The present experimental setup for headspace gas-chromatography
employing external equilibrium cell (HSGC-EC) is similar
to that we have described previously [23,24]. The equilibrium cell
was a jacketed glass vessel of 45 cm3 capacity provided with three
I/O ports one serving for filling the cell and two for headspace sampling.
A photograph of the equilibrium cell (Fig. 1S) is given in Supplementary
material to this paper. The cell was kept at a constant
temperature by a water circulating bath (RC 6 CP Lauda, Germany)
and stirred with a magnetic stirrer. The temperature was stable to
better than ±0.02 K; its absolute value was determined by calibrated
standard mercury thermometers (Karl Schneider, Wertheim,
Germany) to ±0.01 K. An inert pump, Model QG-150 from
Fluid Metering (Syosset, NY, USA) provided a closed loop circulation
of the gas phase between the equilibrium cell and a 6890 Plus
Agilent GC at a rate of 10 cm3 min1. The headspace vapor passed
through a heated stainless steel tubing (approx. 120 C) first into a
pneumatically driven and thermostated (160 C) six port gas sampling
valve, then proceeded into the pump, and finally re-entered
the equilibrium cell at its bottom, bubbling through the liquid
solution under study. The continuous phase contact renewal
speeded up the equilibration which we observed to be complete
within less than 30 min.