# Asynchronous Stepped Fourier Transform Ion Mobility Spectrometry

## TL;DR

This paper introduces a low-cost, asynchronous method for ion mobility spectrometry that improves performance without increasing experimental time.

## Contribution

The novel asynchronous stepped frequency FTIMS method enables system optimization using affordable ADC systems and a Raspberry Pi-based interface.

## Key findings

- Asynchronous FTIMS improves resolving power and signal-to-noise ratio without increasing experimental time.
- A Raspberry Pi 4 SBC can function as a low-cost DAC interface for FTIMS.
- The method works with various ADC systems, maintaining spectral fidelity.

## Abstract

Fourier Transform is a low-cost method for improving
duty cycle,
resolving power, and signal-to-noise ratio in the Ion Mobility Spectrometry
(IMS) experiment in a 2-gate IMS cell. By simultaneously pulsing both
gates through a frequency sweep, the resulting data may be deconvoluted
into a time-based mobility spectrum through a Fast Fourier Transform
(FT). However, inconsistencies common in low-cost function generators
result in spectral artifacts. In this work, an asynchronous stepped
frequency FTIMS method is demonstrated, which uses a simple, software
timed pulse generator compatible with any modern Analog-Digital Converter
(ADC) system. By unlinking the frequency initiation and data collection
using a long rise-time amplifier circuit, a stand-alone FTIMS with
Faraday Plate detection was characterized in both single gate and
FT modes of operation using the same IMS cell. Asynchronous stepped
FTIMS parameters were investigated for system optimization with respect
to resolving power, signal-to-noise ratio, and experimental time.
Once optimized, asynchronous FTIMS demonstrated significant improvements
in resolving power and signal-to-noise ratios without a significant
increase in experimental time. By unlinking the frequency generation
and data analysis, a simple Python script was demonstrated using a
variety of commercially available ADC systems ranging in cost from
several thousand to several hundred dollars (USD) without sacrificing
spectral fidelity. A custom circuit was developed to allow a Raspberry
Pi 4 Single Board Computer (SBC) to function as the data acquisition
and control (DAC) interface for a low-cost stand-alone FTIMS solution.