement of

aqueous solution with phosphate buffer pH 6±0.5 for the Es-

PVC/CMCPSs. The results are in a good agreement with those

obtained from standard drug solution as shown in table (1). In



addition, the ruggedness was checked by using another type of pH-

meter model (Jenway, 3505) for each sensor (1, 2) in table 1.

3.10 Content uniformity of Cipralex® tablets

The content uniformity assay for Es-PVC/CMCPS methods

described good accuracy, precision and reproducible resultsfor the

quality control tests so the sensors can be working for the

quantification determination of escitalopram ions and the percentage

of the recovery of Es-Ox is mainly in acceptance quantitatively.

3.11 Potentiometric monitoring of Cipralex®dissolution

The changes of the dissolution medium caused by the dissolving

drug can be detecting by the sensors PVC/ CMCP monitors to the

dissolution of the tablet. The changes are converted into % of the

concentration in dissolved drug via dedicated (“Potential measured in

mV, to Concentration”). The results are compared to analysis using

UV spectrophotometric. It shows that escitalopram releases

immediately after capsule was ruptured and the releasing was

achieved during 15 min nearly 50% was released, then than 74%

drug was released within 20 min and complete dissolution in the third

stage within 35 min according to USP1.

For the UV spectrophotometric assay, fixed volumes of the

dissolution medium were withdrawn, diluted with 0.01 M HCl,

measured at λ max 240nm and compared with a calibration graph.

Fig. 5 shows the dissolution profiles of escitalopram tablet using both

measurement techniques. The results obtained by PVC/CMCP ISS

and spectrophotometric are almost identical but the use of the ISS

methods sensors have the advantage of more sensitive due to

overcome the matrix effect.

5 Acknowledgements

I gratefully acknowledge the support of National Organization for

drug control and research (NODCAR) in Giza-Egypt, by the

chemicals and dissolution equipment acknowledge the supporting of

Central Research Lab at Nahda University with the other equipments

at the practical work.

6 Competing interests

The sensors developed (PVC/CMCP) are superior as compared

with the escitalopram ISS (PVC) described in the literature28

.

7 Author’s contributions

MA is participated in collection of escitalopram oxalate as raw

material from (NODCAR) and in literature survey.

8 References

1. The United States Pharmacopeia. May 1, 2010 Authorized

USP Pending MonographVersion 2.

2. Sweetman SC. Martindale -The Complete Drug

Reference,PharmaceuticalPressLondon2009; 391:996.

3. Gandhi SV, Dhavale ND, Jadhav VY,Sabnis

SS.Spectrophotometric and Reversed‐phase

High‐performance Liquid Chromatographic Methods For

Simultaneous Determination of Escitalopram Oxalate And

Clonazepam In Combined Tablet Dosage Form.Journal Of

Association of Official Analytical Chemists

International.2008; 91(1): 33-38.

4. Syama B,Suneetha A. Development And Validation of

Liquid Chromatographic Method For Estimation of

Escitalopram Oxalate In Tablet Dosage

Forms.International Journal of Pharma And Bio

Sciences.2011; 2(1): 140-146.

5. Tapobana S, Suddhasattya D, Bhusan HS, Bharat Kumar

D, Mohanty DL,Bhar K. RPHPLC Method For The

Estimation Of Escitalopram In Bulk And In Dosage

Forms.International Journal of Chemistry Research.2011;

2(2): 11-15.

6. Chakole RD, Charde MS, Bhavsar N,Marathe RP.

Simultaneous Estimation of Escitalopram and Clonazepam

By RP-HPLC In Pharmaceutical Formulation.International

Journal of Phytopharmacy. 2012; 2 (1): 25-29.

7. Mahadik MV, Dhaneshwar SR,Kulkarni MJ. Application of

Stability Indicating HPTLC Method For Quantitative

Determination of Escitalopram Oxalate In Pharmaceutical

Dosage Form.Eurasian Journal of Analytical Chemistry.

2007; 2(2): 101 –117.

8. Dhavale N, Gandhi S, Sabnis S,Bothara B. Simultaneous

HPTLC Determination Of Escitalopram Oxalate And

Clonazepam In Combined Tablets.Chromatographia,

2008; 67(5‐6): 487‐ 490.

9. Kakde R, Satone D, Bawane N. HPTLC method for

simultaneous analysis of escitalopram oxalate and

clonazepam in pharmaceutical preparations. JPC- J Planar

Chromat. 2009; 2(6):417-20.

10. Kakde RB, Satone D,Bawane N. HPTLC Method for

Simultaneous Analysis of Escitalopram Oxalate and

Clonazepam In Pharmaceutical Preparations.Journal of

Planar Chromatography.2009; 22(6): 417–420.

11. Soliman SM,Youssef NF. Enantiomeric thin-layer

chromatographic assay of escitalopram in presence of “in-

process impurities”.Journal of Planar

Chromatography.2011; 24(6): 475-481.

12. Shete Y, Pimpodkara N, Mahajana NS, Pore YV, Jadhava

RL,Kuchekar BS. Spectrophotometric Estimation of

Escitalopram Oxalate In Pharmaceutical Dosage



Forms.International Journal of Chemical Sciences.2009;

7(1): 235-237.

13. Kakde RB,Satone DD. Spectrophotometric Method for

Simultaneous Estimation of Escitalopram Oxalate and

Clonazepam In Tablet Dosage Form.Indian Journal of

Pharmaceutical Sciences.2009; 71(6): 702–705.

14. Chaudhari BG,Parmar HR. Spectrophotometric Method

For Determination Of Escitalopram Oxalate From Tablet

Formulations.International Journal of Pharmaceutical

Quality Assurance.2010; 2(1): 9‐12.

15. Vetrichelvan T, Arul K, Sumithra M,Umadevi B.

Colorimetric Method For The Estimation Of Escitalopram

Oxalate In Tablet Dosage Form. Indian Journal Of

Pharmaceutical Sciences.2010;72(2): 269‐271.

16. Sharma S, Rajpurohit H, Sonwal C, Bhandari A,

Choudhary VR,Jain T. Zero Order Spectrophotometric

Method For Estimation Of Escitalopram Oxalate In Tablet

Formulations.Journal of Young Pharmcist.2010; 2(4): 420–

423.

17. Fatema K, Rahman MZ, Biswas S,Akter S. Development

of UV Spectroscopic Method For Nefopam And

Escitalopram As INN Drugs In Tablet Dosage

Form.Stanford Journal Of Pharmaceutical Science.2010;

3(1): 4-10.

18. Sharma S, Rajpurohit H, Sonwal C, Sharma P,Bhandari A.

Simultaneous Spectrophotometric Determination of

Escitalopram Oxalate and Clonazepam Using Multi-

component Mode of Analysis.Journal Of Pharmacy

Research.2010; 3(9): 2303-2305.

19. Serebruany V, Malinin A, Dragan V, Atar D,Zyl L.

Fluorimetric Quantitation of Citalopram And Escitalopram

In Plasma: Developing An Express Method To Monitor

Compliance In Clinical Trials.Clinical Chemical Laboratory

Medicine.2007; 45(4): 513–520.

20. Elham AT, Nahla NS,Shudong W. Micelle Enhanced

FluorimetricAnd Thin Layer Chromatography

Densitometric Methods For The Determination Of (±)

Citalopram And Its S – Enantiomer Escitalopram.Analytical

Chemistry Insight.2009;4:1–9.

21. Singh SS, Shah H, Gupta S, Jain M, Sharma K, Thakkar

P,Shah R. Liquid Chromatography–electrospray Ionisation

Mass Spectrometry Method For The Determination Of

Escitalopram In Human Plasma And Its Application In

Bioequivalence Study.Journal Of Chromatography B.2004;

811(2): 209-215.

22. Johannesson N,Bergquist J. Rapid on-line extraction and

quantification of escitalopram from urine using sol–gel

columns and mass spectrometric detection.Journal of

Pharmaceutical and Biomedical Analysis.2007;43: 1045–

1048.

23. Zheng H, Yang L,Tang WY. Determination of Plasma

Escitalopram With Liquid Chromatography-mass

Spectrometry.Nan Fang Yi Ke Da XueXueBao.2008;

28(11): 2044-2046.

24. Dhaneshwar SR, Mahadik MV,Kulkarni MJ. Column Liquid

Chromatography-ultraviolet And Column Liquid

Chromatography/Mass Spectrometry Evaluation of Stress

Degradation Behavior of Escitalopram Oxalate Journal of

Association of Official Analytical Chemists International

2008; 92(1): 138-147.

25. Suresh PS, Giri S, Husain R,Mullangi R. A Highly

Sensitive LC-MS/MS Method for The Determination of S-

citalopram In Rat Plasma: Application to A

Pharmacokinetic Study in Rats.Biomedical

Chromatography.2010; 24(10): 1052–1058.

26. Greiner C, Hiemke C, Bader W,Haen E. Determination Of

Citalopram And Escitalopram Together With Their Active

Main Metabolites Desmethyl(es-)citalopram In Human

Serum By Column-switching High Performance Liquid

Chromatography (HPLC) And Spectrophotometric

Detection.Journal Of Chromatography B.2007; 848: 391–

394.

27. Sungthong B, Jac P,Scriba G. Development and validation

of a capillary electrophoresis method for the simultaneous

determination of impurities of escitalopram including the R-

enantiomer.Journal of Pharmaceutical and Biomedical

Analysis.2008; 46: 959–965.

28. Al-Amri FMG, Alarfaj NA,AlyAF.Development of New

Sensors for Determination of Escitalopram Oxalate in

Dosage Forms and Biological Fluids.Int.J.Electrochem.Sci.

2013; 8: 10044 – 10058.

29. Issa YM, Khorshid AF. Using PVC ion-selective electrodes

for the potentiometric flow injection analysis of distigmine

in its pharmaceuticalformulation and biological fluids.J. of

Advanced Research.2011; 2:25–34.

30. Ibrahim H, Khorshid A.Modified Carbon Paste Sensor for

Cetyltrimethylammonium Ion Based on Its Ion-associate

with Tetrachloropalladate(II).Analytical Sciences. 2007;

23:573-579.

31. Khorshid A, Amin RR,Issa YM. Fabrication of a Novel

Highly Selective and Sensitive Nano-Molar Cu(I), Cu(II)

Membrane Sensors Based on Thiosemicarbazide and

Acetaldehydethiosemicarbazone Copper Complexes.J.of

ChemicaActa. 2012; 152-58

32. United States Pharmacopeia.National Formulary USP 32–

NF 27. Convention, Inc.: Rockville, MD. 2009.



33. Liddell M, Deng G, Hauck W, Brown W, Wahab S,

Manning R, (2007) Dissolution Technologies, 14(1):28.

34. Khorshid A.F, Issa YM.Modified carbon paste sensor for

the potentiometric determination of neostigmine bromide in

pharmaceutical formulations, human plasma and urine.

Biosensors and Bioelectronics. 2014; 51: 143–149

35. Umezawa Y, Buhlmann P, Umezawa K, Tohda K,

Amemiya S.Potentiometric selectivity coefficients of ion-

selective sensors. Part I. Inorganic cations (technical

report).Pure Appl Chem. 2000; 72: 1851-55.

36. Umezawa Y, Umezawa K, Sato H.Selectivity coefficients

for ion-selective sensors: recommended methods for

reporting KA,B pot values (technical report).Pure Appl

Chem. 1995; 67: 507-511.

37. Guilbault G, Drust R.A, Frant MS, Freiser H, Hansen, et

al.Recommendations for nomenclature of ion-selective

sensors. Pure Appl Chem. 1976; 48: 127-129.

38. Ammann D, Pretsch E, Simon W, Lindner E, Bezegh A,

Pungor E. Lipophilic salts as membrane additives and their

influence on the properties of macro- and micro-electrodes

based on neutral carriers. Anal ChimActa.

1985;171(C):119–129.

39. OeshU, SimonW..Effect of lipophilic salts increase slow

solvation. Anal. Chem.1980; 52:692.

40. Linder E, Umezawa Y.Performance evaluation criteria for

preparation and measurement of macro- and micro

fabricated ion-selective sensors.Pure Appl Chem. 2008;

80(1): 85–104.

41. Skoog DA, Holler FJ, Neiman TA.Principles of

Instrumental Analysis, 5thed. Harcourt Brace College

Publishers. London. 1997.

42. Miller JC, Miller JN.Statistics for Analytical Chemistry.Ellis

Horwood.Chichester.England. 1994.

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