The demand for on-the-spot analysis is met by a miniature mass spectrometer which is preferred to be robust, stable, as small as possible and capable of analyzing different samples by coupling with various ionization methods. However, largely constrained by the atmospheric pressure interface (API), these aspects are difficult to be realized in one system. Herein, we describe the development of a new miniature mass spectrometer with balanced performance. The miniature mass spectrometer is small in size (30 × 30 × 18 cm) but has a continuous API, which was achieved by high-pressure ion trap operation and maximized ion transfer efficiency with the utilization of a differential pumping system. The miniature mass spectrometer was characterized and optimized in terms of stability, sensitivity, mass range, mass resolution and scan speed. Rapid analysis of mixtures was demonstrated by coupling the miniature mass spectrometer with the ambient ionization technique of paper spray. This is the smallest miniature mass spectrometer to date, which has a continuous API.

Previously, we have reported the development of a miniature mass spectrometer with a continuous atmospheric pressure interface (CAPI), and the use of it for non-volatile sample analysis, such as drugs, peptides and proteins. However due to the diffusion effects in the CAPI, especially stronger for light ions, the instrument shows low detection sensitivities for volatile samples when coupling with an atmosphere pressure chemical ionization (APCI) source (>ppmv). In this study, an in-vacuum plasma ionization source was designed and integrated into the system. By performing ionization in the first vacuum stage, ion transfer loss through the CAPI was minimized and tens of ppbv level detection sensitivities were achieved for volatile samples. Due to its improved sensitivity, chemical source tracing was demonstrated in an indoor environment as a simple proof-of-concept example. Furthermore, an aerodynamic sampling method was developed to facilitate directional sample transfer towards the miniature mass spectrometer in an open environment. By coupling this aerodynamic method with the miniature mass spectrometer, remote chemical source sensing could be achieved at a distance of more than two meters. This aerodynamic sampling method could also be applied to other mass spectrometry instruments for enhanced sample sampling in open environments.

With simplified geometry and high ion transfer efficiency, this PP-API would enable miniaturized mass spectrometry systems with high sensitivity.