Water for ICP-OES

During the analysis, the sample is vaporized and ionized to form ions that are further detected by the optical device. Interferences due to reactions with the argon used for the ICP process are well documented and the technique is fairly simple to use by most personal.

Water is not used during the analysis step, however, sample preparation step, blank, and standard preparation require high purity water. The water selected must meet two basic features:

• avoid interferences with the metals being analyzed,
• enable the instrument to run in optimum conditions, i.e. reduce contamination of the ICP-OES

The water quality for ICP, therefore, should meet the following criteria:

• Low ionic content, in order to avoid interference with the analytes.

  A 18.2 MΩ•cm resistivity ensures that no ions will be present in the water at a level that would interfere with the analyses. High resistivity can be achieved via several technologies, including combination of reverse osmosis, electrodeionization and mixed bed ion exchange resins.

• Low particle content to avoid spoiling the nebulizer.

  The particles include hard particles, as well as colloids. Use of a 0.22 µm filter at the final stage of the purification process ensures that no significant particle count will be present in the water.

• Low bacterial count, since bacteria behave as particles, and therefore could spoil the nebulizer as well.

  Use of a 0.22 µm filter at the final stage of the purification process ensures that bacteria levels below 1 cfu/mL.

• Moderate to low organic content.

  Some large organic molecules such as lignin, as well as humic and fulvic acids resulting from natural matter degradation could stick on the nebulizer surface during the atomization step. Those large organic molecules are efficiently removed by combination of reverse osmosis and activated carbon. Other types of organics may also be removed using UV photooxidation process.

Example of data obtained on an Iris Intrepid (Thermo) ICP-OES

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