Abstract A direct method for silicon determination in milk samples by Electrothermal Atomic Absorption Spec- trometry was developed. Palladium was used as chemical modifier at a concentration of 610 mg L –1 ; with this mod- ifier, silicon was stable up to 1800 °C. The precision and accuracy of the method were investigated. The detection limit was 16.2, 2.7 and 7.2 μg L –1 for cows’ milk, human milk and infant formula, respectively. The method was applied to silicon determination in 17 infant formula samples, 13 human milk samples and 12 cows’ milk sam- ples. Keywords Silicon · Milk · Electrothermal atomic absorption spectrometry Introduction Silicon is the second most abundant element on earth, yet its role in nature is still relatively poorly understood. In certain organisms and plants, silicon is extracted from the surface waters (rivers, sea and soil waters), polymerised and incorporated as a stabilising feature in cell walls or in the plant skeleton [1]. For mammals, Si seems to be an es- sential trace element, required in the development of bone, cartilage and connective tissue [2]. The toxic properties of inorganic soluble and insoluble silicon compounds are known to cause lung and kidney problems, e.g. lung fibrosis and Balkan nephropathy [3, 4, 5]. High levels of silicon compounds in drinking water can lead to increase in the frequency of spontaneous abor- tion [6]. Serum silicon levels are high in chronic haemo- dialysis patients [7, 8, 9, 10]. Likewise, considerable inter- est has been raised by the association of Si and Al found as aluminosilicates in senile plaques and neurofibrilary tangles in the brain tissues of patients with Alzheimer’s disease [11, 12]. Birchal and Chapell [13] have suggested that Si may have no direct biological function. However they stated that high concentrations of Si in water might serve as protection from the toxic effects of Al to salmon fry by reducing its bioavailability [14], through the for- mation of aluminosilicates. Thus, silicon is becoming a biological trace element of increasing scientific interest, particularly in connection with neurological disorders as- sociated with Al in dialysis encephalopathy and in Alz- heimer’s disease. However, relatively few analytical data exist on the concentration of Si in physiological fluids in health and disease. A variety of methods has been used for silicon deter- mination including chemical methods [15], flame [16], and inductively coupled plasma atomic emission spectrometry [17, 18, 19], electrothermal atomic absorption spectrome- try (ETAAS) [20, 21, 22, 23] and neutral activation analy- sis [24]. Several papers on the determination of Si in biological fluids by ETAAS have been published [20, 25]. As chem- ical modifier mixed Pd–Mg(NO 3 ) 2 was used by Kristein [26] for silicon determination in food supplements, lan- thanum was used by Lueng [27] for silicon determination in serum and tissue and Zhuoer [28] proposed use of a mixture of La(NO 3 ) 3 , CaCl 2 , NH 4 H 2 PO 4 and Na 4 EDTA for soft tissue digests, whereas La(NO 3 ) 3 and tartaric acid disodium salt were used for analysis of bone digest. Other authors used coated graphite tubes to avoid di- rect contact between sample and graphite; This is of spe- cial importance when carbide-forming elements are deter- mined. Thus, Ortner and Kantuscher [29] improved the P. Bermejo-Barrera · M. C. Barciela-Alonso · R. Domínguez-González · A. Bermejo-Barrera · J. A. Cocho de Juan · J. M. Fraga-Bermúdez Silicon determination in milk by electrothermal atomic absorption spectrometry using palladium as chemical modifier Anal Bioanal Chem (2002) 374: 1290–1293 DOI 10.1007/s00216-002-1632-0 Received: 7 March 2002 / Revised: 27 September 2002 / Accepted: 11 October 2002 / Published online: 14 November 2002 ORIGINAL PAPER P. Bermejo-Barrera (✉) · M.C. Barciela-Alonso · R. Domínguez-González · A. Bermejo-Barrera Department of Analytical Chemistry, Nutrition and Bromatology, Faculty of Chemistry, University of Santiago de Compostela, 15782 Santiago de Compostela, Spain e-mail: pbermejo@usc.es J.A. Cocho de Juan Laboratory of Metabolic and Nutritional Disorders, University Clinical Hospital, 15782 Santiago de Compostela, Spain J.M. Fraga-Bermúdez Department of Pediatrics, University Clinical Hospital, 15782 Santiago de Compostela, Spain © Springer-Verlag 2002