Multiplexed Operation of an Orthogonal Multi-Reflecting TOF Instrument to Increase Duty Cycle by Two Orders

Introduction

Multi-reflecting orthogonal TOF mass spectrometers (MR-TOF) incorporate extended ion flight paths to increase resolution, however this is at the expense of duty cycle. This reduction of duty cycle can be mitigated by accumulation of ions in a storage device between cycles, but both dynamic range of detection and mass accuracy are decreased due to the excessive number of ions per peak. Alternatively, multiplexing of TOF spectra has been proposed by numerous researchers [1, 2, 3]. Here we describe the implementation of Encoded Frequent Pushing (EFP) [4, 5], where a repeated sequence of unique time interval pusher pulses is applied. The method is artifact free and provides duty cycles comparable with conventional, non MR-TOF systems without affecting MR-TOF resolution and mass accuracy.

Methods

In contrast to Hadamard transform methods, EFP involves a pattern of OA start pulses where it’s shifted replica does not coincide at more than one point (with a precision comparable to TOF peak width). Decoding by robust statistical verification of all data points produces no artefacts. The main parameter of the decoding algorithm is the ion population of multiplexed spectrum. Data were acquired using a MR-TOF MS experimental system having a 40m long Folded Flight Path [6] A 1.8 Giga-samples/sec, 12-bit ADC (X6 GSPS Innovative Integration) was used to record 2ms long mass spectra. The decoding was performed in real time using computational resources of the GPU card (NVIDIA).

Preliminary Data or Plenary Speakers Abstract

The experimental results demonstrated two orders improvement of duty cycle and hence sensitivity with no loss of resolution and with dynamic range reaching 5 orders of magnitude in a single ESI-spectrum. There was no degradation of the mass accuracy when using EFP recorded over the mass to charge range 300 to 3000 (using 2-points for internal calibration). In fact, for weaker peaks within the data, inclusion of more ions helped to improve the accuracy of the mass measurement. We also found that EFP does not introduce deviations to the relative intensities of various spectral peaks, except when the signal was at the minimal detectable level. In conclusion, EFP provides a dramatic increase of the duty cycle for multi-reflecting TOF and provides duty cycles, sensitivity, and dynamic range comparable with

non MR-TOF systems. Furthermore, the EFP technique does not compromise the very high resolution and improves mass accuracy characteristics of such MR-TOF mass spectrometers. This was illustrated using a range of peptides admitted both by infusion and LC-MS.

Novel Aspect

High duty cycle multi-reflecting TOF MS using multiplexed data acquisition method without compromising mass accuracy and resolving power.