Parallel chromatographic separations

In our laboratories, a cycle time of 90 sec can be achieved with a dilution factor of 1 25 for a given sample concentration, allowing the purity and identity control of two and a half 384-well microtiter plates per day. The online dilution eliminated an external step in the workflow and reduced the risks of decomposition of samples in the solvent mixture (weakly acidic aqueous solvent) required for analysis. Mao et al.23 described an example in which parallel sample preparation reduced steps in the workflow. They described a 2-min cycle time for the analysis of nefazodone and its metabolites for pharmacokinetic studies. The cycle time included complete solid phase extraction of neat samples, chromatographic separation, and LC/MS/MS analysis. The method was fully validated and proved rugged for high-throughput analysis of more than 5000 human plasma samples. Many papers published about this topic describe different methods of sample preparation. Hyotylainen24 has written a recent review. 

Link et al. have used a two-dimensional chromatographic separation approach to characterize yeast ribosome complex proteins (Link, 1999). This technique employs a cation exchange column (SCX) for the first separation and, subsequently, two parallel reversed-phase HPLC columns (Figure 15.4), and thus works extremely rapidly and efficiently. While the first column loads, the second elutes using an acetonitrile gradient The flow from the column is directed to parallel online MS detectors as well as to offline fraction collection with UV detectors. 

Figure 11-2. (A) A 4-minute HPLC/MS separation of a solution-phase parallel synthesis library. The gradient profile for fast HPLC/MS was 10-90% acetonitrile in H2O in 4 minutes with a l-minute equilibration time. (B) A 1-minute, total cycle time chromatographic separation of the same crude product. (Reprinted from reference 42, with permission.)...

The pyrolyser is usually connected directly to a standard sample injection device or in parallel to the latter. To enhance the efficiency of the subsequent chromatographic separation, the outlet of the pyrolytic cell should preferably be coupled directly to the chromatographic column. 

Chromatography can be scaled up by several means increasing size of the chromatographic separation column, employing more than one (many) chromatographic separation columns in parallel, and increasing the amount of substance for one injection. 

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