Many high-pressure liquid chromatographic methods used for the determination of low molecular weight organic acids in root exudates lack specificity and cannot completely separate mixtures of mono-, poly-, and hydroxycarboxylic acids simultaneously. Hence, a new gas chromatographic (GC) method that is specific for the identification and quantitation of low molecular weight dicarboxylic acids as methyl esters was developed. Samples collected from root exudates of selected durum wheat and flax cultivare grown in sterile hydroponic solutions were extracted and concentrated by anion exchange membranes. Samples were then subjected to methylation in acidified methanol at elevated temperatures and injected into a GC. The five acids investigated in this study-oxalic, malonic, succinic, fumaric, and maleic-required 7 min for elution from a GC column and were quantified using methylmalonic acid as an internal standard. Good recovery and reproducibility as well as a low detection limit of ca. 1 ppm acid in the membrane eluate make this method very suitable for dicarboxylic acid determination in root exudates.

No abstract

No abstract

A gas chromatographic (GC) method was developed for the determination of water extractable and HCl/MeOH extractable low molecular weight dicarboxylic acids in rhizosphere soils of durum wheat (Triticum turgidum var. Durum L.). Rhizosphere soils were collected after 2 weeks of plant growth by first removing the bulk soil from the root system and then by washing off the rhizosphere soil that adhered to the root surface with water. After shaking of the rhizosphere/water mixtures, dicarboxylic acids were concentrated on anion exchange membranes. Rhizosphere soils were then freeze-dried and the samples shaken with 0.5 M HCl in MeOH to remove any remaining dicarboxylic acids adsorbed to the soil particles after the water extraction. The efficiency of HCl/MeOH extraction from three different soils ranged from 85.9 to 106.3% for most acids; however, the recovery of oxalic acid varied with soil type. Oxalic, fumaric, and succinic acids were found in both the water and HCl/MeOH extracts of rhizosphere soils of durum wheat, while malonic acid was present only in the HCl/MeOH extracts. Dicarboxylic acids detected by GC in the water extracts were further identified by ion exclusion and ion exchange liquid chromatography. Washing soil from roots of durum wheat provided an efficient method for the collection of rhizosphere soil. Extraction of these soils with water and HCl/MeOH provided estimates of soluble and non-water-soluble low molecular weight dicarboxylic acids, respectively, using GC. Determination of these acids will aid in further understanding of their role in rhizosphere processes. Keywords: Rhizosphere; dicarboxylic acids; durum wheat

A new extraction method for the HPLC-UV determination of metsulfuron in soil was developed and compared with NaHCO3extraction and a lentil bioassay technique. The new procedure consisted of metsulfuron extraction using anion exchange membranes followed by a dichloromethane concentration of the membrane eluates. Three soils representing different landscape positions were spiked with metsulfuron to yield concentrations in the range of 0 to 40 μg kg−1dry soil and were analyzed by the above procedures. At a given spike rate, the efficiency of the anion exchange membrane extraction was highest for the soil from the upper slope position and lowest for the soil from the lower slope position, indicating that the amount of ion-exchangeable sulfonylurea was affected by soil properties. Similar trends in degree of root growth inhibition were observed for lentil response to metsulfuron presence in soil; percent root growth inhibition was related to the landscape position as the amount of membrane-extractable metsulfuron. The percent shoot growth inhibition was not soil dependent and did not differ among soils. The efficiency of NaHCO3extraction for metsulfuron did not vary with soil type; in the NaHCO3method, because of the buffered alkaline nature of the extraction, differences in soil properties, particularly soil pH, would have less effect on metsulfuron recovery. Because of similar trends for the results of the membrane extraction method and a lentil root bioassay, anion exchange membrane extraction may provide useful information on bioavailable fractions of sulfonylurea herbicides in soil.