Mass Spectrometry

Overview

Mass spectrometry is a large group of methods for analyzing the compounds of a substance. The ADQ series of digitizer is carefully designed for any Time-of-flight based method for Mass Spectrometry.

Optimizing ADQ digitizer for Mass Spectrometry

A high quality MS TOF measures a large span in concentration of substances and accurate resolution of different masses. This implies that the digitizer must have the combination of high dynamic range and high sample rate. SP Devices’ ADQ-series of digitizers are designed to provide the best combination of these parameters. The high resolution is achieved by 14 bit digitizers and application specific firmware for noise suppression. The high sample rate is achieved by interleaving of A/D converters. To maintain high signal quality when interleaving ADCs, the digitizers are empowered by SP Devices’ interleaving technologies ADX and DBS.

Mass resolution through high sample rate

The mass resolution is set by the bandwidth of the detector, that is, how narrow peaks can be generated. Today a typical peak is in the range of a nanosecond. This implies that the digitizer has to provide several GSPS (sample at several GHz) to capture these pulses. The ADQ14 series of digitizers provides 14 bit resolution of up to 2 GSPS. The application note shows how to get 14 bits at 4 GSPS from the ADQ14

Mass concentration through high dynamic range

Although the 14 bits resolution of the ADQ14 is very high, it has to be enhanced many times to meet the requirements of a mass spectrometer. This is done by averaging a large number of repeated measurements. This process produce a huge amount of data. To build an efficient system an averaging function built into the firmware of the ADQ14-FWATD. The output is then only the accumulated result from very many measurements. With the waveform averaging function the dynamic range can reach to about 100 000 : 1.

Efficient processing of low activity methods

Some mass spectrometry instruments has a very low activity. Then the acquired data contains a lot of zeros. To optimize the data flow to the PC, the firmware option ADQ14-FWPD can detect and analyze pulses directly in the FPGA. The zero data is suppressed and only requested information about a pulse is transmitted to the PC for further analysis.

Extended dynamic range through dual channels

A traditional method form enhancing performance when digitizers where operating at 8 bits resolution was to use 2 channels and apply the same signal, but with different gain. In this way, the ratio between the larges and the smallest signal was increased. The same method can be applied on the 14 bits digitizer ADQ14DC-2X , which provide 2 synchronized channels at 2 GSPS each.