ICP–OES or ICP is a common atomic- spectroscopy technique for environmental analysis of water and other samples. To get the atoms in a sample to emit their characteristic frequencies of light, the sample is ionized by plasma generated by the instrument via electromagnetic induction. The plasma torch consists of a radio frequency (RF) coil wrapped around a confinement area through which argon gas flows. Alternating RF current through the coil induces electrical heating in the gas. Temperatures reach thousands of degrees, fully converting the gas into plasma.

ICP is often used to analyze water samples, or dilute solutions derived from soil, food or other materials. A nebulizer converts the sample into an aerosol, and the resulting droplets are introduced into the plasma, which ionizes them. The sample’s molecules decompose into their component atoms, which lose electrons. The atoms recombine and emit the wavelengths of light characteristic of each element. Since all molecules are destroyed, ICP provides a direct measurement of the sample’s elemental composition.

In sequential ICP, the light is detected by a photomultiplier tube (PMT). To scan the complete spectrum, a monochromator separates emitted light so that all parts of the spectrum are presented sequentially to the detector. Some systems have two monochromators and PMTs, with the second system dedicated to UV wavelengths. Comparing the detected wavelengths and their strengths with standard libraries allows the spectrometer to determine the sample’s elemental composition

The most common alternative to sequential ICP uses an array detector, a CCD or CID device, to measure the spectrum simultaneously. Although simultaneous ICP of this type is usually faster than sequential ICP, sequential ICP has higher sensitivity and detection. Sequential ICP also tends to be less expensive than simultaneous ICP. This combination of features makes sequential ICP ideal for environmental testing. Environmental-testing labs, water utilities and government regulatory agencies are the strongest markets for these instruments. While environmental water samples are common, the technique is also used with soils, sludges, slurries, industrial waste and other sample types, such as ore and food.

A number of vendors have left the sequential ICP market and moved entirely to CCD-based instruments, but the market remains steady with several significant vendors. HORIBA Jobin Yvon specializes in high-performance sequential systems with excellent detection levels. Over the past few years, Shimadzu has expanded its business outside Japan. Hitachi High Technologies entered the market via its acquisition of SII Nanotechnology (see IBO 5/31/12). Other participants include Teledyne Leeman Labs, GBC Scientific and Skyray Instrument. The market in 2013 for sequential ICP, including aftermarket and service, was about $65 million.

Sequential ICP at a Glance:

Leading Suppliers

• HORIBA

• Shimadzu

• Hitachi High Technologies

Largest Markets

• Environmental

• Utilities

• Government Testing Labs

Instrument Cost

• $35,000–$100,000