Phase merging tube

FigJ.l Schematic diagram of a merging-tube segmentor. OR, organic phase AQ, aqueous phase Pt, platinum capillary [1]. 

Several instniments have been developed for measuring kinetics at temperatures below that of liquid nitrogen [81]. Liquid helium cooled drift tubes and ion traps have been employed, but this apparatus is of limited use since most gases freeze at temperatures below about 80 K. Molecules can be maintained in the gas phase at low temperatures in a free jet expansion. The CRESU apparatus (acronym for the French translation of reaction kinetics at supersonic conditions) uses a Laval nozzle expansion to obtain temperatures of 8-160 K. The merged ion beam and molecular beam apparatus are described above. These teclmiques have provided important infonnation on reactions pertinent to interstellar-cloud chemistry as well as the temperature dependence of reactions in a regime not otherwise accessible. In particular, infonnation on ion-molecule collision rates as a ftmction of temperature has proven valuable m refining theoretical calculations. 

Special techniques have been developed to measure critical temperature, pressure and density. The most common manner to observe the critical temperature is to heat a sample in a closed tube and measure the temperature at which the boundary (meniscus) between liquid and vapor disappears. This method produces an accuracy of about 0.5 degree in most cases. More sophisticated methods for detecting the merging of the two phases are available, but achieving a reproducibility of better that 0.1 degree is difficult. Some properties of a substance change rapidly in the vicinity of the critical point and many organic compounds decompose at or below the critical temperature. Rapid methods of observation have been developed for these compounds. 

Experimental Procedure (Microscale Experiments) An aqueous solution of CalB (6g/l) is merged at 22 °C with a solution of propionic acid (0.18-1.21 mol/1) and 1-butanol (0.09-1.21 mol/1) in n-decane on a Micronit microfluidic chip. Sixty microliter samples are collected at —12 °C in 0.5 ml tubes, prefilled with 175 ml of n-decane. Each sample is centrifuged to separate the two phases of which the top layer is analyzed by HPLC. 

Merges and Okamoto have also reported the synthesis of a three-dimensional macrocydic structure [34]. The chiral tube 81 was achieved in 15% yield and the two enantiomers were separated using chiral reverse-phase HPLC. CD spectroscopic measurements were acquired for both enantiomers, confirming the chiral separation as well as the structure assignment. 

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