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23(3). Upon condensation with aniline, furfural C4H3OCHO forms a red compound C4H3OCH(C6H4NH2)2 518 nm, the molar light absorption coefficient of which is ε’518 = 6.20*104.
Furfural and its derivatives, when condensed with benzidine, form yellow compounds. At 413 nm, the molar light absorption coefficients of condensation products are ε’413 = 2.00*102 (for furfural), ε2413 = 1.00*103 (for methylfurfural and other derivatives).
For analysis, we took V ml of plastic production wastewater, distilled furfural and its derivatives into a 500.0 ml flask and brought it to the mark with water. The prepared reagent mixture containing aniline was added to a 5.00 ml aliquot and diluted with water to 20.00 ml. The optical density of A518 was measured at 518 nm and a cuvette l = 1.0 cm.
To another 50.00 ml aliquot, benzidine hydrochloric acid solution was added and diluted with water to 100.0 ml. The optical density of A413 was measured at 413 nm and a cuvette l=5.0 cm.
Calculate the concentration (mg/l) of furfural (M(C4H3OCHO) = 96.0854 g/mol) and its derivatives based on methylfurfural (M(C5H5OCHO) = 110.1158 g/mol) in wastewater for the following options:
Option Wastewater sample volume V, ml A518 A413
1 100 0.525 0.450
2,200 0.480 0.410
3,250 0.410 0.350

Answer: 1) 16.27; 95.37 mg/l; 1) 7.44; 43.44 mg/l; 1) 5.08; 29.7 mg/l.
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