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ICP-OES

Introduction

The ICP-OES in our institute is an optical emission spectrometer of the type Vista Pro from VARIAN with an axial inductively coupled plasma and a patented VistaChip CCD simultaneous detector combined with an echelle raster.
We use the ICP-OES for measuring major and trace elements in solution (mainly in 3% HNO3) or couple it to a femtosecond laser. Figure 2 shows elements that can be detected with the OES. The detection limits are different for each element, they are in the range of around 0.05 to 500µg/L. For precise determination of low trace element concentrations, the ELEMENT XR is available at the institute.
A reliable CETAC ASX 510 autosampler is available for high sample numbers.
The ICP-OES is working with a 2 ml conical quartz glass nebulizer, a cyclone spray chamber, and torches made of quartz glass.

Principle

The electrons of all elements are atomized or ionised via high-frequency energy of the argon  plasma. By decrease of the energy level back to the ground state they emit energy as light. The electrons can drop to the ground state directly or step-wise. This results in a rather large number of different characteristic wave lengths for each element. The emitted light will pass a set of  mirrors, and a prism, before arriving at the detector (see Figure 1). The CCD detector is able to detect in the range of 165 nm to 785 nm around 70 different wavelengths within 35 seconds. The detector can't be saturated because the instrument will filter out the respective wavelength immediately.

In order to set up a good method you have to take care about the following:

  • All elements you want to analyze need to be represented in a calibration list. The calibration list should generously encompass the expected concentration of each element.
  • You should choose the most sensitive and characteristic wavelength of each element, depending on its expected concentration. For higher concentrations less sensitivity is required.
  • There are different interferences overlapping the wavelengths of interest. Take care that the distances of  wavelength interferences relative to your chosen elements are at least 8 pm, thereby allowing the software a good signal separation.
FIGURE 1: Shematic mirrow-system and the patented Vistachip CCD simultaneous for the ICP-OES Varian Vista Pro by VARIAN
FIGURE 2: Measurable elements with the ICP-OES Vista Pro are black signed, not measurable elements are grey (by VARIAN)