Direct Determination of Phosphite in Fertilizers by Flow-Injection Amperometry

✍ Scribed by Vanessa Pezza Franzini; Cecílio Sadao Fugivara; Assis Vicente Benedetti; Clóvis Augusto Ribeiro; Eder Tadeu Gomes Cavalheiro; José Anchieta Gomes Neto

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 104 KB
• Volume: 19
• Category: Article
• ISSN: 1040-0397
• DOI: 10.1002/elan.200703935

✦ Synopsis

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.