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 viewing

Radial viewing

Dual 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.”