**2.2. Instrumentation**

A Shimadzu UV-2450 high performance single monochromator UV-VIS spectrophotometer (Shimadzu Corporation, Tokyo, Japan) was used for all analysis of the samples. Solid phase extraction (SPE) was carried out in a VacMaster-24 sample SPE station (VacMaster, Biotage, Sweden). The latter was used to control the sample loading and elution flow rate in the range of 1–3.0 mL min−1. An OHAUS starter 2100 pH meter (Pine Brook, NJ, USA) was used for pH adjustments of the reagents and to measure the pH of samples
