Methods for estimation of preservatives in treated timber and in treating solutions, Part 1: Determination of copper, arsenic, chromium, zinc, boron, creosote and fuel oil
1991 Edition

As per IS 2753 Part 1, Clause 4.3.2 Method II, copper content determination involves digesting wood flour samples in a sequence of acids. For samples up to 5 g, add 40 ml concentrated nitric acid and for 5-15 g, use 80 ml; let stand overnight. Then add perchloric acid (5 or 10 ml), followed by sulfuric acid (10 or 20 ml), digest at low heat until dissolved. Heat over flame until solution is pale yellow, adding nitric acid in increments if darkening occurs. Finally, cool, add perchloric acid again, and heat to fumes. This ensures complete breakdown for accurate copper estimation.

The standard method involves reducing hexavalent chromium with excess ferrous ammonium sulfate, then titrating the remaining ferrous ions with 1% potassium dichromate solution using barium diphenylamine sulphonate as an indicator. The chromium concentration is calculated by subtracting the titrant volume used after sample addition from that used for ferrous alone, divided by 10, yielding the hexavalent chromium content in mg/L or percentage.

For arsenic titration, the reagents include concentrated hydrochloric acid, 50% hypophosphorous acid to precipitate arsenic, concentrated sulfuric acid for digestion, additional hydrochloric acid before titration, methyl orange indicator, and potassium bromate solution as the titrant. The process involves precipitation, digestion, and titration until the disappearance of pink color, ensuring selective arsenic determination.

According to IS 2753 Part 1, creosote and fuel oil are measured by Soxhlet extraction of sawdust samples with ether until the extract is colorless. The ether is evaporated, residue washed with potassium carbonate to remove resins, and weighed. The mixture is then distilled up to 350°C; a portion of the distillate is treated with dimethyl sulphate and allowed to separate, where the volume of the upper layer corresponds to fuel oil content. Creosote is calculated by subtracting fuel oil weight from total extract weight.

Samples should be ground finely to pass through a 425-micron sieve and mixed thoroughly. Weigh 5 to 10 g of wood flour, digest in a Kjeldahl flask with concentrated nitric acid (8 ml per gram) and sulfuric acid (5 ml total), let stand overnight. Heat gently for an hour and gradually increase temperature, adding nitric acid incrementally until the solution is pale yellow. After cooling, dilute to a known volume, agitate well, filter, and analyze aliquots in duplicate. For chromate determination, additional reagents and boiling steps are included before analysis.