AS NZS 1605.2:2018 Methods for sampling and analysing timber preservatives and preservative- treated timber
6.1 PRINCIPLE
The presence of tin compounds in TBTO and TBTN LOSP treated timber are determined by using an alcoholic solution of bromopyrogallol red. Areas containing tin compounds turn blue/violet.
6.2 REAGENT- -BROMOPYROGALLOL RED SOLUTION 0.2%
Dissolve 0.2 g of bromopyrogallol red powder (CAS No.16574-43-9) in 100 mL of ethanol.
Store in a stoppered glass container.
The reagent shall be of analytical reagent quality.
6.3 PROCEDUR E
The procedure shall be as follows:
(a) Cut a transverse section of the treated timber approximately 30 mm along the grain.
(b) Dry the sample in an oven (ca.100°C) for a minimum of 12 h.
(c) Remove the sample from the oven and allow to cool to room temperature.
(d) Cut the sample in half, across the grain.
(e) Apply the bromopyrogallol red solution to one of the freshly cut faces with a brush.
Allow 10 to 15 min for colour development.
The untreated areas remain a pale red while the areas containing tin compounds turn blue/violet.
6.4 PRECA UTIONS
A pale blue colour can develop on unpenetrated zones if oven-drying is incomplete and moisture is still present. The presence of residual organic solvent will also interfere with colour development.
Insufficient time in the oven will fail to degrade the tin compounds sufficiently to produce positive results.
Where freshly treated material containing excess organic solvent is to be tested, it should be gently air-dried before being placed in the oven. This is to avoid the possibility of redistribution of the tin compounds, which may occur as the solvent flashes off, if samples
are oven-dried directly.
7.2.1 Principle
Zinc is determined visually on the surface of timber samples treated with zinc-containing preservative formulations by the formation of a pink colour.
7.2.2 Reagent – Dithizone indicator
Dissolve 0.1 g of dithizone (dimethylthiocarbazone) in 100 ml of chloroform (or other available chlorocarbon solvent) or ethanol. The reagent shall be of analytical reagent quality.
7.2.3 Procedure
The procedure shall be as follows:
(a) Ensure any free solvent from the treatment process has evaporated from the wood and that the wood is surface dry.
(b) Cut a fresh cross-cut face using a fine-toothed saw.
(c) Apply a fine layer of dithizone indicator to the fresh cut face by spray.
(d) Penetrated areas will change to a pink colour within a few seconds. Unpenetrated areas will remain green. Record penetration at 5-10 min from the time the indicator was applied. The colour will start to fade after 30 min.