Boron-containing anions, plants

Ogner [1] has described an automated analyser method for the determination of boron-containing anions in plants. This is based on the formation of a fluorescent complex between these anions and carminic acid at pH 7. The plant tissues are ashed at 550 °C and the residue dissolved in 0.5 N hydrochloric acid prior to adjustment to pH 6-7 with sodium carbonate solution. The solution is excited at 470 nm and fluorescence intensities measured at 585 nm. Interferences by the reaction of some cations with carminic acid are overcome by passing the solution through an ion exchange column to exchange the cations for sodium ions. Analytical recoveries of boron anions were in the range 98-104%. The detection limit of the method was 5 xg/l boron. 

It is important to note that the presence of polyborate anions, as shown in Fignre 2, is only significant in relatively concentrated solutions. This is relevant to the enviromnental and biological aspects of boron chemistry, since boron is present in both natural waters and biological systems at low concentrations. Under these conditions, only B(OH)3 and B(0H)4 are significant species and at near neutral pH, the concentration of the B(OH)4 anion is minor. Ocean waters contain an average boron concentration of about 4.6 g p,g g , which is almost entirely present in the form of naturally occurring boric acid. Boron in plants and animals is also present mainly as boric acid, even if the dietary source of boron is a borate salt. 

Figure 10.108 Trace anion analysis with an electolytically generated tetraborate eluent in a nuclear power plant water containing 2000 mg/L boron. Separator column lonPac AS14 column dimensions 250 mm x 2 mm i.d. eluent 50 mmol/L boric add/KOH gradient 4mmol/L KOH isocratically for 6 min and...

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