Arc/spark spectroscopy is one of several atomic spectroscopy techniques that rely on optical emission spectroscopy (OES). The principle behind these techniques is to excite the atoms in the sample so that they emit their characteristic frequencies of light, which can be analyzed by the spectrometer to identify the individual elements present in the sample. With a well-designed and calibrated system, quantitative analysis can be performed, providing the elemental composition of the sample.

In arc/spark OES, the excitation energy is provided by an electrical discharge: a brief spark or a continuous arc of current. Since metals are excellent electrical conductors, arc/spark spectroscopy is very convenient for the analysis of metal samples. The other main sample type is oils from engines, which are analyzed for traces of wear metals, particulates and other contaminants that may indicate engine wear. Similar analyses can be carried out for hydraulic fluids or refrigerants. Liquid samples generally make use of rotating disc electrode systems, while metal analysis is generally simplified by allowing the metal sample to act as one of the electrodes. Although standard lab systems tend to offer the best analytical performance, the utility of being able to carry out analysis outside the lab has helped make mobile and portable arc/spark systems an important technology.

Most mobile systems are quite rugged and can be operated in demanding conditions in the field or a foundry. While some lack the full functionality of a lab system, others include more advanced options, such as the ability to use argon gas to eliminate potential interferences from analysis in air. Systems range in size from portable benchtop-style units that can be carried to larger units typically mounted on wheeled carts. Most systems have a tethered handheld analysis probe for ease in bringing them to the sample.

Arc/spark has applications at every stage in the life cycle of metals. At foundry and die casting factories, mobile arc/spark is useful in process control. Consumers of metal products may use arc/spark to verify that the correct alloy is present in the product. Certain industrial or military applications require highly specific alloys. Finally, scrap metal is commonly tested with arc/spark to allow proper sorting and recycling of materials. The aforementioned oil analyzers are typically used by military customers to maintain their vehicle fleets or by managers overseeing industrial machinery and vehicles.

Spectro Analytical was the first manufacturer to offer mobile arc/spark systems about 30 years ago. The company has a market share of about 50%. Oxford Instruments, the second-largest mobile arc/spark manufacturer, acquired Metorex (see IBO 9/15/04) and Worldwide Analytical Systems (see IBO 7/31/07) in the mid-2000s; both companies offered mobile and lab arc/spark systems. The total market for mobile arc/spark systems reached $39 million in 2010.

Mobile Arc/Spark Spectroscopy at a Glance:

Leading Suppliers

• Spectro (AMETEK)

• Oxford Instruments

• Arun Technology

Largest Markets

• Metals

• Recycling

• Wear analysis in oil

Instrument Cost

• $20,000–$100,000