* Corresponding author. E-mail address esraarasul@gmail.com (E. R. Radhi) © 2023 by the authors; licensee Growing Science, Canada doi: 10.5267/j.ccl.2023.6.001 Current Chemistry Letters 12 (2023) 677–684 Contents lists available at GrowingScience Current Chemistry Letters homepage: www.GrowingScience.com Batch and merging-zone flow injection methods for determination of tetracycline hydrochloride Esraa Rasool Radhi a* , Khdeeja Jabbar Ali b and Fatima Hydar Abdul Hussein c a Ministry of Education, Kufa, Iraq b Chemistry Department, Education for Girls Faculty, Kufa University, Kufa, Iraq c Faculty of Pharmacy, Kufa University, Kufa, Iraq C H R O N I C L E A B S T R A C T Article history: Received December 25, 2022 Received in revised form January 28, 2023 Accepted May 16, 2023 Available online May 16, 2023 The objective of the present work is to develop batch and merging-zone flow injection methods for sensitive and accurate spectrophotometric determination of tetracycline hydrochloride. The methods depend on the oxidation of the studied drug with potassium permanganate in an alkaline medium, and the absorbance of the green oxidation product was measured at 610 nm. The calibration graphs in both procedures were linear in the concentration ranges of 0.5 – 25 and 1 – 25 μg mL −1 using the spectrophotometric and merging-zone flow injection methods, respectively. Specific and molar absorption coefficients, limits of detection and quantification, and Sandell’s sensitivity were calculated. The suggested procedures were further applied to the quantitative determination of tetracycline in pharmaceutical formulations. © 2023 by the authors; licensee Growing Science, Canada. Keywords: Flow Injection System Batch Methods Tetracycline Hydrochloride Determination Potassium Permanganate 1. Introduction Flow injection analysis (FIA) is an easy and rapid technique that can be employed for unstable reactions or that do not reach the equilibrium state. 1 FIA systems have many advantages, such as the low cost of the system components, reduced consumption of reagent and sample solutions, high analytical frequency, and decreased waste generation. 2 The principal aim of different kinds of FIA techniques is to analyse the maximum number of samples using minimum amounts of sample and reagent and the spent analysis time. 3 The molecular formula of tetracycline is C22H24N2O8, and it possesses a broad spectrum antibacterial effect. Tetracycline is one of the most commonly used antibiotics in animal nutrition, feed additives and veterinary drugs in food-producing animals to promote growth. 4,5 Despite the high consumption of tetracycline, only a small portion of it can actually be absorbed by humans or animals, and it is difficult to biodegrade, 6 so a large quantity of tetracycline is excreted into different environmental media, including soil, surface water, groundwater, and wastewater. 7,8 This will lead to the spread of resistance genes in the environment. 9,10 Several analytical methods have been proposed for assaying tetracycline in pure form or in drug substances by high-performance liquid chromatography, 11,12 spectrophotometry, 13,14 flow injection analysis, 15,16 chemiluminescence, 17,18 spectrofluorimetry, 19,20 and electrochemical methods. 21,22 Most of these analytical methods, except for the flow-injection methods, consume large amounts of reagent, samples and solvents solutions, and take a long time to complete the reaction, in addition to the large amounts of toxic and harmful wastes thrown into the environment. Merging-zone flow injection method is a simple, fast, and effective technique to optimize many simple and complex classical reactions by reducing the consumption of the used solutions, analysis time reduction, and the interfering effect elimination with high reproducibility and throughput, so in the present work, simple, fast, and inexpensive batch and merging-zone flow injection methods were described for the spectrophotometric determination of tetracycline hydrochloride depending on the oxidation reaction with potassium permanganate as an oxidizing agent in an alkaline