Manuela Haller

Sorption of cesium on illite: Non-equilibrium behaviour and reversibility

Abstract Adsorption, desorption, and isotopic exchange experiments have been used to investigate the kinetics and reversibility of cesium sorption on illite. Trace concentrations of cesium were used and experimental conditions were kept close to those of many freshwater environments. Initial adsorption of cesium on illite was rapid but was followed by slower uptake processes with time scales of weeks to months. The uptake proceeded faster and reached much higher Kd values in a Ca2+ environment than in a K+ environment. The apparent reversibility of sorption was affected by both the slow sorption processes and the nature of the competing cation. The desorption equilibration patterns indicate that cesium is released from rapidly accessible sorption sites but that the slow forward reaction continues. On time scales relevant for modelling its transport and retention in aquatic systems, cesium shows partially irreversible behaviour. A mechanistic interpretation for the observed sorption and isotopic exchange behaviour is proposed whereby cesium migrates slowly to energetically favourable interlayer sites from which it is not easily released.

Extraction and isolation of linear alcohol ethoxylates from fish

Abstract The development of an analytical method for determination of alcohol ethoxylates (AEs), important non-ionic surfactants, in fish is described. Combination of matrix solid-phase dispersion (MSPD) extraction with aluminum oxide clean-up allows for determination of AEs in fish samples with recoveries higher than 75%. The use of internal standards allowed for correction of losses during preparation of the individual samples. Incurred AE constituents could be quantified without integration being compromised by interferences for all compounds except for C 14 EO 14 . Parallel determinations of the concentrations of 14 C-C 13 EO 8 in fish by TLC–RAD and liquid scintillation counting and by HPLC measurements after isolation and derivatization yielded very similar results demonstrating the validity of the isolation and measurement method.

Influence of carrier and bactericide on sorption coefficients of hydrophobic organic compounds for two lake sediments

Abstract Sorption coefficients of a series of hydrophobic organic compounds were determined for two sediments, one with a high (RDD sediment) and one with a low organic carbon content (OVP sediment). The chemicals were administered to water using a generator column, or using one of the following carriers (0.5%, v/v): acetone, methanol or propanol. In addition to the influence of the mode of administration, the influence of the bactericide, sodium azide (NaN 3 ), on the sorption coefficients was studied. For most compounds, higher sorption coefficients were found in RDD sediment than in OVP sediment. Only for the most hydrophobic compounds no large differences were found between the sorption coefficients in the two sediments. In RDD sediment, the use of the carriers showed lower sorption coefficients for almost all compounds, and in OVP sediment the use of the carrier showed only for some of the more hydrophobic compounds lower sorption coefficients, than the use of the generator column. The highest dry weight (DW) and total organic carbon (TOC) concentrations were found in the aqueous phase of the high organic carbon sediment (RDD). In addition, methanol and propanol resulted in significant increases in TOC concentrations. The influence of DW and TOC concentrations on the sorption coefficients could, however, not be quantified. Since carriers may have a significant effect on the experimental determination of sorption coefficients, we suggest to use the generator column for administering the compounds, in combination with a bactericide to prevent bacterial activity.

The use of three ferguson-plot-based calculation methods to determine the molecular mass of proteins as illustrated by molecular mass assessment of rat-plasma carboxylesterases ES-1, ES-2, and ES-14

The molecular masses of three rat-plasma carboxylesterases (ES-1, ES-2, and ES-14) were estimated by transverse-gradient polyacrylamide gel electrophoresis and subsequent application of Ferguson-plot-based calculation methods. Two electrophoretic buffer systems were used and the data subjected to either weighted or unweighted regression analysis. The Tris-boric acid buffer system produced significantly higher retardation coefficients than the Tris-glycine system. Molecular mass estimates were significantly higher with the Tris-glycine buffer system. Unweighted instead of weighted analysis produced significantly higher molecular mass estimates. Molecular mass estimates also depended on the calculation method, that is, the choice of calibration relationship with molecular size as a function of retardation coefficient. Three commonly used calibration relationships were compared. On the basis of their accuracy, both the weighted log[retardation coefficient] versus log[molecular mass] plot and the square root of retardation coefficient versus molecular radius were found suitable, provided that the Tris-boric acid buffer was used for electrophoresis. Using the former calibration relationship, the molecular masses of rat-plasma ES-1, ES-2, and ES-14 were 55.5, 61.1, and 65.3 kDa, respectively.

Plasma esterase activities in rats fed magnesium-deficient diets.

In a study with rats it was determined whether dietary magnesium concentration affects plasma esterase activities. The feeding of a diet with 0.01% (w/w) instead of 0.04% magnesium reduced plasma magnesium concentration by 50%. Plasma total esterase, arylesterase and butyrylcholinesterase activities were significantly decreased in the magnesium-deficient rats. In rats fed a diet containing 0.02% magnesium, plasma magnesium concentration was lowered by 30%, and group mean plasma total esterase activity was decreased, but not the activities of arylesterase and butyrylcholinesterase.