------ Raf. J. Sci., Vol. 23, No.2 pp 72-84, 2012------ 72 Spectrophotometric Determination of Tetracycline by Coupling with Diazotised 4-Aminoantipyrine in Presence of Cetylpyridinium Chloride Nabeel S. Othman Rasha J. Al-Ashow Department of Chemistry College of Science University of Mosul (Received 26/ 6 / 2011 ; Accepted 31 / 10 / 2011 ) ABSTRACT A spectrophotometric method for the determination of microgram amounts of tetracycline -HCl(TCH) has been proposed. The method is based on coupling of tetracycline-HCl with diazotized 4-aminoantipyrine in presence of cetylpyridinium chloride in alkaline medium. The molar absorptivity of the formed dye reached to 1.92×10 4 l.mol -1 . cm -1 at 537 nm and Beer ' s law is obeyed within the range of 10-300 μg of tetracycline-HCl /10 ml (i.e.1.0 – 30 ppm). The colour reaction was highly stable, a relative error ranged from - 2.5 to + 0.21 % and a relative standard deviation of ± 0.37 to ± 0.73 %, depending on concentration level of tetracycline-HCl. The proposed method has been applied successfully to the determination of tetracycline-HCl in pharmaceutical preparations. Keywords: Tetracycline-HCl; 4-aminoantipyrine; diazo-coupling; spectrophotometry. ــــــــــــــــــــــــــــــــــــــــــــــــــــ ﺍﻟﺘﻘﺩﻴﺭ ﺍﻟﻁﻴﻔﻲ ﻟﻠﺘﺘﺭﺃﺴﺎﻴﻜﻠﻴﻥ ﺒﺎﻻﻗﺘﺭﺍﻥ ﻤﻊ ﺍﻟﻌﺎﻤل ﺍﻟﻤﺅﺯﻭﺕ4 - ﺍﻤﻴﻨﻭ ﺍﻨﺘﻲ ﺒﺎﻴﺭﻴﻥ ﺒﻭﺠﻭﺩ ﺴﻴﺘﻴل ﺒﺭﻴﺩﻨﻴﻭﻡ ﻜﻠﻭﺭﻴﺩ ﺍﻟﻤﻠﺨﺹ ﺍﻟﺘﺘﺭﺍﺴﺎﻴﻜﻠﻴﻥ ﻫﻴﺩﺭﻭﻜﻠﻭﺭﻴﺩ ﻤﻥ ﺍﻟﺼﻐﺭ ﻓﻲ ﻤﺘﻨﺎﻫﻴﺔ ﻜﻤﻴﺎﺕ ﻟﺘﻘﺩﻴﺭ ﻁﻴﻔﻴﻪ ﻁﺭﻴﻘﺔ ﺍﻗﺘﺭﺍﺡ ﺘﻡ. ﺘﻌ ﺘﻤﺩ ﺍﻟﻤﺅﺯﻭﺕ ﺍﻟﻌﺎﻤل ﻤﻊ ﺍﻟﺘﺘﺭﺍﺴﺎﻜﻠﻴﻥ ﺍﻗﺘﺭﺍﻥ ﻋﻠﻰ ﺍﻟﻁﺭﻴﻘﺔ4 - ﻜﻠﻭﺭﻴﺩ ﺒﺭﻴﺩﻨﻴﻭﻡ ﺴﻴﺘﻴل ﺒﻭﺠﻭﺩ ﺒﺎﻴﺭﻴﻥ ﺍﻤﻴﻨﻭﺍﻨﺘﻲ ﺍﻟﻘﺎﻋﺩﻱ ﺍﻟﻭﺴﻁ ﻓﻲ. ﺍﻟﻤﺘﻜﻭﻨﺔ ﻟﻠﺼﺒﻐﺔ ﺍﻟﻤﻭﻻﺭﻱ ﺍﻻﻤﺘﺼﺎﺹ ﻤﻌﺎﻤل ﻗﻴﻤﺔ ﺒﻠﻐﺕ1.92 × 10 4 ﻟﺘﺭ. ﻤﻭل - 1 . ﺴﻡ - 1 ﺍﻻﻋﻅﻡ ﺍﻟﻤﻭﺠﻲ ﺍﻟﻁﻭل ﻋﻨﺩ537 ﻨﺎﻨﻭﻤﻴﺘﺭ. ﺒ ﻗﺎﻨﻭﻥ ﺍﻟﻁﺭﻴﻘﻪ ﻭﺘﺘﺒﻊ ﻤﻥ ﺍﻟﺘﺭﺍﻜﻴﺯ ﻤﺩﻯ ﻓﻲ ﻴﺭ10 ﺍﻟﻰ300 ﻤﺎﻴﻜﺭﻭﻏﺭﺍﻡ/ 10 ﻤل) ﻤﻥ ﺃﻱ1 - 30 ﺠﺯﺀ/ ﻤﻠﻴﻭﻥ.( ﺠﻴﺩﺓ ﺒﺎﺴﺘﻘﺭﺍﺭﻴﺔ ﺍﻟﻠﻭﻨﻲ ﺍﻟﺘﻔﺎﻋل ﻴﻤﺘﺎﺯ ﻭ ﺒ ﻨﺴﺒﻲ ﺨﻁﺄ ﻴﺘﺭﺍﻭﺡ ﺒﻴﻥ2.5 - ﻭ0.21 % ﻭ ﺒﻴﻥ ﻨﺴﺒﻲ ﻗﻴﺎﺴﻲ ﺍﻨﺤﺭﺍﻑ0.37± ﻭ% 0.73± ﺍﻋﺘﻤﺎﺩﺍ ﻤﺴﺘﻭﻯ ﻋﻠﻰ ﺍﻟ ﺘﺭﻜﻴﺯ. ﺘﻡ ﺘﻘﺩﻴﺭ ﻓﻲ ﺒﻨﺠﺎﺡ ﺍﻟﻁﺭﻴﻘﺔ ﺘﻁﺒﻴﻕ ﻫﻴﺩﺭﻭﻜ ﺍﻟﺘﺘﺭﺍﺴﺎﻴﻜﻠﻴﻥ ﻠﻭﺭﻴﺩ ﻓﻲ ﺍﻟﺼﻴﺩﻻﻨﻴﺔ ﺍﻟﻤﺴﺘﺤﻀﺭﺍﺕ.