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Inductively Coupled Plasma (ICP) and LECO (Combustion Analysis and Inert Gas Fusion) testing are the leading industry methods for testing the elemental composition of metals, ceramics, and other materials.

Each brings a unique capability to accurately and repeatably generate reliable testing results on various materials. When used in conjunction, however, they allow manufacturers and engineers to see the whole spectrum of elements from bulk to trace levels, increasing confidence and trust in their products.

“ICP and LECO testing are invaluable for engineers and manufacturers due to their ability to comprehensively and precisely determine the composition of a variety of materials,” said Dr. Ross Cunningham, Director of Science and Technology at NSL Analytical. “These rapid, robust tests enable enhanced quality control and assurance at every stage of the production cycle, from raw materials to end products.”

What Are the Methods and Principles Behind ICP Testing?

Depending on the required detection range (the percent of an element of interest, from bulk to ultra-trace), ICP testing utilizes one or both of two techniques to precisely detect and measure elements in a wide range of materials. If the sample is initially solid, it is first dissolved in an acid to form a liquid solution. Each technique involves vaporizing, atomizing and ionizing the liquid sample by injecting it into an argon plasma formed by a radio frequency generator, known as an Inductively Coupled Plasma, or ‘ICP’.

Optical Emission Spectroscopy (ICP-OES), otherwise known as Atomic Emission Spectroscopy (ICP-AES) operates on the principle that excited atoms emit light at specific characteristic wavelengths. In this technique, the liquid sample is injected as an aerosol into the plasma, where the intense heat vaporizes the sample and ionizes the atoms therein. When the ions return to their ground state, they release the energy as photons of light, whose intensity is measured with photomultiplier tubes (PMTs) or charge-coupled devices (CCDs). The wavelength of an emitted photon is characteristic of the specific element, while the intensity is proportional to its concentration. This allows for accurate, quantitative analysis of a wide spectrum of elements simultaneously.

Mass Spectrometry (ICP-MS) combines the high-temperature ionization capabilities of ICP with mass spectrometer detection. It is similar to ICP-OES in that the sample is introduced into an argon plasma to be atomized & ionized, but is unique in that this method directly measures the ions the plasma produces.

(NSL was the first commercial lab to put in ICP Mass Spectrometry – all the way back in 1994.)

The charged ions are then extracted through an interface (typically a pair of water-cooled cones) and directed through ion optics (electrostatic lenses) that guide the ions into a mass analyzer where the ions are separated and measured based on their mass-to-charge ratio, or m/z value. The signal generated is directly proportional to the relative concentration of the element in the sample, which is converted to a concentration by comparing it to a calibration standard of a known value.

How Does LECO Testing Work in Elemental Analysis?

While powerful in its breadth of elements and range of detection limits, ICP is not capable of detecting all elements. This is where LECO testing comes in, which is the common brand name of equipment for methods that utilize Combustion Analysis or Inert Gas Fusion to identify specific light elements in a sample that are generally not measurable with ICP, namely for C, S, O, N and H.

Combustion analysis heats a small sample to a high temperature in an oxygen-rich environment, converting Carbon and Sulfur into their gaseous oxides, like CO₂, which are measured using an infrared absorption detector (NDIR).

Inert gas fusion heats the sample in an inert atmosphere like helium or argon to release nitrogen, oxygen, and hydrogen, which are then processed through a series of catalysts, detectors, and scrubbers to independently analyze the constituent elements.

Why Are ICP and LECO Testing So Valuable to Manufacturers?

Simply put: they are the gold standard of elemental testing for quality control.

“These testing methods ensure that the raw materials and finished products meet precise specs for elemental composition,” Cunningham said. “This is a key consideration for performance critical industries like aerospace and defense, automotive, and medical devices, because in today’s world we are constantly demanding more from our materials, and even the smallest out-of-spec variations in trace elements like carbon or sulfur content can impact the material’s properties and fitness-for-use, ultimately undermining the safety or performance of the product.”

Accurate and repeatable elemental analysis allows manufacturers to meet strict compliance and specification targets through each stage of the product lifecycle, whether it’s R&D, quality assurance or failure analysis. While invaluable in making sure elements are present in the appropriate concentrations in alloys and materials, they are equally useful in ensuring contaminants like oxygen or sulfur in alloys or dangerous elements like lead are absent or below dangerous levels for medical or consumer-facing products.

While there is no one-stop-shop test that covers all elements, as ICP and LECO each specialize in detecting different element types, utilizing both techniques gives you the complete picture of your material to boost confidence in your product and assure it meets all quality specifications.

Looking to dive deeper into how third-party testing can support your unique advanced material testing needs? Check out the resources below:

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NSL Analytical Services, Inc. is an independent materials testing lab that specializes in metallurgical, mechanical, chemical, and optical testing for mission-critical industries.

Contact our experienced, accredited team to discover how we can deliver accurate, repeatable testing results with lightning-fast turnarounds, giving you confidence in your material performance and adherence to quality standards and regulations.