2.3. Instrumentation and experimental conditions

The pH of the samples was measured potentiometrically at 20 °C using a pH-meter (HANNA 2211-02 pH/MV/C) bench meter with electrode holder.

HPLC analysis was performed using SCHIMADZU high performance liquid chromatography (HPLC) instrument (Japan) equipped with a diode array detector (DAD) and data handling system comprised of Dell personal computer and SCHIMADZU class-Vp software. Separation was carried out using Ammonia (NH₂) USP L8 analytical column (25 cm × 4.6 mm, 5 µm i.d.). Chromatographic analysis was performed using a mobile phase comprised of a mixture of distilled water: acetonitrile (20:80, v/v) and an injection volume of 5 μL with a flow rate of 1 mL/min. Detection was performed at the wavelength of 195 nm. Temperature was kept at 35 °C during the whole run.

Elemental analysis was carried out using inductively coupled plasma ICP (ICP ACTIVA S), HORIBA JOVYN, with data handling system comprised of Dell personal computer and Activa analyst 5.4.2 software. Samples were prepared using Microwave acid digestion apparatus, Milestone Ethos Start Lab Station with internal temperature sensor, 640-260 terminal with Easy Control software installed and HPR1000/10S high pressure segmented rotor. Analysis of arsenic As and mercury Hg elements was performed using the hydride generator ICP.

GC/MS analysis was done by SCHIMADZU GC/MS-QP2010 GC/MS instrument (SCHIMADZU Corporation, Kyoto, Japan) with data handling system comprised of Dell personal computer and SCHIMADZU GC–MS Real Time Analysis software. The column used was fused silica capillary column (30 m × 0.25 mm i.d., 0.25 µm film thickness) DB-5 (5% phenyl, 95% dimethyl polysiloxane), (J &W Scientific, Rancho Cordopa, CA, USA). The following temperature program was applied: 50 °C for 5 min followed by temperature increase from 50 °C till 320 °C (rate 6 °C/min), then the temperature was kept constant at 320 °C for 5 min (a total run time of 55 min). The injector was used in the split injection mode with split ratio of 1:25. Helium was used as a carrier gas and the flow rate of 1.5 mL/min was applied.