4.2. Calibration and performance parameters comparison for spectrophotometry and OA technique
To select the model for OA measurements at high concentrations, we used the chelation of iron(II) with 1,10-phenanthroline, as (i) it gives the stable product, ferroin and (ii) it shows high sensitivity and reproducibility of photometric measurements and reliable characteristic constants [32], [33], [34], [35] and [36]. Important also is that very highly concentrated aqueous solutions of this chelate could be readily prepared. This reaction was previously tested using photothermal spectroscopy showing its thermal and photostability under laser excitation as well as good reliability [43].