Development and application of colorimetric microassay for determining boron-containing compounds

Abstract

This paper describes the development of a microassay for boron and the application of this microassay for evaluating leachability of boron by post-treatment of southern pine with the calcium precipitating agent NHA (N'N-napthaloylhydroxylamine). The microassay method for quantitative estimation of boron content in treated wood and leachates is a microadaptation of the colorimetric azomethine-H method. The primary advantages of this microassay method are that it uses fewer reagents, uses smaller sample volumes, and conserves time for analysis when a large number of tests are required. Wood blocks were treated with boric acid, disodium octaborate tetrahydrate (DOT), and NHA solutions at several concentrations. Boron leaching performance was evaluated on the blocks using AWPA E 11-97 standard method. Blocks treated sequentially with DOT and then with 0.5 or 1.0 percent NHA solutions showed similar to30% less boron leaching, whereas similar treatment with boric acid and 0.1% NHA solutions did not enhance boron retention compared with the blocks treated with only boric acid. We conclude that precipitation of NHA at higher concentrations decreases or limits boron leaching.