1061-9348/01/5611- $25.00 © 2001 åAIK “Nauka /Interperiodica” 1015 Journal of Analytical Chemistry, Vol. 56, No. 11, 2001, pp. 1015–1019. Translated from Zhurnal Analiticheskoi Khimii, Vol. 56, No. 11, 2001, pp. 1158–1162. Original Russian Text Copyright © 2001 by Ignatova, Volynskii. Attaining the maximum sensitivity and selectivity in electrothermal atomic absorption spectrometry (ETAAS) commonly requires the elimination of matrix effects. A universal approach to this problem is operation under “sta- bilized temperature platform furnace conditions” [1]. Along with purely apparatus design (determination in the gas-stop mode, evaporation from a graphite plat- form, etc.), the use of chemical modifiers has received much attention within the “stabilized temperature plat- form furnace” concept [2, 3]. Commonly, the correct selection of the modifier defines the possibilities of ETAAS in the analysis of real samples. The most common sources of substantial matrix interference in ETAAS are metal chlorides [4]. The evaporation of relatively large amounts of chlorides at the atomization step can lead to huge nonselective light absorption, which exceeds the possibilities of the back- ground corrector [5, 6]. The presence of large amounts of chlorine in the gas phase of the atomizer at the atom- ization step can hinder complete thermal dissociation of analyte chlorides [6]. The use of modern instruments in combination with optimal modifiers makes possible the direct determination of some elements (e.g., sele- nium) in concentrated (above 4%) sodium chloride solutions [7]. An even more complicated matrix is hardly evaporating calcium chloride (boiling tempera- tures 1413 and >1600°C, respectively [8]). The deter- mination of trace impurities in calcium chloride solu- tions is additionally complicated when the atomic absorption spectrometer is equipped with a relatively low-power system for correcting nonselective light absorption based on a deuterium lamp. The aim of this work was to optimize the conditions of ETAAS determination of Cd, Co, Cr, Cu, Mn, and Ni in concentrated calcium chloride solutions. Major attention is given to the selection of optimal chemical modifiers. EXPERIMENTAL Solutions and reagents. All reagents (Reakhim, Moscow, Russia) were of at least analytical grade. Dou- bly distilled water was used for preparing solutions. A reference solution of metals (0.05 μg/mL in 0.2 M HNO 3 ) was prepared by the dilution of a multielement nitrate standard solution (Merck, Germany) with a con- centration of each metal of 1 mg/mL. A 3% solution of Mg(NO 3 ) 2 , a 10% solution of ascorbic acid, and a 10% solution of oxalic acid in 0.2 M HNO 3 were used as modifiers. Apparatus and measurement procedure. We used a 3110 atomic absorption spectrometer with a deute- rium background corrector, an HGA-600 electrother- mal atomizer, and an AS-60 autosampler (Perkin- Elmer, USA). Hollow-cathode lamps were used as light sources, and argon containing less than 7 × 10 –4 % oxy- gen was used as the protective gas. All measurements were performed using graphite tubes coated with pyro- lytic graphite and pyrolytic graphite platforms (Perkin- Elmer). Determinations were performed under the following conditions (wavelength, nm/slit width, nm): Cd (228.8/0.7), Co (240.7/0.2), Cr (357.9/0.7), Cu (324.8/0.7), Mn (279.5/0.2), and Ni (232.0/0.2). The volume of a sample introduced into the atomizers was from 10 to 16 μL (in the presence of the matrix). Con- centrations of solutions that are presented in this work are converted to the total volume of the sample. For analysis, we used a 10% solution of CaCl 2 in water, i.e., Determination of Cadmium, Cobalt, Manganese, Copper, Nickel, and Chromium in Concentrated Solutions of Calcium Chloride by Electrothermal Atomic Absorption Spectrometry S. N. Ignatova and A. B. Volynskii Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 117975 Russia Received December 27, 2000 Abstract—A procedure is developed for the direct determination of Cd, Co, Cr, Cu, Mn, and Ni in concentrated solutions of calcium chloride by electrothermal atomic absorption spectrometry. Ascorbic and oxalic acids and magnesium nitrate were examined as chemical modifiers. Oxalic acid was found to be the best modifier. Although an atomic absorption spectrometer with a background correction system of relatively low efficiency (deuterium lamp) was used, the elements under study can be reliably determined in the presence of oxalic acid at concentrations of calcium chloride in the solution up to 6%. Because cadmium is evaporated before the major part of the given matrix, it can be determined without a modifier. ARTICLES