Mn. Jones et al., EXPERIMENTAL-DETERMINATION OF PARTIAL SPECIFIC VOLUMES OF HUMIC SUBSTANCES IN AQUEOUS-SOLUTIONS, Analytica chimica acta, 314(3), 1995, pp. 149-159
Partial specific volume is an important molecular parameter in the mea
surement of molecular masses by analytical ultracentrifugation and X-r
ay diffraction studies. Humic substances (aquatic fulvic and humic aci
ds and peat humic acid) were isolated from a natural source (Whitray F
ell, UK). The partial specific volumes (<(nu)over bar (2)>) have been
studied by two independent methods, an analytical ultracentrifugation
technique based on simultaneous sedimentation equilibrium measurements
in water and deuterium oxide and by high precision digital densimetry
. Measurements were made in a range of conditions from 0.01 M to 0.5 M
salt concentration and in the humic substance concentration range 0.0
1 to 2 mg ml(-1). Partial specific volumes in the range 0.43 to 0.63 c
m(3) g(-1) were found depending on the samples and conditions. No evid
ence was found for a dependence of (<(nu)over bar (2)>) on humic conce
ntration within the ranges studied. Both methods of measurements gave
results in reasonable accord, The ultracentrifugation method was more
precise for the aquatic fulvic acid than for the more polydisperse hum
ic acids. For the fulvic sample the reproducibility of the ultracentri
fugation method was +/-4.31%, comparable to the average reproducibilit
y of the densimetry method which was +/-4.07% over a range of 12 diffe
rent systems.