Laser ablation (LA) in combination with inductively coupled
plasma
time-of-flight mass spectrometry (ICP-TOFMS) enables monitoring of
elements from the entire mass range for every pixel, regardless of
the isotopes of interest for a certain application. This provides
nontargeted multi-element (bio-)imaging capabilities and the unique
possibility to screen for elements that were initially not expected
in the sample. Quantification of a large range of elements is limited
as the preparation of highly multiplexed calibration standards for
bioimaging applications by LA-ICP-(TOF)MS is challenging. In this
study, we have developed a workflow for semiquantitative analysis
by LA-ICP-TOFMS based on multi-element gelatin micro-droplet standards.
The presented approach is intended for the mapping of biological samples
due to the requirement of matrix-matched standards for accurate quantification
in LA-ICPMS, a prerequisite that is given by the use of gelatin-based
standards. A library of response factors was constructed based on
72 elements for the semiquantitative calculations. The presented method
was evaluated in two stages: (i) on gelatin samples with known elemental
concentrations and (ii) on real-world samples that included prime
examples of bioimaging (mouse spleen and tumor tissue). The developed
semiquantification approach was based on 10 elements as calibration
standards and provided the determination of 136 nuclides of 63 elements,
with errors below 25%, and for half of the nuclides, below 10%. A
web application for quantification and semiquantification of LA-ICP(-TOF)MS
data was developed, and a detailed description is presented to easily
allow others to use the presented method.