Factors influencing retention

Taillardat-Bertschinger, A., Marca-Martinet, C. A., Carrupt, P. A., Reist, M., Caron, G., Fruttero, R., Testa, B. Molecular factors influencing retention on immobilized artiflcial membranes (1AM) compared to partitioning in liposomes and n-octanol. Pharm. Res. 2002, 79, 129-Til. 

Unlike the transformation processes that reduce the total amount of triazine present in soil, retention only decreases the amount available for weed control, microbial transformations, or transport. The amount retained or sorbed by soil can range from 0% to 100% of the amount applied, but sorption on silt loam, loam, or clay loam soils typically ranges from 50% to 80%. Triazine retention in soil is influenced primarily by organic carbon content, soil clay content and type, and soil pH. Other factors influencing retention include the amount of triazine applied, the amount of dissolved organic carbon (DOC) in soil solution, soil water content, and triazine to soil contact time (aging). 

If sorption is 50% efficient but desorption is 100% efficient, the recovery measured is 50%> and it is impossible to know whether sorption or desorption was inefficient or if reduced recovery was produced by a combination of both. Therefore, method development requires either optimizing sorption while controlling desorption, or vice versa using an iterative approach [67,72], Alternatively, a statistical factorial design can be used to determine and optimize quickly variables important to SPE [110]. Using either approach, it is important to consider the major factors influencing retention, including sample pH, sample volume, and sorbent mass. 

Environmental Factors Influencing Metal Retention, Availability and Toxicity. 45... 

One of the first applications of the HPLC method was the investigation of differences in toxin profiles between shellfish species from various localities ( ). It became apparent immediately that there were vast differences in these toxin profiles even among shellfish from the same beach. There were subtle differences between the various shellfish species, and butter clams had a completely different suite of toxins than the other clams and mussels. It was presumed that all of the shellfish fed on the same dinoflagellate population, so there must have been other factors influencing toxin profiles such as differences in toxin uptake, release, or metabolism. These presumptions were strengthened when toxin profiles in the littleneck clam (Prototheca Staminea) were examined. It was found that, in this species, none of the toxin peaks in the HPLC chromatogram had retention times that matched the normal PSP toxins. It was evident that some alteration in toxin structure had occurred that was unique in this particular shellfish species. 

Guo, D., Mant, C. T., Taneja, A. K., and Hodges, R. S., Prediction of peptide retention times in reversed-phase high-performance liquid chromatography II. Correlation of observed and predicted petide retention times and factors influencing the retention times of peptides, /. Chromatogr., 359, 519,1986. 

The retention of the band or peak beyond what V0 predicts depends on the magnitude of the equilibrium constant and logically on the volume Vs or area As of the stationary phase. The equation of importance is Vr — V0+KVS and the net retention V/ = KVS. Two main factors influence the value of the equilibrium constant and these are the chemical nature of the mobile and stationary phases. Chemistry is molecules and while true thermodynamics knows no molecules or forces between molecules, chemists think in terms of molecular properties. Among those properties, there is a consideration of the kinds of forces that exist between molecules. Granted that thermodynamics are energy not force considerations but it is useful to understand the main forces involved in the interaction between molecules. Put another way,... 

FACTORS INFLUENCING IN VIVO DRUG RETENTION Anion or Polyanion Used as Trapping Agent... 

Throughout the text we will relate polymer structure to the properties of the polymer. Polymer properties are related not only to the chemical nature of the polymer, but also to such factors as extent and distribution of crystallinity, distribution of polymer chain lengths, and nature and amount of additives, such as fillers, reinforcing agents, and plasticizers, to mention a few. These factors influence essentially all the polymeric properties to some extent including hardness, flammability, weatherability, chemical stability, biological response, comfort, flex life, moisture retention, appearance, dyeability, softening point, and electrical properties. 

The nominal molecular weight (M.W.) cutoff is provided as a guide to the relative pore size for these membranes. Since many factors influence the actual MW cutoff, tests must be run to confirm retention for any specific application. 

Although the evidence cited indicates that iron influences retention of S in lake sediments, other factors may obscure this influence. First, organic... 

---