The Beginner’s Guide to ICP-MS
You’ve convinced your boss that your laboratory absolutely needs a shiny new quadrupole-based, inductively coupled plasma mass spectrometry (ICP-MS) system for trace element analysis. Now what?
There are a number of excellent commercial ICP-MS systems on the market – all with very similar specifications – so how do you choose the one that best fits your application needs? How do you go about comparing the different designs, hardware components, and performance factors, all of which are of critical importance in the decision-making process?
First, it’s very important to decide what your objectives are, particularly if you are part of an evaluation committee. You can have more than one objective, but they must be clearly defined. Every laboratory’s application demands are unique, so it is important to prioritize before you begin the evaluation process. Capability, usability and reliability are the areas that I feel require particular focus, so let’s take a closer look.
The major reason that the trace element community was attracted to ICP-MS over 30 years ago was its extremely low multielement detection limits. Other multielement techniques, such as inductively coupled plasma optical emission spectrometry (ICP-OES), offered very high throughput but could not achieve ultratrace levels. Even though graphite furnace atomic absorption (GFAA) spectrometry offered much better detection capability than ICP-OES, it did not offer the sample throughput. In addition, GFAA was predominantly a single-element technique and was therefore impractical for carrying out rapid multielement analysis.
These limitations quickly led to the commercialization of ICP-MS as a tool for rapid ultratrace element analysis. However, there are certain areas where ICP-MS is weak. For example, dissolved solids for most sample matrices must be kept below 0.2 percent; otherwise it can lead to serious drift problems. So in applying ICP-MS to real world samples, it’s important to be aware of how different instrumental designs handle these limitations. There are a number of common performance metrics that can be used to measure the capability of an ICP-MS, including:
- Detection limit
- Sensitivity
- Accuracy/Precision
- Long-term stability
- Dynamic range
- Interference reduction
- Sample throughput
Once again, the importance of each metric is dependent on your laboratory’s application needs. Is detection limit performance at the top of your list? Or perhaps the instrument will be used to generate revenue, in which case sample throughput is of greater importance.
Analytical performance is clearly a very important consideration; however, the vast majority of instruments in use today are being operated by technician-level chemists, who may have some experience in the use of AA or ICP-OES, but in no way could be considered ICP-MS experts. Therefore, the usability aspects might be competing with performance capability as the most important selection criteria, particularly if the application does not demand the ultimate in detection limits. Even though usability is dictated by the expertise of the operator, there are some factors that need to be considered. They include, but are not limited to:
- Ease of use
- Routine maintenance
- Sampling accessory compatibility
- Installation requirements
- Technical support and training.
Good instrument reliability is taken for granted nowadays, but it has not always been the case. When ICP-MS was first commercialized, the early instruments were a little unpredictable, and quite prone to breakdowns. However, as the technique became more mature, the quality of instrument components, and hence the reliability, improved. You should therefore be aware of the instrument components that are more problematic than others. This is particularly true when a brand new instrument has been introduced or a model has had a major redesign. In the life cycle of a newly designed instrument, the early years might be more susceptible to reliability problems than when the instrument is more mature.
One final point: it’s very important that you talk to real users in your application field; their experience – and even failures – can also guide you. For further help, you could read my book (1) or join me for my short course at Pittcon:
Pittcon Short Course 58: “How to Select an ICP-Mass Spectrometer: The Most Important Analytical Considerations”, 8:30am-12:30pm, March 10, 2015.
- Robert. J. Thomas, “Practical Guide to ICP-MS: A Tutorial for Beginners”, (3rd Edition; ISBN 978-1—4665-5543-3, CRC Press, FL).
Robert (Rob) Thomas was raised in the mining and industrial communities of South Wales in the UK in the 1960s, where social activities revolved around playing rugby, drinking beer and complaining about the incessant rain! When he finally graduated from Gwent College of Technology, with a graduate degree in chemistry in 1973, he realized there was a bigger world out there and ventured out to experience the bright lights and gold paved roads of the London area, where he ended up working for a US-based analytical instrumentation company. He spent 10 years learning how to communicate with the English-speaking world and applying his chemistry knowledge to the field of Atomic Spectroscopy.
The parent company soon learned of his immense skills and transferred him to Connecticut, USA, in 1987, where he eventually ended up specializing in the field of ICP-MS. Along the way he has become a Fellow of the Royal Society of Chemistry (FRSC) and also a Chartered Chemistry (CChem). He is accredited with over 70 publications on analytical chemistry and 3 textbooks on ICP-MS. For the past 13 years he has been principle of his own consulting company, based in Gaithersburg, MD.
