Determination of Acetic and Formic Acid in Lead Corrosion Products by Ion-exchange Chromatography†

Abstract

Ion-exchange chromatography using a Dionex DX100 ion chromatograph was used to determine the concentrations of acetic and formic acid in corrosion products from the underside of lead roofs on historic buildings in the UK. Acetate and formate ions were extracted from the lead corrosion products by shaking in 2 mM borax solution. Organic acids were separated using a Dionex AS4A-SC ion-exchange column and 2 mM borax solution as eluent and detected by chemically suppressed conductivity detection. A linear calibration curve was obtained over the range 1–100 ppm for acetate and formate ions with correlation coefficients r² = 0.9987 and 0.9997 and limits of detection of 0.12 and 0.10 ppm, respectively, with a 25 mm³ sample volume. The RSD of a mid-range standard (10 ppm, six replicates) was 1.4% for acetate and 1.0% for formate. The recoveries of acetate and formate ions from the lead oxidation products were 97.5 and 98.6%, respectively. High concentrations of organic acids were found in samples collected from many of the sites which suffered severe underside lead corrosion, confirming a wider role of organic acids in the accelerated breakdown of lead roofs.