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

Abstract

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 2 1 n 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.

UniChromCD for Demultiplexing Time-resolved Charge Detection-Mass Spectrometry Data

“…The theory behind HT demultiplexing has been described in detail previously. 19,20,24,25,37,38 The core of the implementation used here is a convolution of the HT kernel (described in the Supplementary Information) with the multiplexed chromatogram, which uses the Fourier convolution theorem:…”

Hadamard Transform Ion Mobility Spectrometry Based on Matrix Encoding Modulation

“…The Hadamard multiplexing technique significantly improves the SNR of DT-IMS compared to the average method [ 11 ]. Subsequently, researchers have proposed numerous novel approaches to eliminate the defects of HT-IMS to further improve its performance, including inverting the modulation sequence [ 14 , 15 , 16 ], spectral reconstruction [ 17 ], continuously varying the duty cycle of the modulated pulse [ 18 ], modifications to the modulation sequence [ 19 , 20 , 21 ], the application of false peak detecting and minimizing algorithms [ 22 , 23 ]. These works focused on the improvement of HT-IMS using various measurement methods and data processing techniques; however, they failed to discover the deviation between the mathematical description of Hadamard transform and the actual signal acquisition process of IMS.…”