Mass spectrometry images provide a wonderful means of visualising molecules with high sensitivity, excellent specificity and in a label-free manner. They are rich in information and useful as a guide to the location of molecules in a sample.
However without a full understanding they can sometimes lead people astray. The most common pitfall is to believe that an increased intensity in an image is always due to an increased concentration of the molecule in the sample. More often than not this is true, occasionally however it is decidedly false. The culprit is the notorious and badly understood 'matrix effect'.
To investigate this effect, ISAC's partners at the
National Physical Laboratory (NPL) have generated mixed reference materials of well-known composition and studied them using SIMS. Some of the ions, such as fluoride ions, have an intensity proportional to the composition. Others do not, such as acetate ions which arise from the second component in the mixture. NPL's work, published as an invited paper in a special issue of the International Journal of Mass Spectrometry entitled 'MS 1960 to Now' is the first serious investigation of the matrix effect in organic secondary ion mass spectrometry.
This work will lead to a greater understanding of how to extract reliable compositional data from imaging mass spectrometry, as well as understanding how the infamous matrix effect might be turned to some use. For example, the researchers point out that different ions display different matrix effects and this could be used to identify nanoscale phase separation of materials in secondary ion mass spectrometry. Watch this space!
Read the full paper:
The matrix effect in organic secondary ion mass spectrometry Find out more about NPL's
National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI)
Posted on Thursday 2nd July 2015