A Spectrophotometric Flow Injection Method for Determination of Ultratrace Amounts of Phenylhydrazine by Its Inhibition Effect on the Reaction of Thionin and Nitrite

Table 1

Variable ranges study and optimum conditions for the determination of phenylhydrazine.

Parameter studied	Range studied	Optimum level
Wavelength (nm)	200–700	602
Sulfuric acid concentration (mol L^−1)	0.2, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, 5.0	2.0
Thionin concentration (×10^−4 mol L^−1)	0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0	2.5
Sodium nitrite concentration (×10^−4 mol L^−1)	0.1, 0.3, 0.5, 0.7, 0.9, 1.1, 1.3, 1.5	0.9
Flow rate (mL min^−1)	0.2, 0.3, 0.4, 0.5, 0.6	0.3
Mixing coil [I] (cm) [phenylhydrazine + H2SO4 + sodium nitrite]	50, 75, 125, 175, 225, 275	75
Mixing coil [II] (cm) [phenylhydrazine + H2SO4 + sodium nitrite + thionin]	50, 75, 125, 175, 225, 275	125
Injection volume (μL)	50, 100, 200, 250, 300, 400	200