Zn Interferences Upon the Na 330.237 nm Line

Terri was analyzing samples for Sodium by ICP-OES using the 330.237 nm line at concentrations near the detection limit. She had trouble with the repeatability of the measurements. Terri noticed that our Analytical Periodic Table showed this line could be influenced by the presence of Zinc. She wanted to know more about this interference, as well as how she might improve the reliability of her measurements.

	RE: Zn Interferences Upon the Na 330.237 nm Line Dear Terri,      When using the Na 330.237 nm line, Zn can interfere from the 330.259 nm Zn line. Any interference would be due to background correction problems. These result from the use of a background point for the Na 330.237 nm measurement that is on the "long" wavelength side of the Na line. Most instruments will be able to resolve the aforementioned lines, unless there is an amount of Zn that is ~ 10 times greater than the Na. If this is the case, you may experience some wing overlap difficulties and an increase in the Na intensity measurement from the Zn. Levels of Zn that are 0.01 times that of the Na level will cause background correction error if the background point is on the long wavelength (Zn) side of the Na line.      When working very near the detection limit in matrices that may present difficulties with spectral interference, I find it very useful to extract the data from the actual spectral scans of the standards and samples. This process involves a justified lack in trust in the ability of the system software to make the proper determination of the intensity. We have not found any easy way, other than to manually obtain each spectrum and in some manner, depending upon the supporting software, make the background correction and a determination of the net intensity. This process is much slower, but the reliability of the data will be limited (to the ability of the instrument to detect Na at 330.237 nm). In addition, the sensitivity of the measurement may be improved through a reduction in the power applied to the plasma and an increase in the sample Ar. I hope these suggestions are of help.     Paul R. Gaines, Ph.D. Serving you in chemistry