J. Calvin Giddings

Mineralogical and textural controls on the organic composition of coastal marine sediments: Hydrodynamic separation using SPLITT-fractionation

Abstract SPLITT-fractionation was used to sort hydrodynamically surficial sediments from the Washington margin, USA, into sand- (>250, 63–250 μm), silt- (35–63, 17–35, 8–17, 3–8 μm), and clay-sized (1–3, 0.5–1, 64 μm) from the shelf, where terrestrially-derived vascular plant debris accounted for >95% of the organic matter. Organic matter that could not be separated from the inorganic sediment accounted for >90% of the total organic carbon in most fractions, and loadings of organic carbon increased as the surface area of the inorganic particles increased. For the sand- and silt-sized fractions, the observed relationship of 0.81 ± 0.04 mg C m−2 (r = 0.97) was consistent with the hypothesis that a monolayer of organic matter is sorbed to the mineral surfaces. Clay-sized particles had lower organic loadings (0.37 ± 0.07 mg C m−2, r = 0.85), probably because the large interlamellar area of expandable clays was inaccessible to most organic molecules. After correcting for interlamellar area, clay-sized particles have the same organic carbon: surface area relationship as sands and silts (0.78 ± 0.08 mg C m−2, r = 0.96). The relationship over all the particle sizes was 0.76 ± 0.03 mg C m−2, (r = 0.96). While total organic matter concentrations were largely controlled by sediment surface area, the elemental composition of the organic matter appears to be partially affected by sediment mineralogy, and shifted from carbon-rich material (atomic C:N ~ 18.0) in larger, quartz-dominated fractions to N-rich material (C:N ~ 9) in the smaller, clay mineral-dominated fractions. Nitrogen enrichment relative to carbon (atomic N:C) was correlated with the amount of total clay (r = 0.80), smectite (r = 0.79), and the iron content (r = 0.74) of the sediments. Measurements of stable carbon isotopes indicate that clay-sized particles preferentially transport sorbed soil organic matter to deep sites while sand-sized fractions contain terrestrial plant debris (discrete and sediment-associated) that is transported along the shelf. The concentrations of terrestriallyderived organic matter in organic matter from shelf and slope sediments was estimated to be 60–85% and 10–15%, respectively. The quantity, bulk chemical composition, and distribution of marine and terrestrially derived organic matter to Washington margin sediments are influenced by 1. (1) the surface area of the sediment minerals, 2. (2) the mineralogical composition of the sedimentary matrix, and 3. (3) the natural hydrodynamic sorting of sedimentary materials along the continental margin. The major fraction of organic material in these sediments is sorbed to mineral grains. Interactions between organic material and mineral surfaces strongly influence the distribution and elemental composition of the organic material present in marine sediments.

Biochemical distributions (amino acids, neutral sugars, and lignin phenols) among size-classes of modern marine sediments from the Washington coast

Abstract In order to examine relationships of organic matter source, composition, and diagenesis with particle size and mineralogy in modern marine depositional regimes, sediments from the continental shelf and slope along the Northwest Pacific rim (Washington coast, USA) were sorted into hydrodynamic size fractions (sand: >250, 63–250 μm; silt: 35–63, 17–35, 8–17, 3–8 μm; and clay-sized: 1–3, 0.5–1,

Nonequilibrium Theory of Field‐Flow Fractionation

A rather general nonequilibrium theory is developed for a new separation concept, field‐flow fractionation. This treatment accounts for the axial dispersion of a solute zone in a narrow tube subject to simultaneous displacement by anisotropic diffusion and by an arbitrary group of velocity vectors representing flow and applied field contributions. To good approximation, zone dispersion is found to obey Ficks law, a result characteristic of nonequilibrium theories of chromatography. An equation for the effective diffusion coefficient is deduced. Expressions are obtained for a two‐dimensional case with a general power‐series expansion for flow velocity; a numerical result is acquired for a special limiting case.

A System Based on Split-Flow Lateral-Transport Thin (SPLITT) Separation Cells for Rapid and Continuous Particle Fractionation

Abstract In this paper we introduce a versatile separation system based on the operation of some rather simple separation cells termed SPLITT cells. These thin cells are capable of acting singly or in linked arrays depending on the problem at hand. Separation in the cells can be driven by sedimentation, electrical, and related forces, by diffusion, and by various gradients. SPLITT cells resemble FFF channels and are subject to similar methods of construction, except for the requirement for various split-flow elements in different parts of the SPLITT system. The separation path, across the narrow dimension of the thin SPLITT cells, is extremely short (often <1 mm), leading to rapid separation. The system is capable of continuous operation. The combination of continuous processing and rapid separation is anticipated to provide a relatively high throughput, despite the low volume of the cells. The optimization of throughput is discussed. Because separation takes place without the distortion accompanying some...

Electrical Field-Flow Fractionation of Proteins

Protein separation has been achieved by electrical field-flow fractionation, a heretofore unrealized separation technique. Some advantages of this method relative to electrophoresis are the low voltage required, the lack of adverse heating and support effects, and the existence of the method as an elution technique. A comparison of theoretical and experimental retention shows good agreement.

Observations on Anomalous Retention in Steric Field-Flow Fractionation

Abstract We discuss two anomalies that have characterized our recent work in steric field-flow fractionation (steric FFF): (a) retention has been found to vary with flow rate, contrary to simple theory; and (b) low density cells elute earlier than theory predicts. After reviewing the theory, we describe experiments in both gravitational and centrifugal fields applied to two spherical beads (microporous silica and polystyrene latex) of essentially equal sizes but different densities. The velocity dependence of retention is verified for both kinds of particles, but we find that retention depends dramatically on density as well. We speculate that these anomalous dependencies originate in a velocity-dependent lift force acting to pull the particle away from the wall. This hypothesis is supported by the observation that an increase in field strength increases retention. We conclude that a controllable field strength (as in a centrifuge) is an important asset in steric FFF, permitting increased separation speed...

Characterization of near-wall hydrodynamic lift forces using sedimentation field-flow fractionation

Abstract In field-flow fractionation (FFF), a family of high resolution techniques for the separation of particles and polymers, the measured retention time of entrained particles eluting through a thin (50-500 μm) parallel plate channel is determined by the transverse forces acting on the particles during their migration. For particles in the size range ∼l-100μm an applied transverse driving force (in the present case sedimentation) rapidly brings the particles into balance with hydrodynamic lift forces, so that the two force vectors are equal in magnitude but opposite in direction. By subjecting latex microspheres of known size and density to a specified rotation rate in a centrifuge, the applied sedimentation force is known and thus the magnitude of the lift forces is immediately obtained. The transverse particle position can be determined from the measured particle retention time. Thus lift forces can be determined as a function of particle size, transverse position, and flowrate. This strategy has be...

Colloid characterization by sedimentation field-flow fractionation: I. Monodisperse populations

This paper initiates a series of reports intended to develop, refine, and evaluate the methodology of sedimentation field-flow fractionation (sedimentation FFF) applied to the characterization of colloidal materials. Particle parameters subject to characterization include effective mass, actual mass, density, polydispersity, diffusivity, and various particle dimensions. Monodisperse particle populations are the focus of this paper; size distribution and other studies will follow. The general advantages of sedimentation FFF noted for such studies include the theoretically predictable characteristics of the method, experimental flexibility and redundancy, use of nearly any desired suspending medium, small (<1 mg) sample requirements, high resolution, and fraction collection for additional characterization. For monodisperse populations, it is shown that both retention and peak dispersion measurements lead to the various mass and dimensional parameters noted above. The fundamental theory of retention and peak dispersion is summarized; various equations are then derived showing how particle diameter and other particle parameters relate to retention and peak dispersion measurements. Experimental data are reported for five polystyrene latex beads in the nominal diameter range 0.220−0.945 μm measured in two sedimentation FFF systems. Both rigorous and approximate procedures for calculating particle diameter d were divided into three categories: those based on retention measurements (R) only, those based on peak dispersion or plate height (H) only, and those based on a combination (RH) of the two measurements. Analysis of the results suggests that d obtained from rigorous R methods are accurate to about 1–3%. However, it appears that measured peak width may be ∼20% too large, giving d values ∼5% too small by H methods and ∼40–50% too large by RH methods. Various approximations for R, H, and RH methods are evaluated. In another direction, polydispersity values appear accurate to within 1% or better. However, particle density calculated using a combination of retention and peak dispersion data is in error by a factor of ∼3, in contrast to the ∼0.002 g/cm3 accuracy yielded by retention measurements.

Steric Field-Flow Fractionation: A New Method for Separating I to 100 μm Particles

Abstract Steric field-flow fractionation (steric FFF) is described as a high field limit of normal FFF that separates particles according to their diameter or radius. Retention equations are used to describe the phenomenon; these equations lead to the suggestion that steric FFF is applicable to particles from 1 to 100 μm as a minimum range. Conditions that control resolution are discussed, and fundamental similarities and differences between steric FFF on one hand and normal FFF and hydrodynamic chromatography on the other hand are noted. Optimum flow conditions are discussed and the complication of describing the migration of irregular particles is noted. Preliminary experiments with glass beads of 10 to 30 μm diameter demonstrate the existence of fractionation.

The role of lateral diffusion as a rate-controlling mechanism in chromatography

A general method is outlined for calculating lateral nonequilibrium when the rate-controlling steps involve lateral diffusion only. The nonequilibrium is responsible for a contribution to the diffusion, or to the plate height, of a zone in a column. The latter is easily calculated from the nonequilibrium. The stationary phase models chosen for calculation include a flat film of uniform thickness, homogeneous spheres, cylindrical rods and pores of nonuniform depth. These models are useful in describing gas, ion exchange and paper chromatography. Mobile phase models include uniform and parabolic flow; both between parallel faces and in circular tubes. The roles of two simultaneous diffusion processes is considered, and the conditions under which these contribute additive terms are discussed. Examples of both additive and nonadditive cases are shown. Finally, the rate-controlling influences of stationary phase and mobile phase diffusion are compared. The importance of parabolic flow, in contrast to uniform flow, is shown at R values near unity.