Mass spectrometry enables molecules to be imaged with high sensitivity, specificity and in a label-free manner. Mass spectrometry images are also rich in information and can be a useful guide to the location of molecules in a sample. However, the technique does have its pitfalls; one of which is the matrix effect. Matrix effects in secondary ion mass spectrometry (SIMS), a significant issue, have been investigated by researchers from the National Physical Laboratory (NPL; UK).
In most cases an increased intensity in an image correlates to an increased concentration of that molecule in the sample; however, sometimes this is not true. The reason for this is the matrix effect.
The matrix effect is possibly the most significant unresolved issue in SIMS. To investigate the effect, the NPL has generated mixed reference materials of well-known composition and studied them using SIMS.
In their work, the scientists from the NPL describe the production and SIMS analysis of binary mixtures of organic thin films, for which the total composition was known with reasonable certainty. It was demonstrated that it is possible to establish the magnitude of the matrix effect in said mixtures using thin layers of one material inside another.
The team also studied films of known composition using mixtures comprising of Irganox 1010, and one or another of Irganox 1098 and Fmoc-pentafluoro-l-phenylalanine. Their findings showed that the first mixture displayed a small, but significant, matrix effect and very strong effects in the second mixture.
It is hoped that this work will increase our understanding of how to extract reliable compositional data from imaging mass spectrometry, and help us understand how the matrix effect may be turned to some use.
Sources: Shard AG, Spencer SJ, Smith SA, Havelund R, Gilmore IS. The matrix effect in organic secondary ion mass spectrometry. Int. J. Mass Spectrom. 377(1), 599—609 (2015); What does my image really mean?