each, making a total swept volume of 336 nL. The swept volume is defined as the total volume in the injector, including the sam- ple loop/groove and connecting bore holes, and is different from the actual volume selected by the sampling valve for introduction into the column. The sample volume injected in all experiments was 30 nL unless stated otherwise. Time-gated injections were car- ried out in all experiments with the injection valve being switched at different time intervals as a function of flow rate. On-column detection was accomplished immediately after the monolithic
stationary phase at a detection wavelength of 214 nm using a Crystal 100 variable wavelength UV–vis absorbance detector (Thermo). The detector rise time was set at 1 s, corresponding to a time con- stant value of 0.45s, and data were collected at a frequency of 10 Hz. Data acquisition was performed with Chrom Perfect soft- ware (Mountain View, CA, USA), and all peak analysis was done using Microsoft Excel. Every reported value represents the average of three repetitive measurements under the same conditions. All of the experiments were conducted at room temperature.
A second LC system designed and constructed by VICI Valco Instruments (Houston, TX, USA) was used to compare the dif- ferences in extra-column variance. This recently reported system consisted of a nano-flow pumping system with integrated injection valve [35]. The integrated 8-port injection valve had an internal V-shaped sample loop with a swept volume of 130 nL. Detection was performed using the same Crystal 100 variable wavelength UV detector described in the previous paragraph