2996 Photodiode Array Detector: Analytical and Microbore Flow Cells
A mixture of five analgesics was separated on a 2.1 mm i.d. column using a 2 minute, linear gradient at five different flow rates and was detected using the 2996 PDA detector with either the analytical or microbore flow cells. The average peak widths and peak heights achieved with each flow cell are listed in Table 1. There is an improvement in peak widths of approximately 30% when the microbore cell is used. This results from the reduced cell volume (8.0 μL to 2.7 μL) and the reduced tubing volume (0.009” tubing replaced with 0.005” tubing). However, the reduced cell volume comes at the cost of a decreased flow cell path length (10 mm to 3 mm) resulting in a reduction in signal. The dependence of absorbance signal on flow cell path length is described by Beer’s Law (A=εbc where A is absorbance, ε is molar absorptivity, b is path length, and c is concentration). Table 1 shows that the average drop in signal due to the decreased path length of the microbore flow cell is approximately 60%. The choice of whether to use the microbore cell will depend on the purpose of the method. If increased peak capacity is required, the microbore flow cell should be used since the decreased peak width will increase resolution. However, if sensitivity is more important, the analytical flow cell should be used to achieve the maximum signal.
