Spectrophotometric Methods for the Assay of Pyrilamine Maleate Using Chromogenic Reagents

Simple, accurate and reproducible UV spectrophotometric methods were established for the assay of pyrilamine maleate (PYRA) based on the formation of oxidative coupling and precipitation, charge transfer complexation products. Method A includes the oxidative coupling reaction of PYRA with 3-methyl-2benzathiazolinone hydrazone (MBTH) in presence of Ce(IV). The formation of oxidative coupling product with 4-amino phenazone (4-AP) in presence of K3Fe(CN)6 is incorporated in method B. Precipitation/charge transfer complex formation of the PYRA with tannic acid (TA)/Metol-Cr(VI) in method C were proposed. The optical characteristics such as Beers law limits, molar absorptivity and Sandell’s sensitivity for the methods (A-C) are given. Regression analysis using the method of least squares was made to evaluate the slope (b), intercept (a) and correlation coefficient (r) and standard error of estimation (Se) for each system. Determination of pyrilamine in bulk form and in pharmaceutical formulations were also incorporated.


Introduction
Pyrilamine (as maleate PYRA) is an antihistamine with a low incidence of side effects.It is effective for use in perennial and seasonal allergic rhinitis, vasomotor rhinitis, allergic conjunctivitis due to inherent allergens and foods, mild uncomplicated allergic skin manifestations of urticarea and angiodesma, angioedema, demographism and aneceoratum of reactions of blood or plasma.It is an antagonizing agent that competes for receptor sites with natural histamine, a biogenic amine present in most body cells and tissues.
A very few physicochemical methods appeared in the literature for the assay of PYRA 1 in biological fluids and pharmaceutical formulations.Most of them are based on visible spectrophotometric methods [2][3] , HPLC [4][5][6][7][8] , GC [9][10] , fluorimetry [11][12][13] , LC-MS 14 , GC-MS [15][16][17] , & TLC 18 , Mass 19 .The analytically useful functional groups in PYRA have not been fully exploited for designing suitable visible spectrophotometric methods and so still offer a scope to develop few more visible spectrophotometric methods with better sensitivity, selectivity, precision and accuracy.The author has made some attempts in this direction and succeeded in developing visible spectrophotometric methods by exploiting various functional groups of PYRA.All these methods have been extended to pharmaceutical formulations as well.

Experimental
An Elico, UV -Visible digital spectrophotometer with 1 cm matched quartz cells were used for the spectral and absorbance measurements.An Elico LI-120 digital pH meter was used for pH measurements.

Method A
Aliquots of standard PYRA solution (0.5-3.0 mL, 25 µg.mL -1 ) were transferred into a series of 25 mL calibrated tubes.Then 0.5 mL (8.56x10 -3 M) of MBTH solution was added and kept aside for 5min.After that 1 mL (1.58x10 -2 M) of ceric ammonium sulphate was added and kept aside for 10 min.The volume was made up to the mark with distilled water.The absorbance was measured at 460 nm against a similar reagent blank.The amount of PYRA was computed from its calibration graph (Figure 1).

Method B
Aliquots of standard PYRA (0.5-3.0 mL, 25 µg.mL -1 ) solution, 0.5 mL of pyridine, 1 mL of 4AP (4.92x10 -2 M) and 0.5 mL of K 3 [Fe(CN) 6 ] (1.22x10 -1 M) were added successively into a series of 10 graduated tubes and the total volume in each flask was brought to 10 mL with distilled water and kept aside for 5 min.The absorbances were measured at 500 nm against a reagent blank.The coloured species was stable for 30 min.The drug concentration was deduced from a calibration graph (Figure 2).

Method C
Aliquots of standard drug solution (0.5-3.0 mL 400 µg/mL) were delivered in to a series of centrifuge tubes and the volume in each test tube was adjusted to 3.0 mL with 0.01 N HCl.Then 1.0 mL of Tannic acid was added and centrifuged fro 5 min.The precipitate was collected through filtration and subsequently washed with 2.0 mL of distilled water.The filtrate and washings were collected in a 25 mL graduated test tube.Then 15ml of p H 3.0 buffer and 1.5 mL of PMAP solution were successively added.After 2 min, 2.0 mL of Cr (VI) solution was added and the volume was made up to the mark with distilled water.The absorbance was measured after 5 min at 560 nm against distilled water.A blank experiment was also carried out omitting the drug.The decrease in absorbance and intern drug concentration was obtained by substracting the absorbance of the test solution from the blank.The amount of drug was calculated from Beer's law plot (Figure 3)

Method C
Step I Step II

Results and Discussion
The optimum conditions for the color development of methods A, B and C were established by varying the parameters one at a time, keeping the others fixed and observing the effect produced on the absorbance of the colored species.
The list of proposed and reported methods was given in Table 1.The optical characteristics such as Beers law limits, molar absoptivity and Sandell's sensitivity for the methods (A-C) are given Table 2. Regression analysis using the method of least squares was made to evaluate the slope (b), intercept (a) and correlation coefficient (r) and standard error of estimation (Se) for each system.
The accuracy of the methods was ascertained by comparing the results by proposed and reference methods, statitistically by the t-and F-tests.The comparison shows that there is no significant difference between the results of studied methods and those of the reference ones.The similarity of the results is obvious evidence that during the application of these methods, the excipients are usually present in pharmaceutical formulations do not interfere in the assay of proposed methods.As an additional check of accuracy of the proposed methods, recovery experiments were carried out.The recoveries of the added amounts of standard drug were studied at three different levels.Each level was repeated for 6 times.From the amount of drug found, the % recovery was calculated.The higher λ max values of all the proposed methods have a decisive advantage since the interference from the associated ingredients should be generally less at higher wavelengths than at lower wavelengths.Thus the proposed visible spectrophotometric methods are simple and sensitive with reasonable precision, accuracy and constitute better alternatives to the existing ones to the routine determination of PYRA in bulk forms and pharmaceutical formulations.

Conclusion
The proposed methods exploit the various functional groups in PYRA molecule.The decreasing order of sensitivity (∈ max ) among the proposed methods are (Method A > Method B > Method C) respectively.The concomitants which do not contain the functional groups chosen in the present investigation do not interfere in the color development by proposed methods.Thus the proposed methods are simple, sensitive and selective with reasonable precision and accuracy and constitute better alternatives to the reported ones in the assay of PYRA in bulk form and pharmaceutical formulations (Table 3).

Table 1 .
List of proposed and reported visible spectrophotometric methods

Table 2 .
Optical and regression characteristics, precision and accuracy of the proposed

Table 3 .
Assay of PYRA in pharmaceutical formulations