Monolithic capillary columns based on divinylbenzene were synthesized using different alcanols as porogens. Prepared columns were tested in separation of polystyrene standards according to their molar mass (MM) and were characterized by corresponding calibration graphs. It was demonstrated that a decrease of alcanol chain length from dodecanol to octanol resulted in a decrease of column permeability and in an improved column ability to separate polystyrene standards. In contrast, removing a good solvent from porogen mixture results in an increase of column permeability and in a decrease of column performance toward polystyrene standards. Optimized synthetic conditions included porogen composed of nonanol and toluene or mesytilene, and the column prepared with this porogen was capable of separating a mixture of 14 polystyrene standards with MM ranged from several millions to oligomers.

Monolithic capillary columns based on pentaerythritol triacrylate and pentaerythritol tetraacrylate were synthesized using different compositions of polymerization mixtures and different polymerization conditions. The impact of porogen type and porogen/monomer ratio on the porosity of synthesized monoliths was investigated. Porogen type appears to be the main factor influencing the separating properties of the monolithic sorbent. Using optimal polymerization conditions (porogen type, porogen/monomer ratio, reaction temperature, time etc.) monoliths with a porous structure optimized for polymer separations can be obtained. The monolithic capillary columns containing porous sorbents with optimized porosity are capable of separating 10 to 12 polystyrene standards in one chromatographic run utilizing both size exclusion chromatography and hydrodynamic chromatography separation mechanisms.

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All drugs showed concentration-dependent behavior on all four columns. As a rule, with very low amounts of drugs injected, a decrease of retention time (and retention index) could be observed; when higher concentrations of drugs were injected, retention times increased markedly, sometimes accompanied by peak splitting. Table 1 gives an overview of the retention times obtained and the retention indices for the highest and lowest observation for each drug. These retention indices were calculated using a mixture of drugs with known retention indices *) (1000 ng per drug injected). A graphic representation of the concentration dependence of retentions for the drugs on a CP-SiI 5 CB column is given in Figure 1.Of the columns tested, the CP-SiI 5 narrow bore and the CP-SiI 5 CB showed the most pronounced concentration dependence effects. However, with the narrow bore column the lowest retention times are seen around 10-20 ng injected, whereas forthe CB column ( Figure 1) the lowest retention times are seen around 400-1000 ng injected. Note that on the CP-Sit 5 narrow bore column the injection volumes were 2 pI and the highest amount injected was 2000 ng.On the CB column all substances showed considerable concentration dependence effects, resulting in large differences between the retention indices associated with the highest and lowest retention times observed for an individual substance (largest difference 90 RI-units for caffeine). On the other three columns, concentration dependence was observed in particular with nitrazepam and strychnine. On the CP-SiI 5 narrow bore column, the difference between the highest and lowest retention 2 ) 0 n packed OV-1 columns. time for nitrazepam was more than 1.7 min, which corresponded to 130 RI-units. All concentration effects were reproducible and independent of injection sequence as tested over a two-month period.The above observed concentration dependent retention behavior would seem to represent a serious drawback towards the applicability of splitless capillary gas chromatography for screening purposes in toxicology. The mechanisms responsible for these phenomena are not yet fully understood and are being investigated in more detail. Additional work on this topic, including the effects of drug mixtures and of endogenous compounds from biological matrices, is also in progress. AcknowledgmentThisworkwassupported in part byaFellowshipgranted tooneof us(M.8.) by the

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