Reagent

pH (solvent)

λ, nm

ε∙10⁻⁴

Beer’s law range (μg∙ml⁻¹)

Pyrocatechol violet

1.6 - 2.0

2.2 - 2.3

600

0.93

0.2 - 6.0

Rodanid

2.5 MHCl (water + acetone)

385

3.5

0.08 - 9.0

4-Nitropyrocatechol + tetrazolium violet

0.7 MH₂SO₄ (C₂H₄Cl₂)

440

1.59

0.41 - 4.54

Pyrocatechol + tetrazolium violet

0.4 - 1 MH₂SO₄ (CHCl₃)

390

1.60

1.25 - 11.78

Bromopyrogallol red

5.8 - 6.6

560

4.75

DTP + AP₁

3.8 - 5.0 (CHCl₃)

440

2.9

0.05 - 4.0

DTP + AP₂

3.5 - 4.9 (CHCl₃)

438

2.8

0.05 - 3.8

DTP + AP₃

3.3 - 4.7 (CHCl₃)

435

2.6

0.06 - 3.8