Tangential-flow ultrafiltration

To aid in the characterization of the DOM pool, marine organic chemists have developed techniques fiar separating compounds into size fractions. Tangential flow ultrafiltration is used to isolate a high-molecular-weight (HMW) fraction from a low-molecular-weight (LMW) fraction. The size cutoff between these is approximately 1 tun, which equates... 

Tangential-flow ultrafiltration was used with approximately 150-L samples of centrifugate from the ship-based centrifuges. 

Relatively few biochemicals can be measured directly in natural waters because concentrations of individual compounds are low (nanomolar) and salts and other components often interfere with these analyses. DOM can be concentrated and isolated from natural waters for more thorough chemical characterization, and two approaches for DOM isolation, adsorption onto solid phases and ultrafiltration are now widely used. The adsorption of DOM onto XAD resins is used to isolate a fraction of DOM that is operationally defined as humic substances (Thurman, 1985). More recently, tangential-flow ultrafiltration with 1000 Da cutoff membranes has been used to isolate the high-molecular-weight or colloidal fraction of DOM (Benner et al., 1992, 1997). 

Humic substances account for 40-70% of the DOC in rivers and 5-25% of the DOC in the ocean (Table I). It is important to note that recoveries of adsorbed humic substances from XAD resins are not quantitative, so the chemical characteristics of the recovered humic substances are not necessarily representative of all the humic substances retained by the resin. Tangential-flow ultrafiltration retains 45-80% of the DOC in rivers and 25-40% of the DOC in the surface ocean (Table I). Essentially all of the DOC retained during ultrafiltration is recovered for chemical characterization. In general, ultrafiltration recovers a larger fraction of the DOM from these systems. These methods also isolate DOM based on different mechanisms. Adsorption onto XAD resins at low pH chemically fractionates the DOM and isolates the more hydrophobic components, whereas ultrafiltration principally separates components of DOM on the basis of size and shape. 

Benner, R., B. Biddanda, B. Black, and M. McCarthy. 1997. Abundance, distribution, and stable carbon and nitrogen isotopic compositions of marine organic matter isolated by tangential-flow ultrafiltration. Marine Chemistry 57 243—263. 

H NMR spectra have been used to analyze 11 DOM samples that were isolated from seawater using tangential-flow ultrafiltration and one sample that was isolated using dialysis (Aluwihare et al., 1997). A linear combination of three endmembers (carbohydrates, lipids, and acetate) was sufficient to account in some detail for the... 

Powell, M. J., and Timpermann, A. T. (2005). Quantitative analysis of protein recovery from dilute, large volume samples by tangential flow ultrafiltration. J. Memb. Sci. 252(1-2), 227-236. 

Hoffmann S. R., Shafer M. M., Babiarz C. L., and Armstrong D. E. (2000) A critical evaluation of tangential-flow ultrafiltration for trace metals studies in freshwater systems 1. Organic carbon. Environ. Sci. Technol. 34, 3420-3427. 

Lahoussine-Turcaud V., Wiesner M.R., Bottero J.-Y. (1990), Fouling in tangential-flow ultrafiltration the effect of colloid size and coagulation pretreatment. Journal of Membrane Science, 52,173-190. 

Adams and Byrne, 1989 Pant et al., 1999 Turrion et al., 2000, 2001). However, given the risk of hydrolysis with higher temperatures (Cade-Menun et al., 2002 Turner et al., 2003b), lyophilization may be the safest method. Water samples have been concentrated by tangential-flow ultrafiltration (Nanny and Minear, 1994a,b, 1997a,b ... 

When seawater is further size fractionated by cross (or tangential) flow ultrafiltration [9, 12-21], 10-40% of the DOC (Fig. 2) is retained by membranes with molecular weight cutoffs of 1-10 kDa (equivalent to spherical diameters of... 

Online collection/concentration of samples through the use of cross (tangential) flow ultrafiltration has also found a number of applications. 

Recent innovations in filtration technology include tangential flow ultrafiltration methods that act as preconcentration methods for studies of marine biopolymers such as proteins (see also the section on Adsorption techniques below). 

Recently HM-type acids have been separated from the same freshwater source in parallel by DAX-8 (nonionic polymethyl methacrylate resin, analogous with XAD-8), DEAE and PVP sorbents, and tangential-flow ultrafiltration [4,14]. The total amount (% of DOM) of HM-type acids (humic substances) obtained by different sorbents were approximately 64/DAX-8, 77/DEAE, and 80/PVP, and approximately 97% of the original DOM consisted... 

Morrison, M.A and Benoit, G., Investigation of conventional membrane and tangential flow ultrafiltration. Artifacts and their application to the characterization of freshwater colloids. Environ. Sci. Technol., 38, 6817,2004. 

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