Seven colorimetric methods were conducted to detect formalin in either in
water solutions, or in milk containing different concentration of formalin (1-1000 ppm).
The methods used were : Hehner's test (1) ; Leech's test (2) ; Shrewsbury and
Knapp's test (3) ; Nash's reagent (4); Chromotropic acid method (5) ; Schryver's test
(6) and phenythydrazin potassium ferrocyanid test (7). It was noticed that methods (4)
and (5) were more sensitive than others for detecting formalin in water solutions,
whereas the most sensitive methods to detect formalin in milk samples were (2), (4)
and (5). On the other hand, with water-base solution, methods (1), (2) and (3) failed to
detect either low or high formalin concentrations, while methods (6) and (7) failed only
to detect the lower concentrations. The same trend was obtained with milk samples
except method (2) which was sensitive for all concentrations. Methods (4) and (5) were selected to detecte the prasence of formalin presence in the whey of acid coagulation cow's milk (with sulphuric or acetic acid), and in the distilate obtained by indirect distilation of milk samples. The results obtained by using method (4) were always less than the actual polluted concentrations and represent - 58-62% In the case of acid whey and 37-52% in the indirect distilation method. Examination of the presence of formalin in acid whey by using method (5) to detect it, however, more accurate results were obtained by using indirect distilation method compared with method (4) (53-70% VS. 37-52%, respectively.).