A simple stopped-flow method with continuous pumping for the spectrophotometric flow-injection determination of boron in plants

An alternative way of stopping a processed sample inside a flow-through detector is proposed. A commutating device permits the peristaltic pump to operate continuously, thus avoiding problems associated with the pump inertia often found in analyzers requiring pump stoppage. The feasibility of the approach is demonstrated by improving the spectrophotometric determination of boron in plants, which is based on a relatively slow reaction. Effects of commutating times, flow rates, manifold dimensions and reagent concentrations are studied. With the same analytical frequency (60 h^?1) and azomethine-H consumption (2.1 mg per sample) of the original procedure, the proposed system provides better sensitivity because of a three-fold increase in the sample-processing time and the absence of significant sample dispersion. Reproducible results (r.s.d. for typical samples usually less than 1%) are in agreement with those obtained with the original procedure.