Determination of boron by using a quartz crystal resonator coated with N-methyl-D-glucamine-modified...

A nongravimetric quartz crystal resonator for determination of boron was proposed. The key step is the preparation of a polymer that forms a complex with boron (from borate ion). The polymeric film is deposited on one face of an electrode-separated quartz crystal. The backbone of the polymer is poly(epichlorohydrin), which is modified to anchor N-methyl-D-glucamine. After reticulation and reduction, the film presents high stability and sensitivity to boron at pH 8.5. A carrier solution containing 50 mM EDTA ensures high conductivity and the elimination of several interfering metal ions. Boron is strongly retained by the film, and a positive shift of the oscillating frequency is proportional to its concentration. Boron is eluted with 1 mL of a 1 M mannitol solution. For a 0.160-mL sample loop and concentration up to 600 microM, the calibration sensitivity was 1.67 Hz/microM and the LOD was 2 microM. This limit could be lowered to 0.3 microM by using a 1.00-mL sample loop. In both cases, it was possible to detect 3 ng of boron. It was estimated that the nongravimetric sensor is at least 10 times more sensitive that a hypothetical gravimetric sensor.