Implementation of an Open-Source Multiplexing Ion Gate Control for High Kinetic Energy Ion Mobility Spectrometry (HiKE-IMS)

With ion mobility spectrometry increasingly used in mass
spectrometry
to enhance separation by increasing orthogonality, low ion throughput
is a challenge for the drift-tube ion mobility experiment. The High
Kinetic Energy Ion Mobility Spectrometer (HiKE-IMS) is no exception
and routinely uses duty cycles of less than 0.1%. Multiplexing techniques
such as Fourier transform and Hadamard transform represent two of
the most common approaches used in the literature to improve ion throughput
for the IMS experiment; these techniques promise increased duty cycles
of up to 50% and an increased signal-to-noise ratio (SNR). With no
instrument modifications required, we present the implementation of
Hadamard Transform on the HiKE-IMS using a low cost, high-speed (600
MHz), open source microcontroller, a Teensy 4.1. Compared to signal
average mode, 7- to 10-bit pseudorandom binary sequences resulted
in increased analyte signal by over a factor of 3. However, the maximum
SNR gain of 10 did not approach the theoretical 2n−1 gain largely due to capacitive coupling
of the ion gate modulation with the Faraday plate used as a detector.
Even when utilizing an inverse Hadamard technique, capacitive coupling
was not completely eliminated. Regardless, the benefits of multiplexing
IMS coupled to mass spectrometers are well documented throughout literature,
and this first effort serves as a proof of concept for multiplexing
HiKE-IMS. Finally, the highly flexible Teensy used in this effort
can be used to multiplex other devices or can be used for Fourier
transform instead of Hadamard transform.