Deep-sea mining and deep-sea exploration require methods for material analysis that can be used directly in the deep sea. A promising method is double-pulse laser-induced breakdown spectroscopy (LIBS), which was already used to measure zinc emission lines up to 600 bar. In this paper, the detection limits for zinc and copper in brass alloys were investigated using double-pulse LIBS at up to 600 bar to show up to which water pressure zinc and copper can be detected for the respective alloy. A double-pulse laser with a wavelength of 1064 nm, a pulse duration of 5-7 ns and a pulse energy of up to 266 mJ (in single-pulse mode) for each pulse was used. To optimize the emission spectrum for the respective water pressure, the delay between the laser pulses was varied. It was found that the detection limit for zinc and copper in brass alloys decreases with increasing water pressure.