Novel Pinhole Emitter Chip for Micro Supercritical Fluid Chromatography–Mass Spectrometry with Integrated Dilution-Free Fluidic Back-Pressure Regulation

We present a novel chip-based device featuring a pinhole emitter for mass spectrometry (MS) coupling with integrated fluidic back-pressure regulation for supercritical mobile phases. This design enables facile coupling of packed capillary columns used for supercritical fluid chromatography (SFC) with atmospheric pressure ionization mass spectrometry. The monolithic microfluidic chips were fabricated using selective laser-induced etching, seamlessly integrating multiple functions, including comb-shaped particle retention structures for column packing and ports for zero-clearance connection with standard fused silica capillaries. The integrated restrictive pinhole MS emitter generated by dielectric breakdown is a key innovation of the micro SFC–MS platform. It enables a controlled decompression of the supercritical CO₂-based mobile phase within few micrometers to efficiently transfer the analytes from the compressed supercritical fluid into the ambient gas phase in front of the MS orifice. The inclusion of an arrowhead-shaped fluidic element further enables precise, dilution-free back-pressure regulation. With a minimal postcolumn volume of just 3 nL, the system shows excellent MS coupling performance, as demonstrated by rapid SFC–MS analysis of pharmaceuticals and natural products.