Lunges reagent

Blank sample of the Lunges reagent with sodium nitrate (NaNO ₃ ) in columns 1 and 2 and sodium nitrite (NaNO ₂ ) in columns 3 and 4 shortly after the addition

Blank sample of the Lunges reagent with sodium nitrate (NaNO ₃ ) in columns 1 and 2 and sodium nitrite (NaNO ₂ ) in columns 3 and 4 after stirring

Lunge's reagent is a solution named after Georg Lunge , made from Lung I ( sulfanilic acid ) and Lung II ( 1-naphthylamine , also α-naphthylamine) and is used in inorganic analysis for the qualitative and quantitative detection of nitrite and nitrate .

Reaction scheme for the reaction of the lung reagent with nitrite. By adding 2-3 drops of lung I and II, the sulfanilic acid  ( 1 ) first forms a diazonium salt  ( 2 ), which further reacts with 1-naphthylamine  ( 3 ) to form an azo dye  ( 4 ) and quickly turns the solution red .

For the detection of nitrate, it must first be reduced to nitrite using zinc dust and glacial acetic acid ( ethanoic acid ) .

${\displaystyle \mathrm {NO_{3}^{-}+Zn+2\ H^{+}\rightarrow \ NO_{2}^{-}+Zn^{2+}+H_{2}O} }$

To carry out the detection, a little zinc powder and above it acetic acid sulfanilic acid ( 1 ) and the α-naphthylamine ( 3 ) are placed in a test tube and wait to see whether the solution is already discolored red by impurities. If this is not the case, a little of the substance to be investigated (as a solution or solid) can be added for detection.

In order to detect nitrate in the presence of nitrite, the latter must be reduced to nitrogen with amidosulfuric acid before adding zinc :

${\displaystyle \mathrm {HNO_{2}+(NH_{2})HSO_{3}\rightarrow \ H_{2}SO_{4}+N_{2}+H_{2}O} }$

Since the detection reaction is extremely sensitive, it is advisable to carry out a blank test in parallel .

Due to a suspected carcinogenic effect of the α-naphthylamine is nowadays usually by α-naphthyl-ethylenediamine (Di hydrochloride replaced).

Further detection of nitrites is carried out using the Grieß reagent according to Johann Peter Grieß .

Disorder

Some anions , such as bromide (Br ^- ), iodide (I ^- ), chlorate (ClO ₃ ^- ), iodate (IO ₃ ^- ), sulfide (S ²⁻ ), sulfite (SO ₃ ²⁻ ), thiosulfate (S ₂ O ₃ ²⁻ ), thiocyanate (SCN ^- ), chromate (CrO ₄ ²⁻ ), yellow ([Fe (CN) ₆ ] ⁴⁻ ) and red blood liquor salt ([Fe (CN) ₆ ] ³⁻ ) can interfere with the reaction and thus affect the evidence. Br ^- , I ^- and S ²⁻ can be precipitated by silver sulphate , S ²⁻ can also be mixed with cadmium acetate , so that cadmium sulphide precipitates. With CrO ₄ ²⁻ , barium chloride is used, barium chromate then precipitates .

Individual evidence

1. ^ S. Ebel and HJ Roth (editors): Lexikon der Pharmazie , Georg Thieme Verlag, 1987, p. 405, ISBN 3-13-672201-9 .
2. ↑ Hans P. Latscha, Gerald W. Linti , Helmut A. Klein: Analytical Chemistry. Basic chemistry knowledge 3 . Springer, Berlin; 4th, completely revised Edition 2003; ISBN 3-540-40291-8 ; P. 614.
3. ↑ Eberhard Gerdes: Qualitative Inorganic Analysis . Vieweg Friedr. + Son Ver; 2., correct. u. revised Edition 2000; ISBN 3-528-16667-3 ; P. 198.

literature

• Joachim Straehle and Eberhard Schweda: Jander / Blasius: Textbook of analytical and preparative inorganic chemistry . Hirzel Verlag Stuttgart; 15th, revised. Edition, ISBN 3-7776-1146-8 ; P. 614.