The material has been filtered at 0.45 µm and acidified with HNO3 to around pH 1.5. Certified valuesCd . 0.175 nmol/kgMo. 103 nmol/kg Pb. 0.117 nmol/kgCu . 3.9 nmol/kg Ni . 4.4 nmol/kg Zn . 25.7 nmol/kgIndicative values for Al, As, V