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a specific application. Alternatively, standard silica gels can be blended together to give a mixed gel with definitive exclusion properties for specific separations. The exclusion properties of a silica gel cannot be obtained with sufficient accuracy for chromatographic use from nitrogen adsorption data or mercury porosity tests. It is necessary to determine the range of pore diameters and pore volume of a silica gel by a special experimental procedure that is designed to obtain accurate retention volume measurements for solutes eluted in relatively small elution volumes. In exclusion chromatography, all the peaks will be contained in a mobile phase volume equivalent to that of the total pore volume of the column. Consequently, the column volume itself must be large and a column 25 cm long and 4.6 mm I.D. is a practical size to obtain results having adequate accuracy. The sample volume used should be 0.5 to 1.0 ml in volume and the detector should have a low sensor volume (cf. 2

methanes will give a straight line with slopes and intercepts that are predicted by equations (19), (20) and (21).      Experimental Data The data of Martire et al. (8) are included in table (1). The actual data published was the specific retention volume of each solute at four different temperatures, 30˚C, 40˚C, 50˚C and 60˚C respectively and was reported to have been determined with a precision of better than +/-2%. However, by multiplying each specific retention volume by the density of the stationary phase (n-octadecane) at the respective temperature, the retention volume per ml of each solute could be obtained which is numerically equal to the distribution coefficient (see Gas Chromatography

is not altogether surprising as the volume fraction of each phase would be expected to determine the probability that a given solute molecule will interact with a molecule of that phase. This is analogous to the partial pressure of a solute in a gas determining the probability that a solute molecule will collide with a gas molecule. Thus, doubling the concentration of one phase doubles the probability of solute interaction with that phase and consequently doubles its contribution to retention. It is also clear that the linear relationship between distribution coefficient and phase concentration allows the contributions from the interactions of each phase to be summed directly, but their logarithms can not This was, of course, in conflict with some contemporary thinking and cast doubts on the thermodynamic procedure for describing the effect of stationary phase composition on solute retention. The effect of stationary phase composition on retention is often taken into

nbsp; They are as follows, where () is the specific retention volume of a noncomplexing solute with a vapor pressure () and a noncomplexing stationary phase having a molecular weight (); where () is the specific retention volume of the same noncomplexing solute with a pure complexing stationary phase having a molecular weight ();  

where () is the specific retention volume of a complexing solute  with a vapor pressure () with a pure complexing stationary phase having a molecular weight ();   where () is the specific retention volume of a complexing solute  with a vapor pressure () with a pure noncomplexing stationary phase having a molecular weight ().     If the two stationary phases have the same physical properties, except for one being polar (having a complexing capability), then a reasonable assumption would be that, By rearranging

or for analyses that are carried out to ensure adherence to regulatory standards as in environmental and pollution studies. The following tests are recommended as minimal for a new column and the results should be compared with the data obtained from the previous column as received. 1/ The column permeability should be measured i.e., the pressure required to produce a given flow rate e.g., a flow rate of 1 ml per minute. 2/ The column dead volume should be measured by determining the retention volume of an unretained solute 3/ The column efficiency should be measured for a set of standard solutes. If possible, the solutes should be chosen, from those likely to be present in the samples to be analyzed. Solutes eluting at (k') values of 2, 5 and 10 would be appropriate. 4/ The corrected retention volumes of a series of solutes spanning a (k') range of 1 to 20 should be determined and their retention ratios calculated. All the measurements should fall within 5% of the