title: Hybrid flow system integrating a miniaturized optoelectronic detector for on-line dynamic fractionation and fluorometric determination of bioaccessible orthophosphate in soils.
abstract: An integrated Sequential Injection (SI)/Flow Injection (FI) system furnished with a miniaturized LED-based fluorometric detector is presented in this work for expedient bioaccessibility tests of orthophosphate in soils. Equipped with a microcolumn of conical shape containing 50 mg of soil, the hybrid flow system was resorted to on-line dynamic leaching and real-time quantification of pools of mobilizable orthophosphate using a bi-directional syringe pump and multiposition valve. The flexibility of the flow manifold was harnessed to explore both bi-directional and uni-directional flow extraction modes with the added degree of freedom of on-line dilution of extracts whenever needed. Bioaccessible orthophosphate was split in three fractions, the so-called NH4Cl fraction containing labile exchangeable phosphates, the alkaline fraction with Fe and Al-bound phosphates and the acidic fraction containing Ca-bound phosphates. The prevailing molybdenum blue photometric detection method is replaced by spectrofluorometric detection based on the ion pair formation between the phosphomolybdate heteropolyacid and rhodamine B with the subsequent quenching of the dye fluorescence. The dedicated optoelectronic detector was integrated in a secondary FI manifold and operated according to the fluorometric paired emitter-detector diode (FPEDD) principle involving two light emitting diodes as fluorescence inductors and one as detector of LED-induced fluorescence. Demonstrated with the analysis of a standard reference material (SRM 2711) and a real agricultural soil, the developed FI/SI fractionation system with FPEDD detection is proven reliable against the standard molybdenum blue method (p>0.05), and useful for investigation of the leaching kinetics of orthophosphate in bioaccessibility tests through in-line recording of the extraction profiles.
authors.affiliation: Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Fiedoruk
authors.affiliation: FI-TRACE group, Department of Chemistry, University of the Balearic Islands, Carretera de Valldemossa km 7.5, E-07122 Palma de Mallorca, Spain.
authors.forename: David J
authors.initials: DJ
authors.lastname: Cocovi-Solberg
authors.affiliation: Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
authors.forename: Łukasz
authors.initials: Ł
authors.lastname: Tymecki
authors.affiliation: Department of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland.
authors.forename: Robert
authors.initials: R
authors.lastname: Koncki
authors.affiliation: FI-TRACE group, Department of Chemistry, University of the Balearic Islands, Carretera de Valldemossa km 7.5, E-07122 Palma de Mallorca, Spain. Electronic address: manuel.miro@uib.es.
authors.forename: Manuel
authors.initials: M
authors.lastname: Miró
mesh_terms: D005591:Chemical Fractionation / Q000295:instrumentation; D004867:Equipment Design; D017022:Flow Injection Analysis / Q000295:instrumentation; D005470:Fluorometry / Q000295:instrumentation*; D057230:Limit of Detection; D008904:Miniaturization; D010710:Phosphates / Q000032:analysis*; D012987:Soil / Q000737:chemistry*
chemical_list: D010710:Phosphates; D012987:Soil
keywords: Bioaccessibility; Flow analysis; Fluorometric detection; Orthophosphate; Paired emitter–detector diode; Soil