Nitrate test to 2.5 micrograms and a concentration of 1 in 25,000 parts. Devarda's alloy (Copper/Aluminium/Zinc) is a reducing agent. When reacted with nitrate in sodium hydroxide solution, ammonia is liberated. The ammonia formed may be detected by its characteristic odor, and by damp red litmus paper's turning blue, signalling that it is an alkali — very few gases other than ammonia evolved from wet chemistry are alkaline. Aluminium is the reducing agent in this reaction that will occur. Diphenylamine may be used as a wet chemical test for the presence of the nitrate ion. In this test, a solution of diphenylamine
Nitrophenyl pentadienal solution of naphthoresorcinol is added to a swab of the item in question and then concentrated hydrochloric acid is added. The observation of a red color indicates a positive test. Napthoresorcinol was frequently used in early organic chemistry investigations to determine the presence of aldehyde groups in solution, a red adduct is formed in acidic solution. Nitrophenyl pentadienal Nitrophenyl pentadienal, nitrophenylpentadienal, NPPD, or METKA (Russian for "mark") colloquially known as "spy dust", is a chemical compound used as a tagging agent by the KGB during the Cold War Soviet Era. Soviet authorities in Moscow tracked Americans by applying an almost