Abstract: An environmental sampler is configured to deliver a pre-determined volume of external environmental sample and internal standard sample to the mass spectrometer on each cycle of advancing and retracting movement of a sampler rod under control of a stepper motor. This allows the external environmental sample to be accurately analyzed for its trace contents against a known, standard sample in the same sample period, thereby providing a real-time calibration of the analysis results in each sample period. The samples arc taken in precise, pre-determined volumes through two sets of machined grooves formed on the surface of the sampler rod. The sets of machined grooves deliver the samples to the mass spectrometer through alignment with a vacuum channel to an outlet port which is scaled off from the external environment and an internal standard sample reservoir.