4 The Nature of Commercial Humic Acids Downloaded by UNIV OF CALIFORNIA SANTA CRUZ on September 4, 2014 | http://pubs.acs.org Publication Date: December 15, 1988 | doi: 10.1021/ba-1988-0219.ch004
Patrick MacCarthy Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401 Ronald L. Malcolm U.S. Geological Survey, Box 25046, Mail Stop 408, Denver Federal Center, Denver, CO 80225
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In a follow-up to a study based primarily on solid-state C-NMR spectroscopy, commercial humic acids were investigated by infrared spectroscopy. Pronounced similarities were observed between the infrared spectra of all the commercial materials, and these "humic acids" appear to be partly in the salt form or complexed with metals. The commercial materials differ somewhat from each other in terms of their mineral compositions. The infrared spectra of the commercial materials are not remarkably different from humic acids isolated from peat, soils, and leonardite, but pronounced differences between these two classes of materials are revealed by C-NMR spectroscopy. The use of commercial humic acids as analogues of soil and water humic substances is criticized in this chapter. The adverse impact of high ash content on elemental analyses is illustrated, and the desirability of using direct methods for elemental determinations is discussed. 13
SE OF COMMERCA IL HUMC I ACIDS AS ANALOGUES
\J of soil and water humic substances has been escalating over the past decade. The literature on this subject has been reviewed (I). The same article contains a detailed char acterization of various commercial humic acids by elemental analysis and solid-state C - N M R spectroscopy, and compares the commercial products with humic and fulvic acids that were isolated from soils and streams. A l though the commercial products bear some similarities to the soil and stream humic substances, there are, nevertheless, significant differences between 1 3
0065-2393/89/0219-0055$06.00/0 © 1989 American Chemical Society
In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.
Downloaded by UNIV OF CALIFORNIA SANTA CRUZ on September 4, 2014 | http://pubs.acs.org Publication Date: December 15, 1988 | doi: 10.1021/ba-1988-0219.ch004
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AQUATIC HUMIC SUBSTANCES
the two classes of materials. As a result, the use of commercial humic acids for simulating the properties and behavior of true soil and water humic substances needs to be reevaluated. Problems with the use of the commercial humic acids are further compounded by the lack of information on the source and methods of isolation and treatment, i f any, of these materials. The objectives of this chapter are to provide further information on the commercial humic acids from five different suppliers, to discuss the nature of the commercial humic acids, and to illustrate the adverse impact of high ash content on the elemental analysis of humic substances.
Experimental Materials ami Methods The following commercial humic acids were used: No. 1: K&K humic acid (lot No. 215316, 1974) obtainedfromK&K Laboratories, Plainview, NY; No. 2: CPL humic acid (1974) obtainedfromChemicals Procurement Laboratories, College Point, NY; No. 3: Fluka-Tridom humic acid Got No. 159128115, 1974) from Fluka Chemical Corp., Hauppauge, NY; No. 4: Pfaltz and Bauer humic acid (batch 1, 1974) and No. 5: Pfaltz and Bauer humic acid (batch 2, 1981) obtained from Pfaltz and Bauer, Stamford, CT; No. 7: Aldrich humic acid Got No. 113027, 1974); and No. 8: Aldrich humic acid, sodium salt (lot No. LE3601KE, 1981)fromAldrich Chemical Company, Milwaukee, WI. Dopplerite (No. 10) was obtainedfroman outcrop at Stinking Springs, Fremont County, near Jackson, WY; this sample was used as dugfromthe outcrop and was not treated in any way. Peat for this study was obtained at a depth of about 1 m at the Peatland Experimental Station, Glenamoy, County Mayo, Ireland. Leonardite was taken from a homogenized 1000-kg sample obtained at the Biscoyne Mine, Bowman County, SD. This large sample of leonardite represents one of the bulk reference materials of the International Humic Substances Society,fromwhich one of the standard humic acids (No. 12) has been extracted. The Irish peat humic acid (No. 11) (2) and the leonardite humic acid were obtainedfromthe bulk materials by extraction with sodium hydroxide. The ash content of two of the commercial materials (Nos. 5 and 8) was diminished by subjecting the materials to liquid-liquid extraction with methyl isobutyl ketone (3), and the resulting materials are designated as sample Nos. 6 and 9, respectively. Soil humic acid (No. 13) was extracted from the Sanhedron Al horizon near Petrolia, Mendocino County, in the Mattole River Valley of Northern California, by using a modified sodium hydroxide extraction procedure for soils (4). Dissolved stream humic acid (No. 14) was isolatedfromOhio River water with a methyl methacrylate resin (XAD-8) extraction procedure (5). Elemental and ash contents were determined by Huffman Laboratories, Golden, CO. All elemental contents were determined by direct methods. Ash content was determined by combustion to constant weight at 750 °C in an oxygen atmosphere. The elemental and ash contents are given in Table I. Infrared spectra were recorded using KBr disks (1% sample) on an IR spectrophotometer (Perkin Elmer Model 580). Solid-state C-NMR spectra were measured by G. Maciel, Colorado State University, Fort Collins, CO. All NMR spectra were run by the cross-polarization magicangle spinning (CPMAS) technique. 13
In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.
In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.
NOTE: All results are expressed on a percent-by-weight, ash-free, and moisture-free basis.
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Table I. Elemental Contents of Commercial Humic Acids and Selected Humic Acids from Dopplerite, and Leonardite Ν S F> C H Total Sample 0 4. 49 0.68 0. 15 106. 0 63. 25 5. 17 32. 22 1. K&K humic acid 34. 81 0.81 0. 72
