Sizing low molecular weight

The sub-division size ( low molecular weight compound , oligomer and polymer ) is self-explanatory but also not without difficulties. This arises primarily from the uncertainty assodated with the term oligomer and indeed it is perhaps not appropriate to be too spedfic here. In general however a low molecular weight compound is a molecule without any repetitive structural aspects, an oligomer is a molecule where certain structural components are repeated a number of times, e.g. oligopeptide, tetraporphyrin etc. A polymer is... 

Baker s yeast cells Saccharomices cerevisae) were successfully immobilized on to silica gel and used in selective online trace enrichment of selected pesticides, including linuron, in various types of natural waters.This technique relies upon the fact that microorganisms are able to absorb pesticides from water in the environment. Cell membranes contain many classes of lipids and lipoproteins, which contribute to pesticide absorption. Since the diffusion rate across membranes is inversely proportional to molecular size, low-molecular weight compounds, such as pesticides, can be extracted from water and isolated by naturally occurring high-molecular weight substances, such as humic acids, which are abundantly present in environmental waters. 

---