The introduction of UHPLC columns with very high efficiencies (> 300.000 plates/m) has put very stringent requirements on the performance of UHPLC systems. The separation efficiency for small bore or capillary columns packed with small particles can easily be compromised by external contributions to dispersion caused by connection capillaries, auto-samplers and detection devices.
Besides the use of UV-DAD detection, the combination of UHPLC with mass spectrometry (MS) has proven to be a robust and widely applicable platform for the high sensitivity analysis of many types of chemical compounds. The majority users employ columns of 2.1 mm internal diameter (ID). For sample limited applications however, a reduction in diameter down to capillary- or nano-column format may be required. Since the operation of nano-flow systems still remains far from routine, capillary columns (ID ≤0.5mm) or small bore columns (ID ≤1mm) could exhibit a good compromise between system robustness and enhanced sensitivity.

When designing an optimum UHPLC system configuration for specific column dimensions and applications, it is crucial to understand the dispersion contributions of individual extra-column components. Other factors such as detector sensitivity, pressure drop and injector functionality are also to be kept in consideration.

The authors have investigated the dispersion contributions of various system parts including connection capillaries, detection cells and auto sampler set-ups with an UHPLC system coupled to an UV- detector.
In order to evaluate the extra-column contribution of MS detection, a triple quadrupole (QQQ) MS with an Agilent Jet-Stream ESI-source was coupled to a fully optimized UHPLC system.

The impact of different system configurations/detection modes on column performance and detection sensitivity was investigated for a range of column dimension (0.3 – 2.1 mm ID) under isocratic and gradient conditions.