Direct and Combined Methods for the Determination of Chromium, Copper, and Nickel in Honey by Electrothermal Atomic Absorption Spectroscopy J. C. RODRI ÄGUEZ GARCI ÄA, J. BARCIELA GARCI ÄA, C. HERRERO LATORRE,* S. GARCI ÄA MARTI ÄN, AND R. M. PEN ˜ A CRECENTE Departamento de Quı ´mica Analı ´tica, Nutricio ´n y Bromatologı ´a, Facultad de Ciencias, Universidad de Santiago de Compostela, Campus de Lugo, Avenida Alfonso X El Sabio s/n, 27002 Lugo, Spain In the present work, direct methods for the determination of chromium, copper, and nickel in honey by electrothermal atomic absorption spectroscopy were developed using experimental design as an optimization tool. Once the optimum conditions for the individual methods were established, a direct method for the combined determination of the three elements was optimized using the response surface tool. Palladium was used as chemical modifier in all cases. Honey was diluted in water, hydrogen peroxide, and nitric acid. Triton X-100 was added to minimize the matrix effect and the viscosity of the sample. The RSD (better than 10%) and the analytical recovery (98-103%) were acceptable for all of the developed methods. Calibration graphs were used in the four methods to determine the concentration of the analytes in the sample. The detection limits of the combined method (0.21, 0.35, and 0.37 μgL -1 for Cr, Cu, and Ni, respectively) were similar to those obtained for the individual methods (LOD ) 0.17, 0.21, 0.33 μgL -1 for Cr, Cu, and Ni, respectively). The direct- combined proposed method has been applied to the determination of chromium, copper, and nickel content in representative honey samples from Galicia (northwestern Spain). The concentrations found in the analyzed samples were in the range of (5.75 ( 0.64)-(26.4 ( 0.38) ng g -1 of Cr, (79 ( 7.8)- (2049 ( 80) ng g -1 of Cu, and (12.6 ( 1.36)-(172 ( 6.88) ng g -1 of Ni. KEYWORDS: ETAAS; chromium; copper; nickel; combined determination; honey; chemical modification; palladium 1. INTRODUCTION Nickel, chromium, and copper are heavy metals emitted to the atmosphere from industrial sources: mining production, ore refining, chemical manufacture, coal-fired power plants, and combustion of fossil fuels. Metal particles may be spread on the earth, or they can fall with rain drops after reactions (1). Nickel, chromium(VI), and copper are toxic at high concentra- tions; however, traces of Cu and Cr(III) (2) are essential for human life. The functions of Ni in the organism are not well understood, and it has not been established as an essential element in human beings (3). Knowledge of environmental pollution requires that the polluting substances be monitored. However, detection and measurement of certain pollutants in the environment are not evident. In the past few years, several methods (4) with appropriate analytical characteristics and acceptably low cost and based on the use of bioindicators (such as algae, lichens, and pine needles) have been proposed. Since 1935, many studies have considered beehive products to be adequate environmental markers for certain pollutants such as heavy metals. Honey is a good biological indicator as long as heavy metals present in the atmosphere are translocated from the environment to the flower’s nectar and finally to honey (5). Therefore, honey analysis is considered to be an appropriate measure of the surroundings in which the hive is located. Being a widely consumed product, information records about metal content in honey are relevant to ensure its quality (6). In addition, the combination of trace and metal content data of honey with modern statistical data evaluation techniques is a good approach to detect geographical and botanical origins of the product (7). For all of these reasons, simple, cheap, and exact methods for determining heavy metals in honey are widely demanded by producers, consumers, and regulatory bodies. Electrothermal atomic absorption spectroscopy (ETAAS) is one of the most useful and powerful analytical techniques for the determination of trace and ultratrace elements in different samples. Other techniques such as inductively coupled plasma atomic emission spectroscopy (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS) are usually employed for multielemental honey analysis (8-10). However, these two techniques also present inconveniences. Honey sample analysis * Corresponding author (telephone +34-982 285 900, ext. 24064; fax +34-982 285 872; e-mail cherrero@lugo.usc.es). 6616 J. Agric. Food Chem. 2005, 53, 6616-6623 10.1021/jf050887o CCC: $30.25 © 2005 American Chemical Society Published on Web 08/02/2005