Hydrocyanic acid, cyanides, and numerous nitrile derivatives are produced on a large scale and used in different fields of human activities in spite of their high environmental threat [1][2][3][4].Several chemical and physicochemical methods were proposed for the environmental control of hydrocyanic acid and its salts [5][6][7][8][9]. However, the development of rapid, sensitive, selective, and convenient methods has remained an issue of the day.Chemiluminescence analysis best meets the requirements for the determination procedure and apparatus [10]. An indicator system based on 3-aminophthalic acid hydrazide (luminol) is used in chemiluminescence analysis. In alkaline solutions, luminol strongly luminesces under the action of radical oxidants [11,12].We have observed the rapid development of the intense chemiluminescence of luminol in alkaline solutions in the presence of cyanide ions, p-nitrobenzaldehyde ( p-NBA), and hemin. This phenomenon was used for developing a procedure for the quantitative chemiluminescence determination of cyanide ions. EXPERIMENTAL Reagents.Chemically pure 3-aminophthelic acid hydrazide (luminol) was purified by double recrystallization from conc. HCl (GOST 3118-67). p-Nitrobenzaldehyde (GOST 14049-68) was doubly recrystallized from 40% ethanol. Reagent-grade hemin (Biokhimreactiv), analytical-grade EDTA disodium salt dihydrate (GOST 10652-63), ethanol (TU 19 P-39-69) purified by distillation, analytical-grade KOH (GOST 4203-65), and analytical-grade KCN (MRTU 6-09-3799-67) containing 98.9% KCN were used. Water was doubly distilled in a Pyrex distillation unit. Apparatus. The integral luminescence intensity of luminol in a solution was recorded on a Lik chemiluminescence analyzer for liquids (certificate no. 14437/270303, State Register no. 24512-03). A portable version of the analyzer with 220-V line supply and Lenpipetten DP-1 (200 µ L) and Justor 1100 (200-1000 µ L) Nichiryo samplers was used. Procedure for determining cyanide ions. Reagent solutions. To prepare a mixed luminol reagent, 0.1 g of luminol, 0.5 g of EDTA disodium salt (to mask transition metal ions), and 20 mL of ethanol were dissolved in 1.0 L of a 0.1 M aqueous solution of KOH. An ethanolic solution of p-NBA (10 mg/mL), a 0.01 M KOH solution, and a hemin solution (0.025 mg/mL) in 0.01 M KOH were used. A standard solution scale in the range from 10 -2 to 10 -7 mg/mL CN -was prepared from a solution of KCN (0.1 mg/mL CN -) in 0.01 M KOH using successive dilutions.Determination of cyanide ions in the range from 5 ¥ 10 -3 to 5 ¥ 10 -5 mg/mL. The luminol reagent (0.2 mL), 0.1 mL of a p-NBA solution, and 0.1 mL of a hemin solution were successively placed in the cell of the Lik analyzer. The microammeter readings corresponding to background luminescence due to the addition of hemin were compensated with an adjustable resistor. A sample solution (0.1 mL) was introduced, and a stopwatch was started simultaneously. The chemiluminescence intensity was recorded after 60 s. Blank experiments were conducted, in which 0.1 mL of 0....