Fast-sequential determination of cadmium and copper in milk powder and infant formula by direct solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry

A sequential and direct solid sampling (SS) method to determine cadmium (Cd) and copper (Cu) in milk powders and infant formulas was developed using a high-resolution continuum source graphite furnace atomic absorption (HR-CS GFAA) spectrometer. The analysis was performed using a unique sample aliquot and in one measurement run. Absorbance measurements were carried out at the main analytical lines for Cd (228.802 nm) and Cu (324.754 nm). Experimental conditions were optimized using aqueous standards and a skimmed milk powder certified reference material (ERM®–BD150). Palladium was added as chemical modifier in standards and samples. For Cd determination, a pyrolysis temperature of 900 °C and an atomization temperature of 1400 °C were used. Afterwards, the wavelength was automatically changed, and Cu was determined from the same aliquot of sample using an atomization temperature of 2200 °C. Calibration was performed using aqueous standards. Using three pixels (CP ± 1) for the quantification of both elements and a sample mass of 0.9 mg, the limits of quantification (LOQs) and the upper limits of the linear range (ULLRs) were 2.1 µg kg−1 and 56 µg kg−1 for Cd (1.9 to 50 pg), and 0.021 mg kg−1 and 1.7 mg kg−1 for Cu (0.019 to 1.5 ng), respectively. The linear response of Cu was expanded up to 4.7 mg kg−1 (4.2 ng) by using the approach of measuring at the wings of the absorption line. The developed methodology was applied to analyse different commercial milk powder and infant formula samples with successful results.