A valve mechanism which is adapted to be connected directly to the inlet of a gas chromatographic column for selectively directing either a gas or a liquid sample into the column. The valve mechanism comprises a valve body having an elongated channel extending entirely therethrough, the channel being coaxial with the column when the valve is attached thereto whereby a syringe may be extended through the channel into the column for direct column injection of a liquid sample. The valve body receives the opposite ends of a sample loop, sample gas inlet and outlet tubes and a carrier gas inlet tube. The valve mechanism also includes a rotatable valve plug which is operative, in a first position, to connect the carrier gas inlet tube directly to the elongated channel for injection of the liquid sample; the valve plug being further operative, in the first position, to connect the sample gas inlet and outlet tubes to the ends of the sample loop so that the loop is filled with the sample gas. Upon rotation to a second position, the valve plug is operative to connect the carrier gas inlet tube to the elongated channel via the sample loop whereby the carrier gas flushes the sample gas trapped in the sample loop into the column.
