An improved membrane inlet system is presented for the in situ, online and real time quantification of major and trace gases in aquatic environments. The high sampling frequency and simultaneous measurements of gases like CO2 and methane (CH4) are the key benefits to use these sensors (e.g., InSpectr200-200) in the marine science. Disadvantage of the MIMS is the detection limit of the trace gases like methane. The large quantity of water vapor that passes the MIS downgrades the detection limit or could cause condensation of water in the sensor section. To improve the detection limit we designed a cryotrap system that reduce the water vapor in the analytical line significantly and build a security system to protect the sensor unit in case of membrane rupture. The in situ operable cryotrap is a robust system in a self-contained pressure housing with an energy consumption of less than 10 Watt and a service life time of about 10 hours. Our assessment showed that the cryotrap is freezing more than 98% of the water vapor out at an operating temperature of -85 °C of the analytical line and therefore the detection limit of e.g., methane was lowered from more than 100 nmol L-1 to 16 nmol L-1. Field results showed that the improved MIMS can be used to detect low and rapid concentration changes of trace and also major gases in small scale.