Abstract: Potassium (K) is an important impurity element in high-purity quartz and accurate determination of its content is of great significance for the evaluation of the quality of high-purity quartz products. Via ultra-trace K in high-purity quartz samples were dissolved by atmospheric acid dissolution method, an inductively coupled plasma mass spectrometry (ICP-MS) determination method for K was established and the interference of multi-atomic molecular ions was eliminated by cold plasma with low RF power in ICP-MS and 50 ng/mL rubidium was used as the internal standard elements in this process. Background interference in mass spectrometry for the determination of potassium was greatly eliminates. And the sample weight, RF power, sampling depth and atomized gas flow were optimized in this work. Finally, under the optimal conditions of 1.000 0 g of weight sample, 800 W of RF power, 5.6 mm of sampling depth and 1.06 L/min of atomized gas flow rate, K element standard series solutions were determined and the mass spectrometry intensity of K showed good linear relationship with ρ(K) in the range of 0.100~50 ng/mL with the correlation coefficients of calibration curve was 0.999 6. The detection limit and quantification limit of K in high-purity quartz were 0.057 μg/g and 0.191 μg/g, respectively. Typical commercial high-purity quartz samples were selected for the application experiment of this method, and the relative standard deviations (RSD) for 9 parallel measurements were between 2.9%~5.1% and the recoveries of K were between 96.4%~105.4%.