Choosing the right instrument for environmental sample analysis

Both ICP-OES and ICP-MS are widely used for trace element analysis. Choosing between ICP-OES or ICP-MS depends on the following parameters:

  1. Instrument performance
    ICP-OES quantitation is based on measurement of excited atoms and ions at the wavelength characteristics for the specific elements being measured. ICP-MS, however, measures an atom’s mass by mass spectrometry (MS). Due to the difference in metal element detection, the lower detection limit for ICP-MS can extend to parts per trillion (ppt), where the lower limit for ICP-OES is parts per billion (ppb). Obviously, if the elements for detection have regulatory limits that are below or near the lower detection limit of ICP-OES, ICP-MS is the instrument of choice.

  2. Characteristics of the environmental sample
    ICP-OES is mainly used for samples with high total dissolved solids (TDS) or suspended solids and is, therefore, more robust for analyzing ground water, wastewater, soil, and solid waste. It can be used for drinking water analysis as well. But in general, ICP-OES is used to measure contaminants for environmental safety assessment and elements with a higher regulatory limit. ICP-MS, on the other hand, is especially useful for analyzing samples with low regulatory limits. In addition, ICP-OES has much higher tolerance for TDS (up to 30%). ICP-MS has much lower tolerance for TDS (about 0.2%) although there are ways to increase the tolerance. Although both ICP-OES and ICP-MS can be used for high matrix samples, sample dilution is often necessary for use on ICP-MS. In addition, if a sample contains analytes of great difference in concentration, ICP-MS has wider dynamic linear range so the sample may not be diluted to detect these elements at the same time.

  3. Regulatory requirements
    In the U.S., the regulatory compliance monitoring for ICP-OES is governed by EPA Methods 200.5 and 200.7. EPA Method 200.7 was approved for use as axial view of ICP-OES and is therefore the EPA method for compliance monitoring by ICP-OES. EPA Method 200.8 governs regulatory compliance using ICP-MS. Both EPA 200.7 and 200.8 can be used for compliance of the Safe Drinking Water Act (SDWA) and the Clean Water Act (CWA).
    For drinking water regulatory compliance or SDWA compliance, either ICP-OES or ICP-MS alone is not sufficient. Regulatory compliance can be accomplished by the combination of ICP-OES (for minerals) and ICP-MS, or ICP-OES and GFAA (using EPA 200.9), or ICP-MS and GFAA (for minerals). ICP-OES cannot be used to measure arsenic, mercury, and some other toxic metals with very low regulatory limits using EPA Method 200.7. ICP-MS can’t be used to measure the minerals (Na, K, Ca, Mg, and Fe) in drinking water using EPA Method 200.8. It is also important to mention that current EPA Method 200.8 version 5.4 cannot use collision cell technology for drinking water analysis, reducing the power to use ICP-MS to minimize polyatomic interferences.

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Comparison of ICP-MS and ICP-OES Advantages and Methods

ICP-MS

Main advantages

ICP-MS is becoming a workhorse for metal analysis in water not only because it offers lower detection limit. The following features also contribute its wide range of environmental applications:

  • Wide dynamic range
  • Efficiently remove polyatomic spectral interferences using collision cell technology
  • Rapid semi-quantitative analysis
  • Isotopic analysis
  • Speciation capability

Regulatory methods

  • EPA 200.8
  • EPA 321.8 (IC-ICP-MS)
  • EPA 6020
  • ISO/DIS 17294-1:2004
  • ISO 17294-2:2016
  • NEN 6427:1999

ICP-OES

Main advantages

ICP-OES is used for all the matrices of environmental samples especially for high-matrix samples. The following features also contribute its wide range of environmental applications:

  • Only analytical grade reagents are sufficient
  • Simpler method development does not need a specialist with highly technical expertise
  • Overall is a cheaper option if the elements do not need lower detection limit that ICP-MS delivers

Regulatory methods

  • EPA 200.5
  • EPA 200.7
  • EPA 6010
  • ISO 11885:2007
  • ISO/TC 190/SC3/WG1 N0252
  • NPR 6425:1995
  • NEN 6426:1995
  • EN 12506: 2003

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