The disclosure relates to instrument assemblies that can include a sample introduction port coupled to a chamber configured to receive the sample from the sample introduction port and provide analysis of the sample with a valve between the sample introduction port and the chamber. The instrument assemblies can include a septum housing assembly coupled to an analysis chamber interface with the interface including a valve and a cam rotatably mounted to the septum housing assembly and/or coupled to the valve. Analysis methods are also provided that can include introducing a sample to an instrument through both a sample introduction port and a valve coupled to the sample introduction port, and, after introducing the sample, closing the valve to seal the sample introduction port from a remainder of the instrument, with the remainder of the instrument being configured to analyze the sample after the introducing through the sample introduction port.