Adsorption tube samples, storage

Much less data are available on the adsorption of elements onto surfaces from blood or urine samples. Stoeppler (1980) did not detect any loss of added Ni from urine samples onto polyethene container walls. Concentrations of nickel or chromium in urine samples, spiked with small concentrations of the metals and stored for 6 months at 4°C did not show a decrease (Kiilunen et al.. 1987). The lUPAC reference method for nickel in urine calls for acidification of urine quality control samples with nitric acid and storage in polypropene tubes with a screw-cap at -20°C (Brown et al., 1981). No adsorption of cadmium onto container walls (type not specified) was seen from urine acidified to pH < 2 (Stoeppler and Brandt, 1980). 

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