Analysis of cadmium in soils and plants is not straightforward due to the low concentrations in these matrices, especially for plant material where contamination from extraneous sources can lead to erroneously high results.
When sampling plants to determine cadmium concentrations, it is imperative that the plant sample is clean and free from soil and dust contamination. Sampling equipment must be clean and samples should be taken and placed in clean paper bags and protected from dust or aerosol contamination. Beware also of some skin creams and sun creams on hands that can lead to contamination.
Samples should be sent promptly to laboratories that are proficient in analysis of cadmium. Ask the laboratory if they have been certified proficient in cadmium analysis by the Australasian Soil and Plant Analysis Council (ASPAC) - https://www.aspac-australasia.com/