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RATIONALE: There are many chemical measurement scenarios that would benefit from hand portable mass spectrometry tools including forensics, environmental monitoring, and safety and security. High pressure mass spectrometry (HPMS) facilitates miniaturization by significantly reducing vacuum system requirements. Previous work demonstrated HPMS using helium buffer gas, but HPMS conducted using ambient air would further reduce the size and weight of a portable instrument while also reducing logistical demands by eliminating the need for a helium supply. METHODS: Mass spectrometry was performed at pressures exceeding 1 Torr with ambient air as the buffer gas. A glow discharge electron ionization source and a miniature cylindrical ion trap mass analyzer with a radius of 0.5mmwere used. Mass analysis was possible at these pressures with increased radiofrequency (RF) drive frequencies (10 MHz) compared with commercial ion traps (∼1 MHz). A differentially pumped chamber was used so that mass spectrometry could be performed at high pressures and detection performed at low pressures with an electron multiplier. RESULTS: HPMS with air buffer gas was demonstrated using a suite of volatile organic compounds (VOCs). The glow discharge ionization source was optimized for operation using air. Mass spectral peak widths increased a factor of 8 compared with helium, as expected, but useful chemical information was still acquired. A mixture of VOCs was detected with ambient air as the buffer gas, showing that valuable mass information can be gained using HPMS without the requirement of an onboard buffer gas source. CONCLUSIONS: HPMS significantly reduces the pumping requirements required for miniature mass spectrometers and the use of ambient air buffer gas further reduces size, weight, and logistics requirements. Mass analysis at high pressures of ambient air is another important step for the development of hand portable mass spectrometers. [ABSTRACT FROM AUTHOR]

When working on biotherapeutic process development, the analysis of spent cell culture media is often a daily practice during the optimization of bioreactor conditions and media composition. The introduction of parallel microbioreactor systems has decreased the complexity and costs of process development by allowing for concurrent studies of multiple bioreactor and media variables. However, the bioreactors' small volumes (typically less than 250 mL) limit the volume of media one can extract for daily sampling. We describe a means to analyze spent media with an integrated microchip capillary electrophoresis mass spectrometer (CE-MS) analyzer with minimal sample volume requirements and rapid analysis time. The platform was evaluated with a parallel microbioreactor system (ambr® 250) culturing a Chinese hamster ovary (CHO) cell line stressed by varying levels of ammonia (NH3). The spent media analysis identified net increases in the levels of the amino acids (AA) Ala, Arg, Asp, Glu, Gly, His, Ile, Leu, Lys, Phe, Thr, Trp, Tyr, and Val in all bioreactors, with Gly levels showing increases in excess of 8-fold initial levels in all bioreactors. Other media components either steadily decreased in concentration or were completely depleted by the end of culture. For example, Asn was depleted in all of the unstressed and 10 mM NH3-stressed bioreactors, but was approximately twice as high as the initial levels in the 30 mM NH3-stressed bioreactors at the end of the culture periods. Also, the 30 mM NH3-stressed condition may have caused either complete degradation or rapid consumption of choline, since it was no longer present starting at the t = 36 h sampling. Overall, the monitored media components were observed to have independent trajectories based on feeding and consumption by the cells, and depending on the stressed condition. The capability to have more frequent spent media analyses would allow for real-time observation of these process changes and associated control strategies. [ABSTRACT FROM AUTHOR]