Quantification of Cu and Zn in antifouling paint films by XRF

Methods to determine the release of biocides (e.g. copper) and substances of concern (e.g. zinc) from antifouling paints are required for both the development of efficient products and their environmental risk assessment. To date, there are only two standardized methods available to estimate such release rates, but their reliability has been put into question. An alternative method, allowing determination of environmental release rates in the field of metallic or organometallic biocides by X-Ray Fluorescence (XRF), has been developed and applied in recent years. In this study, the potential for standardization of the XRF method is investigated through evaluation of its accuracy, precision and transferability between instruments. Accurate quantification of copper (Cu) and zinc (Zn) in μg cm^-2, despite differences in chemical composition, was demonstrated through comparison of calibration regression slopes for ten different antifouling paints and confirmed through the measurement of validation samples. Universal antifouling paint calibration curves are proposed for the determination of Cu and Zn in thin paint films, with a prediction uncertainty of around ±130 μg/cm² for both metals. The transferability of the method to another instrument was also demonstrated. For both analyzers, concentrations of validation samples were within 5% of those determined through wet chemical analysis. Pre-requisites and recommendations for the application of the method as well as its applicability to both short- and long-term release rate studies in the field are also presented and discussed.