Determination of boron in natural water and products derived from grape using an automated flow injection analysis system with piezoelectric detection

An automated flow injection analysis system with piezoelectric detection is proposed as a sensitive and selective method for boron. The detector is an electrode-separated piezoelectric quartz crystal coated with N-methyl-D-glucamine-modified poly(epichlorohydrin). The film ability to retain boron allows the adjustment of the linear dynamic range and the sensitivity by varying the injected sample volume. In the present work, the sample volumes were varied from 0.5 to 5.0 mL. Among several ionic species, germanate is the only one that can interfere in the method. Nevertheless, it can be eliminated by addition of sulfide to the sample. The method was successfully applied to the determination of boron concentration in samples of natural water (from 1.71 to 309 mug L-1) and products derived from grape juice (from 2.06 to 6.21 mg L-1). A pretreatment with hydrogen peroxide in alkaline medium was required due to the great amount of sugars in the grape products.