radii of a molecule, is quite impossible. The word hydrophobic literally means "fear of water" and appears to have been provoked by the immiscibility of a dispersive solvent such as n-heptane with a very polar solvent such as water. However, n-heptane and water are immiscible, not because water molecules repel heptane molecules but because the forces between heptane molecules and the forces between water molecules are much greater than the forces between a heptane molecule and a water molecule. Immiscibility occurs because water molecules and heptane molecules interact very much more strongly with themselves than with each other. Water, in fact, has a small but finite solubility in n-heptane, and similarly n-heptane a small but finite solubility in water. Despite water-water interactions and hydrocarbon-hydrocarbon interactions being very much stronger than water-hydrocarbon interactions, the latter do, to a limited extent, exist and water-hydrocarbon interactions are

phase before they become denatured. It is clear that this is because there is virtually no unassociated methanol present in the mixture which could cause protein denaturation since all the methanol is in a deactivated state by association with water. Katz, Lochmüller and Scott also examined acetonitrile/water, and tetrahydrofuran(THF)/water mixtures in the same way and showed that there was significant association between the water and both solvents but not to the same extent as methanol/water. At the point of maximum association for methanol, the solvent mixture contained nearly sixty percent of the methanol/water associate. In contrast the maximum amount of THF associate that was formed amounted to only about 17% and for acetonitrile the maximum amount of associate that was formed was as little as 8%. It follows that acetonitrile water mixtures would be expected to behave more nearly as binary mixtures than methanol/water or THF/water mixtures

a dispersive solvent such as n-heptane with a very polar solvent such as water. n-heptane and water are immiscible, not because water molecules repel heptane molecules, they are immiscible because the forces between two heptane molecules and the forces between two water molecules are much greater than the forces between a heptane molecule and a water molecule. Thus, water molecules and heptane molecules interact very much more strongly with themselves than with each other. Water has, in fact, a small but finite solubility in n-heptane, and n-heptane has a small but finite solubility in water. Although water-water interactions and hydrocarbon-hydrocarbon interactions are much stronger than water-hydrocarbon interactions, the latter does exist and is sufficiently strong to allow mutual solubility. The term "hydrophilic force", literally meaning "love of water" force, appears to merely be the complement to "hydrophobic".

between the water and acetonitrile and water and tetrahydrofuran, but not nearly to the same extent as methanol and water. At the point of maximum association in methanol-water mixtures, the solvent contained nearly 60% of the methanol/water associate. In contrast the maximum amount of THF associate that was formed was only 17%, and that for acetonitrile as little as 8%. It follows that acetonitrile/water mixtures would be expected to behave more nearly as binary mixtures than methanol/water or THF/water mixtures. The components of the mobile phase which can interact with the solute and thus control retention in a methanol-water mixture will be methanol unassociated with water, water unassociated with methanol and the methanol water associate. However, for dispersive and moderately polar materials it will be the unassociated methanol that will predominantly control solute retention. This was also demonstrated by Katz et al. (11) Katz et al. also plotted the distribution

Water The apparent anomalous behavior of methanol-water and other water-solvent mixtures with respect to retention provoked Katz et al. (11) to investigate the association of methanol and water. This work was carried out to determine whether, in fact, such mixtures did not constitute binary mixtures but were actually ternary mixtures, the third component being the methanol-water associate. Their, arguments and subsequent experiments were as follows. An equilibrium between methanol and water can be expressed as follows,                                                                              (7) where (M) is the molar concentration of water, (W) is the molar concentration of methanol, (MW) isthemolar concentration ofmethanol/water associate, and (k) is the "association" constant

Materials in Water Trace analysis by sample concentration followed by separation on high mass sensitivity chromatographic instrumentation lends itself well to water analysis. The water, in almost any volume, can be pumped through a sample pre column packed with a suitable reverse phase and almost all organic material including organic ions will be extracted efficiently as a sharp band on the front of the sample trap. An example of the use of this procedure in the analysis of different water samples is shown in figure 32.       J. Chromatogr.,185(1979)27    Column length 50 cm, column diameter 1 mm, packing ODS-2 10 mm, flow rate 40 ml/min., linear gradient over 1 hr from methanol/water (60:40) to pure methanol.   Figure 32. Chromatograms of Water Samples Employing Small Bore Columns in Conjunction with Low Dispersion Instrumentation