2.7. Quality control and quality assurance
The standard reference material of Cr (p.a.) was used for the calibration and quality assurance for each analytical batch. All solutions
were prepared using p.a. reagents and deionised water (18 M,
Millipore). The methodologies used in this work were selected in
order to fulfil the general standards for quality controls required for
microbiological analyses [14,15]. The values informed for the analytical determinations agree with the precision of the instruments
used, on the other hand the uncertainty values for the microbiological determinations are lower than 10%.