E pure system

Throughout the experiment, analytical-grade chemicals and reagents were utilized (Sigma- Aldrich, Merck, Taufkirchen, Germany). Chemicals and reagents used in this study include de-ionized water (resistivity > 18 MΩ·cm, manufactured using an E-pure system, Thermo Scientific, Waltham, MA, USA), nitric acid (67%, BDH), hydrogen peroxide (30%, Sigma Aldrich), HCl (37%, Loba, Mumbai, India), and certified reference material (CRM) for Ni (1000 ± 3 mg/kg; Cica-Reagent; CAS-285772B), for Pb, Cd, Cr, Ni, and Zn (1000 ± 3 mg/kg; Sigma Aldrich, Honeywell Specially Chemicals Seelze GmbH, Seelze, Germany), and for SRM 2976-Muscle tissue (Sigma-Aldrich Chemie GmbH, Taufkirchen, Germany). All chemicals and reagents were used without further purification, and the working standard was prepared from stock CRM following the standard procedure.

An atomic absorption spectrophotometer (Model: AA-7000, Shimadzu, Japan) equipped with a GF (GFA 7000) and an autosampler (ASC 7000) was used. A cathode lamp was used and operated according to the manufacturer’s instructions for the analyses of Pb (283.0 nm, 10 mA, and slit 0.7 nm), Cd (228.8 nm, 10 mA, and slit 0.7 nm), and Cr (357.9 nm, 10 mA, and slit 0.7 nm), respectively. Nitric acid (HNO₃, 69%), hydrogen peroxide (H₂O₂, 30%), and standards of Pb, Cd, and Cr were used for sample preparation. A microwave acid digestion system (MADS) (Ethos Easy Milestone) was used for conducting the digestion process. The standard bulk solutions were made daily by diluting respective metals stock standard solutions using 1% (w/w) (HNO₃, 69%). The autosampler was used for preparing standard solutions. Deionized water (18 MW/cm) produced using an E-pure system (Thermo Scientific, United States) was used to prepare all the solutions and clean and wash all containers and glassware before use.