This precipitate was the 2,4-dinitrophenylhydrazone, which is the product of the reaction between the 2,4-dnph and the aldehyde as depicted in Figure 2 .
The formation of micelles as precipitates is due to the formation of 2,4-dinitrophenylhydrazone indicating the presence of formaldehyde during the photocatalytic reaction.
EBC was collected by means of our designed and patented device in terms of recommendations. During 10-15 min of free respiration, usually, 1.5-2.0 ml of EBC was obtained in which the following indices were detected: Total protein content (g/L) by Lowry's method, EBC proteolytic activity by the lysis of albumin, azocasein, and azocollagen by Veremeyenko's method, the content of aldehyde and ketone derivatives of 2,4-dinitrophenylhydrazone
(AKDNPH) of the main and neutral character by Dubinina's method, the content of nitrogen monoxide metabolites (NMON) by Yemchenko's method (1994) in Gozhenko's modification (2002), total, enzymatic, and non-enzymatic fibrinolytic activity by Kukharchuk's method.
The extent of oxidized proteins was expressed as 2,4-dinitrophenylhydrazone
(nmol per mg protein) using a molar extinction coefficient for 2,4-dinitrophenylhydrazone
of 2.2 x [10.sup.4 ][M.sup.-1] [cm.sup.-1].
The content of carbonyl groups in proteins (CP) was measured by determining the amount of 2,4-dinitrophenylhydrazone
formed upon the reaction with 2,4-dinitrophenylhydrazine .
However, it is clearly apparent that most of reported spectrophotometric researches in the literature either employed 2,4-dinitrophenylhydrazone (Schwimmer and Weston's procedure)  or salicylaldehyde (Straub's procedure)  with continues modifications and improvements.
Also, 0.2% w/v stock solution of 2,4-dinitrophenylhydrazone (Merck, USA) was prepared by dissolving the appropriate weight in 250 ml of HCL 1 M.
In brief, proteins precipitated with trichloroacetic acid were suspended and incubated in a solution containing 10 mM 2,4-dinitrophenylhydrazones
(DNPH) and 2 N HCl for 1 hour at 15 C.
Determination of nanogram amounts of carbonyls as 2,4-dinitrophenylhydrazones
by high-performance liquid chromatography.
Kim, "Contrasting recovery patterns of 2,4-dinitrophenylhydrazones
(DNPH) derivative of carbonyls between liquid and gas phase standards using HPLC-based analysis," Atmospheric Environment, vol.