Indian Journal of Chemical Technology Vol.lO, July 2003, pp. 382-385

Articles

Precipitation and complex formation reactions based titrimetric and spectrophotometric methods for the determination of

diphenhydramine hydrochloride K Basavaiah* & V S Charan

Department of Chemistry, University of My sore, Mysore 570 006, India.

Received 4 April 2001; revised received 18 March 2003; accepted 28 March 2003

T.wo simp~e, accuraty and · s~lC?,Ctive method& for t,he-,determination of diphen~ydr;mtine in pharmaceutical grade sample an<Un dosag~ forms are described. The ·titrimetiic method is J?ased o.n the. precipitation of the chloride content of the drug as :AgCiwj th, a known exces.s q(si.lver nitrate ·and' b~ck titration Of ihe .residual silver nitrate with tlp.ocyanate using iron (ill) as indicator. The reaction, stol.cbiometry and the ra!lge of determination have been eyaluated. The spectrophotof!!etric method involves the displacem_ent of thiocyanate of mercuric thiocyanate from the ionized chloride and the subsequent reaction of the liberated thiocyanate with iron(ll) to form the familiar red coio\II'ed complex, Fe(SCN)2

+ which is measured spectro­photometrically at 460 nm;. Jbe Beer' s· law is obeyed over the range 5-45 J.Lg mL-1 of diph~nhydrarni-ne HCl, the · molar ab­sorptjvity and Sandell se1_1sitivi~y- being 3.45 x 103 L moL'1 cm-1 and 84.5 ng cm-2, respectively at 460 nm. The reaction variables have been optimized. The methods have bee!J found to be very_ simple, cost-effective and reliable for three dosage formS coniaining diphenhydramine hydrochJoride.

Diphenhydramine hydrochloride (DPH), 2-(diphenyl­methoxy) N, N-dimethyl ethylamine hydrochloride, is a conventional antihistamine of the H1 type (receptor antagonist), which can block most of the reactions of histamine in the body. Like man¥ other antihista­mines, it has pronounced sedative properties. It also has antiemetic, anticholinergic and local anaesthetic properties.

Diphenhydramine is found in many pharmaceutical preparations, it is usually given orally but it has also been given in severe allergies by deep intramuscular or slow intravenous injection. It is used in cough mixtures, for the control of symptoms of parkinson's disease, for prevention and treatment of nausea and vomitting. It has also been given with methaqualone as a hypnotic and a 2% water miscible cream has been used for allergic dermatoses and bums 1.

The therapeutic importance of DPH has prompted the development of many methods for its determina­tion in body fluids and pharmaceutical preparations. The alkalimetric titration method2 suffers from inter­ference from ephedrine. Non-aqueous titrimetric methods3-7 which are the methods of general applica­bility require scrupulously anhydrous medium. DPH

*For correspondence (E-mail:' basavaiahk@yahoo.co. in; Fax: 0091-821-421263,0091-821- 516133)

has been determined by precipitating it with potas­sium iodobismuthate ion, filtering of the precipitate and titrating the unreacted bismuth in the filtrate with EDT A 8, the steps being complex and time-consuming. Titration with sodium tetraphenylborate9 requires carefully controlled pH.

Majority of the spectrophotometric methods sug­gested for DPH involve extractions of the chromogen into the organic solvent before measuring the absorb­ance. They are based on reactions such as ion-pair formation 10

'12, charge-transfer complex formation 13'14,

addition compound formation 15'16 and ternary com­plex formation 17-19. They involve tedious extraction step and suffer from such disadvantages as low sensi­tivity17-19, careful pH control 10-12, insufficient accuracy and precisiton, and/or longer extraction time. Methods based on reduction20 reaction and formation of mixed aggregates with surfactants21 have also been reported. Recently a flow injection method based on ion-pair formation with bromocresol green has been described by Prapatsom et al. 22 .

In the present investigations, precipitation reaction and displacement followed by complex formation re­actions involving the ionized chloride of DPH have been utilised for micro titrimetric and sensitive spec­trophotometric determination of DPH. The chloride content of DPH is precipitated with a known excess of

Basavaiah & Charan: Titrimetric and spctrophotometric methods for determination of diphenhydramine hydrochloride Articles

silver nitrate and the unreacted precipitant being back titrated with potassium thiocyante using iron(III) as indicator. The spectrophotometric procedure involves the reaction of chloride with mercuric thiocyanate to form soluble chloro mercurate(II) complex ion with the liberation of thiocyanate ions which then react with iron(III) to form red coloured complex which is measured at 460 nm. The absorbance is proportional to the thiocyanate ion concentration which in turn is proportional to the chloride and DPH concentration ..

Experimental Procedure The absorbance measurements were made on an

Elico model SL-171 digital spectrophotometer pro­vided with 1-cm matched glass cells. All chemicals used were of analytical reagent-grade. Double dis­tilled water, second time distilled over alkaline potas­sium permanganate was used throughout. Silver ni­trate (AR grade, Indian Drugs and Pharmaceuticals Ltd, Hyderabad, Assay: 99.9%) solution (-0.04 M) was standardized by using pure sample of NaCl23

(Merck, Assay: 99% ). Potassium thiocyanate (AR grade, S.D. fine chem Ltd., Mumbai, Assay: 99%) (-0.02 M) was standardized by Volhard method24

.

Iron(III) (AR grade, S.D. Fine Chern Ltd., Mumbai, Assay: 99%) indicator was prepared by dissolving -10 g of iron(lll) alum in 1: 1 nitric acid (AR grade, S.D. Fin_e Chern Ltd. , Mumbai, Assay: 69-71%) (100 mL) and boiling the solution to expel the oxides of nitrogen. Iron(lll) nitrate (AR grade, BDH sample, Mumbai, Assay: 98.5%) reagent was prepared by dis­solving 15.1 g of sample in 45 mL of 72% perchloric acid (AR grade, S.D. Fine Chern Ltd., Mumbai, As­say: 70-72%) and diluting to 100 mL with water. A saturated solution of mercuric thiocyanate (GR grade, Loba Chemie, Assay: 99%) in methanol (AR grade, S.D. fine chem Ltd., Mumbai, Assay: 99.5%) and 1:1 nitric acid were prepared in the usual way. Chloride­free nitrobenzene (AR grade, S.D. fine chem Ltd., Mumbai, Assay: 99%) was used for titrimetric work.

Pharmaceutical grade DPH was gifted by Parke­Davis, India Ltd., and was used as such. A stock stan­dard solution containing 4 mg mL-1 DPH was pre­pared for titrimetry. This solution was diluted step­wise to provide a working solution of 100 )lg rnL·'.

Titrimetric method To a 10 mL aliquot of solution containing 6-40 mg

of DPH, 2 mL of 1: 1 nitric acid were added followed by 5 mL of 0.04 M silver nitrate solution by means of a pipette. The contents were shaken for a minute, 2

mL of nitrobenzene were added and shaken vigor­ously until the silver chloride was coagulated. Then; iron(lll) indicator (0.5 mL) was added, and the excess of silver nitrat~ titrated with 0.02 M potassium thio­cyanate to a permanent red colour end-point. A blank was run in the same way with 10 mL of chloride free water.

Spectrophotometric method Into a series of 10 mL standard flasks were trans­

ferred 0.5, 1.0, 1.5 ..... 4.5 mL of 100 )lg mL-1 of DPH solution by means of a micro burette. A 1 mL volume of iron(lll) reagent and 2 mL of mercuric thiocyanate reagent solution were added and diluted to volume with water. The absorbance of the solution was meas­ured at 460 nm against the reagent blank after 5 min. The increase in absorbance was plotted against the drug concentration.

Formulations Twenty tablets were finely powdered. An amount

of the powder equivalent to 200 mg of DPH was ex­tracted with three 30 rnL portions of water and filtered into a 100 mL standard flask. Washed the filter and diluted to mark with water and subjected to analysis using the general procedures. In respect of benadryl syrup, 10 rnL containing 25 mg of DPH was used as such for titrimetric analysis. For spectrophotometric work the syrup was sequentially diluted to obtain 100 )lg rnL- 1 of DPH and subjected to analysis.

Results and Discussion

Optimisation of experimental variables The stoichiometric study revealed that the reaction

between DPH and AgN03 proceeds in the molar ratio of 1: 1 which is in conformity with the following reac­tion scheme :

DP. HCl ~ DPH+ + cr

cr + Ag+ ~AgCI (S)

A 0.5 mL of iron(lll) indicator and 2 mL 1: 1 nitric acid were found to give satisfactory results. Since AgCI is more soluble than AgSCN leading to low values for chloride content and drug recovery, 2 mL of nitrobenzene were added to eliminate this source of error25

•

Fig. 1 shows the absorption spectra of the complex and the reagent blank against the blank and water,

383

Articles

respectively. The absorption is maximum at 460 nm which is in agreement with the earlier observations in perchloric acid medium26

•27

. Since the method is es­sentially the measurement of iron(III) thiocyanate complex, variables that influence the sensitivity and stability of the colour were optimised. Of the several acids tested as the reaction medium, perchloric acid was preferred because of high sensi tivity and stability of the colour and lower blank absorbance.

Different sources of iron(Ill) may be used, such as iron(III) nitrate27

, iron(III) alum28 and iron perchlo­rate29. Iron(III) nitrate was used since it gave better sensitivity and because of high chloride content in iron perchlorate. A 1 mL volume of the reagent solu­tion was found optimum in a total volume of I 0 mL,

0.4 or--------------------,

., "' c: •

0.3

-e 0.2 ~ .0 <

0.1

A

B

0+--.---r-~--r--~--.---r-~

400 420 440 460 480 500 520 540 560

Wavelength,nm

Fig. !-Absorbance spectra: A : 300 )lg DPH + 2 mL mercury (II) thiocyanate+ l mL iron (Ill) nitrate per I 0 mL versus reagent blank 8 : Reagent blank versus water.

Indian J. Chern. Technol., July 2003

and 2 mL of mercuric thiocyanate were found to yield optimum absorbance. The colour formation was com­plete in 5 min and stable for a further period of 2 h. Solvents such as water26

, ethanof7 and methanol30

have been used _to prepare mercuric thiocyanate solu­tion and in the present investigation methanolic solu­tion was found to give a higher sensitivity.

Analytical parameters Titrimetry was found to be applicable in the range

6-40 mg, outside which the results were deviant. The relationship between the titration end-point and the drug amount was examined by calculating the corre­lation coefficient value, r, via linear least squares treatment and was found to be 0.9750 indicating that the reaction between DPH and AgN03 occurs stoichi­ometrically in the ratio of 1:1 in 6-40 mg range.

Beer' s law is obeyed in the range 5-45 Jlg mL-1 of DPH. The apparent molar absorptivity and Sandell sensitivity were 3.45 x 103 L moL-1 cm· 1 and 84.5 ng cm-2

, respectively. The linear plot gave the regression equation.

A=- 0.0098 + 0.0121 C

Where, A, is the absorbance and C concentration in Jlg mL- 1

, and with a correlation coefficient of 0.9620 (n=10). The limit of detection was 0.74 Jlg mL-1 and the limit of quantification 2.4/ Jlg nlL-1

•

Accuracy ,and precision To find out the accuracy and precision of the meth­

ods, seven replicate determinations in the same solu­tion containing three different levels of DPH were performed. The percentage recovery, the RSD and range of error at 95% confidence level presented in Table 1 indicate high accuracy and precision of the methods.

Table !- Evaluation of accuracy and precision of the proposed methods

Titrimetry Spectrophotometry

Drug Drug Error,% RSD, % Range of Drug Drug Error,% RSD, % Range of taken, mg found*, error,% taken, )lg found*, error,%

mg )lg

10 10.19 1.90 1.31 1.30 100 101.67 1.67 1.85 1.84

15 15.09 0.60 0.88 0.87 250 248.39 0.64 0.78 0.78

25 25.25 1.00 0.74 0.73 300 300.90 1.30 1.09 1.08

30 29.75 0.83 0.10 0.10 400 401.65 0.41 0.88 0.87

*Values obtained for seven determinations.

384

Basavaiah & Charan: Titrimetric and spctrophotometric methods for determination of diphenhydramine hydrochloride Articles

Table 2-Results of determination of DPH in tablets• and syrup• by the proposed methods

Method Brand name Label claim Found*,% recover~± SD Student's F-value mg Proposed Reference t-value (6.39).

method method (2.77)

Benadryl capsules 25 101.73 ± 0.31 101.90 ± 0.68 0.51 4.81 Titrimetry 50 101.16 ± 0.44 101.90 ± 0.68 2.05 2.39

Benadryl syrup 12.5 99.10 ± 1.20 101.90 ± 0.68 2.02 3.11

Benadryl capsules 25 100.24 ± 1.58 101.90 ± 0.68 2.15 5.40 Spectrophotometry 50 101.33 ± 0.73 101.90 ± 0.68 1.27 1.15

Benadryl syrup 12.5 101.40 ± 0.39 101.90 ± 0.68 1.44 3.04

*Average value of five determinations • Marketed by Parke-Davis •values in the parenthesis are the tabulated values at the 95% of confidence level.

Interferences Bromide which interferes in titrimetry and sul­

phate, phosphate, ethyl and isopropyl alcohol, and acetone which interfere in the spectrophotometric procedure are not present in either the reagents em­ployed or in the dosage forms used. Hence the meth­ods are free from error due to them.

Application The present methods have been successfully ap­

plied for the determination of DPH in capsules and syrup. The results summarized in Table 2 suggest that the methods can be economically used for the accu­rate analysis of formulations containing DPH. The results also indicate that excipients like starch, talc, lactose, sodium alginate and magnesium stearate do not interfere in the determination.

Conclusions The proposed methods are simple, fast and accu­

rate. The time required for analysis in either method is less than 15 min. There is no need for preliminary separation of DPH from excipients.

Acknowledgements The authors thank the Quality Control Manager of

M/s Parke Davis, India, for kindly providing pure DPH as gift.

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