MULTISITE DETECTION IN FLOW-ANALYSIS .2. MONOSEGMENTED SYSTEMS WITH RELOCATING DETECTORS FOR THE SPECTROPHOTOMETRIC DETERMINATION OF BORON IN PLANTS

Monosegmented systems with detector relocation are proposed. The sample is injected with an air plug positioned at its tailing portion in order to minimize dispersion. After the peak maximum, the detector is displaced from its original position, allowing the air phase to be discarded without flowing through it. The sample portion inside the detector is either trapped or pushed towards waste. The advantages and limitations of the approach are described, and the need for an optional washing stream is discussed. As an application, an improved system for the spectrophotometric determination of boron in plants is proposed. Four samples are simultaneously processed at a sampling frequency of 120 h-1. With a low reagent consumption (0.52 mg of Azomethine-H per determination), the system yields precise results (R.S.D. < 3%), in agreement with those given by inductively coupled plasma atomic emission spectrometry.