Metal-organic framework stationary phases for one- And two-dimensional micro-gas chromatographic separations of light alkanes and polar toxic industrial chemicals

Despite promising advances with metal-organic frameworks (MOF) as stationary phases for chromatography, the application of MOF for one- and two-dimensional micro-gas chromatography (μGC and μGC × μGC) applications has yet to be shown. Micro GC (μGC) columns coated with two different MOF, namely, HKUST-1 and ZIF-8, were employed for the rapid separation of high volatility light alkane hydrocarbons (natural gas) and determined the partition coefficients for toxic industrial chemicals, using μGC and μGC × μGC systems. Complete separation of natural gas components, methane through pentane, was completed within 1 min, with sufficient resolution to discriminate n-butane from i-butane. Layer-by-layer controlled deposition cycles of the MOF were accomplished to establish the optimal film thickness, which was validated using GC (sorption thermodynamics), quartz-crystal microbalance gravimetric analysis, and scanning electron microscopy. Complete surface coverage was not observed until after -17 deposition cycles. Propane retention factors with HKUST-1-coated μGC and a state-of-the-art polar, porous layer open-tubular stationary phase were approximately the same at -7.5. However, with polar methanol, retention factors with these two stationary phases were 748 and 59, respectively, yielding methanol-to-propane selectivity factors of 100 and 8, respectively, a 13-fold increase in polarity with HKUST-1.