BS 5666-7:1991

This standard BS 5666-7:1991 Methods of analysis of wood preservatives and treated timber is classified in these ICS categories:

• 71.100.50 Wood-protecting chemicals
• 79.040 Wood, sawlogs and sawn timber

This Part of this British Standard details procedures for the determination of the total tin content present in solutions and in treated wood containing bis(tri-n-butyltin)oxide. The methods have been found suitable for the determination of tin in the presence of the following:

copper naphthenate;

dieldrin (HEOD);

γ-hexachlorocyclohexane (γ-HCH, lindane);

pentachlorophenyl laurate;

pentachlorophenol and other chlorophenols;

2-phenylphenol;

zinc naphthenate;

water-repellent waxes and resins.

It is assumed that all the tin determined by these methods has been derived from bis(tri-n-butyltin)oxide and hence the tin contents are expressed in terms of bis(tri-n-butyltin)oxide.

With aged samples of treated wood, it is occasionally difficult to acid extract all the tin, particularly if iron or some other cations are present. The method described in 2.4.4 has been shown to ensure that, in all cases, the proportion of tin not extracted is unlikely to affect the validity of the determination. The wet ashing technique used in the colorimetric method (see clause 3) ensures that tin in all types of samples is brought into solution.

The recommendations made as to the size of sample to be taken for the analysis of preservative solutions assume that the bis(tri-n-butyltin)oxide content is about 1 % by mass. For samples of other compositions, adjustments may have to be made in the quantity taken for analysis. It is difficult to make recommendations as to the mass of the wood sample to be analysed since the predominant factor is the quantity of preservative within the wood rather than the mass of the wood itself. It may be necessary to make some adjustment to the values quoted in the standard, either to the mass of the treated wood sample taken for analysis or to the level of dilution of the tin solution resulting from extraction. Furthermore, it should be noted that the range of concentrations suggested for the calibration solutions used in these methods may have to be adjusted to suit the sensitivity of the instruments being used.

Two methods are described, the first involving atomic absorption spectrometry and the second colorimetry.

NOTE The titles of the publications referred to in this standard are listed on the inside back cover.

Two methods: atomic absorption spectrometric and colorimetric.