The Kurnakov test, also known as Kurnakov's reaction, is a chemical test devised by Soviet chemist Nikolai Semenovich Kurnakov.   It utilizes the phenomenon of the trans effect to distinguish the pairs of cis- and trans-isomers of square complexes of [PtA2X2] (A=NH3, X=halogen or acid radical) type by treating them with thiourea. It is commonly used in platinum mining.
Kurnakov test is used to distinguish between cisplatin and transplatin. In hot aqueous solution, the cis compound reacts with aqueous thiourea to give a deeper yellow solution from which yellow needles of tetrakis (thiourea) platinum(II) chloride deposit on cooling, while the trans compound gives a colourless solution from which snow white needles of trans-bis(thiourea)diaammineplatinum(II) deposit on cooling.  
- The Life and Work of Nikolai Semenovich Kurnakov
- Kurnakow, N. (1894). "Ueber complexe Metallbasen; Erste Abhandlung". Journal für Praktische Chemie. 50: 481–507. doi:10.1002/prac.18940500144.
- Kauffman, George B. (1983). "Nikolaĭ Semenovich Kurnakov, the reaction (1893) and the man (1860–1941) a ninety-year retrospective view". Polyhedron. 2 (9): 855–863. doi:10.1016/S0277-5387(00)81400-X.
- Kong, Pi-Chang; Rochon, F.D. (1979). "cis- and trans-Platinum compounds of substituted pyrimidines and their products from thiourea in Kurnakov's reaction". Canadian Journal of Chemistry. 57 (5): 526–529. doi:10.1139/v79-086.
- Woollins, J (1983). "The detection of trace amounts of trans-Pt(NH3)2Cl2 in the presence of cis-Pt(NH3)2Cl2. A high performance liquid chromatographic application of kurnakow's test". Polyhedron. 2 (3): 175–178. doi:10.1016/S0277-5387(00)83954-6.