Determination of trace elements in pumpkin seed oils and pumpkin seeds by ICP-AES

Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for the determination of the elements present in pumpkin seed oil and pumpkin seeds. After extraction of the oil from pumpkin seeds a residue was obtained. For the determination of elements three types of samples were used: oil, seeds and the residue (after oil extraction). Three different digestion types were applied: open vessel and closed vessel digestion in a steel bomb as well as microwave digestion in a closed system. For most elements of interest the measured concentration differs depending on the digestion method used. After microwave digestion a good reproducibility for ICP-AES measurements for all elements was found. Determination of Zn by ICP-AES is possible both after open and closed vessel digestion (steel bomb or microwave digestion). No loss of volatile compounds in pumpkin oil during preparation or microwave digestion prior to ICP-AES analysis could be observed. In general, the recoveries for all elements in pumpkin seed oils and seeds were >95%, for S only they were <50%. Differences in the element concentration were found for seed oil obtained from the same seeds but prepared by two different procedures, extracted by Soxhlet and commercially produced after roasting of the seeds. The differences of the measured element concentrations after application of different types of dissolution procedures are discussed. The closed vessel dissolution was found to be the best procedure prior to the ICP-AES determination of metals. The method is evaluated by application of the standard addition method and by recovery experiments. Addition of salt during the oil production procedure causes approx. 10 times the Ca, K, Mg, and Na amounts compared to the Soxhlet extracted oil produced in the laboratory. Higher amounts of Na could be registered in the residues as well. The LODs were <0.1 mug g(-1) for Ca, Cd, Mg, Mn, Ti, and Zn, in the range of 0.1 to 0.8 mug g(-1) for Co, Cu, Fe, K, Mo, Na, Ni, Pb, and V, and >0.8 mug g(-1) for Al, Cr and P in pumpkin oil samples.