tailieunhanh - Humic Matter in Soil and the Environment: Principles and Controversies - Chapter 3

Khai thác, phân đoạn các chất Humic VIỆC TÌM KIẾM CHO EXTRACTANTS Một thủ tục phân tích thích hợp là cần thiết để đạt được mục đích chiết xuất chất humic thực. Trái ngược với sự cô lập, quan điểm và thanh lọc được xem xét ở đây như các bộ phận tách rời của các thủ tục khai thác. Mục đích là để có được các hợp chất humic thực sự bị cô lập từ mỗi khác, và miễn phí từ chiết xuất vật liệu hoặc chất gây ô nhiễm đồng. Ofhumic hỗn hợp acid, fulvic axit, protein và các. | CHAPTER 3 EXTRACTION AND FRACTIONATION OF HUMIC SUBSTANCES THE SEARCH FOR EXTRACTANTS A proper analytical procedure is necessary for achieving the purpose of extracting the real humic substances. Contrary to the general opinion isolation and purification are considered here as integral parts of the extraction procedure. The aim is to obtain the real humic compounds isolated from each other and free from co-extracted materials or contaminants. A mixture of humic acid fulvic acid protein and other compounds cannot be called humic acid before the latter is separated from fulvic acid and cleaned by a purification procedure. In the chemical industry a mixture of formic acid and other organic acids is also not called formic acid unless this acid is separated from the other acids and adequately purified. The success of the extraction procedure depends on the use of the most correct extraction reagent. The early methods have used NaOH which is accepted as the ideal extractant for humic substances in the old days. However with the advancement of humic acid chemistry in the twentieth century its suitability has been challenged 1. Copyright n 2003 by Marcel Dekker Inc All Rights Reserved. by a number of scientists Chaminade 1946 Bremner 1950 Dubach et al. 1963 Flaig et al. 1975 . Concerns of creating artifacts by NaOH extraction have started a worldwide search for new perhaps more suitable reagents for the extraction of humic substances. Hayes 1985 has provided a detailed account on the theory and chemical characteristics that a proper extracting reagent should have for an effective extraction of humic substances and quoted four chemical properties for a reagent to be accepted as the ideal solvent. He considers water to also be an excellent reagent for extraction of humic matter. In contrast a different concept for setting criteria has been used by Stevenson 1994 who believes that an ideal extraction procedure should meet the following criteria 1. The method should lead .