Simultaneous determination of nitrate, chloride, sulfate, and phosphate in plant materials by ion chromatography

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Abstract
Simultaneous determination of anions in plant materials is needed. A simple and precise ion-chromatographic (IC) method for simultaneous determination of NO3-, Cl-, SO42-, and PO43- in plant samples was developed. It involves extraction of these anions with deionized water and their simultaneous determination by IC. The averages of 10 plant samples by the IC method agreed closely with those obtained by the steam-distillation method for NO3- (0.158 vs 0.164%), titrimetric method using AgNO3 and K2CrO4 for Cl- (1.22 vs 1.19%), and colorimetric heteropoly blue method for PO43- (0.335 vs 0.330%). The average SO42--S value of 10 plant samples by the IC method (0.067%) was somewhat lower than the corresponding value (0.075%)obtained by the reduction and colorimetric determination of methylene blue. The IC method is based on separation of the anions by a separator column containing Dionex low-capacity anion-exchange resin in the HCO3- form and on converting the various anions to their corresponding acids by a suppressor column containing a strong cation-exchange resin in the H+ form. A solution of 3.0 mM NaHCO3 + 1.8 mM Na2CO3 was used as the eluent, and electrical conductivity is used as the mode of detection. The method is precise and accurate and can detect as little as 0.1 mg/l of NO3--N, Cl-, SO22--S, or PO4-P3-P in plant extracts. In addition to those anions, malic acid was separated and determined. With the IC method, the 4 anions indicated and malic acid can be determined simultaneously in 2 mL of plant extract in approximately 20 min.