An interface converting a cone flow into a rectangular flow is attached to a conventional nozzle with a circular orifice. This assembly can be heated to 300 °C, due to a metal‐to‐metal contact between an orifice and a plunger and to a Teflon‐insulated copper wire of an electromagnet. At the top of the interface, two razor blades are attached to convert the rectangular flow into a slit flow. The enhancement factor (long axis/short axis) is 6 in fluorescence measurements. The signal intensity obtained by the slit nozzle is four times larger than the best value obtained by the conventional circular nozzle.