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Table 5 Total metal concentration of the humic acid fractions

From: Chemical and spectroscopic characterization of insoluble and soluble humic acid fractions at different pH values

Fraction Ca K Mg Na
(mol kg−1) (mol kg−1) (mol kg−1) (mol kg−1)
pH 1 Insoluble 0.07ad 0.13ad 0.17ad 0.31a
Soluble nd nd nd nd
pH 3 Insoluble 0.11abcd 0.18a 0.22a 0.50a
Soluble 0.14abcd 0.06b 0.03b 1.69b
pH 5 Insoluble 0.12abcd 0.28c 0.55c 0.97c
Soluble 0.16bcd 0.07b 0.11d 2.32d
pH 7 Insoluble 0.09cd 0.33c 0.67e 1.00c
Soluble 0.14d 0.10bd 0.17ad 2.21d
  1. Within columns, values followed by the same letter are not significantly different (P < 0.05). nd, not determined because of the low amount of sample.