Determination of metals (Ca, Cu, Fe, K, Mg, Mn and Zn) content was performed with flame atomic absorption spectrometry (F-AAS) by calibration curve method. Atomization of samples proceeded in the flame acetylene/air; rate of injection of samples into the flame was 4.5 mL min-1. Wavelengths used for the metals determination were 422.7, 285.2, 766.5, 213.9, 324.8, 279.5 and 248.3 nm for Ca, Mg, K, Zn, Cu, Mn and Fe, respectively. Determination of all metals content was performed with atomic spectrometer VARIAN SpectrAA 110. Limits of detection (LOD) and limits of quantification (LOQ) of the metals determination are given in Table 4. Determination of Cd, Zn and Cu was performed with flame atomic absorption spectrometry in samples prepared with dry decomposition. Atomization of samples was proceeded in the flame acetylene/air; rate of injection of samples into the flame was 4.5 mL min-1. Wavelengths used for the metals determination were 228.8, 324.8 and 213.9 nm for Cd, Cu and Zn, respectively. Determination of Pb was performed with atomic absorption spectrometry with electrothermic atomization by Varian SpectrAA 280Z atomic absorption spectrometer furnished with GTA 120 electrothermic atomizer at wavelength 283.3 nm.

1.1.3 Determination of dry weight

Dry matter of straw samples was determined by drying at 105 0C in a laboratory oven and of that grain at 130 0C to constant weight (ISO 612).