Wavelength Tech Forum: ICP & ICP-MS

The speed of ICP-OES (inductively coupled plasma-optical emission spectroscopy) and the versatility of ICP-MS have made these two techniques invaluable for elemental analysis. The experts on this month's Technology Forum agree that while ICP-OES has been a steady contender in the market for a few years, the relatively new ICP-MS is growing fast. Our roundtable participants are Don Potter, ICP-MS programs manager at Agilent Technologies, Inc.; John Olesik, adjunct associate professor in the department of geological sciences at Ohio State University; Shane Elliott, plasma technologies product manager at Varian, Inc.; and Eileen Skelly Frame of Full Spectrum Analytical Consultants.

The opinions expressed here are solely those of the participants.

Could you give us a comparison of the ICP-OES and ICP-MS markets right now? How have they changed in recent years?

(Potter) The ICP-OES market is more mature than the ICP-MS market. This is reflected in the comparative growth rate of the markets and in the rate of development of the two technologies. The worldwide ICP-OES market growth is essentially flat, while the ICP-MS market has shown consistent growth over the past 10 years and will continue to do so until a new or different elemental analysis technique comes along. Over the past five years, the rate of adoption of ICP-MS by routine labs has increased at the expense of ICP-OES and GFAA. This shift will continue. The application range of ICP-MS has also expanded, especially by the growing need for speciation analysis.

(Elliott) The worldwide ICP-OES market has been relatively flat over the last 3-5 years. There has been a shift towards solid-state detector (SSD)-based systems, while sequential systems are becoming less popular. This shift is due in large part to the speed and flexibility of solid-state systems. The ICP-MS market has been growing strongly over the past 3-5 years, with growth in the 10-15% p.a. range. Some of this growth has been due to lower regulatory limits for trace element detection that ICP-OES struggles to meet. New technology in the form of interference management devices has also been a catalyst in this growth rate.

(Frame) ICP-OES and ICP-MS markets have changed in recent years, with moves in many commercial and environmental labs away from slower, single element AAS to SSD-based ICP-OES systems for their dirty samples (high dissolved solids solutions) and collision cell technology-based ICP-MS systems for clean samples. The ICP-OES market can be considered to be more mature than the ICP-MS market, but the growth rates are not too different. The rapid multi-element capability of ICP-OES and ICP-MS, coupled with detection limits equal to or better than GFAAS, provides the high throughput and lower cost per sample required by these laboratories.

Have there been any major changes in ICP systems or technology in the past five years? Do you think there is still room for improvement in ICP systems?

(Potter) There hasn't been much change in ICP-OES technology, which is now a mature technique. It is unlikely there will be any significant improvement in ICP-OES sensitivity or selectivity in the future, though there will be some improvements in size and usability (software). ICP-MS advanced significantly with the development of collision/reaction cell (CRC) systems over the past five years and the full impact of this has not yet been realized. These systems now account for about 80% of all ICP-MS sold, and they are replacing ICP-OES and especially GFAA instrumentation in many labs. Even so, there is plenty of room for improvement in ICP-MS capabilities.

(Olesik) Most ICP-OES instruments now use imaging detectors. Over the past five years, the major change in ICP-MS instruments has been their ability to reduce spectral overlaps by either the use of CRC systems or a sector field mass spectrometer. Although ICP-based instruments are among the most successful ever, there is certainly room for improvement.

(Elliott) The fundamental technology used in ICP-OES systems has remained relatively unchanged over the past five years. There have been improvements in speed and software systems, but the core technology has remained largely unchanged. Further enhancements in speed and throughput have been realized in the area of sample introduction and wash out through the use of switching valves and other productivity enhancing accessories. Of course, there is always room for improvement. Continuous improvements in speed will come, although gains will be minimal. Some improvements in detection capability and wavelength coverage are also probable.

(Frame) New optical designs in ICP-OES spectrometers from different manufacturers have greatly increased light throughput to the detector. This allows the attainment of LODs equal to those of axial plasmas using radial plasmas, with their ability to handle higher dissolved solids without the interferences associated with axial viewing. There is always room for improvement in the sample introduction system, although many innovations have been introduced over the past few years.

This month, the EPA introduced new regulations for Arsenic testing, stating that only GFAA, hydride AA, and ICP-MS will be suitable for arsenic measurement in drinking water. How do you think this will affect the ICP-MS market? Or will it?

(Potter) There won't be a huge immediate impact since most environmental labs in the U.S. are already using ICP-MS for arsenic. However, this shows that ICP-MS is becoming the predominant technique for metals analysis, and this will continue as regulated limits decrease and as ICP-MS technology further improves.

(Olesik) Many environmental labs that measure arsenic probably have one of these techniques already, although the new regulations could lead to some additional ICP-MS purchases.

(Elliott) This will have some effect on the ICP-MS market, but the effect will not be as dramatic as some think.

Environmental testing has been a predominant application for ICP. What makes ICP such a good tool for this application?

(Potter) Undoubtedly it is the high sample throughput of both ICP-OES and ICP-MS. While ICP-OES has the additional advantage of being more rugged and easy to use, ICP-MS has better detection limits. Beyond that, CRC-ICP-MS offers better quantitation in high matrix samples, though as yet there are no CRC-specific EPA methods.

(Olesik) Once the method details and QC protocols are worked out for a particular type of sample, the ICP techniques are fast, accurate, sensitive, and selective for multi-element analyses of similar samples.

(Elliott) In addition to the speed of modern simultaneous ICP-OES instruments, the technique is robust and stable, has a good dynamic range, and adequate detection limits for the majority of environmental applications.

(Frame) ICP-OES is an excellent tool for environmental applications, compared to AAS, because of its multielement capability, permitting rapid analyses and high throughput. ICP-OES can handle samples with much higher dissolved solids than can ICP-MS, so it is certainly useful for any environmental application other than drinking water. The high dynamic range of ICP-OES permits analysis of everything from ultratrace to major analytes without the dilutions often required by ICP-MS.

In the future, do you see ICP retaining its importance in the environmental field? Are there other applications that ICP might see more use in?

(Potter) I don't see any new technique on the horizon that is going to replace ICP-OES or ICP-MS in any industry. To some extent, ICP-MS will continue to replace ICP-OES instruments in all industries, although there will always be a place for ICP-OES. Also, CRC-ICP-MS will capture much of the high-end GFAA market over the next few years.

(Olesik) ICP-OES and ICP-MS will certainly continue to be important for environmental analysis. There has been a lot of talk about the need for speciation in addition to elemental analysis; it remains to be seen how large this application will become and the exact role of ICP. Recently, there have been exciting new reports of ICP-MS for biological applications. Improved ability to measure S and P by ICP-MS, the potential use of metal tags, and compound-independent element sensitivity make ICP-MS ideal for quantitation, which is a challenge for molecular MS. So ICP-MS can be complementary to molecular MS for biological applications.

(Elliott) In the short to medium term, ICP-OES will remain an important tool in the environmental field. Emphasis on lower regulated detection limits will drive the market more to ICP-MS in the medium to long term, but the speed and robustness of ICP-OES will mean that you will see ICP-OES instruments in environmental labs for a long time. ICP-OES will continue to grow in the traditional AAS industrial markets such as manufacturing, chemical/petrochemical, and metals/mining.

(Frame) ICP-OES will certainly retain its importance in the environmental field because of its ability to handle dirty samples. It could improve its position with respect to ICP-MS even more, especially for industrial applications, if the ICP-OES manufacturers follow the increasingly common marketing of an integrated chromatography system for speciation using the ICP-MS as an element-specific detector, especially for As speciation. ICP-MS will continue to grow in the semiconductor industry, where its low detection limits are required.