Direct Determination of Phosphite in Fertilizers by Flow‐Injection Amperometry

Abstract

A sensor based on graphite electrode modified with palladium-platinum-palladium film is proposed for phosphite determination by flow-injection amperometry. The modified electrode was prepared by a sequential cathodic deposition of Pd, Pt and Pd on a graphite electrode from 0.5% m/v PdCl 2 þ 28% m/v NH 4 OH and 2% m/v H 2 PtCl 6 þ 10% v/v H 2 SO 4 solutions. After suitable conditioning, the electrode showed catalytic activity for phosphite oxidation when 0.15 V was applied. The proposed system handles approximately 50 samples per hour (0.01 -0.05 mol L À1 Na 2 HPO 3 ; R 2 ¼ 0.9997), consuming ca. 70 mL of sample per determination. The limit of detection and amperometric sensibility were 5 Â 10 À4 mol L À1 and 1.5 mA L mol À1, respectively. The proposed method was applied to analysis of fertilizer samples without pre-treatment. Results are in agreement with those obtained by spectrophotometry and titrimetry at 95% confidence level and good recoveries (96 -109%) of spiked samples were found. Relative standard deviation (n ¼ 12) of a 0.01 mol L À1 Na 2 HPO 3 sample was 2%. The useful lifetime of modified electrode was around 220 determinations. For routine purposes it means that this electrode can be continuously used for 5 hours.

A Glimpse of Recent Developments in Brazilian Analytical Chemistry

“…Several flow cell configurations and working electrodes were proposed for the determination flavonoids in tea samples (Pedrosa et al 2006a), phosphite in fertilizers (Franzini et al 2007), procaine in pharmaceutical formulation (Bergamini et al 2007), L-lactate in blood samples (Lowinsohn and Bertotti 2007), paracetamol in pharmaceuticals (Pedrosa et al 2006b), and L-dopa in pharmaceuticals . A sequential injection system for determining methyl parathion in water samples and a potentiometric flow injection system to determine inositol phosphates and phosphate in seeds and grains, animal nursing feed, soybean meal, and corn (Parra et al 2005) were also proposed.…”

Let’s Make White Phosphorus Obsolete

“…One potential drawback of this method is that under earth’s oxygen-rich atmosphere, phosphate is preferred thermodynamically over phosphite, and it is known that phosphite is oxidized naturally to phosphate either under atmospheric conditions or under the catalysis of microorganisms. Despite this, the method could still present an advantage because phosphite has the potential to be more easily sensed using devices due to its electrochemical response . Thus, even if phosphite is eventually oxidized to phosphate, it would provide a source of fertilizer that could be accurately monitored in the short term and applied more strategically than is currently the case for phosphate fertilizers.…”

Direct Determination of Phosphite in Fertilizers by Amperometric Titration

“…Among analytical techniques usually employed for phosphorus determination are atomic absorption spectrometryAAS , inductively coupled plasma optical emission spectrometryICP OES , gravimetry , , spectrophotometry − , amperometry , , and titrimetry .…”

“…A palladium film on a platinum electrode has been proposed in a manual voltammetry procedure for phosphite, but the poor adherence of the palladium film at the electrode surface impaired its application to real samples (11). This cumbersomeness was circumvented after development of a new sensor based on a graphite electrode modified with a palladium-platinumpalladium film by a sequential cathodic deposition of palladium, platinum, and palladium on a graphite electrode (12). The determination of phosphite by classical titrimetry using iodine as titrant was proposed recently (13), but the identification of the end point, manifested by the appearance of faint yellow, was considered the main drawback of the method.…”