Determination of total fluoride in preservative-treated wood by ion selective electrode, without steam distillation

IRG/WP 96-20086

M J Kennedy

An analytical method was developed to determine total fluoride in wood treated with aqueous fluoride or borate-fluoride formulations. Ground wood was mixed with 60% sodium hydroxide solution and oven-dried overnight before furnacing at 600°C. The cool fused product was dissolved in warm water before adding a powerful complexant/buffer solution containing sulphosalicylic acid and EDTA. Fluoride was measured by ion-selective electrode (ISE) against appropriately matrix-matched calibration standards containing 1, 10, or 100 ppm F. The method compared favourably with two alternatives; one employed the time-consuming distillation step included in the AWPA A2 1994 method, with a titration finish, and the second employed a double fusion and ISE finish, using TISAB buffer. The chosen buffer system exhibited better capacity than TISAB to complex excesses of model interferant Al. B and Si were also accommodated. Recovery from spiked Eucalyptus maculata (at 0.05-0.5% m/m F) was 94-96%. Precision when analysing Alstonia scholaris containing 0.35% m/m F was about 2%. The method enables better throughput than the AWPA A2 94 method


Conference: 96-05-19/24 Guadeloupe, France

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