title: Flow systems exploiting in-line prior assays.
abstract: An expert sequential injection system involving a prior assay is proposed for spectrophotometric determination of phosphate and eventually zinc in soil extracts. The result of phosphate determination is the basis for a concentration-oriented decision regarding to the need or not for zinc determination. Zinc was only determined if a threshold value (peak height corresponding to 5.0mgl(-1)P) was surpassed. The methods involved formation of molybdenum blue and the Rhodamine 6G/ammonium thiocyanate/Zn(2+) ternary complex. Variations in the threshold value were < 2% during 4h operating periods, false responses were not verified, and the analytical time was reduced in about 30%. Precise results (R.S.D. <3%P and < 1% Zn) in agreement with spectrophotometry and flame atomic absorption spectrometry were obtained. The innovation permits faster information processing, as well as a reduction in the number of measurements, number of analytical steps, laboratorial time, and consumption of sample and reagents, thus waste generation.
authors.affiliation: Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, P.O. Box 96, Piracicaba SP 13400-970, Brazil.
authors.forename: Viviane
authors.initials: V
authors.lastname: Grassi
authors.forename: Ana Cristi B
authors.initials: AC
authors.lastname: Dias
authors.forename: Elias A G
authors.initials: EA
authors.lastname: Zagatto