Method development for the determination of cadmium in fertilizer samples using high-resolution continuum source graphite furnace atomic absorption spectrometry and slurry sampling

Abstract

The determination of cadmium (Cd) in fertilizers is of major interest, as this element can cause growth problems in plants, and also affect animals and humans. High-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS) with charge-coupled device (CCD) array detection overcomes several of the limitations encountered with conventional line source AAS, especially the problem of accurate background measurement and correction. In this work an analytical method has been developed to determine Cd in fertilizer samples by HR-CS GF AAS using slurry sampling. Both a mixture of 10 μg Pd + 6 μg Mg in solution and 400 μg of iridium as permanent modifier have been investigated and aqueous standards were used for calibration. Pyrolysis and atomization temperatures were 600 °C and 1600 °C for the Pd-Mg modifier, and 500 °C and 1600 °C for Ir, respectively. The results obtained for Cd in the certified reference material NIST SRM 695 (Trace Elements in Multi-Nutrient Fertilizer) of 16.7 ± 1.3 μg g −1 and 16.4 ± 0.75 μg g −1 for the Pd–Mg and Ir modifier, respectively, were statistically not different from the certified value of 16.9 ± 0.2 μg g −1 on a 95% confidence level; however, the results obtained with the Ir modifier were significantly lower than those for the Pd–Mg modifier for most of the samples. The characteristic mass was 1.0 pg for the Pd–Mg modifier and 1.1 pg Cd for the Ir modifier, and the correlation coefficients (R 2) of the calibration were > 0.99. The instrumental limits of detection were 7.5 and 7.9 ng g −1, and the limits of quantification were 25 and 27 ng g −1 for Pd–Mg and Ir, respectively, based on a sample mass of 5 mg. The cadmium concentration in the investigated samples was between 0.07 and 5.5 μg g −1 Cd, and hence below the maximum value of 20 μg g −1 Cd permitted by Brazilian legislation.