Wavelength Tech Forum: ICP and ICP-MS

This month’s Technology Forum looks at the topic of ICP and ICP-MS and the trends and issues surrounding it. Joining us for this discussion are Julian Wills and Karen Harper, with Thermo Fisher Scientific; Timothy J. Alavosus, with VHG Labs; Vanaja Sivakumar, with SPEX CertiPrep; and Kenneth Neubauer, with PerkinElmer.

How has the solid-state detector changed the industry?

(Wills/Harper) The introduction of the solid state detector was revolutionary in terms of speed of analysis, available wavelengths and flexibility. No longer does the analyst have to specify how many PMT channels they require and second-guess what analysis they may need to do for the future.

(Alavosus) The solid state detector has had a tremendous impact on the industry. Available in a relatively wide arrangement of resolution and imaging configurations, each instrument manufacturer has been able to select the type of detector that best fits the design of their instrument.

The original detector used in commercial ICP applications was the photomultiplier tube (PMT). The PMT had the advantage of a wide dynamic range and excellent sensitivity, but due to size constraints, only a limited number of analyte wavelengths could be analyzed simultaneously on an ICP spectrometer (about 60-65 total wavelengths). While other instrument configurations allowed sequential analysis of virtually an unlimited number of wavelengths, these methods were very slow and impractical for the use of large numbers of wavelengths.

Thus many labs faced a compromise when using ICP: If they routinely analyzed a fixed number of elements in consistent sample matrices, they could select a simultaneous spectrometer for high sample throughput. However, they could not add an additional element or wavelength without a great deal of effort in changing the configuration of the spectrometer and adding an additional photomultiplier tube. If instead the lab analyzed many different elements in a wide variety of sample matrices, they would typically select a sequential instrument configuration. Again, though, this would greatly limit sample throughput, never realizing the speed of a simultaneous instrument.

The advent of the solid-state detector essentially ended the speed vs. versatility dilemma (and pretty much retired the PMT, as well). The nature of the design of most solid-state detectors allows the operator to select virtually any wavelength for any (ICP) element. Multiple wavelengths can be analyzed and saved for each element. This can be especially useful for overcoming matrix and related effects, and allows for the analysis of even the most complex materials.

Further, many the design of many instruments allows for the post-processing of data, so that even wavelengths that were not originally selected with the analytical method may be added later, without the need for re-analysis of the sample. This functionality is truly remarkable from the analyst’s viewpoint, as a lost, expired, or simply used-up sample can be re-processed without the need for the actual material.

(Sivakumar) Introduction of solid-state detectors has increased the speed of analysis while allowing flexibility. Inter-element or background corrections can be made easily. Also, it is easier to select another line where the corrections are not critical. There is less variation and more reproducibility of output.

(Neubauer) The solid-state detector in ICP has redefined the field. There are virtually no PMT-based instruments available. They have greatly expanded ICP capability and usefulness over classic instrumentation.

What applications can ICP have in the consumer field?

(Wills/Harper) Almost every consumer field is touched by ICP these days, from monitoring the water we drink, the air that we breathe, to the food chain from soil assessment to final product. You can find ICP in the oddest places too, like your local DIY shop – where ICP has been used to test the quality of the metal used to manufacture nails, the toxic elemental content of the paint, and the ink used to print the receipts. It is pretty hard to find an area that doesn’t require elemental analysis along any part of its life cycle.

(Alavosus) I guess I don’t consider ICP a consumer-type of product. It is used by laboratories to enhance their efficiencies over slower techniques such as Atomic Absorption. If the question instead relates to general applications of ICP, they are quite numerous, and include environmental testing (water, soil, etc.); the analysis of new and used oils; food analysis; the analysis of metals and alloys; and much more.

(Sivakumar) With the advent of sophisticated software, improvement in the methodology, and detection limits, more and more industries can adopt better screening methods for trace elements and precise quality control. Instrument set-up conditions can be easily designed to tackle varying degree of sensitivity from element to element to suit the task. It is the instrument of choice for various applications.

(Neubauer) ICP’s have become the technique of choice for many consumer applications, food, fuels, base metal quality control, while many environmental applications and product safety (lead in paint for example) remain ones best done via an ICP.

What impact has ICP had on the environmental industry?

(Wills/Harper) ICP (both optical and MS) has made a huge impact in aiding analysts to monitor and detect all types of environmental samples in a fast and precise manner. Their multi-element advantage has allowed older, labor-intensive techniques to be made redundant whilst offering an increase in sensitivity and reliability.

(Alavosus) The US EPA requires the analysis of 21 elements for drinking water analysis (method 200.7); certain other commonly-used methods such as the Research Conservation and Recovery Act (RCRA) requires 7; EPA method 6010 includes well over 20 metals analyzed with ICP. Without ICP, these metals would have to be analyzed with atomic absorption, which, even with today’s automated instruments, is a painfully slow technique.

(Sivakumar) Since measurements can be done faster and with more accuracy, it is easier to support the results/findings with confidence. With enhanced sensitivity for elements like arsenic and selenium, ICP could replace more cumbersome techniques like graphite AA, and the techniques that depend heavily on operator skills.

(Neubauer) Until the success of ICP-MS, ICP-OES was the technique of choice for the majority of environmental applications. Virtually every lab making these measurements started with an ICP-OES. It was their workhorse instrument and its profits made many labs successful.

In your eyes, is ICP-OES or ICP-MS the better technique?

(Wills/Harper) It absolutely depends on the application; there are definite applications, such as clinical where ICP-MS excels, whereas for matrix-heavy applications such as metallurgy, my first choice would be ICP-OES. Across other applications however, ICP-OES and ICP-MS share the stage quite well, such as environmental applications which are equally suited to either technique.

(Alavosus) They are different techniques. ICP-MS has a couple of orders of magnitude better sensitivity over ICP-OES. However, it is limited to much “cleaner” samples (i.e. having less total dissolved solids and less complex matrices). So, the tradeoff is that ICP-MS can see lower levels of materials, but the original sample often must be diluted to get you there. It is also a somewhat less user-friendly technique than ICP-OES. When you get down to it, though, they both have their place in today’s lab, probably on equal footing. However, almost all analytical labs will purchase an ICP-OES system long before an ICP-MS, due largely to the sheer simplicity of analysis with the former.

(Sivakumar) It depends on the task. When elements are present at ppm level concentrations, it is better to use ICP. When determining at ppb or ppt level, obviously ICP-MS is preferred. Since ICP-MS requires clean room conditions for sample prep and more dilutions, it is time consuming.

(Neubauer) They are complementary. The ICP-OES is the choice until your detection requirements fall in which case you would use an ICP-MS. The tradeoff is that ICP-MS instruments are more challenging to use. Most labs use their ICP when samples permit and the ICP-MS is reserved for applications that require its performance. Another area where ICP-OES is preferred is in the analysis of high-matrix samples, such as brines and metallurgical samples. However, recent advances in sample introduction have made high-matrix sample analysis easier with ICP-MS.

What developments on the horizon in ICP have you most intrigued?

(Wills/Harper) With optical ICP, the trend seems to be leaning towards accessories now, and we have been having lots of fun playing with lasers and other solid sampling techniques of late, although I believe that they need some work in the automation field to bring them into the lab as an everyday technique. For ICP-MS, the introduction of advanced technologies (i.e. collision cell and high mass resolution) has finally fulfilled the technique’s promise of true interference-free, multi-elemental trace elemental analysis. This detection capability is becoming of increasing interest as a complementary source of information in life science applications for example in ‘tagging’ individual proteins with a trace element that can subsequently be detected by ICP-MS.

(Alavosus) The detectors can still evolve a bit more, getting better sensitivity and allowing better resolution of spectral overlap. I am very impressed at high-speed autosampling methods that are currently coming into maturity. This is critical for today’s high-throughput lab – since profit margins are usually quite low per sample, labs must be able to put through more and more volume without sacrificing performance. Evolution of detectors will also lead to smaller and smaller instrumentation, which is certainly exciting compared to the original 1-meter systems that were extremely large in size, in some cases as big as three refrigerators put together.

Finally, I would like to see some enhancements in sample introduction. For example, in the analysis of oil-based materials, it is often difficult to analyze sulfur. That is because if samples are composed of different matrices with different volatilities, a rather extensive wash-out period is often required to ensure that the samples are behaving similarly in the plasma. Special water-cooled spray chambers are often used to address this, but with varying degrees of success.

(Sivakumar) Continued advancements on the (digital configuration of) detector and the power supply allow lower detection limits, improve reliability, and reproducibility.

(Neubauer) Productivity improvements – faster throughput and greater data reliability.

What do you think?

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