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

Abstract

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 vessels, were evaluated. Average temperatures and maximum pressures attained during the maple syrup sample digestion were 140°C and 190 psi (1310 kPa) for low-pressure vessels and 200°C and 500 psi (3450 kPa) for moderately high-pressure vessels. All digested samples were clear and colorless and their residual carbon content was less than 1%, indicating successful decomposition of the organic matrix. The residual acid concentrations in the final analytical solutions were 2.2±0.3% and 2.5±0.2% (w/w) for low and moderately high-pressure vessels, respectively; this is suitable for inductively coupled plasma-mass spectrometery (ICP-MS) analysis. The digested 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), respectively. Satisfactory recoveries were also obtained for seven selected elements. Lead-spiked maple syrup check standards were digested, and lead concentrations 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, Cu, Mn, V and Zn) in maple syrup were also determined.