Bioequivalence & Bioavailability
Research Article
Volume 2 Issue 2 - 2016
Spectrophotometric Determination of Sodium Salicylate in Pharmaceutical Preparations by Coupling with Diazotized Para-Amino Benzoic Acid
Mohauman Mohammad AL-Rufaie*
Chemistry Department, Kufa University, Iraq
Received: July 17, 2016 | Published: September 20, 2016
*Corresponding author: Mohauman Mohammad AL-Rufaie, Chemistry Department, College of Science, Kufa University, Iraq, Email: ;
Citation: AL-Rufaie MM (2016) Spectrophotometric Determination of Sodium Salicylate in Pharmaceutical Preparations by Coupling with Diazotized Para-Amino Benzoic Acid. MOJ Bioequiv Availab 2(2): 00020. DOI: 10.15406/mojbb.2016.02.00020


A rapid, sensitive and simple spectrophotometric procedure for the assay of the smaller amounts measures from sodium salicylate at pharmaceutical preparations (topical-solution) was examined. The procedure is focus on a diazotization and reaction coupling between sodium salicylate and diazotized para-amino benzoic acid in alkaline medium for the formation of an intensive bright yellow soluble water colour which was being stable, which gives highly absorption at 452nm. The law of Beer was Introduced on the range of concentration from (2-30) μ of sodium salicylate, the molar absorptivity and the sensitivity of Sandell index were 8.5013×1031 mol-1 cm-1, 0.0188 μg/cm2 subsequently, The procedure does not need to the control of temperature and the extraction by the solvent. The perfect circumstances for all colour increasing are portrayed and the examined procedure has been very good application on the assay of sodium salicylate at topical-solution preparations. The general excipients materials and additives did not affect the examined procedure.

Keywords: Diazotization coupling reaction; Spectrophotometric determination; Sodium salicylate; Para-amino benzoic acid


Sodium salicylate is the crystalline powder and white or almost white colour, or crystals with small, colourless or flakes shiny, water freely soluble, ethanol sparingly soluble (96 per cent). It is a sodium 2-hydroxybenzene carboxylate, C7H5NaO3, where as its chemical structure is shown in Figure 1 [1].

Figure 1: Chemical structure of sodium 2-hydroxybenzene carboxylate.

Sodium salicylate was a salt for sodium with salicylic acid. It was formed by the reaction between sodium phenolate and carbon dioxide by using higher pressure and temperature. In the literature ,Where it had extracted by methyl salicylate that it was obtaining from winter green plants or from sweet birch tree that result from the bark by adding it with surplus of consented solution (sodium hydroxide) and making reflux operation for it with heating [2].

The substance is utilized as therapy as an antipyretic and a pain relieving. Sodium salicylate additionally performs about as non-steroidal calming (NSAID) drug, also it affects as anti cancer in the infected cells [3-5] and otherwise necrosis [6]. It was using as Potential alternative for aspirin drug that was giving to sensitive people for this drug. It may additionally be utilized as a phosphor for the discovery of vacuum ultraviolet radiation and electrons [7].

In the present work, the stable diazotized para-amino benzoic acid reagent has been proposed to determine sodium salicylate in pharmaceutical preparations (topical-solution) by the reaction (azo-coupling) in basic medium. The serious splendid yellow that was resulting in the product it was spectrophotometrically computed at 452 nm. The new analytical method is accurate, rapid and simple. The procedure was making a very good application in the investigation for sodium salicylate in pharmaceutical preparations (topical-solution).

Experimental Apparatus

  1. Every absorbance and spectral estimations were performed on double-beam applied UV-Visible 160 digital recording spectrometer (Japan).
  2. Heating-cooling water bath (Haake, Fe3).
  3. Analytical balance (Sartorius BL 210S).
  4. pH meter, Jenway 3020.

Material and Reagents

The Chemical substances that were utilized in the procedure with very high purity degree and did not required to purification, all solutions were obtained by the next steps.

Sodium salicylate (500 μ solution

This solution is supplied by dissolution for (0.05g) of sodium salicylate (SDI) in 100mL deionized water. This solution is at that point exchanged to a dim bottle where it is steady for no less than 1 month [1].

Para-amino benzoic acid (3 x10-3M) (Diazotized reagent solution)

 It was obtained by dissolution (0.01 gm) of para-amino benzoic acid (Fluka) with highly purity in (5mL) of deionized water after that (2 mL) of 1 M HCl (BDH) was added and shacked well, then Continued by adding of (0.009 gm) from sodium nitrite (BDH) shake completely, after that the volume was diluted to (25 mL) and the was cooling at temperature degree 5 °C for 30 min, The solution was taken to a dark bottle and leaved in the refrigerator that was steady for two weeks.

Hydrochloric acid (BDH) (1M)

It was provided by dissolution reasonable measure of concentrated hydrochloric to (100 mL) by deionised water.

Sodium hydroxide (BDH) (0.5M)

It was supplied by dissolution (2.0 gm) of sodium hydroxide at (100 mL) volumetric flask; the volume was completed to the lebal with deionized water.


Separately, volumetric flasks (25mL) the volumes was increasing of (500 μ ) sodium salicylate from the standard working solution were exchanged to cover a range between (2-30) μ in the end dissolution, (0.5M) sodium hydroxide (1mL) solution, (2 mL) form diazotized para-amino benzoic acid solution (0.003M) are added and dissolute to the lebal by deionized water. After that it was mixing very well, then it was leaving for (15min) at (25 °C), the intensive bright yellow colour for the result was gave the highly absorbance measured at 452 nm against a blank reagent that was including all the materials without the sodium salicylate and the calibration curve was built.

Assay procedure for salicylic acid in pharmaceutical preparations

A topical-solution sample (25 mL) was conveyed to volumetric flasks (100 mL) then it was dissolute to the mark with deionized water. An aliquot for this solution (1mL) was put in volumetric flask (25 mL), (2mL) (0.003M) diazonium agent, 1mL (0.5M NaOH), that were adding , the completed volume to the lebal by deionized water, put away for (15 minutes), the measured absorbance for this solution was at 452 nm. The salicylic acid concentration was given by utilizing the calibration curve officially made and portrayed previously.

This procedure was obtained for 3 trade kinds for topical-solution that was giving in the following

  1. Avomack topical-solution (MECP, Riyadh-KSA): containing 16.7% w/w Salicylic acid according to the product label.
  2. Duo film topical-solution (ITD, Sligo, Ireland): containing 16.7% w/w Salicylic acid, according to the product label.
  3. Nocal topical-solution (Jordan): containing 10% w/w Salicylic acid, as indicated by the item mark.

Furthermore, the % Salicylic acid produced by the suggested technique is as per the following.

Sodium salicylate, It was result from the multiply of the quantity of the salicylic acid per the sample by the conversion factor of 1.159, which was being equal to the output of dividing the molecular weight of sodium salicylate on the molecular weight of the salicylic acid.

Results and Discussion

The perfect reaction circumstance was studied, the impacts of different parameters on the optical characteristics for the azo colour have been examined and the reaction circumstances are given.

Reagent volume effect

The diazonium reagent (0.003M) volumes was examined by utilizing the range between (0.1-5 mL) on the absorbance intensity, it was has been studying (2 mL) volume was the perfect volume.

Acid volume effect

The presence of acid that was adding in the suggested procedure resulted in a increasing on the absorbance intensity for the formed product, so thus, acids like CH3COOH, HCl, H2SO4 and HNO3 are checked up, all these acids was giving verging on equivalent intensity, therefore HCl was chosen for the next tests and, (2 mL) volume was the perfect from the chosen acid that was obtaining highly sensitive which it utilized in following experiments.

Base volume effect

The colour product formed was giving highly absorbance and it was making more stable and intense in basic medium, so that, the various basic solutions effect on the colored result were examined like ammonium hydroxide sodium hydroxide, sodium acetate, sodium carbonate and potassium hydroxide. Highly stability and sensitivity were given just when the reaction was performed with the attendance of sodium hydroxide solution. The various concentrations of NaOH effect were examined, (0.1-4 M) volumes for the using base with concentration (0.5 M) appears to be ideal. The (0.5 M) NaOH volumes effect were as well examined between (0.1 to 5 mL) (1mL) volumes was the perfect volume and utilizing in the next tests.

Order Addition effect

The ideal order of addition that obtains the maximum absorption was (D+B+R) wherever (B=base, D=drug substance and R=reagent) which was choosing in the following experiments.

Temperature effect

The produced compound the studied procedure was examined at various temperatures. The absorbance values that obtained from The outcomes demonstrate that it was staying about consistent in the range of temperature 0-70 °C, While, the absorbance value at the increasing temperatures was Reduced, demonstrating the disintegration of the result on the heating for a long time. The stability of the colored compound was between 15-20 °C so that, this range of temperature was chosen in examined procedure.

Reaction Time effect

The highly intensity of colour arrived after that the sodium salicylate was reacting instantly with the solution of reagent. It was making steady after time (15 minute). So that (15 minute) evolution time was taken as the prefect in the common method of assay. The colour resulted was steady for (2 days).

The practical circumstances for the investigation for sodium salicylate were instituted. The reaction Diazonium happened in the acidic medium [8] and (1M) concentration for hydrochloric acid was chosen [9], the absorbance for the colour compound formed has been highly stable and intense in basic medium [10].

Absorption Spectra [11]

The dilute solutions from sodium salicylate in under the foregoing from the Practical circumstances, was blending with diazotized para-amino benzoic acid in Attend the sodium hydroxide, the bright yellow intense colour compound instantly established. It gives highly absorption at 452nm at the same time the reagent solution (blank) gives no absorption at the same wavelength (Figure 2) gives the spectra of absorption. The highly absorption wavelength was at 452nm it was yet utilized for the next determinations.

Figure 2: The spectra of absorption.

Calibration Curve [12]

By using the established practical circumstances. The linear relationship between the concentration of sodium salicylate and the absorbance was noted during the range of concentration (2- 30μ (Figure 3) and a correlation coefficient and the intercept were 0.9990, 0.0821 respectively. The beer's law was given negative deviation at the concentrations up to (30 μ from the sodium salicylate. The molar absorptivity was 8.5013×1031 mol-1 cm-1.

Figure 3: Calibration curve of sodium salicylate (SS).

Precision and accuracy [13]

To investigate the precision and accuracy of the calibration curve, sodium salicylate was designating at three various concentrations. The results appeared in Table 2 was demonstrated a good satisfactory accuracy and precision.

Product Nature of and the Mechanism of Reaction [14,15]

To observe the structure for the product compound (the ratio between sodium salicylate to diazotized para-amino benzoic acid) for the intense bright yellow azo colour that was resulting from reaction, mole-ratio method and Job’s method of continuous variations have been utilized. The data that was resulting discover that the colour has been established by the reaction of sodium salicylate with diazotized para-amino benzoic acid with a ratio of 1:1, Figure 4 & 5 demonstrating a mono azo colour with possibly of the next schema Figure 6. The stability constant was computed for the azo dye in the aqueous solution, by using the circumstances of practical method, the constant was equal to .28×106 1.mole-1.

The regression equation was given, and the analytical data for this method are obtained in the next (Table 2)

Figure 4: Mole ratio plot.

Figure 5: Continuous variation plot.

Figure 6: Colored Azo dye.

Pharmaceutical Product

Conc. Salicylic Acid
µg. ml-1

E %

Rec. %


Conc. Sod. Salicylate
µg. ml-1*



Avomack Topical-Solution

























































Table 1: Salicylic acid investigation in some pharmaceuticals by utilizing the suggested technique.

*Every of the values that was utilizing in the table. It relates with the quantity.


Conc. of Sodium Salicylate mg per 25ml

Error %*


R.S.D %*





















Table 2: Precision and accuracy of examined procedure.

Interferences Effect [16]

The probably analytical enforcements were evaluated for the new suggested Procedure, the interferences effect for the excipients on the different levels for the quantitative assay of (20μ Salicylic acid by utilizing the studied procedure have been tested, the results are obtained in Table 3.


Studied Method

Regression Equation


Linear Range (μg ml-1)


Correlation Coefficient, r2


Detection Limit (μg ml-1)


Average of Recovery %


Average of RSD %


Sandell’s Sensitivity (μg cm-2)


Molar Absorptivity (l mol-1 cm-1)


Table 3: Analytical properties of the developed method for the investigation of sodium salicylate.


Conc. of Salicylic acid µ


REC% Recovery













Mg Stearate




Polyvinylpyrrolidone (PVP)




Benzoic Acid








Table 4: Excipients effect on the investigation (20 μ of salicylic acid.

Pharmaceutical Preparation

Rec.* % proposed method

Rec.* % standard method

Sodium Salicylate Pure



Avomack Topical-Solution



Duo film Topical-Solution



Nocal Topical-Solution



Table 5: Application of the examined and standard procedures for the investigation of topical-solution having Salicylic acid.

Application Procedure

The examined procedure were checked up on the quantification of salicylic acid in topical- solution preparations. Three kinds of topical-solution preparations having salicylic acid were tested, they was obtaining a better precision and accuracy as appeared in Table 6. The examined procedure was given successful comparison with the standard procedure [1].


A sensitive, simple, rapid and precise spectrophotometric procedure has been evaluation for the investigation of microgram quantities of sodium salicylate in the aqueous solution depended on the diazotization reaction coupling with para-amino benzoic acid the procedure does not need to the control of temperature control and solvent extraction.


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