Proceedings of the International scientific and practical conference ―Paris Science and Education Forum‖ (March 2-4, 2026) / Publisher website: www.naukainfo.com. – Paris, France, 2026. - 293 p.

95 Abstract. A new titrimetric method is proposed for the quantitative determination of codeine phosphate in the substance and capsules based on the quantitative oxidation of codeine by means Diperoxydecanedioic acid in weakly alkaline medium (рН=8.5) to the corresponding N-oxide with subsequent determination of the unreacted excess of the oxidant by the iodometric titration method. The advantages of the proposed method are the possibility of selective determination of much smaller amounts of the drug than by non-aqueous titration, in the presence of other components without prior separation with satisfactory accuracy (RSD ≤ 1%). The LOQ is 0.05 mg, which is an order of magnitude lower than in known titrimetric methods. Also second method is proposed and the possibility of quantitative determination of codeine phosphate in the substance and Tusoret® Day/Night capsules of 30 mg (white capsule) and 50 mg (blue capsule) by voltammetry in the form of N-oxide, previously obtained using diperoxydecanedioic acid is shown. The linearity curve for the developed method was constructed by measuring the maximum values of the current strength of the obtained waves I, in μA at a given potential of –1.02 V and plotting this dependence on the concentration. The method corresponded to linearity in the range (1-10)·10-5 mol/L with a correlation coefficient of 0.996. The codeine content in Tusoret® Day/Night capsules was determined by the calibration graph method. RSD≤ 2.5% (n=7; P=0.95%).The developed method does not involve the use of harmful solvents, expensive equipment and standard samples, is simple and fast to perform. Keywords : Сodeine phosphate, capsules, Diperoxydecanedioic acid. Codeine N-oxide, iodometric titration, voltammetry. Codeine is a monomethyl ester of morphine (Chemical name: 7,8-didehydro- 4,5α-epoxy-3-methoxy-17-methylmorphinan-6α-ole phosphate) used mainly in combination preparations for unproductive reflex cough. The chemical structure of codeine is given in Fig 1.