Extraction of humic acids from a natural matrix by alkaline pyrophosphate. Evaluation of the molecular weight of fractions obtained by ultrafiltration |
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Authors: | D Tonelli Renato Seeber Claudio Ciavatta Carlo Gessa |
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Institution: | (1) Dipartimento di Chimica Fisica e Inorganica, Università di Bologna, Viale Risorgimento, 4-40136 Bologna (Italy), IT;(2) Istituto di Chimica Agraria, Università di Bologna, Via Berti Pichat, 10-40127 Bologna (Italy), IT |
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Abstract: | Fractions of humic acids, resolved by ultrafiltration of extracts from a sample of peat treated with alkaline pyrophosphate
solution, have been submitted to high-performance size-exclusion chromatography, with the aim of determining the molecular
weight distributions. Anomalous peaks, located at retention volumes higher than those corresponding to the main signal, are
present in the elution profiles relative to the lightest fractions. These peaks are more intense when using a refractive index
detector rather than a UV detector. Elemental analysis data for the lightest fractions suggested that the spurious peaks are
due to the presence of inorganic material. The hypothesis that pyrophosphate interacts with humic acids in the course of the
extraction has been confirmed by colorimetric determination of the phosphorus content in the different fractions. As a consequence,
the extraction procedure has been modified by using 0.1 mol/L NaOH as extractant.
The average molecular weights of the various fractions, following NaOH extraction, result in substantial agreement with those
obtained following pyrophosphate solution extraction (if the ‘pyrophosphate peaks’ present in the chromatographic profile
are discarded in the calculations).
Received: 18 November 1996 / Revised: 18 February 1997 / Accepted: 23 February 1997 |
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