Closed-vessel microwave acid digestion of commercial maple syrup for the determination of lead and seven other trace elements by inductively coupled plasma-mass spectrometry

A method was developed and applied for the determination of lead and other trace elements (As, Cd, Co, Cu, Mn, V and Zn) in 8 commercial maple syrups. Samples were digested using closed-vessel microwave heating. Two different types of microwave vessels, low-pressure and moderately high-pressure vess els, were evaluated. Average temperatures and maximum pressures attained du ring the maple syrup sample digestion were 140 degrees C and 190 psi (1310 kPa) for low-pressure vessels and 200 degrees C and 500 psi (3450 kPa) for moderately high-pressure vessels. All digested samples were clear and color less and their residual carbon content was less than 1%, indicating success ful decomposition of the organic matrix. The residual acid concentrations i n the final analytical solutions were 2.2 +/- 0.3% and 2.5 +/- 0.2% (w/w) f or low and moderately high-pressure vessels, respectively; this is suitable for inductively coupled plasma-mass spectrometery (ICP-MS) analysis. The d igested syrup samples were analyzed using ICP-MS. Spike recovery for lead, after digestion in the low-pressure and moderately high-pressure digestion vessels, were 100 +/- 2% (n = 5, 95% CI) and 98 +/- 1% (n = 5, 95% CI), res pectively. Satisfactory recoveries were also obtained for seven selected el ements. Lead-spiked maple syrup check standards were digested, and lead con centrations were in the range of certified values. Lead levels ranged from 18 to 367 ng/g. Concentrations of seven other trace elements (As, Cd, Co, C u, Mn, V and Zn) in maple syrup were also determined. (C) 2000 Elsevier Sci ence B.V. All rights reserved.