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In this work, a novel splitless nanoflow gradient generator integrated with a stop-flow injector was developed and evaluated using an on-column UV-absorption detector. The gradient pumping system consisted of two nanoflow pumps controlled by micro stepper motors, a mixer connected to a serpentine tube, and a high-pressure valve. The gradient system weighed only 4 kg (9 lbs) and could generate up to 55 MPa (8000 psi) pressure. The system could operate using a 24 V DC battery and required 1.2 A for operation. The total volume capacity of the pump was 74 μL, and a sample volume of 60 nL could be injected. The system provided accurate nanoflow rates as low as 10 nL/min without employing a splitter, making it ideal for capillary column use. The gradient dwell volume was calculated to be 1.3 μL, which created a delay of approximately 4 min with a typical flow rate of 350 nL/min. Gradient performance was evaluated for gradient step accuracy, and excellent reproducibility was obtained in day-to-day experiments (RSD < 1.2%, n = 4). Linear gradient reproducibility was tested by separating a three-component pesticide mixture on a poly(ethylene glycol) diacrylate (PEGDA) monolithic column. The retention time reproducibility was very good in run-to-run experiments (RSD < 1.42%, n = 4). Finally, excellent separation of five phenols was demonstrated using the nanoflow gradient system.

A new version of the pulsed discharge electron capture detector (PDECD) has been developed and characterized. Changes to the old version include a slightly altered detector geometry, replacement of the polymer insulation with sapphire and quartz, and the use of methane dopant gas instead of nitrogen or hydrogen. Various operating parameters have been investigated and optimized, including discharge current, dopant gas, bias voltage, and sample introduction position. The resulting detector is more inert and more sensitive (a limit of 36 fg for lindane) and capable of operation at temperatures as high as 400 °C. By running 23 halocarbon compounds on the improved PDECD and on a (63)Ni-ECD using the same GC system, we find that the PDECD is superior to (63)Ni-ECD in terms of sensitivity, linearity, and response time. We attribute the enhanced sensitivity to a lower positive ion concentration, which in turn lowers the electron-positive ion rate of recombination. Pesticides (including some real-world samples) have also been analyzed on the PDECD. The results demonstrate that the PDECD can replace the radioactive ECD typically used in these analyses.