Bradbury-Nielsen vs. Field switching shutters for high resolution drift tube ion mobility spectrometers

Abstract

A key component in the design of every drift tube ion mobility spectrometer (IMS) is the ion shutter which 4 controls the injection of ions into the drift tube. Especially, compact drift tube IMS require very short injection 5 pulses to achieve high resolution and therefore require fast ion shutters. Thus, it is important to find an ion 6 shutter principle that can be readily scaled towards these short injection widths without causing major non-7 idealities in the injection process, such as drift field inhomogeneities, ion loss and ion discrimination by 8 mobility. In this paper, we compare different ion shutter principles, foremost the Bradbury-Nielsen gate and a 9 field switching design. It is shown through theoretical considerations and field simulations that the Bradbury-10 Nielsen shutter is more universally applicable and typically less complex for long injections widths but field 11 inhomogeneities associated with its operating principle impede the scaling process. Thus, the currently less used 12 field switching shutters will become the superior principle when very short injection widths are required, as this 13 shutter principle allows for single digit microsecond widths.

A universal relationship between optimum drift voltage and resolving power

“…• Field homogeneities at the beginning of the drift tubes can be prevented through a suitable ion shutter design. The use of a field switching shutter provides an advantage over a Bradbury-Nielsen shutter design in this regard [11]. • Additional detector rise times can be avoided through properly shielding the detector with the aperture grid [12; 4].…”

Miniaturized high-performance drift tube ion mobility spectrometer

“…It has been shown, that X-rays can be considered as nonradioactive substitute for the 3 H ionization source, but the Xray source should be placed orthogonally to the axis of the drift tube to avoid any offset current on the detector [14,15]. Ions are injected into the drift region using a field switching shutter as described in [16]. To keep production cost low, the Faraday detector is manufactured from standard PCBs.…”

Simulation aided design of a low cost ion mobility spectrometer based on printed circuit boards

“…The basic layout of the PCB-IMS is similar to a typical stacked ring design, consisting of ionization region, drift region and a detector shielded by an aperture grid. A tritium source is used for ionization and ions are injected into the drift tube using a field switching (FS) shutter [12]. To minimize interferences on the ion signal, the current amplifier is directly attached to the backside of the PCB detector.…”