New European standards require that specifications for the preservative treatment of timber are written in terms of the penetration and retention of preservative within the treated commodity that result from the treatment process. In order to check compliance with this type of specification, suitable methods of quantitative analysis must be available. This paper presents the results of a study by BRE and four commercial companies on the methods currently used in the UK to quantify the retention of CCA and creosote in treated timber. When analysing CCA-treated wood, different retention values were obtained with different methods of analysis and even with the same method when different operating parameters were selected. It has been concluded that either a single agreed method of analysis for CCA within Europe is required or more precisely defined operating conditions are required for each instrumental method which includes a method verification procedure. Data from traditional methods of assessing retention of creosote in transmission poles (e.g. charge volume uptake and weight differences) did not coincide with retention values obtained by quantitative analysis using the method in the European prestandard proposed as the reference method for creosote retention determination. Direct quantitative analysis of creosote treated timber selected from single charges showed large variations in creosote retention. It was concluded that recommendations for sampling in EN 351-2 do not take proper account of retention variations within a treated component nor of the difficulty in obtaining an analytical sample from a component once selected for examination. Greater care should be taken in defining the location within a component from which an analytical sample should be taken. In addition, a representative value for density is required in order to convert preservative content, determined as m/m from analysis, to the units used to express retention (kg/m3). This cannot easily be obtained and it is recommended that retention be expressed in m/m terms.

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