A method of drilling sub-sea oil and gas production wells in which a liquid hydrocarbon substance, such as a natural gas liquid, is injected into the drilling mud supplied to the well in order to reduce the mud density. The housing is spring-mounted in a capsule in such a way that the capsule and the loud-speaker housing define an intermediate space. The ambient pressure source is compatible with various mass analyzers, particularly with mass spectrometers and solves many problems associated with conventional MALDI sources operating under vacuum.