Novel Pinhole\nEmitter Chip for Micro Supercritical\nFluid Chromatography–Mass Spectrometry with Integrated Dilution-Free\nFluidic Back-Pressure Regulation

We present a novel\nchip-based device featuring a pinhole\nemitter\nfor mass spectrometry (MS) coupling with integrated fluidic back-pressure\nregulation for supercritical mobile phases. This design enables facile\ncoupling of packed capillary columns used for supercritical fluid\nchromatography (SFC) with atmospheric pressure ionization mass spectrometry.\nThe monolithic microfluidic chips were fabricated using selective\nlaser-induced etching, seamlessly integrating multiple functions,\nincluding comb-shaped particle retention structures for column packing\nand ports for zero-clearance connection with standard fused silica\ncapillaries. The integrated restrictive pinhole MS emitter generated\nby dielectric breakdown is a key innovation of the micro SFC–MS\nplatform. It enables a controlled decompression of the supercritical\nCO<sub>2</sub>-based mobile phase within few micrometers to efficiently\ntransfer the analytes from the compressed supercritical fluid into\nthe ambient gas phase in front of the MS orifice. The inclusion of\nan arrowhead-shaped fluidic element further enables precise, dilution-free\nback-pressure regulation. With a minimal postcolumn volume of just\n3 nL, the system shows excellent MS coupling performance, as demonstrated\nby rapid SFC–MS analysis of pharmaceuticals and natural products.