A design for a simple gas doser, which incorporates a movable shutter, is presented. The operation of this doser is demonstrated using the dosing and subsequent temperature programmed desorption of butanethiol on Au{100}-(5 X 20). The sticking probability for adsorption of the butanethiol at 100 K was measured to be s = 0.85+/-0.05. The butanethiol desorption showed two features corresponding to the desorption of the chemisorbed monolayer at 500 K, and physisorbed multilayers at 140 K. The chemisorbed monolayer feature was not observed in the desorption of the parent molecular ion at 90 amu, but was observed at 56 amu, suggesting that desorption was accompanied by decomposition of the chemisorbed butanethiolate species. The primary gas phase product appears to be 1-butene. Auger electron spectroscopy showed that the thiolate sulfur remained on the surface until above 700 K.