2.4. Calibration procedure
For the quantitative analysis of the samples, external calibration
technique was followed. Standard solutions were prepared in
19.6% (w/w) HNO3 (the same percentage of acid present in the
samples) by diluting a multi-element standard solution containing
all the elements. The calibration curves for all the analytes were
built on six different concentrations, from the limit of detection
(LOD) of the corresponding element up to 200 ng/g. All the measurements
were carried out using the full quantitative mode analysis.
The correlation coefficients for all the calibration curves were
at least 0.9999, showing good linear relationship throughout the
ranges of concentrations studied. The absence of polyatomic interferences
was checked by measuring several isotopes of the elements
and checking the isotopic ratio in the digested solution of
the samples.