Normal-phase high pressure liquid selection

A RhNaY (1 wt.% Rh) catalyst was prepared by ion exchange using an aqueous solution of [Rh(NH3)6]Cl3 (226, 229), followed by treatment with a CO/H2 (1/1) mixture at 130°C and 80 atm pressure. The catalyst so formed was observed to have good activity and high total aldehyde selectivity ( 95%) for the liquid-phase hydroformylation of hexene-1. Some typical results are shown in Table VI, which indicate that the normal/iso aldehyde product ratio is similar to that obtained with homogeneous rhodium carbonyl catalysts (223). 

The mass spectrometer is a very sensitive and selective instrument. However, the introduction of the eluent into the vacuum chamber and the resulting significant pressure drop reduces the sensitivity. The gas exhaust power of a normal vacuum pump is some 10 ml min-1 so high capacity or turbo vacuum pumps are usually needed. The gas-phase volume corresponding to 1 ml of liquid is 176 ml for -hexane, 384 ml for ethanol, 429 ml for acetonitrile, 554 ml for methanol, and 1245 ml for water under standard conditions (0°C, 1 atmosphere). The elimination of the mobile phase solvent is therefore important, otherwise the expanding eluent will destroy the vacuum in the detector. Several methods to accomplish this have been developed. The commercialized interfaces are thermo-spray, moving-belt, electrospray ionization, ion-spray, and atmospheric pressure ionization. The influence of the eluent is very complex, and the modification of eluent components and the selection of an interface are therefore important. Micro-liquid chromatography is suitable for this detector, due to its very small flow rate (usually only 10 p min - ). 

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