Table 1.

Results obtained for the standard reference materials together with certified value.

SRM	Element	Certified value (μg g−1)	Measured value
Pine needles	Pb	0.167 ± 0.013	0.161 ± 0.102
NIST-SRM 1575a	Cd	0.233 ± 0.009	0.214 ± 0.013
Spinach leaves	Pb	0.200 ± 0.006	0.198 ± 0.012
NIST-SRM 1570	Cd	2.890 ± 0.070	2.830 ± 0.095