The nitrogen isotopic compositions of lunar soil have important implications for the sources of lunar volatiles and even the evolution of the moon. At present, the research on the lunar nitrogen isotopic compositions is mainly based on the lunar meteorites and the samples brought back by the Apollo and Luna missions. However, volatiles adsorbed on the surface of the lunar soil may be lost due to changes in temperature and pressure, as well as vibration and shock effects when the sample is returned. At the same time, in the case of low N content in the sample, since N is the main component of the earth’s atmosphere, it is easily affected by the atmosphere during the analysis process. Therefore, in situ nitrogen isotopic analysis of lunar soil on orbit is necessary to avoid the problems mentioned above and is one of the primary science goals for the Lunar Soil Volatile Measuring instrument on Chang’e-7 spacecraft. After the nitrogen purification procedure, the volatiles in lunar soil that are released through single-step or stepped heating techniques diffuse to the quadrupole mass spectrometer to obtain the N contents and isotopic compositions of the lunar soil. This paper introduces the ground test for N isotopic analysis of lunar soil in orbit according to the Lunar Soil Volatile Measuring Instrument. After long-term repeated measurements, the background and CO-corrected Air-STD ¹⁴N/¹⁵N ratio is 268.986 ± 4.310 (1SD, n = 35), and the overall reproducibility of measurements is 1.6%. The accuracy of N isotopic compositions is calculated to be better than 5%, which can distinguish different sources of N components in lunar soil.

The Lunar Soil Volatile Measuring Instrument, a key payload of the Chang’e-7 mission, employs a quadrupole mass spectrometer (QMS) to directly analyze gases released from lunar regolith at different temperatures, aiming to determine the types and abundances of volatiles. However, the evolved gases are often complex mixtures, and their direct introduction into the mass spectrometer may compromise the measurement accuracy due to interactions among different species. To investigate the interference from gases on volatile quantification, systematic experiments were performed with one or two gases out of H₂, He, N₂, Ar, CO₂, and CO on a flight-like laboratory unit of the payload. Results show that the QMS exhibited excellent reproducibility and linear response (R² > 0.99) for all pure gases tested. Furthermore, the sensitivity of gases varied in mixtures and was jointly influenced by gas composition and volume fraction. For instance, compared with the sensitivity values obtained in pure gas measurements, the sensitivity of CO was slightly enhanced when mixed with Ar but was reduced when mixed with H₂ or He. A significant sensitivity enhancement of up to 4.6 folds was observed for H₂ when mixed with He. However, as its fraction increased, the sensitivity of a component in a binary mixture exhibited a decreasing deviation and was almost constant when its fraction was above 60%. Based on these findings, we developed a sensitivity correction method which employs an iterative algorithm to obtain more accurate partial pressures calculated from the gas measurement signals. Applications of the method on H₂–He mixtures and a pre-mixed CO–N₂ standard gas demonstrated that the relative errors of calculated pressures can be reduced to within ±10%. This method would significantly improve the accuracy of gas pressure calculated from in situ volatile measurement data and also provides a valuable reference for similar QMSs.

This study prepared an adsorption-based water-containing lunar regolith simulant under low-temperature conditions to investigate H₂O behavior in simulated lunar environments. Experiments established that water binds to regolith particles via adsorption rather than existing in liquid/solid states, with critical initial pressure thresholds identified at various temperatures to ensure pure adsorption conditions. Crucially, coexisting substances extend H₂O preservation to −100 °C, suggesting substantial water retention in lunar polar regolith even under extreme cold. Sublimation modeling further revealed phase transition boundaries, indicating water ice likely persists in both permanently shadowed regions and illuminated polar areas. These findings provide fundamental insights into: adsorption-driven enrichment/preservation mechanisms of lunar water, thermodynamic stability thresholds at ultralow temperatures, and water ice distribution patterns across lunar polar terrains. The data advance understanding of lunar water’s stability and extractability, offering critical scientific support for future in situ resource utilization and sustained lunar exploration.