Determination of chromium, cadmium and lead in food-packaging materials by axial inductively coupled plasma time-of-flight mass spectrometry

Abstract

Inductively coupled plasma mass spectrometry (ICP-MS) with a time-of-flight (TOF) analyser was used for the determination of chromium, cadmium and lead in six food-packaging materials (paper and paper board). The samples (0.20–0.25 g) were digested in concentrated nitric acid in a high pressure microwave oven at 180 °C within 15 min. Two different plasma conditions were applied: cool plasma conditions (0.76 kW; 0.85, 0.89 and 15.5 l min −1 nebuliser, auxiliary and plasma gas flow rate, respectively) for the determination of chromium and normal plasma conditions (1.21 kW; 0.66, 0.68 and 13.6 l min −1 nebuliser, auxiliary and plasma gas flow rate, respectively) for the determination of cadmium and lead. External calibration was used in combination with rhodium (40 ng g −1) as an internal standard. The detection limits (DL = 3S.D./sensitivity) under the conditions used corresponded to 0.01 ng g −1 ( 52 Cr ), 0.06 ng g −1 ( 53 Cr ), 0.07 ng g −1 ( 111 Cd ), 0.03 ng g −1 ( 114 Cd ) and 0.02 ng g −1 ( 206 Pb and 208 Pb ). The precision (R.S.D.) for six replicate determinations (10 s integration time) of 1 and 10 ng g −1 of each analyte varied from 0.72% ( 206 Pb ) to 4.43% ( 111 Cd ). The contents of chromium, cadmium and lead in the examined materials were evaluated using the signals of 52 Cr , 114 Cd and 208 Pb . They were in the range: 0.25–0.50 μg g −1 for Cr, not detected (nd) to 0.12 μg g −1 for Cd and 0.28–0.35 μg g −1 for Pb in paper and 0.50–0.64 μg g −1 for Cr, nd to 0.09 μg g −1 for Cd and 0.67–0.99 μg g −1 for Pb in paper board.