Column stability reactive systems

Sorption of Cu(tfac)2 on a column depends on the amount of the compound injected, the content of the liquid phase in the bed, the nature of the support and temperature. Substantial sorption of Cu(tfac)2 by glass tubing and glass-wool plugs was observed. It was also shown that sorption of the copper chelate by the bed is partialy reversible . The retention data for Cr(dik)3, Co(dik)3 and Al(dik)3 complexes were measured at various temperatures and various flow rates. The results enable one to select conditions for the GC separation of Cr, Al and Co S-diketonates. Retention of tfac and hfac of various metals on various supports were also studied and were widely used for the determination of the metals. Both adsorption and partition coefficients were found to be functions of the average thickness of the film of the stationary phase . Specific retention volumes, adsorption isotherms, molar heats and entropy of solution were determined from the GC data . The retention of metal chelates on various stationary phases is mainly due to adsorption at the gas-liquid interface. However, the classical equation which describes the retention when mixed mechanisms occur is inappropriate to represent the behavior of such systems. This failure occurs because both adsorption and partition coefficients are functions of the average thickness of the film of the stationary phase. It was pointed out that the main problem is lack of stability under GC conditions. Dissociation of the chelates results in a smaller peak and a build-up of reactive metal ions. An improvement of the method could be achieved by addition of tfaH to the carrier gas of the GC equipped with aTCD" orFID" . ... 

Another concern with packed-bed reactors is reproducibility. There are two parts to reproducibility can multiple packed-bed reactors be made reproducibly and what is the stability of the reactor The first question concerning reproducibility can be answered as follows. The art of packing a column is at times difficult and each individual analyst will have different success. However, all packed-bed reactors can be calibrated in the FIA system. A variation in the performance level between reactors of less than 10% is acceptable. The second reproducibility question concerns the loss in reactivity due to reagent degradation or saturation of the reactive sites. In the ideal case the reactivity of the column should not change with respect to time, thereby producing a reproducible signal for the same concentration of analyte. This is a more difficult problem. Ideally, the analyst should find the reactor conditions that will minimize loss of activity. In practice, especially with enzymes, this condition will not be met. Frequent calibrations will be needed to insure the most accurate results. 

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