2. Experimental
2.1. Reagents and materials
All reagents used were of analytical grade and doubly
distilled water was used in all preparations. Stock
solutions of nitrite and nitrate (100 mg ml−1) were prepared
from their sodium salts. 4-nitroaniline solution
(267 mg l−1) and 1-naphthol solution (400 mg l−1)
were prepared in 20% ethanol; 24% sodium hydroxide,
1% sodium carbonate and 16% disodium EDTA
solutions were prepared in water. The white PUF
was obtained locally, cleaned and cut into foam parallelepipeds
of 10 mm×35 mm×2 mm before use, as
described elsewhere [17].