~~ ~ zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA SHORT COMMUNICATION Determination of Heavy Metals in Concentrated Refined Sugar and Raw Syrups with Differential Pulse Polarography and Anodic Stripping Voltammetry Zidane zyxwvut KbouliJ ClaudeJambon, Michelle Cbatelut, ’ and Olivier Vittori Iaboratoire d’electrochzmzeAnulytique, iinzrw-wk Claude Bernard, 4-5 Bd du zyxw 2 2 Nouembre 1928, 69622 Villeurhanne Cedex, France Keceriled December 27, I991 ABSTRACT zyxwvutsrqp The behavior of copper, lead, cadmium, and zinc is investigated in concentrated solutions of refined beetroots sugar. The diffusion coefficients are found to decrease less than predicted by the Walden’s rule, so trace determinations down to lo-- M were measured by differential pulse polarogrdphy (DPP). Using anodic stripping voltammetry at a mercury film electrode, it was found that the refined sugar of alimentary grade contained: 57 (Cu), 34 (Zn), 1 (Cd), and 6 (Pb) pg/kg of dry sugar. For industrial syrups, resulting from a treatment by lime and water vapor of the raw material, some problems were encountered. Determination of copper and zinc was impossible, while that of lead and cadmium was possible after one liter of diluted syrup, at about 250 g I-’, had been treated with 20 g of activated carbon to absorb the major part of organic impurities. The lead and cadmium contents were found to be 20 (Pb) and 3.5 (Cd) zyxwvuts pg kg-’. KEY WORDS: Sugar analysis, Syrup analysis, Trace metals, Vokanimetry INTRODUCTION Anodic stripping pulse voltammetry (ASPV), normal pulse polarography (NPP), and differential pulse polarograpliy (DPP) are very sensitive methods for the determination of heavy metals in aqueous solutions [l]. LJsually, they are comparable in sensitivity to atomic absorption spec- troscopy, or ionic chromatography. Other techniques such as plasma spectrometry, neutronic activation and laser microprobe mass analysis are more expensive. In a hi- ological matrix, they often require a sample preparation involving a multi-step procedure, which is often tinie- consuming and implies high-purity reagents [ 2-71, Polarographic techniques have been widely used in aqueous media, even in the presence of inert soluble organic compounds, provided that they were at low con- centration levels [8-10]. Some attempts to determine heavy metals in sugar solutions have been reported, but only in refined ones (11-141. In this article, we are concerned with the determi- nation of copper, lead, cadmium, and zinc in very con- centrated saccharose solutions (up to 830 g I-’) and in raw industrial syrups, coming directly from sugar man- ufactures corresponding to the first extraction step of beetroots by water vapor and lime treatment. The pro- cedure described here tries to minimize the sample preparation to a single step, easy to handle and nonin- fluent on the initial metal content. zyx EXPERIMENTAL Anodic stripping and polarographic measurements were performed with a I’KG5 pulse polarograph (Tacussel, France) and an SE 790 X-Y-t recorder (HBC, Goertz, Aus- tria.) The cell was equipped with a three-electrode sys- tem: the reference WAS a sdturated calomel electrode (SCE) while the auxilliary electrode was a platinum wire. For DC, NPP, and DPP, the working electrode was a mercury drop, the drop time was 2.5 seconds and a 20 mV pulse was selected. For ASPV, the working electrode was a mercury film deposited on a 3 mm diameter glassy car- bon rotating electrode (Tacussel, France). The mercury film was always prepared in a separate cell containing a 2 X lo-’ M Hg(N05) solution with 0.25 M HNOj as sup- porting electrolyte. The potential was fixed at -0.2 V (vs. SCE) and a 15 minute deposition time was found to be suitable to obtain 3 pm thick, reproducible films. Then the electrode was rinsed and transferred into the sample cell. The stripping time was fixed at 10 minutes, with a ‘To whom any correspondence should be addressed. zyx 0 1993 VCH Publishers, Inc 1040-0397/93/$5.00 + 25 zyxwvu 339