Abstract Methods for the direct determination of Ni in human blood serum and urine by electrothermal atomic absorption spectrometry (ETAAS) are described. Hydro- gen peroxide was proposed as matrix modifier, assisting thermal decomposition of proteins during the ashing step. A pyrolysis temperature of 1,200 °C was found to be opti- mal while 2,100 °C and 2,200 °C were found to be optimal atomizing temperatures for Ni in serum and urine respec- tively. Calibration was performed by using a calibration curve prepared with aqueous standard solutions of Ni (glycine must be used as modifier for Ni in aqueous solu- tions). The limits of detection, defined as the blank values plus 3 times the standard deviation of the blank values, were 0.2 μg/L for both serum and urine samples. Relative standard deviations for serum samples with concentra- tions of Ni in the range 0.5–2 μg/L were 10–15% and for urine samples with Ni concentrations in the range 0.5–2.5 μg/L were 8–10%. Keywords Nickel · Serum · Urine · Electrothermal atomic absorption spectrometry · Determination Introduction The determination of Ni has been the subject of numerous investigations in view of the industrial and environmental importance of this element on the one hand, and of its bi- ological relevance on the other, since Ni is one of the es- sential trace elements in the human body. Electrothermal atomic absorption spectrometry (ETAAS) is one of the most frequently used techniques among the instrumental methods applied to Ni determination in blood serum and urine. Two main approaches can be dis- tinguished in determination of Ni in blood serum and urine samples: preliminary separation and preconcentra- tion of Ni [1, 2, 3, 4, 5, 6], or direct sample introduction into the graphite tube [7, 8, 9, 10, 11]. Separation proce- dures are time consuming and may introduce contamina- tion and serious systematic errors. Although direct spec- trometric determination is therefore preferable, matrix in- terferences were seen as limiting factors in this case. In many papers some of these problems are overcome by us- ing prior sample dilution with water [12], Triton X-100 [13, 14], nitric acid [15, 16] or by a mixture of nitric acid and Triton X-100 [10, 17, 18]. Chemical modifiers (NH 4 H 2 PO 4 [7, 10] or Pd [2, 5, 6]) have also been recom- mended for Ni ETAAS determination in blood serum and urine samples. The purpose of the present study was to define optimal temperature programs and suitable modifiers for interfer- ence-free direct ETAAS determination of Ni in serum and urine. In the procedure developed, hydrogen peroxide was used as the matrix modifier and glycine as the element modifier. Calibration against aqueous standard calibration curves is recommended. Analytical quality assurance was carried out by analyzing standard reference materials. The proposed and validated method was applied to the deter- mination of Ni in the serum and urine of normal individu- als, electroplating workers and patients on dialysis (serum samples only). Materials and methods Instrumentation. The atomic absorption spectrometer Varian Spec- tra AA 640Z Zeeman AAS, equipped with a GTA100 graphite fur- nace (Varian, USA) and PSD-100 autosampler (Varian, USA), was used. Argon was applied as protective gas and 10 μL serum or urine was injected into the graphite furnace. Operating conditions were as summarized in Table 1. Reagents and samples. The standard solutions were prepared by dissolving a Merck stock solution containing 1 g/L Ni in nitrate Nadica Todorovska · Irina Karadjova · Trajče Stafilov ETAAS determination of nickel in serum and urine Anal Bioanal Chem (2002) 373 : 310–313 DOI 10.1007/s00216-002-1328-5 Received: 13 November 2001 / Revised: 18 March 2002 / Accepted: 10 April 2002 / Published online: 23 May 2002 TECHNICAL NOTE N. Todorovska Institute of Preventive Medical Care and Toxicology, Military Health Institution Center, 1000 Skopje, Macedonia I. Karadjova Faculty of Chemistry, University of Sofia, 1126 Sofia, Bulgaria T. Stafilov (✉) Institute of Chemistry, Faculty of Science, Sts. Cyril and Methodius University, POB 162, 1000 Skopje, Macedonia e-mail: trajcest@iunona.pmf.ukim.edu.mk © Springer-Verlag 2002