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Pak. J. Anal. Environ. Chem. Vol. 12, No. 1 & 2 (2011) 55-60
Spectrophotometric Determination of Primaquine by
Coupling with Diazotized p-Nitroaniline
Application to Pharmaceutical Formulations
Ferial Mahmood El-Samman, Asma Natiq Al-Irhayim* Department of Chemistry, College of Science, Mosul University, Mosul, Iraq Received 06 July 2010, Revised 12 August 2010, Accepted 10 October 2011 -------------------------------------------------------------------------------------------------------------------------------------------- Abstract
A simple spectrophotometric method for the determination of primaquine phosphate has been
developed. The method is based on the coupling reaction of primaquine phosphate in acidic
medium with diazotized p-nitroaniline, to form a yellow-orange water-soluble azo dye that shows
maximum absorption at 482 nm. Beer’s law is obeyed over the concentration range 5-300 µg of
primaquine phosphate in a final volum of 25 ml, i.e., 0.2-12 ppm with a molar absorptivity of
6.6104 l mol-1 cm-1 and Sandell’s sensitivity index of 0.0068 µg.cm-2, a relative error of -0.63 to
+0.32% and a relative standard deviation of ±0.18 to ±2.8%, depending on the concentration level.
Interferences due to excipients have been examined. The proposed method has been applied to the
assay of primaquine phosphate in pharmaceutical formulations (tablets).
Keywords: Primaquine; diazotized p-nitroaniline; spectrophotometry.
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Introduction

Primaquine
involves the dissolution of the sample in anhydrous Pentane-1,4-diamine] is an antimalarial drug that is acetic acid with gentle heating. When cooled, the very important for the radical cure of relapsing sample is titrated against perchloric acid [11], and vivax or ovale malaria and it eliminates tissue the end point is determined potentiometrically. infection. It is a member of the 8-aminoquinoline group of drugs and is often administered in been described for the determination of primaquine phosphate. Some of these methods are comprised There are various analytical procedures for of coupling of primaquine phosphate with the assay of Primaquine, an HPLC [3, 4], diazotized reagents [12, 13] to form an intensely- facilitating metabolic and pharmacokinetic studies coloured azo dye. Other colorimetric methods are [5]. A capillary electrophoresis method has been based on the reaction of primaquine with chloanily, developed that allows the separation and tetracyanoethylene [14, 15, 16] are reported. Some pharmaceutical formulations [6]. Other methods of these methods are time-consuming [12, 14] less such as voltammetry [7], gas chromatography- sensitive [16], require organic solvents [12], buffer mass spectrometry [8], and ultra-performance liquid chromatography [9] (UPLC) have also been proposed. The British Pharmacopoeia method [10] Pak. J. Anal. Environ. Chem. Vol. 12, No. 1 & 2 (2011)
the final solution was within the working range primaquine has been worked out, depending on p-nitroaniline to form a highly coloured dye that Procedure
has proved successful for the determination of primaquine in pharmaceutical preparations. An aliquot of standard solution containing 5-300 µg of primaquine phosphate was transferred Experimental
to a 25 ml volumetric flask. 2 ml of diazotized p- Apparatus
nitroaniline (5 mM) solution is added followed by 2 ml of 0.2 M acetic acid solution and diluted to Absorption spectra are carried out using the mark. The solution was mixed thoroughly and Shimadzu UV-Visible recording Spectrophoto- the absorbance was measured at 482 nm against the reagent blank within 2 h using 1-cm cells. Results and Discussion
carried out on a single beam Spectrophotometer Absorption spectra
dye formed as a result of mixing a dilute aqueous Philips PW 9420 pH-meter with a combined glass solution of primaquine phosphate and diazotized p- nitroaniline in acidic medium. The azo dye formed shows maximum absorption at 482 nm (Fig. 1), in Reagents
contrast to the reagent blank. The colour is formed immediately and is stable for at least 120 minutes.  Chemicals used are of analytical reagent grade. The calibration graph is linear over the range 0.2 -  Working primaquine phosphate solution, 12 ppm. The apparent molar absorptivity has been Diazotized p-nitroaniline reagent solution, .)
iv 0.200
5mM: A 0.1727 g of p-nitroaniline is dissolved in about 50ml distilled water. Then 20 ml of 1 M HCl is added and solution is heated, the clear mixture is then transferred to a 250 ml volumetric flask and is cooled to 0-5oC in an ice-bath. 8.65 ml of 1% NaNO2 is added and the mixture is stirred 400.0 50.0 (nm/Div.) 650.0
vigorously. After 5 min the solution is made up to Wavelength, nm
volume in 250 ml volumetric flask with cold water. Figure 1. Absorption spectra.
The solution is stored in a brown bottle in a refrigerator and is stable for at least one week. Effect of surfactants
Primaquine tablets solution: Four tablets The effect of different types and amounts were powdered accurately weighted and the weight of surfactants (cetyltrimethylammonium bromide of the powder equivalent to one tablet was (cationic surfactant), sodium dodecyl sulfate dissolved and transferred into a 100 ml calibrated (anionic surfactant) and Tween 80 on the colour flask and made up to volume with water. The intensity of the yellow dye has been examined and solution was filtered and the clear filtrate used for the results showed that the addition of surfactants the determination. An appropriate volume of the gives no significant effect. Therefore, it has been sample solution was diluted further with water so recommended to eliminate the use of surfactants in that the concentration of primaquine phosphate in Pak. J. Anal. Environ. Chem. Vol. 12, No. 1 & 2 (2011)
Effect of acid added
Table 2. Effect of different amounts of bases on absorbance of
Azo-dye.
Absorbance /ml of Base used
0.1 M of Base
examined for their effect on the colour intensity of the azo dye. The experimental order of the acid (sample+acid+diazotized reagent or sample + diazotized reagent + acid) added have no effect on the intensity of the coloured azo dye Table 1. Table 1. Effect of different amounts of acids on absorbance of
Azo-dye.
Absorbance/ ml of Acid used
0.1 M of Acid
Choice of diazotized reagent and amount
Diazotized p-nitroaniline reagent has been selected in this study because of following reasons; its the strongest diazonium electrophile ever used (due to the presence of the strong electron- withdrawing nitro group), the strongest colour contrast observed in its azo dye production (due to the presence of the p-nitro resonating group), the most sensitive diazo-coupling reaction diazotized p-nitroaniline reagent can give with aromatic components [17, 18] and the colour of the diazotized reagent solution is faint yellow thus giving lower blank values. The effect of the Effect of base
amount of diazotized p-nitroaniline reagent on the maximum absorbance of the dye formed has been investigated and the results are illustrated in various bases (NaOH, KOH, Na2CO3, NaHCO3, investigated for their effect on the colour intensity Table 3. Effect of amount of diazo reagent solution on absorbance.
of the azo dye. The colour of the azo dye changes from yellow-orange in acidic media to orange then Primaquine
Absorbance/ ml (5 mM) diazotized reagent
phosphate
to yellowish-brown and also becomes turbid as the amount of base increases (then pH of final reaction mixture is nearly five or more). In addition the blank changes from colourless in acidic media to medium because of strong colour contrast and better expected selectivity of determination because most compounds are activated towards 2 ml of 5 mM diazotized reagent has been selected for the procedure, since it gives the 4 ml of 0.1 M of the acid) is selected for the Pak. J. Anal. Environ. Chem. Vol. 12, No. 1 & 2 (2011)
Effect of time on color development
The effect of time with different amounts of primaquine phosphate has been investigated for Nature of the dye
maximum production of the dye and longer stability period Table 4. The maximum absorbace reading is given immediately and remains constant indicates that the dye has a composition of 1:1 for at least 120 minutes, independent of primaquine to diazotized p-nitroaniline reagent, the structure of the azo dye is represented in scheme 1. Table 4. Effect of time on colour development.
Absorbance/ g of primaquine phosphate
Scheme-1. Yellow-orange azo dye

Accuracy and precision
primaquine has been determined at three different concentrations Table 6. The low value of relative error and relative standard deviation shows that the Effect of organic solvents
Table 6. Accuracy and precision of the method.
Relative*
Amount of primaquine
Relative*
optical properties of the azo dye has been tested. standard
Phosphate taken (g)
The reaction mixture has been diluted using deviation%
different organic solvents and the data are shown Table 5. Effect of various organic solvents on the absobance of the
azo dye.

Absorbance
*Average of five determinations
Effect of interferences
In order to assess the possible analytical applications of the present proposed method, the interfering effect of foreign substances on the determination of 100 µg of primaquine phosphate is shown in Table 7. It is evident from the table that the proposed method is quite selective. Pak. J. Anal. Environ. Chem. Vol. 12, No. 1 & 2 (2011)
Table 7. Effect of excipients on the determination of different
using the present method in the determination of amount of primaquine phosphate.
Interferent
Recovery %
added g
Table 9. Comparison of the methods and experimental t-test
values.
Recovery %
British
Drug (tablets)
Present
pharmacopeia
method
method
The results show no significant difference Application of the method
between the present method and the standard To test the applicability of the present method it has been applied to the determination of primaquine phosphate in to drugs Table 8. some of analytical variables obtained from the present method and another spectrophotometric Table 8. Determination of primaquine phosphate in tablets.
g Primaquine
Manufacturing
Recovery*
Table 10. Comparison of the methods.
phosphate
Present
measured
Literature
Analytical parameters
Present method
contains primaquine phosphate 26.3 mg which is From the results, it can be shown that good agreement has occurred between the amount of primaquine phosphate present and that measured Comparison of the methods and t-test

and British pharmacopeia standard method [10] for the determination of primaquine phosphate in two * Sulaiman S.T. and Amin D., Inteern. J. Environ. Anal. Chem.18 drugs, is based on the t-test to show the ability of Pak. J. Anal. Environ. Chem. Vol. 12, No. 1 & 2 (2011)
M. L. P. M. Arguelho, M. V. B. Zanoni and over the published methods that it occurs at room N. R. Stradiotto, Anal. Lett., 38 (2005) 1415. temperature and not specific for a particular. I. Brondz, A. B. Fialkov, and A. Amirav, J. Conclusion
V. G. Dongre, P. P. Karmuse, P. R. Pilla and A. Kumar, J. of Pharm. and Biomed. precise, and accurate determination of primaquine British Pharmacopeia on CD-ROM (System phosphate with an application to pharmaceutical analysis. The short analysis time and low costs are the main advantages of this method for routine A. D. Skoog, and D. M. West, Fundamental of Analytical Chemistry, (Rinehart and References
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