TPTZ is a colorimetric reagent commonly used in the detection of iron.1,2 TPTZ forms a complex with Fe(II) that can be quantified by colorimetric detection at 594 nm as a measure of iron concentration.
References
1. Collins, P.F., and Diehl, H. 2,4,6-Tripyridyl-s-triazine as a reagent for iron. Determination of iron in limestone, silicates, and refractories. Anal. Chem. 31(11), 1862-1867 (1959).
2. Dehghani, Z., Dadfarnia, S., Shabani, A.M.H., et al. Determination of iron species by combination of solvent assisted-dispersive solid phase extraction and spectrophotometry. Anal. Bioanal. Chem. Res. 2(1), 13-21 (2015).