Microfabrication of high temperature micro-reactors for continuous flow isotope ratio mass spectrometry

Abstract

Robust, high temperature micro-reactors for online conversion of organic compounds were microfabricated in high purity fused silica to enable stable isotopic compositional analysis of individual compounds in mixtures using advanced gas chromatography (GC) separation techniques, such as fast GC and comprehensive 2D GC, coupled to isotope ratio mass spectrometry (IRMS). These microreactors could also be manufactured at larger channel dimensions to enable robust operations for normal GCC-IRMS applications. Photolithography was used to define the reactor channel pattern on high purity fused silica, with a protective layer of amorphous silicon. A two-step isotropic wet etching process, using 49% HF, selectively created semi-circular cross-section micro-channels of arbitrary diameters (56-209 lm), with tapered sections leading to input/output ports ([400 lm) that accept fused silica capillary tubing used in GC and MS peripherals. Pairs of symmetric mirror image substrates were aligned and bonded to form enclosed circular channels. The resulting micro-reactors are more robust than the standard designs made of fragile-fused silica capillary or alumina tubes of relatively large bore, and are gas tight at temperatures up to 1,000°C. Fast GC plugs of CH 4 with and without the reactor revealed that peak shapes are minimally affected by the micro-reactor when carrier flow rate and channel diameter are optimized. Peak shapes with full widths at half maximum of 250 ms are shown for plugs of CH 4 through a fast-GC-combustion-IRMS system interfaced with a micro-reactor containing a CuO/NiO combustion source, enabling carbon isotope ratio measurements of CH 4 with a precision of SD(d 13 C) = ±0.28%. The devices enable arbitrarily narrow bores and long path channels that can be operated as open tubes or loaded with a reactant, in a small, robust package.

Manufacturing and characterization of a ceramic microcombustor with integrated oxygen storage and release element

“…earth sciences, forensic science, biomedicine and archeology, applies isotope ratio measurements of carbon for multiple objectives, mainly categorized as isotopic fractionation or radiometric dating. In isotopic fractionation of carbon, which normally focuses on stable isotopes, e.g., the ratio of 13 C to 12 C, the sample is usually converted to CO 2 [1]. Therefore, combustion plays an important role in sample preparation.…”

“…Using lithography techniques and wet etching, H. J. Tobias et al [1] fabricated a high-temperature microreactor (78×30×2 mm 3 ) for on-line conversion of organic gas compounds in high-purity fused silica. Cu and Ni wires were inserted in the reactor after manufacturing, and were thermally oxidized in situ to be used as the source of oxygen during the combustion.…”

Calibration and data processing in gas chromatography combustion isotope ratio mass spectrometry

“…Schematically represented in Figure , GCC‐IRMS for CSIA of C uses an online reactor held at approximately 950 °C positioned between the GC and IRMS to combust organic molecules to CO 2 and H 2 O. This is accomplished using a fused silica or ceramic tube filled with CuO and NiO with a Pt catalyst or micro‐reactors filled with CuO or an oxidized Cu alloy . A 4‐port valve or back‐flush system is used to divert organic solvent from the reactor, preventing the rapid depletion of the oxygen source; alternatively, a high‐capacity injector that vents most evaporated solvent prior to introduction of analytes onto the column can be used to avoid dead volumes associated with additional connections.…”

“…This is accomplished using a fused silica or ceramic tube filled with CuO and NiO with a Pt catalyst or micro-reactors filled with CuO [42] or an oxidized Cu alloy. [43][44][45][46] A 4-port valve or back-flush system is used to divert organic solvent from the reactor, preventing the rapid depletion of the oxygen source; alternatively, a high-capacity injector that vents most evaporated solvent prior to introduction of analytes onto the column can be used to avoid dead volumes associated with additional connections. Thereafter, CO 2 is admitted to the IRMS through an open split for analysis.…”

Picomolar‐scale compound‐specific isotope analyses

“…of the solvent diversion mechanism, commercial combustion reactors, capillary transfer lines, and Nafion water trap. Reducing the number of fittings in the flow path and installing custom narrow‐bore components will help to minimize post‐column peak broadening …”