Jordan Journal of Chemistry Vol. 7 No.1, 2012, pp. 87-102

87

JJC

Use of Charge Transfer Complex Formation Reaction in Spectrophotometric Microdetermination of Some Drugs

Mohammed S. Al-Enizzi, Theia'a N. Al-Sabha*, Thabit S. Al-Ghabsha

Chemistry Department, College of Education, Mosul University, Mosul, Iraq

Received on Aug. 12, 2011 Accepted on Dec. 27, 2011

Abstract A spectrophotometric method is proposed for the determination of isoniazid, mesalazine,

salbutamol and thymol drugs in their pure forms and in pharmaceutical preparations, based on

the charge-transfer (CT) complex formation reaction with o-chloranil as π-acceptor. Linear

calibration graphs were obtained in the concentration range 1-16 and 2-20 µg ml-1 for isoniazid

at 360 and 520 nm respectively, 1.25-30 µg ml-1 at 571.5 nm for mesalazine, 1.25-50 µg ml-1 for

salbutamol and 2.5-80 µg ml-1 at 410 nm for thymol at room temperature. The molar absorptivity

values are in the range 3460 and 14360 l.mol-1.cm-1 and the lower limit of detection limits are in

the rang 0.1432-1.3164 µg ml-1 for all the studied drugs. The stoichiometry of the drug-o-

chloranil complexes was found to be 1:1 except mesalazine which was found to be 1:2. No

interference was observed from common pharmaceutical excipients. The procedure is

characterized by its simplicity with accuracy and precision. The proposed method was applied

successfully for the determination of the drugs in their pharmaceutical formulations.

Keywords: Charge transfer; Spectrophotometry; O-chloranil; Drugs

Introduction Isoniazid (INH; isonicotinoylhydrazine) (I), is the most potent and selective

tuberculostatic antibacterial agent in the therapy of tuberculosis [1]. It inhibits the growth

of tubercle bacillus in vitro in concentration less than 1 µg ml-1. It is also used as a

propylactic agent for persons constantly exposed to tubercular patients[2].

Mesalazine is chemically known as 5-amino-2-hydroxy benzoic acid; (II), also

known as mesalamine, is an anti inflammatory drug used to treat inflammation of the

digestive tract (crohn’s disease) and mild to moderate ulcerative colitis. It is a bowl-

specific amino salicylate drug that is metabolized in the gut and has its predominant

actions there, thereby having fewer systemic side effects [3].

Salbutamol, [1-(4-hydroxy-3-hydroxymethylphenyl)-2-(t-butylamino) ethanol] (III),

also known as albuterol, is a β2 adrenergic receptor agonist, primarily used in the

treatment of bronchial asthma and other forms of allergic airways disease. The drug is

also used in obstetrics for the prevention of premature labour and as a nasal

decongestant [4,5].

* Corresponding author: e-mail: dr_theiaa@yahoo.co.uk

88

Thymol (2-isopropyl-5-methylphenol); (IV), is a natural monoterpene phenol

derivative of cymene, is part of a naturally occurring class of compounds known as

biocides, with strong antimicrobial attributes when used alone or with other biocides

such as carvacrol. Additionally, naturally-occurring biocidal agents such as thymol can

reduce bacterial resistance to common drugs such as penicillin. Numerous studies

have demonstrated the antimicrobial effects of thymol, ranging from inducing antibiotic

susceptibility in drug-resistant pathogens to powerful antioxidant properties [6].

(I) (II)

(III) (IV)

Many Spectrophotometric methods depending on using various reagent have

been reported for the determination of the intended drugs. N‐Bromosuccinimde [7],

4,5‐dihydroxy‐1,3‐benzenedisulfonic acid in the presence of sodium metaperiodate [8],

diazotized 4,4-methylene-bis-m-nitroaniline [9], 4,4’‐sulphonyldianiline [10], and 1,2-

naphthoquinone-4-sulfonic acid [11] are used for the determination of isoniazid. p-

Dimethyl amino benzaldehyde, 2,2 –bipyridyl or potassium ferricyanide in the presence

of ferric chloride [3], N-(1-naphthyl)ethylenediamine dihydrochloride [12],

tetracyanoethylene (TCNE) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) [13]

are used for the determination of mesalazine. 4-Chloro-7-nitrobenzo-2-oxa-1,3-

diazole[14], Folin-Ciocalteau [15], 3-methyl-2-benzo thiazolinone hydrazone

hydrochloride in presence of ceric ammonium sulphate [16], 4-amino-N,N-

dimethylaniline in the presence of sodium hydrogen carbonate and potassium

hexacyanoferrate(III) [17], 4-aminoantipyrine[18] and 2,6-dichloroquinone chlorimide and

7,7,8,8-tetracyanoquinodimethane [19], 1,10-phenanthroline and 2,2'-bipyridyl in the

presence of Fe (III) [20] are used for the determination of salbutamol. p-

Phenylenediamine in the presence of potassium hexacyanoferrate(III) [21], sodium

89

nitroprusside in the presence of hydroxylamine [22] and potassium permanganate [23]

are used for the determination of thymol.

Some other drugs have been determined spectrophotometrically based on their

complex formation reaction with π-acceptors such as DDQ, p-chloranil, TCNE, TCNQ,

[24-30]. o-Chloranil (o-CA) has received much less attention, since some electron

donor-acceptor complexes involving o-CA as π-acceptor have been studied [31–33].

The present paper reports the spectrophotometric determination of some amino

and phenolic drugs based on their interaction, as n-donors, with o-CA as π-acceptor, in

organic solution forming charge transfer complexes.

Experimental Apparatus

Shimadzu UV-1650 PC UV-Visible spectrophotometer equipped with a 1.0-cm

path length silica cell, Philips PW (9421) pH-meter with a combined glass electrode

was used for pH measurements. All calculations in the computing process were

performed in Microsoft Excel for Windows. Reagents

All reagents were of analytical-reagent grade which were provided by BDH and

Fluka companies. Stock solutions of the drugs were prepared in concentration of 100

µg ml-1 for isoniazid, 250 µg ml-1 for mesalazine and salbutamol and 500 µg ml-1 for

thymol, by dissolving the calculated amounts in distilled water. The stock standard

solution of drugs remain stable for two to three weeks at room temperature in the dark.

The solution of o-CA (5x10-3M) was prepared daily in acetonitrile and absolute ethanol

for the determination of isoniazid and mesalazine respectively and in acetone for

determination of salbutamol and thymol. Sodium hydroxide (1x10-2M) was prepared by

dissolving 0.1 g in 250 ml of distilled water.

General procedure

Accurately measured suitable volume of isoniazid, mesalazine, salbutamol and

thymol were transferred from stock solution to 5-ml volumetric flasks and diluted to

obtain 1-16 or (2-20), 1.25-30, 1.25-50 and 2.5-80 µg ml-1 for the drugs mentioned

above respectively. To each flask containing drugs in the order mentioned above, 0.2,

0.5, 0.5 and 0.2 ml of o-CA and 1.0, 1.0, 0.5 and 0.5 ml of NaOH were added. The

solutions were diluted to the mark with ethanol for mesalazine, acetone for salbutamol

and thymol and with acetonitrile for isoniazid. The absorbances were measured at

571.5, 375, 410 and 360 (520) nm for mesalzine, salbutamol, thymol and isoniazid

versus their respective blanks respectively.

Pharmaceutical Preparations

A. Tablets and capsules

Twenty tablets or capsules were weighed to determine the average weight of

tablet or capsule and was finely powdered. Into a 100-ml measuring flask the amount

was transfered and dissolved in 10 ml ethanol-water mixture (50:50, v/v) by shaking for

90

10 min, then mixed well and filtered if necessary. An accurately measured volume of

the filtrate was transfered to a 50 ml measuring flask and completed to the mark with

distilled water. Solutions of lower concentrations were prepared by appropriate dilution

with distilled water. The general procedure was then proceeded.

B. Syrup

Accurately 5 ml of syrup sample which is equivalent to 2 mg of salbutamol was transferred into a 50 ml calibrated flask and diluted to the mark with distilled water. An aliquot of the drug solution was analysed as described in general procedure. C. Mouthwash

Appropriate volume of lastarim (0.06 % thymol) was diluted with distilled water and aliquot of the drug solution was analysed as described in general procedure. Standard addition procedure

A constant volume of the solution containing a fixed amount of drug in pharmaceutical formulation is added to a series 5-ml volumetric flasks. Then a series of increasing volumes of stock solution were added. Finally, each flask is made up to the mark with solvent and mixed well. The solutions were analysed as described in general procedure. Results and discussion Effect of solvents

Different solvents such as methanol, ethanol, acetonitrile, acetone and water as

medium for the reaction have been tried in order to achieve maximum sensitivity and

complex stability, As shown in table1. It was found that on using water as solvent for all

drugs and acetone as solvent for o-CA in the case of thymol and salbutamol, but using

ethanol and acetonitrile in the case of mesalazine and isoniazid respectively in the

presence of NaOH and dilution with the same solvent were gave maximum color

intensity. Dilution with water gave turbid solutions. Therefore; these systems of

solvents are recommended in this method.

Table 1: Effect of solvents on absorbance of drug-o-CA complexes Drug

dissolved in

o-CA dissolved

in

Dilution

by

Isoniazide λmax Abs

Mesalazine

λmax Abs

Salbutamol

λmax Abs

Thymol

λmax Abs

Water

methanol

methanol

506 364.5

0.021 0.206

565

0.258

531

356.5

0.072 0.062

398.5

0.292

methanol methanol methanol 492.5 369.5

0.009 0.099

454 0.185 - Turbid 399 0.263

Water Ethanol Ethanol 368.5 0.147 571.5 0.260 539.5 374.5

0.069 0.044

334 0.276

Ethanol Ethanol Ethanol 492.5 364.4

0.016 0.101

354 0.062 - - 373 0.201

Water Acetone Acetone 424.5 0.053 576 0.210 536 375

0.092 0.221

410 0.373

Acetone Acetone Acetone 423.5 0.002 - - - - 411 0.365

Water Acetonitrile Acetonitrile 520 360

0.150 0.351

570 0.091 531 386

0.077 0.103

424 0.309

Acetonitrile Acetonitrile Acetonitrile 374.5 0.134 - - - - 419 0.340

91

Charge transfer electronic spectra

The electronic spectra of charge transfer (CT) complexes of the studied drugs

as n-donors with o-CA as π-acceptor are recorded in acetonitrile for isoniazid, in

ethanol for mesalazine, in acetone for salbutamol and thymol and in the presence of

NaOH. The electronic spectra were scanned against their respective blank reagents.

New bands with maximum absorption at 571. 5 , 375 and 410 nm were appeared for

mesalazine, salbutamol and thymol drugs respectively, while isoniazid shows two

bands at 360 and 520 nm (Figure 1). The blank reagent has no absorption at λmax of

each drug-o-CA complex.

Figure 1. Absorption spectra of (a) 16 µg ml-1 isoniazid, (b) 40 µg ml-1 salbutamol, (c) 70 µg ml-1 thymol and (d) 20 µg ml-1 mesalazine against their respective reagent blank (a´,b´,c´,d´) under optimum conditions.

Optimization of experimental conditions

The optimum conditions for the color development of the complexes were

established by varying the parameters one at a time, keeping the others fixed and

observing the effect produced on the absorbance of colored species. The following

experiments were conducted for this purpose and conditions so obtained were

incorporated in general procedure.

Effect of pH and buffer solutions

The effect of pH on the absorption of the complexes were studied using different

pH values ranged from 2 to12 by using of 0.01 M HCl and NaOH. It was found that the

complexes are formed at pH values of 7.2, 9.8, 8.0 and 6.6 by addition of NaOH to the

isoniazid (5 µg ml-1), mesalazine (12.5 µg ml-1), salbutamol (12.5 µg ml-1) and thymol

(50 µg ml-1) respectively (Figure 2). Decrease in absorbances was observed through

addition of HCl, which may be attributed to the liberation of hydrogen chloride.

d ́

a´

b´

c´

92

Therefore different buffers of higher pH values are prepared to examine the sensitivity.

A negative effect was observed on the color intensity.

Figure 2: Effect of pH on the absorbance of CT-complexes

Effect of bases

To obtain high sensitivity for the complexes, different bases such as sodium

hydroxide, potassium hydroxide, sodium carbonate and sodium bicarbonate with fixed

volume and a concentration of 0.01M were examined by addition to a fixed amount of

each drug. It was found that sodium hydroxide gave maximum color intensity for all

studied drugs (Figure 3), and the optimum amounts of this base were found to be 1.0

ml for mesalazine and salbutamol and 0.5 ml for thymol and isoniazid which were used

in the subsequent experiments.

Effect of o-CA concentration

The effect of changing the o-CA concentration on the absorbance of solution

containing a fixed amount of each drug was studied. It was observed that the

absorbance increases with increasing o-CA concentration and reached maximum on

using 0.2, 0.2, 0.5 and 0.5 ml of 5×10-3M o-CA for INH, mesalazine, salbutamol and

Figure 3: Effect of bases on the absorption of o-CA – drug complexes.

Thymol Salbutamol

Abs

orba

nce

Mesalazine

KOH

NaOH

Na2CO3

NaHCO3

Isoniazid (520 nm)

Isoniazid (360 nm)

0

0.1

0.2

0.3

0.4

Na2CO3

KOH

NaOH

NaHCO3

0

0.1

0.2

0.3

0.4

4 5 6 7 8 9 10 11pH

Isoniazid (360nm)

Isoniazid (520nm)

Thymol

Salbutamol

Mesalazine

Absorbance

93

thymol respectively (Figure 4). Therefore, these volumes of this concentration were

used in the subsequent work.

Figure 4: Effect of o-CA concentration on the absorption of 5, 50, 12.5 and

12.5 µg ml-1 for isoniazid, thymol, salbutamol and mesalazine respectively.

Effect of temperature and reaction time

The reaction time was determined by following the color development at room

temperature and in thermostatically controlled water-bath at different temperatures.

The absorbance was measured at 5 and 10 minutes intervals against reagent blank

treated similarly. It was observed that maximum absorbance and stability was obtained

at room temperature (25○C) for all studied drugs. It was found that complexes gave

maximum absorption within 5-90 and 5-50 minutes for salbutamol and mesalazine

respectively and the color was fading slowly thereafter. Constant absorbance values

were obtained in the range 15-50 minutes for isoniazid measured at 360 and 520 nm,

and 10-75 minutes for thymol and the color was increased slowly thereafter (Figure 5).

Figure 5: Effect of the time on the absorbance of (♦) 5 µg ml-1 isoniazid at 360 nm, (□)isoniazid at 520 nm, (▲) 50 µg ml-1thymol, (ж) 12.5 µg ml-1mesalazine and (x) 12.5 µg ml-1salbutamol measured at room temperature.

0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60 70 80 90 100 110 120

Time (min.)

Abs

orba

nce

Volume (ml) of o-CA

Isoniazid (520 nm) Isoniazid (360 nm) ThymolSalbutamol

0

0.1

0.2

0.3

0.4

0.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Mesalazin

××××××××××

×A

bsor

banc

e

94

Effect of surfactant

Effect of various surfactants including sodium dodecyl sulphate (SDS),

cetylperydinum chloride (CPC), cetyltrimethylammonium bromide (CTAB), Tween-80

and Triton x-100 were tested. It was found that these surfactants decreased the

absorbance of solutions.

Effect of order of addition

To obtain optimum results the order of addition of reagents should be followed

as given under the general procedure, otherwise a loss in color intensity was

observed.

However; the optimum reaction conditions for developing the color intensity of

the studied o-CA-drug complexes are summarized in table 2.

Table 2: Optimum conditions for the determination of drugs with o-CA reagent

RT = Room temperature (25○C)٭

Quantification

In order to investigate the range in which the colored complexes adhere to

Beer's law, the absorbance of the complexes were measured at their corresponding

λmax value after developing the color by following the general procedure for individual

calibrations for a series of solutions containing increasing amounts of each drug

(Figure 6). The Beer's law limits and molar absorptivity values were evaluated and

given in table 3, which are indicated that the method is sensitive. The linearity was

represented by the regression equation and the corresponding correlation coefficient

for the studied determined drugs by the proposed method represents excellent

linearity. The relative standard deviation (RSD) and accuracy (average recovery %) for

the analysis of six replicates of each three different concentrations for each drug

indicated that the method is precise and accurate. Limit of detection (LOD) are in the

accepted range below the lower limit of Beer's law range.

Drug

λmax (nm)

Temp. (°C)

o-CA 5× 10-3 M

(ml)

NaOH 1×10-2 M

(ml)

Dilution

by

Development time (min)

Stability period (min.)

Final pH

Isoniazid

360 520

RT*

0.2

0.5

Acetonitrile

15

35

7.209

Mesalazine

571.5 RT 0.2 1.0

Ethanol 5 45 9.810

Salbutamol

375

RT

0.5

1.0

Acetone

5

85

8.054 Thymol

410 RT 0.5 0.5

Acetone 10 65 6.602

95

Table 3: Summary of optical characteristics and statistical data for the proposed

method

Parameter

Isoniazid a

Mesalazine

Salbutamol

Thymol

Beer's law limits (µg ml-1) 1-16, 2-20

1.25-30

1.25-50

2.5-80

Molar absorptivity (l.mol-1. cm-1) 14357,5550

3460 9850 1140

LOD (µg.ml-1) 0.1663,0.2801

0.1432 0.7781 1.3164

Average recovery (%)b 99.89, 100.36 100.41 98.96 98.96

Correlation coefficient 0.9993, 0.9988 0.9996 0.9987 0.9988

Regression equation (Y)c

Slope, a 0.1048, 0.0405

0.0226 0.0171 0.0076

Intercept, b - 0.0490, -0.0191

0.0365 0.0421 0.0083

RSD b ≤ 1.16, ≤ 1.0 ≤ 3.89

≤ 4.31

≤ 4.39

a Measured at 360 and 520 nm respectively. b Average of six determinations. cY = a X + b, where X is the concentration of drug in µg ml-1.

Figure 6: Calibration graphs for determination of (♦)Isoniazid at 360 nm, (■)Isoniazid at

520nm, (▲) mesalazine at 571 nm, (●) salbutamol at 375 nm and () thymol at 410nm.

Interference

The extent of interference by some excipients which often accompany

pharmaceutical preparations were studied by measuring the absorbance of solutions

containing fixed amount of drug and various amounts of diverse species in a final

volume of 5 ml. It was found that the studied excipients did not interfere seriously

(Table 4). Slight positive interference was observed in the presence of large excess of

excipients. However; an error of 5.0 % in the absorbance readings was considered

tolerable. Typical results are given in table 4.

Abs

orba

nc

Conc.,µg/ml

96

Table 4: Effect of excipients for assay of the studied drugs

Thymol

Salbutamol

Mesalazine

Isoniazid at 520nm

Isoniazid at 360nm

Foreign compound

Recovery (%)

Fold excess Added

Recovery

(%)

Fold excess Added

Recovery

(%)

Fold excess Added

Recovery

(%)

Fold excess Added

Recovery

(%)

Fold excess Added

97.36 99.46

101.58 106.32

2 4 8

10

100.67 101.79 104.39 119.50

2 4 8

20

100.08 102.08 102.48 104.42

2 4 8

20

100.94 100.56 102.26 101.88

2 5

10 20

99.79

100.84 101.26 100.21

2 5

10 20

Glucose

101.12 100.86 101.58 100.40

2 4 8

10

100.89 100.60 106.10 128.13

2 4 8

20

102.24 101.52 100.56 102.72

2 4 8

20

95.29 95.86 98.17 99.06

2 5

10 20

99.79 100.21 100.84 101.05

2 5

10 20

Lactose

97.62 100.44 99.08 98.42

2 4 8

10

97.84 102.23 100.89 118.08

2 4 8

20

97.84 98.96 98.56 99.52

2 4 8

20

94.54 96.80 97.74

100.56

2 5

10 20

98.74 100.21 99.16 99.58

2 5

10 20

Arabic Gum

100.60 102.96 100.92 101.18

2 4 8

10

101.19 101.49 101.04 102.46

2 4 8

20

102.01 101.44 103.92 104.96

2 4 8

20

99.06 99.62

100.02 100.56

2 5

10 20

100.21 100.63 100.21 100.01

2 5

10 20

Sodium Chloride

100.60 100.86 101.04 99.74

2 4 8

10

100.74 102.23 104.84 116.15

2 4 8

20

100.48 102.72 103.52 106.00

2 4 8

20

98.68 100.02 99.62

100.02

2 5

10 20

99.16 100.21 100.84 99.58

2 5

10 20

Sucrose

96.38 106.58 104.86 108.70

2 4 8

10

103.65 103.20 113.54 140.25

2 4 8

20

98.56 100.24 101.44 100.72

2 4 8

20

98.17 100.94 96.80

101.51

2 5

10 20

99.37 100.84 99.16

100.84

2 5

10 20

Starch

Stoichiometry and Stability constant

The molar ratio of the complexes formed between the studied drugs and o-CA

reagent was investigated by applying the mole ratio and continuous variation (Job's)

methods [34]. The results indicated that all complexes were formed in the ratio of 1:1

except for mesalazine which was formed in the ratio of 1:2 mesalzine to the reagent

(Figures 7 and 8). This finding supports that the n-π٭ CT complex is formed through

the hydroxyl and amino groups [35,36]

97

Figure 7: The stoichiometry of the o-CA-drug complexes by Job method

Figure 8: The stoichiometry of the drug-o-CA complexes by mole ratio method

According to the results described above, the apparent stability constant was

estimated by comparing the absorbance of a solution containing stoichiometric

amounts of each drug and o-CA (As) to one containing an excessive amount of o-CA

reagent (Am). The average conditional stability constants of the complexes are

calculated by applying equation (1) for isoniazid, thymol, salbutamol and equation (2)

for mesalazine :

Kc=1-α/ α2 C ................................................................................................ (1)

Kc=1-α/ 4α3 C 2 ............................................................................................ (2)

α =Am-As/Am

Isoniazid at 360nm

Isoniazid at 520nm

Thymol at 410nm

Salbutamol at 375nm

Mesalazine at 571.5nm

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 1 2 3

Abs

orba

nce

Mole ratio (reagent/drug)

Abs

orba

nce

Volume ratio of drug (Vd/Vd+Vr)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 0.2 0.4 0.6 0.8 1

Isoniazid at 360 nm

Isoniazid at 520 nm

Thymol at 410 nm

Salbutamol at 375 nm

Mesalazine at 571.5 nm

98

where Kc is the stability constant, α the dissociation degree and C is the concentration

of the complex which is equal to the concentration of drug. The results shown in table

5 indicate that the products are relatively stable.

Table 5: Stability constants of the o-CA-drug complexes

Drug Drug

Vol. ml Absorbance

α Average K c (L.mole-1) ٭ As ٭ Am

Isoniazid at 360nm

0.20 0.40 0.60

0.171 0.367 0.521

0.343 0.812 1.198

0.5015 0.5480 0.5651

3.64x104

Isoniazid at 520nm 0.20 0.40 0.60

0.074 0.133 0.189

0.132 0.308 0.458

0.4394 0.5682 0.5874

4.53 x104

Mesalazine 0.20

0.35 0.50

0.194 0.307 0.361

0.268 0.452 0.596

0.2761 0.3208 0.3943

8.70x108 (L2.mol-2)

Salbutamol 0.15

0.40 0.60

0.039 0.088 0.165

0.162 0.395 0.568

0.7593 0.7772 0.7104

1.79 x104

Thymol 0.20 0.40 0.60

0.022 0.082 0.295

0.164 0.322 0.461

0.8658 0.7453 0.3601

5.184 x103

Average of three determinations ٭

Reaction mechanism

The interaction of any of the investigated compounds with o-CA in polar

solvents, such as acetonitrile, ethanol or acetone, was a charge-transfer complexation

reaction between the n-donors drugs and the π-acceptor (o-CA), followed by the

formation of a radical anion. Complete electron transfer from the donor to the

acceptor moiety took place with the formation of intensely colored radical ions with

high molar absorptivity values, (scheme 1)

99

OO

ClCl

Cl

Cl

OH

OH

R

OHR

H3C

N

HNO

NH2

HO2C

HO

NH2

OO

ClCl

Cl

Cl

OH

OR

H

OO

ClCl

Cl

Cl OO

ClCl

Cl

Cl

OO

ClCl

Cl

Cl

R

H3C

O

H

N

HNNH2

CO2H

ON

O

O

ClCl

Cl

Cl

H

H

H

O

OO

ClCl

Cl

Cl

OH

OR

H

OO

ClCl

Cl

ClR

H3C

O

H

OO Cl

ClCl

ClO

O

ClCl

Cl

Cl

N

HNNH2

O

OO

ClCl

Cl

ClCO2H

ON

H

H

H

Ethanol

Aceton

e

Ace

tone

Acetonitrile

RCH2

CHOH

H3CC

CH3

CH3

HN R CHCH3

CH3

Scheme 1: Proposed mechanism of charge transfer complex formatiom reaction for assay of the drugs by o-chloranil

Analysis of pharmaceutical formulations

The proposed method was successfully applied to determine the intended drugs

in their commercial tablets, capsules, syrup and mouthwash. The results given in table

6 indicated that the method is a reproducible and accurate. The validity of the method

was confirmed by applying the standard addition procedure (Figure 9) and the results

suggested that there is no interference from any excipients, which are present in

commercial dosage forms, (Table 6).

100

Table 6: Assay of the drugs in some pharmaceutical formulations by the proposed method

and standard addition procedure.

Drug determined

Pharmaceutical preparation

Drug content

(mg)

Drug content (mg) found

Direct method

Recovery٭ (%)

Standard addition

Recovery (%)

Isoniazida (at 360 nm)

Tablet

100

99.13

99.13

96.30

96.30

Isoniazida (at 520 nm)

Tablet

100

102.19

102.19

99.42

99.42

Lastarimeb Mouthwash 0.06% 0.0597% 99.51 0.060 100

Butadina

Tablet

2.0

2.02

100.95

2.05

102.55

Butadina

Syrup

2.0

2.05

102.55

1.98

99.44

Mesacolc

Tablet

400

405.18

101.30

406.66

101.66

Mesacolc

Capsule

400

415.8

102.99

409.23

102.30

.Average of four determinations ٭a Manufactured by Samarra Drug Industries, Iraq b Manufactured by Homas – Syria c Manufactured by Universal Pharmaceutical Industries unipharama–Damascus - Syria

101

Figure 9: Standard addition plots of the studied drugs

Conclusion The proposed spectrophotometric method is sensitive (trace amounts can be

determined), accurate (average recovery range 98.96-100.41%), precise (RSD ≤ 4.39)

and simple since it does not need neither temperature control nor solvent extraction

step. The proposed method was applied successfully for the assay of the

pharmaceutical preparations for the studied drugs i.e., isoniazid, mesalazine,

salbutamol and thymol.

References [1] Gelone S. O; Donell J. A., "Anti Infectines", Chapter 90, in Renimgton, The Science and

practice of pharmacy, Gerbinoo, P. P. (Directore) 21ist ed., Lippincott Williams and wilkins, Baltimore, Maryland, U. S. A., 2005, p. 1663.

[2] Chatwal G. R., "Anititubercular and antileprosy drugs", chapter 25, In "Synthetic Drugs". 2nd ed. (Arora M, ed.) Himalya Publishing House, Delhi, 1990, p. 374.

[3] Narala S. R.; K. Saraswathi, Int. J. Res. Pharm. Biomed. Sci., 2010, 1, 10-13. [4] Reynolds J.E.F., "The Extra Pharmacopoeia / Martindale", 30th Ed., p.1255, The

Pharmaceutical Press, London, 1993. [5] Gilman A.G.; Goodman, L.S; Rall, T.W.; Murad, F., "Goodman and Gilman's the

pharmacological basis of therapeutics", 7th Ed., MacMillan Publishing Company, New York, 1985, pp.172-173.

[6] http://4mec.org/index.php?wiki=Thymol

0

0.4

0.8

1.2

1.6

2

-6 -4 -2 0 2 4 6 8 10 12

y=0.1063x+0.2027

y=0.1095x+0.3117 y=0.1071x+0.4227

2µg ml-1

3µg ml-1

4µg ml-1

Isoniazid added, µg ml-1 (measured at 360 nm)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

-30 -20 -10 0 10 20 30 40 50 60 70

y=0.0077x+0.0759 y=0.0078x+0.1125 y=0.1071x+0.4227

10µg ml-1

15µg ml-1

20µg ml-1

Thymol added, µg ml-1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

-15 -10 -5 0 5 10 15 20 25 30 35 40Salbutamol added, µg ml-1

y=0.0172x+0.0853

y=0.0171x+0.1331

y=0.0169x+0.176

5µg ml-1

7.5µg ml-1

10µg ml-1

Abs

orba

nce

0

0.2

0.4

0.6

0.8

-8 -4 0 4 8 12 16 20Mesalazine added, µg ml-1

y = 0.023x + 0.0571

y=0.0223x+0.1174 y=0.0224x+0.1719

2.5µg ml-1

5µg ml-1

7.5µg ml-1

Abs

orba

nce

102

[7] Barsoum B. N.; Kamal M. S; Diab M. M., Res. J. Agr. Bio. Sci., 2008,4, 471- 484. [8] Gowda B. G.; Melwanki M. B.; Seetharamappa J.; Murthy K C S, Anal. Sci., 2002,18,

839-841. [9] Mohamed Z. H.; El Sayed L.; Wahbi A. A., J. Anal. Chem., 2005, 60, 822-827. [10] Nagaraja P. et al., Turk. J. Chem., 2002, 26, 743-750. [11] Li Q. M.; Yang Z. J., J. Chin. Chem. Soc., 2006, 53, 383-389. [12] Patel K. M.; Patel C.N.; Panigrahi B.; Parikh A.S.; Patel H.N., Pharm Analysis, 2010, 2,

284-288. [13] Al-Sabha T. N.; . Altaee O. A, J.Edu & Sci., 2008, 21, 49-62. [14] El-Enany N.; Belal F.; M. Rizk, Chem. analit., 2004,49, 261-269. [15] Sadler N. P.; Jacobs H., Talanta, 1995,42, 1385-1388. [16] Ravisankar K. S.; Rao V.V.; Kumar V.K.; Nagoji K.E. V.; Rao E. B. M., Ind. Pharm.,

2006,5, 65-67. [17] Burns D. T.; Chimpalee N.; Chimpalee D.; K. Leiwongcharoen, Anal. Chim. Acta, 1992,

260, 65-68. [18] Dol I.; Knochen M., Talanta, 2004,64,1233-1236. [19] Mohameda G. G.; Khalilb S. M.; Zayed M. A.; El-Shall M. A., J. Pharm. Biomed. Anal.,

2002, 28,1127-1133. [20] Al-Sabha T. N., J. Edu. & Sci., 2007,19, 25-35. [21] Corbett J. F., Anal. Chem., 1975, 47, 308–313. [22] Mohammad I. Kh., J. Edu. Sci., 2005,17, 41-49. [23] Backheet E. Y., Phytochem. Anal., 1998, 9,134-140. [24] Al-Ghabsha T. S.; Al-Sabha T. N.; Al-Mtaiwti S. M., Univ. Sharjah J. Pure & App. Sci.,

2007, 4, 13-28. [25] Al-Ghabsha T. S.; Al-Sabha T. N.; Al-Iraqi G. A., Microchem. J., 1987, 36, 323-325. [26] Al-Sabha T. N., Arab. J. Sci. Engin., 2010, 35, 27-40. [27] Salem H., Afri. J. of Pharm. and Pharm., 2008, 2,136-144. [28] Al-Ghannam S.; Belal F., J. AOAC Intern., 2002, 85, 1003-1008, [29] Amin A. S.; El-Beshbeshy A. M., Microchim. Acta, 2001,137, 63 – 69. [30] Al-Sabha T. N.; Omar A. Al-Taee, Tikrit J. Pure Sci., 2010, 5, 275. [31] Ray A. K.; Bhattacharya S.; Banerjee M.; Mukherjee A. K., Spectrochim. Acta A Mol

Biomol Spectrosc., 2002, 58,1375-1378. [32] Chakravarty B.; Datta K.; Mukherjee A.K.; Banerjee M.; Seal B.K., Indian J. Chem. 1998,

37A, 865-870. [33] Chakravarty B.; Mukherjee A.K.; Seal B.K., Spectrochim. Acta Part A, 2001, 57, 223. [34] Hargis L.G., "Analytical Chemistry, Principles and Techniques", Prentice- Hall Inc., New

Jersey. (1988) pp. 424- 427. [35] Bhattacharya S.; Banerjee M.; Mukherjee A. K., Spectrochim. Acta Part A, 2001, 57,

2409–2416. [36] Datta K.; Mukherjee A. K.; Banerjee M.; Seal B. K., Spectrochim. Acta Part A, 1997, 53,

2587–2594.