All reagents used in the presented work were of analytical
reagent grade unless otherwise stated. Double deionised
water (Milli-Q Millipore 18.2 MX/cm conductivity)
was used for all dilutions. Acids like HNO3, H2O2, and
HCl were of suprapur quality (E. Merck). All the plastic
and glassware were cleaned by soaking in dilute HNO3
(1 + 9) and were rinsed with distilled water prior to use.
The standard solutions of analytes used for calibration
were produced by diluting a stock solution of 1000 mg/l
of the given element supplied by Sigma–Aldrich (St Louis,
MO, USA).