Acidic Functional Groups of IHSS Samples

Cat. No. Source Carboxyl Phenolic Q1 Log K1 n1 Q2 Log K2 n2 N RMSE
 

 
Sources: (1) School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, U.S.A.; (2) Department of Chemistry, Environmental Sciences Ph.D. Program, Ball State University, Muncie, IN, U.S.A.
References: (1) J. D. Ritchie and E. M. Perdue, Geochim. Cosmochim. Acta, 67, 85-96 (2003); (2) S. J. Driver and E. M. Perdue, Advances in the Physicochemical Characterization of Dissolved Organic Matter: Impact on Natural and Engineered Systems, American Chemical Society, 1160: 75-86 (2014).
Solutions containing 0.36 ± 0.01 g L-1 (on a dry ash-free basis) of an IHSS sample in 0.1 M NaCl were titrated from their initial pH values of 3.0-3.3 to final pH values of 10.5-10.7 in 25-35 minutes, using 6-8 mL increments of carbonate-free 0.100 M NaOH. All titrations were conducted under a N2 atmosphere in a thermostated water bath at 25.00 ± 0.02 °C. At least three titrations were obtained for each sample. The stock solutions of soil, peat, leonardite, and Summit Hill humic acids also contained 0.002 M NaOH, which was needed to effectively disperse/dissolve those samples, and an equivalent quantity of HCl that was added just before a titration was started.
Carboxyl is the charge density (meq/g C) at pH 8.0; Phenolic is two times the change in charge density (meq/g C) between pH 8.0 and pH 10.0.
The overall charge density (in meq/g C) of a humic substance increases systematically with pH (or with the concentration of H+). The equation on the right, known historically as a modified Henderson-Hasselbalch equation for two classes of binding sites, was used to fit titration data and obtain the set of model fitting parameters in this table. modified Henderson-Hasselbalch
The fitting parameters of the model were obtained by a nonlinear least-squares fit of the model to aggregated sets of replicate titration data. Q1 and Q2 are the maximum charge densities of the two classes of binding sites, Log K1 and Log K2are the mean log K values for proton binding by the two classes of sites, and n1 and n2 are empirical parameters that control the width (in log K) of a class of proton binding sites. N is the number of fitted titration data points, and RMSE is the root mean-square error for fitting this model to the data (see Reference). This model, also known in more recent literature as a Langmuir-Freundlich equation, is the primary building block of the NICA class of models.
An * means that a sample is no longer available, and nd means that an item was not determined.
Standard HA
Suwannee River I * 1S101H (1) 9.59 4.24 10.69 4.42 3.79 2.28 9.68 1.11 113 0.0673
Suwannee River II 2S101H (1) 9.13 3.72 9.74 4.35 3.30 4.48 10.44 1.73 171 0.0815
Elliott Soil 1S102H (1) 8.28 1.87 8.90 4.36 3.16 0.85 9.80 1.00 169 0.0943
Pahokee Peat 1S103H (1) 9.01 1.91 9.64 4.22 3.20 0.94 9.86 1.00 145 0.0865
Leonardite 1S104H (1) 7.46 2.31 8.17 4.59 3.32 1.13 9.72 1.31 106 0.0532
Standard FA
Suwannee River I 1S101F (1) 11.44 2.91 12.00 3.80 3.21 1.48 9.52 1.00 109 0.1053
Suwannee River II 2S101F (1) 11.17 2.84 11.66 3.76 3.24 2.05 9.84 1.45 123 0.1072
Elliott Soil I * 1S102F (1) nd nd nd nd nd nd nd nd nd nd
Elliott Soil II 2S102F (1) 13.24 2.27 14.12 3.67 3.62 0.74 9.53 1.00 111 0.1375
Pahokee Peat I * 1S103F (1) 13.34 2.32 14.22 3.99 3.33 0.76 9.57 1.00 117 0.1028
Pahokee Peat II 2S103F (1) nd nd nd nd nd nd nd nd nd nd
Reference HA
Suwannee River * 1R101H (1) nd nd nd nd nd nd nd nd nd nd
Pahokee Peat 1R103H (1) 8.87 2.05 9.54 4.26 3.25 1.01 9.85 1.00 117 0.0773
Nordic Lake 1R105H (1) 9.06 3.23 10.32 4.32 4.22 1.64 9.89 1.11 105 0.0740
Summit Hill Soil 1R106H (1) 7.14 2.42 7.53 4.47 3.12 1.31 9.23 1.57 106 0.0480
Waskish Peat 1R107H (1) nd nd nd nd nd nd nd nd nd nd
Reference FA
Suwannee River 1R101F (1) 12.23 3.11 12.94 3.81 3.36 1.60 9.62 1.00 115 0.1312
Pahokee Peat * 1R103F (1) 15.24 1.78 16.25 3.73 3.54 1.31 10.74 1.00 129 0.1586
Nordic Lake 1R105F (1) 11.16 3.18 12.15 3.79 3.95 1.49 9.67 1.00 107 0.1121
Waskish Peat 1R107F (1) nd nd nd nd nd nd nd nd nd nd
Pony Lake FA 1R109F (2) 7.09 1.75 6.91 4.52 1.92 1.43 9.48 1.77 1256 0.0340
Aquatic NOM
Suwannee River I 1R101N (1) 9.85 3.94 10.57 3.94 3.60 2.61 9.74 1.19 112 0.0725
Suwannee River II 2R101N (2) 11.21 2.47 11.20 4.16 3.44 1.60 9.99 1.03 1705 0.1360
Nordic Lake 1R108N (1) nd nd nd nd nd nd nd nd nd nd
Upper Mississippi River 1R110N (2) 12.43 0.83 12.51 3.47 2.69 0.91 10.00 1.00 1626 0.0800
Bulk Materials
Elliott Soil BS102M (1) nd nd nd nd nd nd nd nd nd nd
Pahokee Peat BS103P (1) nd nd nd nd nd nd nd nd nd nd
Leonardite BS104L (1) nd nd nd nd nd nd nd nd nd nd