DIN 11885 Water Quality - Determination of Selected Elements by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES)

The standard “DIN 11885 Water quality - Determination of selected elements by inductively coupled plasma optical emission spectrometry (ICP-OES)” developed by the German Institute for Standardization (DIN) describes a method for determining dissolved elements, particle-bound elements (particles) and total element content in different types of water, e.g. groundwater, surface water, raw water, drinking water and wastewater, on the basis of the following elements: aluminium, antimony, arsenic, barium, beryllium, bismuth, boron, cadmium, calcium, chromium, cobalt, copper, gallium, indium, iron, lead, lithium, magnesium, manganese, molybdenum, nickel, phosphorus, potassium, selenium, silicon, silver, sodium, strontium, sulfur, tin, titanium, tungsten, vanadium, zinc and zirconium.

Taking into account specific and additional interferences, these elements can also be determined in digestions of water, sludge and sediments (e.g. water digestions specified in the ISO 15587-1 or ISO 15587-2 standards).

The method described is suitable for particulate matter mass concentrations in wastewater below 2 g/l. The scope of this method can be extended to other matrices or to higher particulate matter quantities if it can be shown that additional interferences are taken into account and corrected. It is up to the user to demonstrate fitness for purpose. Recommended wavelengths, quantification limits and significant spectral interferences for selected elements are included in a table provided in the standard. This table lists the elements at recommended wavelengths for analysis and the most significant spectral interferences.

Several types of interference effects can contribute to inaccuracies in the determination of trace elements. These effects include:

• Spectral interferences are categorized as follows:
  • Superimposition of a spectral line from another element. These effects can be compensated for using computer correction of the raw data.
  • Unresolved overlap of molecular band spectra. These effects can probably be overcome by choosing an alternative wavelength.

If appropriate equipment is available, wavelength scanning can be performed to detect potential spectral interference.

• Background effects are categorized as follows:
  • Background contribution from continuous or recombination events.
  • Background contribution from stray light from line emission of elements in high concentration.

The effect of background interferences can often be compensated for by background correction adjacent to the analyte line.

For the purposes of this standard, the following terms and definitions apply:

• Accuracy is the closeness of agreement between a test result and an accepted reference value. The term accuracy, when applied to a set of observed values, describes a combination of random error components and common systematic error components. Accuracy includes precision and accuracy.
• Analytes are the elements that need to be determined.
• The background equivalent concentration is the element concentration required to produce an analyte signal of the same intensity as the background signal.
• The calibration blank solution is prepared in the same manner as the calibration solution but excludes the analyte.
• A calibration solution is a solution prepared from stock solutions or a certified standard used to calibrate the instrument.
• A calibration control solution is a solution of known composition within the range of calibration solutions but prepared independently.
• Determination is the entire process from preparation of the test sample solution to measuring and calculating the final result.
• The instrument performance control solution is the solution used to determine and control instrument drift for analytes of interest.
• Linearity is the straight line relationship between the measurement (signal) result and the amount of the component to be determined (concentration).
• The detection limit is the smallest amount or concentration of an analyte that can be reliably distinguished from zero in the test sample.

The basis of the described method is the measurement of light emission by an optical spectroscopic technique. Samples are misted and the produced aerosol is carried to a plasma torch where excitation occurs. Characteristic emission spectra are produced by radio frequency inductively coupled plasma (ICP). The spectra are dispersed by a grating spectrometer and the intensities of the lines are monitored by a detector. The signals from the detectors are processed and controlled by a computer system. An appropriate background correction technique is used to compensate for variable background contributions in the determination of trace elements.

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