The perspective below was published in the Spectroscopy 35th Anniversary Issue, June, 2020.
icpTOF product manager, Dr. Martin Tanner, responded to the question:
WHAT ARE THE MOST IMPORTANT QUESTIONS THAT WILL BE ANSWERED, OR NEED TO BE ANSWERED, BY MASS SPECTROMETRY IN THE NEXT 5 YEARS?
Trace inorganic analysis with inductively coupled plasma mass spectrometry (ICP-MS) will continue to become more ‘organic’ over the coming years. Simultaneously, mobile ICP-MS platforms will need to be developed to address an increasing number of environmental questions outside of the laboratory.
ICP-MS is widely used as a trace metal detector for environmental and geological research and in the pharmaceutical and semiconductor industries. Biological and medical research have recently emerged as new frontiers for inorganic trace analysis, where ICP-MS is increasingly used for characterization of single cells and imaging of tissue samples.
Advances in ICP-MS sensitivity and the ability to simultaneously measure many analytes at high-speed have enabled multi-element analysis of individual nanoparticles and cells. Single particle ICP-MS is now routinely used to measure natural metal content in individual biological cells. With the help of antibodies and metal labels, single particle ICP-MS can even characterize the type and state of cells based on bio-molecular properties. In comparison to optical systems, the use of isotopically pure metals instead of fluorescence markers multiplies the number of parameters than can be simultaneously measured.
Developments in laser ablation technology have further expanded the spectrum of trace-element, biological analyses based on ICP-MS. Owing to reduced dispersion of ablated material, single laser pulses are now recorded by the MS as transient signals lasting only a few milliseconds. This allows operation at high laser frequency and with ever smaller spot sizes. High-resolution, two-dimensional images of biological tissue can now be measured in relatively short times (e.g., 1 megapixel in 3 hours), making it practical to develop high-throughput experimental workflows.
Spatial resolution of individual cells in a thin tissue section requires laser spot diameters of 1 micrometer or smaller. The sample volumes removed at these resolutions are correspondingly minute. Recent increases in MS sensitivity allow measurement of the distribution of elements in cells by LA-ICP-MS. Interaction of metals in tissues as in platinum chemotherapy can be studied, and natural elements and even bio-molecules can be detected through specific antibody-based metal labelling.
ICP-MS analysis has gained its popularity because of advantages in detection power and selectivity. However, X-ray, electron, and ion beam sources have also evolved and will likely continue to be important tools. Ever increasing computing power allows for better calculation of complex matrix effects caused by interactions of the source beam and the generated photons with the sample matrix, improving quantification and speed of analysis. The next few years will show how photometric and mass spectrometric methods will be used complementarily. With its advantages, however, inorganic MS will certainly claim an important role in biological analysis.
ICP-MS instruments have been on the market for almost 40 years and have become a staple in laboratories around the world. While many other methods have been successfully moved from the laboratory into the field, ICP-MS has not yet made the leap. With current high interest in trace elemental analysis in the environment, the moment is right for this important development. From measuring small particles with high metal content created in combustion processes to analyzing brake dust having respirable particle sizes, there is intense need for real-time measurements of small inorganic particles at their sources.
Mobile LA-ICP-MS will also benefit the characterization of uranium waste produced in energy generation. Only ICP-MS currently offers the potential to provide accurate results in a short time and with high detection power to examine such nuclear waste on site and characterize it for final disposal. With a mobile ICP-MS, transports of active samples to external laboratories could be avoided. Direct detection and monitoring would as well be available on-site after nuclear accidents.