What is viewing ICP-OES
The method of carrying the light from the plasma to the detector impacts the results
When combining inductively coupled plasma (ICP) with optical emission spectroscopy (OES), the analysis depends on how the plasma is viewed in an ICP-OES device. The method that the spectrometer uses in plasma observation is typically axial-, radial-, or dual-view. Each method comes with some strengths and weaknesses, and some methods make a better fit with specific applications. This article reviews that information, includes a real-world example, and describes a new viewing technology.
Axial viewingIn a platform that uses axial viewing, the light ‘looks’ down the length of the plasma’s axis—that is, the direction of the light is parallel to the plasma. This approach delivers lots of light to the optical system, which supplies more information to the detector. “In many analyses, this is a benefit, leading to increased sensitivity in detecting trace-element emissions”.
The large amount of light captured in this method, though, includes information from the sample of interest plus background. The background can be considerable. Also, matrix interferences, which originate in the cooler plasma tail, can degrade the precision and accuracy.
Still, this method works well in some applications, especially when sensitivity matters more than precision. This method provides the lowest detection limits—a factor of 10 better than radial-view platforms of the past and maybe 3–4 times better than today’s best radial-viewing platforms. That makes this approach appealing for trace-element analyses, especially in environmental and industrial applications.
On the downside, the more complex design of an axial-based instrument requires more maintenance and cleaning.
With a radial-viewing instrument, the light is perpendicular to the longitudinal axis of the plasma. So, this method analyzes a slice of the plasma, and less light leads to less sensitivity. The less light, though, comes with less interference from background and matrices. That means that a radial system provides more precision than an axial one. According to the spectroscopy paper, “Users prefer radial models when seeking higher stability and especially higher matrix compatibility.”A radial-based instrument is also easier to clean and maintain than an instrument with axial viewing.
If a user needs the axial- and radial-viewing approach, a dual-view analyzer should be considered, because it allows both. This kind of instrument costs a little more, and the complication of providing dual techniques increases the maintenance and cleaning challenges. Nonetheless, when a user needs sensitivity, the axial mode can be used. To eliminate matrix interferences and expand the linear range to analyze higher concentration levels, switch to radial viewing.
The sample type that a lab must analyze impacts the choice of the best mode. “For oil, soil, and high-level work, use radial,” says Tsourides. “For trace analysis in, say, plant tissue, switch to axial.”
In North Carolina, Charlotte Water handles public water and wastewater for nearly one million customers. At more than 125 years old, this is the largest public water company in the Carolinas—performing about 235,000 laboratory analyses every year. In 2017, this utility pumped an average of 107 million gallons of drinking water per day and treated more than 79 million gallons of wastewater a day.
In the analyses, says Cody Gibson, laboratory analyst II at Charlotte Water, “We use ICP-OES for water and environmental samples, particularly industrial wastewater and minerals analysis.”
This lab includes a SPECTROBLUE TI, which has a twin interface that allows axial or radial viewing. “Most samples are analyzed in axial-view because we require high sensitivity and lower detection limits,” Gibson explains. “Minerals are viewed radially to minimize spectral interferences.” (The use of instrument names is for identification only and does not imply endorsement by Charlotte Water or the City of Charlotte.)
When asked what method is preferred, Gibson says, “We run a method including both axial and radial with our twin-interface SPECTROBLUE.” He adds, “We prefer this method because of the various matrices run by ICP-OES in our lab.”
The spectroscopy paper notes: “Some vendors recommend dual-view models to most or all of their customers, no matter what the application. This may be ill-advised.” As Tsourides says, “On all dual-view systems, one or both of the views—axial and/or radial—will be compromised analytically.”
- Welcome to OPTOSKY booth at the fifth China International Import Expo (CIIE) 2022-11-02 58
- About Integrating Sphere Fundamentals and Applications 2022-10-28 111
- VOCs are the main culprits of air pollution 2022-10-27 64
- Optosky-XRF spectrometer-FAQ 2022-10-10 110
- What is a pinhole of confocal microscopes？ 2022-09-23 104
- FIELDSPEC FAQ 2022-08-22 211
- How to test the nitrous nitrogen in water quality? 2021-05-18 84