One of the problems in liquid chromatography is the injection of a sample into the chromatographic column free of the inclusion of bubbles or gas. Such inclusion may result from so-called cavitation, in which, for example, because of turbulence and perhaps a momentary small drop in pressure some portion of the liquid sample is vaporized to create a bubble. Such inclusion may also occur by the failure to completely immerse into the liquid the aperture or orifice through which the sample is intended to pass into a sample conduit prior to injection. Bubble inclusion in the injection may result in the chromatograph providing poor or even false results. Peak spreading may result. Large inclusion of air or gas may upset or alter the balance of the column and the detector so that a lengthy equilibration time must be attended while the column is flushed with eluent. Visual observation is often inadequate for the timely detection of bubble inclusion whether small or gross, and is largely incompatible with desirable automatic operation.