Invited Paper AS-MoA7
Adventures in Mass Spectrometry Imaging - From Pictures to Words

Monday, October 28, 2013, 4:00 pm, Room 204

The three principal mass spectrometry imaging techniques are secondary ion mass spectrometery (SIMS), matrix assisted laser desorption ionisation mass spectrometry (MALDI MS) and the growing family of ambient mass spectrometries. These powerful techniques allow molecular imaging in 2 and 3 dimensions, from macroscale to the nanoscale and in ambient conditions in real-time. The adage says that “a picture is worth a thousand words”. However, images can be seductive⁽¹⁾ but the interpretation of the picture to words of understanding requires a robust metrology framework.

In SIMS, one of the most important advances has been the use of large cluster ions, most notably, argon clusters to allow 3D imaging with a depth resolution approaching 5 nm. The metrology will be reviewed and recommendations for optimum analysis conditions provided. Important artefacts including the effect of primary and secondary ion on the relative depth position and effects of electron beam damage will be identified. The lateral resolution of SIMS for organics is two orders of magnitude worse, which is insufficient for many important applications such as measuring intracellular drug concentration. Future prospects to meet these challenges will be discussed.

Ambient mass spectrometries, such as desorption electrospray ionisation (DESI) and plasma assisted desorption ionisation (PADI) are relatively new but are growing strongly owing to their ability to analyse in situ. We have recently conducted a VAMAS interlaboratory study on the repeatability and constancy of the relative intensity and preliminary results will be presented. PADI has great promise for the analysis of polymers including depth profiling, however, present PADI sources are limited to the mm range.^.NPL and the University of Liverpool are developing novel sources with an aim to achieve 10 micrometre spatial resolution. Recent developments in PADI metrology will also be highlighted.

MALDI is a popular technique for tissue imaging since large peptides and protiens may be detected. However, the sample preparation results in a complex of the matrix, tissue and analyte. NPL has recently started a new metrology programme to support MALDI MS imaging and progress will be presented.

NPL has recently established a National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI) including all the above techniques. An important objective of the centre is to provide the metrology and standardisation that ensures that pictures do translate to meaningful knowledge.

References:

1. J C Vickerman, Analyst 136, (2011) 2199