3D printed two-in-one on-capillary detector: Combining contactless conductometric and photometric detection for...

In this work, for the first time, a 3D printed two-in-one on-capillary detector, combining contactless conductometric detection (C⁴D) and photometric detection (PD), is fabricated for capillary electrophoresis (CE). The C⁴D Faraday shield (FS) is printed using electrically conductive composite polylactic acid (PLA) to minimize the stray capacitance. Non-conductive PLA is also used to print the insulator of FS to prevent the electrical conduction with two stainless steel electrodes. A novel collimator, consisting of two partially aligned pinholes, is printed by conductive material to collimate the light-emitting diode beam. The C⁴D detection has a signal-to-noise ratio of 1092 ± 2 for 200 μM potassium on a 25 μm id capillary. The PD detection shows excellent linearity with stray light down to 8% and an effective path length at 73% of a 75 μm id capillary. The analytical performance is demonstrated by CE separation and detection of cations. PD shows limits of detection (LODs) of 1.3, 0.9, and 1.7 μM for cobalt, copper and zinc, which are complexed with 4-(2-Pyridylazo) resorcinol, while C⁴D shows LODs of 1.2, 1.4, 21 and 2.6 μM for potassium, sodium, cobalt and zinc, respectively.