An Improved Calibration Approach for Traveling Wave Ion Mobility Spectrometry: Robust, High-Precision Collision Cross Sections.

The combination of ion-mobility (IM) separation with mass spectrometry (MS) has impacted global measurement efforts in areas ranging from food analysis to drug discovery. Reasons for the broad adoption of IM-MS include its significantly increased peak capacity, duty-cycle, and ability to reconstruct fragmentation data in parallel, all of which greatly enable the analyses of complex mixtures. More fundamentally, however, measurements of ion-gas molecule collision cross sections (CCSs) are used to support compound identification and quantitation efforts as well as study the structures of large biomolecules. As the first commercialized form of IM-MS, Traveling Wave Ion Mobility (TWIM) devices are operated at low pressures (∼3 mbar) and voltages, are relatively short (∼25 cm), and separate ions on a timescale of tens of milliseconds. These qualities make TWIM ideally suited for hybridization with MS. Owing to the complicated motion of ions in TWIM devices, however, IM transit times must be calibrated to enable CCS measurements. Applicability of these calibrations has hitherto been restricted to primarily singly charged small molecules and some classes of large, multiply charged ions under a significantly narrower range of instrument conditions. Here, we introduce and extensively characterize a dramatically improved TWIM calibration methodology. Using over 2500 experimental TWIM data sets, covering ions that span over 3.5 orders of magnitude of molecular mass, we demonstrate robust calibrations for a significantly expanded range of instrument conditions, thereby opening up new analytical application areas and enabling the expansion of high-precision CCS measurements for both existing and next-generation TWIM instrumentation.

Monitoring of radon gas in caves of the Yorkshire Dales, United Kingdom.

A number of vocational training courses are held in caves in the Yorkshire Dales region of the United Kingdom. The instructors and students involved in these courses have the potential to be exposed to enhanced levels of radon ((222)Rn) and its progeny as a result of their occupations. A prior radiological risk assessment for the training courses recommended that an environmental monitoring programme be carried out to establish the radon concentrations in the caves, and that the caving instructors wear personal radon dosemeters. Radon gas concentrations varied seasonally, being at their highest in summer and their lowest in winter. The lowest result was 40  Bq m(-3) recorded in Lower Longchurn cave during winter, whilst the highest result was 4440  Bq m(-3) recorded in Crackpot cave during the summer. As the individuals involved in the caving are entering atmospheres with radon gas concentrations in excess of 400  Bq m(-3), the Ionising Radiation Regulations 1999 (GB Parliament 2000 Ionising Radiations Regulations 1999 (London: Stationary Office) SI 1999/3232) apply. A system of work is therefore in place to control exposure to radon. This system of work stipulates an initial dose investigation level of 1 mSv, a second dose investigation level of 2 mSv and an annual dose limit of 6 mSv. The highest annual dose recorded to date is 2.2 mSv, although the average (median) annual dose is only 0.5 mSv.