Development of an automated flow injection analysis system for determination of phosphate in nutrient solutions.

BACKGROUND: A fully automated flow injection analysis (FIA) system was developed for determination of phosphate ion in nutrient solutions. This newly developed FIA system is a portable, rapid and sensitive measuring instrument that allows on-line analysis and monitoring of phosphate ion concentration in nutrient solutions. The molybdenum blue method, which is widely used in FIA phosphate analysis, was adapted to the developed FIA system. The method is based on the formation of ammonium Mo(VI) ion by reaction of ammonium molybdate with the phosphate ion present in the medium. The Mo(VI) ion then reacts with ascorbic acid and is reduced to the spectrometrically measurable Mo(V) ion. New software specific for flow analysis was developed in the LabVIEW development environment to control all the components of the FIA system. The important factors affecting the analytical signal were identified as reagent flow rate, injection volume and post-injection flow path length, and they were optimized using Box-Behnken experimental design and response surface methodology. RESULTS: The optimum point for the maximum analytical signal was calculated as 0.50 mL min-1 reagent flow rate, 100 µL sample injection volume and 60 cm post-injection flow path length. The proposed FIA system had a sampling frequency of 100 samples per hour over a linear working range of 3-100 mg L-1 (R2 = 0.9995). The relative standard deviation (RSD) was 1.09% and the limit of detection (LOD) was 0.34 mg L-1 . CONCLUSION: Various nutrient solutions from a tomato-growing hydroponic greenhouse were analyzed with the developed FIA system and the results were found to be in good agreement with vanadomolybdate chemical method findings. © 2018 Society of Chemical Industry.

Preparation of electrochemically treated nanoporous pencil-graphite electrodes for the simultaneous determination of Pb and Cd in water samples.

A simple and rapid analytical method of determining Pb2+ and Cd2+ in water samples using an electrochemically pretreated pencil-graphite electrode (EP-PGE) is proposed for the first time in the literature. An electrochemically pretreated pencil-graphite electrode was prepared by performing potential cycling between -0.3 V and 2.0 V in 0.1 mol L-1 H3PO4 solution to improve its ability to electrochemically sense Pb2+ and Cd2+ ions. Square-wave anodic stripping voltammetry (SWASV) was used as the electroanalytical method. The electroanalytical parameters that influence the stripping determination of Pb2+ and Cd2+ were optimized based on experimental results. The magnitude of the peak oxidation current was adjusted in order to optimize the value of each parameter. Applying the resulting disposable electrode under the optimized conditions led to good selectivity and sensitivity in the determination of Pb2+ and Cd2+ ions. Interference from coexisting ions was also investigated. The resulting sensor was successfully tested by applying it to a standard reference water sample. Under the optimized conditions, the limits of detection were 0.46 µg L-1 for Pb2+ and 1.11 µg L-1 for Cd2+ using the electrode. Relative standard deviations (%RSD) were 2.76 for Pb2+ and 2.85 for Cd2+. The linear working ranges of the electrode for Pb2+ and Cd2+ ion detection were 5-45 µg L-1 and 10-40 µg L-1, respectively. Graphical abstract Preparation of nanoporous pencil-graphite electrode by cyclic voltammetry and stripping voltammetric screening of Pb and Cd.