MALDI-7090MALDI Mass Spectrometer

Introduction

In many life science applications there is a growingrequirement for high-throughput MALDI TOF-TOF massspectrometers. This can now be realized through theintroduction of the MALDI-7090™ high resolutionMALDI TOF-TOF mass spectrometer, which is capable ofrunning at laser repetition rates of 2 kHz in MS andMS/MS acquisition modes.

During the MALDI process, a plume of analyte and matrixmolecules is formed through UV laser irradiation. Theionized molecules are accelerated into the time-of-flightanalyzer region through apertures in the sourceelectrodes by an electric field formed between theelectrodes. However, some of the matrix material andanalyte is not ionized and this neutral plume continuesto expand from the sample spot until it is deposited onsurfaces in the vicinity of the ion source.

Over time the contamination can build up until aninsulating layer is formed that charges up and adverselyaffects the operation of the ion source. Although theMALDI-7090 is equipped with unique wide-bore ionoptics which help to minimize this process, at some pointthe source electrodes must be cleaned. In a high-throughput environment it becomes impractical to ventthe instrument every time the source needs cleaning.

The MALDI-7090 ion source incorporates TrueClean™, acompletely new and unique method of source cleaningthat has been designed to effectively and automaticallyremove contamination from source electrodes. Thispatented method exploits the fact that most of thecontamination on the electrodes was originally desorbedfrom the sample spot using UV laser irradiation and thuswill be readily desorbed from the electrodes if it is againirradiated with UV light of sufficient energy density.

Key features and benefits of this design are:

• The use of integrated scanning reflective optics todirect and refocus the output of the MALDI UV laser(already employed in the instrument), onto thecontamination to be removed

• Very effective and rapid desorption of the materialfrom the ion optics surface

• Fully automatic efficient source electrode cleaningwithout the need for source removal or venting

• Avoids significant heating of the electrodes or the useof a second (IR) laser, thus preventing shortcomingsassociated with earlier techniques

TrueClean: Novel Automated UV Laser-basedMALDI TOF-TOF Source Cleaning for the MALDI-7090

TechnicalReport

No.MO374

First Edition: May 2013

Kratos Analytical Ltd.Wharfside, Trafford Wharf Road, Manchester M17 1GP, UKPhone: +44 161 888 4400 Fax. +44 161 888 4402URL http://www.shimadzu.com/an/

For Research Use Only. Not for use in diagnostic procedures. The contents of this publication aresubject to change without notice. Shimadzu does not assume any responsibility or liability for anydamage, whether direct or indirect, relating to, or arising out of the use of this publication.

© Shimadzu Corporation, 2013

MALDI-7090: Standard acquisition configuration

In the standard configuration, the UV laser beam isdirected through the large aperture ion optics onto theMALDI sample plate at near-normal incidence.

The plate is imaged using a high-definition colour camerausing high resolution diffraction limited optics.Furthermore, wide aperture optics help to provide anenhanced image of the sample spot.

MALDI-7090: Electrode cleaning configuration

TrueClean source cleaning configuration is initiated bymoving the sample stage and positioning a concavereflector (mirror) close to the ion optic axis. Appropriateadjustment of the laser optics shifts the laser focus suchthat the beam is directed and refocussed close to thesurface of the contaminated electrode by the mirror. Thefocus is optimized to give sufficient energy density todesorb the contamination whilst maximizing the areacleaned. The beam is readily scanned across the electrodeby translating the mirror in the horizontal plane.

TechnicalReport

MALDI-7090 No.MO374

Conclusion

TrueClean provides rapid and very efficient cleaning ofthe electrodes of MALDI-7090 ion source, without theneed for removing the source or venting the sampleanalysis chamber.

The method has been found to be effective in cleaningall common MALDI matrices from electrodes even whenan appreciable layer of contaminant material has beenallowed to build up.

electrodes

sample plate carrier

sample spot

sample plate

desorbed neutralplume

desorbed ionsaccelerated

through apertures

incident UVlaser beam

electrodes

refocussedlaser spot

concavereflector

intermediatelaser focus

sample plate carrier

incident UVlaser beam

Before

After

During

Example of an area cleaned using TrueClean