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)μg.ml^–1 of sodium salicylate, the molar absorptivity and the sensitivity of Sandell index were 8.5013×10³1mol^–1cm^–1, 0.0188μg/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 (96per cent). It is a sodium 2–hydroxybenzene carboxylate, C₇H₅NaO₃, where as its chemical structure is.¹ 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).

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.

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 μg.ml^-1) 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 μg.ml^-1 ) sodium salicylate from the standard working solution were exchanged to cover a range between (2-30) μg.ml^-1 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.

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.

1. 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.

2. 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, (2mL) volume was the perfect from the chosen acid that was obtaining highly sensitive which it utilized in following experiments.

3. 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, (0.1–4M) volumes for the using base with concentration (0.5M) appears to be ideal. The (0.5M) NaOH volumes effect were as well examined between (0.1 to 5mL) (1mL) volumes was the perfect volume and utilizing in the next tests.

4. 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.

5. 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.

6. 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 medium⁸ 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 spectra¹¹

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 1 gives the spectra of absorption. The highly absorption wavelength was at 452nm it was yet utilized for the next determinations.

Figure 1 Chemical structure of sodium 2-hydroxybenzene carboxylate.

Calibration curve¹²

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 (2–30μg.ml–1) (Figure 2) 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 (30μg.ml–1) from the sodium salicylate. The molar absorptivity was 8.5013×103l mol–1 cm–1.

Figure 2 The spectra of absorption.

Precision and accuracy13

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 3, Figure 4 demonstrating a mono azo colour with possibly of the next schema. 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 3 Calibration curve of sodium salicylate (SS).

Interferences effect¹⁶

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 (20μg.ml–1)of Salicylic acid by utilizing the studied procedure have been tested, the results are obtained in Table 3.

Application procedure

The examined procedure were checked up on the quantification of salicylic acid in topical– solution preparations Table 4. Three kinds of topical–solution preparations having salicylic acid were tested, they was obtaining a better precision and accuracy as appeared in Table 5. The examined procedure was given successful comparison with the standard procedure.¹

Figure 4 Mole ratio plot.

Figure 5 Continuous variation plot.

Figure 6 Colored Azo dye.

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.

None.

The author declares no conflict of interest.

1. British Pharmacopoeia. The Stationery Office on behalf of the Medicines and Healthcare products Regulatory Agency (MHRA). 5th ed. London, 2007.
2. Lehman JW. Operational Organic Chemistry. 4th ed. 2009.
3. Klampfer L, Jörg, Hans–Georg W, et al. Blood. PMID. 1999;93(7):942386.
4. Rae C, Susana L, Steven JT, David JM. Proceedings of the National Academy of Sciences of the USA, 2007;104(31): 12790.
5. Stark LA, Kirsten R, Owen JS, et al. Aspirin activates the NF–κB signalling pathway and induces apoptosis in intestinal neoplasia in two in vivo models of human colorectal cancer. Carcinogenesis. 2007;28(5):968–976.
6. Schwenger P, Edward YS, Jan V. Inhibition of Tumor Necrosis Factor–induced p42/p44 Mitogen–Activated Protein Kinase Activation by Sodium Salicylate. The Journal of Biological Chemistry. 1996;271(14):8089.
7. Samson J. Pied Publications. 2012. 432 p.
8. Morrison RT, Boyed RN. Organic Chemistry. 3rd ed. 1973. 451 p.
9. Al–Abachi MQ, Al–Delami AMS, Al–Najafi AS. Analyst. 1988;113:1661.
10. Roberts JD, Caserio MC, Benjamin WA. Basic Principles of Organic Chemistry. New York; 1964.
11. Al–Rufaie MMW. Journal of pharmacy and pharmaceutical sciences. 2016;5(3):172.
12. Abdul Satar RS. Ph. D. Thesis, Baghdad University. Iraq; 2006.
13. Al–Rufaie MM, Al–Sharefy AN, Kathem KH. Spectrophotometric Determination of Doxycycline Hyclate in Pharmaceutical Preparations Using Oxidative coupling reaction. Journal of Applicable Chemistry. 2013;2(4):931–939.
14. Rathod KM, Thaker NS. Synthesis and Antimicrobial Activity of Azo Compounds Containing m–Cresol Moiety. Chemical Science Transactions. 2013;2(1):25–28.
15. Marmion DM. Hand book of colorant. New York: Wiley; 1999.
16. Al–Rufaie MM, Al–Sharefy AN, Kathem KH. International Journal of Uni. Pharmacy and Bio Sciences. 2013;2(4):2319.