Study on the performance of different types of three-dimensional chromatographic systems

The maximum achievable performance of possible types of three-dimensional chromatographic systems (LC×LC×LC) has been investigated. The Pareto-optimization approach was applied to establish a trade-off between three main objectives (total peak capacity, analysis time and dilution of the sample) and Pareto-front values were obtained. The performances of (x)LC×(x)LC×(x)LC (three-dimensional separation in space), (t)LC×(t)LC×(t)LC (three-dimensional separation in time) and the hybrid (x)LC×(x)LC×(t)LC system were compared mutually and with two-dimensional chromatographic systems. It was found that (x)LC×(x)LC×(x)LC performs best in terms of maximum achievable peak capacity in shortest analysis time. Based on current thin-layer-chromatography performance it should be possible to obtain a peak capacity of 50,000 within 20min. If contemporary column-packing standards can be upheld the achievable limit is approximately 50% higher. However, in an (x)LC×(x)LC×(x)LC chromatographic system analytes remain in the separation domain after the analysis, which complicates the detection. Use of an (x)LC×(x)LC×(t)LC system with elution in the last dimension alleviates the detection problem. The maximum achievable peak capacity in the same analysis time is lower for (x)LC×(x)LC×(t)LC than for (x)LC×(x)LC×(x)LC. Using the same (reasonable) length of the separation domain (e.g. a cube 200×200×200 mm) for both systems, it is possible to achieve peak capacities of 78,000 for (x)LC×(x)LC×(t)LC operated in the gradient mode, which is twice higher than for an (x)LC×(x)LC×(x)LC system. A three-dimensional (three-column) time-based (t)LC×(t)LC×(t)LC system does not greatly improve the performance of (t)LC×(t)LC in terms of (maximum) peak capacity and (minimum) analysis time. Dilution factors in (t)LC×(t)LC×(t)LC are very high. Decreasing the dilution has a detrimental influence on the peak capacity. The trade-off between these objectives is of crucial importance. The influence of several parameters (length of the separation domain, particle size, etc.) on the performance of chromatographic systems was investigated, optimal ranges were found.