H3po4

All chemicals used are of analytical grade. Orthophosphoric acid, H₃PO₄ (Loba Chemie), Hydrochloric acid, HCl (Loba Chemie CAS No: 7647-01-0, 37% purity), Sodium hydroxide, NaOH (Reckland Scientific Ec No: 215-185-5, 97% purity), Sodium Chloride, NaCl (Loba Chemie 99.5%, CAS: 7647-14-5), Malachite Green dye (CAS No.: 569-64-2; C₂₃H₂₅ClN₂ (chloride); molar mass 364.911 g mol⁻¹).

Analytical grade KH₂PO₄, K₂HPO₄ and H₃PO₄ were from Loba Chemie Pvt. Ltd. (Mumbai, India) while triethylamine and triethanolamine were from BDH Laboratory Supplies (Poole, UK). Tert-butylammonium hydroxide was from Sigma-Aldrich (Steinheim, Germany). HPLC grade acetonitrile (Scharlau, Barcelona, Spain) was used as organic modifier. Purified water was prepared using distillation by GFL distillation machine type 2001/4 (Gesellschaft für Labortechnik mbH, Burgwedel, Germany). Azithromycin dihydrate working standard was donated by the Drug Analysis and Research Unit, University of Nairobi, Kenya. The working standards of erythromycin A oxime, erythromycin A imino ether, N-demethylazithromycin, decladinosylazithromycin and azathromycin standards were purchased from Pfizer Inc. (Groton, CT, USA). Azithromycin tablets and suspensions were randomly purchased from various pharmacies in the Central Business District of the City of Nairobi. The innovator brand, Zithromax^®, was from Pfizer Laboratories Ltd. (Nairobi, Kenya). Azithromycin bulk sample was from SkyLight Chemicals (Nairobi, Kenya).

Gum tragacanth (GT), (molecular weight = 8.4 × 10⁵ g mol⁻¹), potassium persulfate (KPS), N,N’-methylenebisacrylamide (NMBA), N,N-dimethylacrylamide (DMA) were purchased from Sigma-Aldrich (Sigma Aldrich Chemicals Pvt. Ltd., Delhi, India). Graphite powder, H₃PO₄, KMnO₄, H₂O₂ and concentrated H₂SO₄ (98 wt %) were obtained from LOBA-Chemie (Loba Chemie Pvt. Ltd., Tarapur, Maharashtra, India). Hg²⁺ and Cr⁶⁺ ions solutions were obtained by dissolving mercury chloride (Sigma Aldrich Chemicals Pvt. Ltd., Delhi, India) and potassium chromate (Sigma Aldrich Chemicals Pvt. Ltd., Delhi, India) reagents in distilled water.