In 1961, the American inventor Thomas Reed invented the inductively coupled plasma (ICP) torch. By using a radiofrequency magnetic field, Reed's device could fully atomize a sample introduced to it in the form of an aerosol. Unbeknownst to Reed, he had invented what would soon become one of the most valued pieces of spectroscopic equipment in the world. Around 20 years later, the ICP torch would transform analytical chemistry by enabling two techniques: ICP mass spectrometry (ICP-MS) and ICP atomic emission spectroscopy (ICP-AES).1
ICP-MS and ICP-AES use an inductively coupled plasma (typically argon) to atomize and ionize a sample. In practice, this is accomplished through a fairly complex array of spectroscopic equipment. In ICP-MS, this spectroscopic equipment is used to "skim" off some of the ionized sample for injection into a mass spectrometer. In ICP-AES, different spectroscopic equipment is used to analyze the optical emissions of atoms and ions in the sample.
Below is a rundown of the key pieces of spectroscopic equipment used in an ICP setup.
Nebulizers for ICP
Typically, ICP techniques start with a liquid sample. Nebulizers are a key piece of spectroscopic equipment, used to convert liquid samples into aerosol form to be introduced to the plasma. "Pneumatic” nebulizers are a particularly common piece of spectroscopic equipment, using a high-speed flow of gas (again, usually argon) to disperse the liquid into a fine mist. Ultrasonic nebulizers provide an alternative approach, using high-frequency acoustic waves to break up the sample – these are typically more expensive than pneumatic spectroscopic equipment but can produce better results.
Humidifiers for Spectroscopy
Ordinarily, dry argon gas is used as a nebulizer gas. However, when using samples with very high total dissolved solids (TDS), this can result in “salting out” – the formation of salt crystals on various parts of the spectroscopic equipment. A humidifier is used to introduce moisture into the nebulizer gas before it reaches the sample, which can reduce the formation of salt deposits at the nebulizer and injector tips.
Spray Chambers for ICP
Spray chambers are another piece of spectroscopic equipment used to prepare the sample for ionization. They are used to filter out larger droplets from the aerosol produced by the nebulizer, giving control over the size distribution and improving precision. Often, nebulizers, humidifiers and spray chambers will be integrated into a single piece of spectroscopy equipment known as a sample introduction kit.
ICP Torch
The ICP torch is the central piece of spectroscopic equipment in any ICP-MS or ICP-AES setup. Consisting of three concentric quartz tubes, the ICP torch is where the ionization of argon forms the plasma itself (or, less commonly, helium) gas. With plasma temperatures approaching 10,000 Kelvin (hotter than the sun's surface), this piece of spectroscopic equipment must use a cooling layer of argon gas to prevent the torch itself from melting. In the center of the torch, the aerosolized sample is introduced to the argon plasma, causing almost complete atomization and ionization of the sample.2
RF Coil
A radiofrequency (RF) coil is the driving force behind plasma creation in the torch. It uses high-frequency magnetic fields to effectively rip apart argon atoms, separating electrons and atomic nuclei to create a plasma.
Interface Cones
Interface cones are possibly the most important pieces of spectroscopic equipment in any ICP-MS system.3 They perform the challenging task of sampling a representative selection of analyte ions and transporting them into the ion optics within the mass spectrometer. Sampler and skimmer cones are precision pieces of spectroscopic equipment, and your choice of interface cone should be carefully considered.
Accessories
The process of converting a liquid sample into an aerosol, fully ionizing it, sampling analyte ions and transporting them into a mass spectrometer is far from straightforward.3 A number of auxiliary pieces of spectroscopic equipment are required to shepherd aerosol, gas and plasma through an ICP system: these include all manner of o-rings, seals, tubing and connectors.
Delta Scientific is a world-leading provider of ICP spectroscopic equipment. From o-rings to RF coils to sample introduction kits, we stock over 3,000 pieces of ICP spectroscopic equipment to suit any system requirements. To find out more, get in touch with Delta Scientific today.
References and Further Reading
- Mueck, L. A technique to carry a torch for. Nat Methods 12, 12–12 (2015).
- Wilschefski, S. & Baxter, M. Inductively Coupled Plasma Mass Spectrometry: Introduction to Analytical Aspects. The Clinical biochemist. Reviews 40, 115–133 (2019).
- Neufeld, L. ICP-MS Interface Cones: Maintaining the Critical Interface between the Mass Spectrometer and the Plasma Discharge to Optimize Performance and Maximize Instrument Productivity. Spectroscopy 34, 12–17 (2019).