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Short answer. Inductively coupled plasma mass spectrometry (ICP-MS, often searched as “inductively coupled plasma mass spectroscopy”) dissolves a sample, turns it into a spray, ionizes it in a radiofrequency plasma, and sorts the resulting ions by mass-to-charge ratio to measure trace elements. What a result is worth depends as much on sample handling and quality-control samples as on the instrument.
Definition and scope
ICP-MS is an elemental analysis technique. In the words of U.S. EPA Method 200.8, sample material in solution is introduced by pneumatic nebulization into a radiofrequency plasma where energy transfer processes cause desolvation, atomization and ionization. The ions are then separated by mass and counted. EPA’s method title uses “spectrometry”; “spectroscopy” is a common search spelling for the same technique. It is a branch of analytical chemistry and uses a mass spectrometer as its detector stage.
Method 200.8 applies to dissolved elements in ground, surface and drinking water, and to total recoverable elements in those waters plus wastewaters, sludges and soils. Its list covers 21 elements: Al, Sb, As, Ba, Be, Cd, Cr, Co, Cu, Pb, Mn, Hg, Mo, Ni, Se, Ag, Tl, Th, U, V and Zn.
How ICP-MS works: from nebulizer to detector
Method 200.8 describes the pathway in three stages.
1. Introduction and ionization
The liquid sample is nebulized into the plasma. Energy transfer in the plasma desolvates, atomizes and ionizes the sample material.
2. Extraction and mass separation
Ions are extracted from the plasma through a differentially pumped vacuum interface and separated by mass-to-charge ratio in a quadrupole mass spectrometer. The method sets a minimum resolution of 1 amu peak width at 5% peak height.
3. Detection and correction
An electron multiplier or Faraday detector counts the ions. The method states that corrections must compensate for isobaric elemental interferences and for polyatomic ions derived from the plasma gas, reagents or sample matrix, and that drift and matrix suppression or enhancement must be corrected with internal standards. See the guides on polyatomic interference correction and internal standards in quantitative mass spectrometry for depth on those two steps.
What must happen before the instrument
A reading is only as good as the solution that reaches the nebulizer. These conditions come straight from Method 200.8.
| Condition | What the method says |
|---|---|
| Dissolved solids | Should not exceed 0.2% (w/v), to reduce interferences (section 1.3). |
| Direct analysis without digestion | Allowed for drinking water that is acid-preserved and has turbidity below 1 NTU; not for silver (section 1.4). |
| Digestion or extraction | Required for total recoverable determinations when elements are not in solution, such as soils, sludges, sediments and particulates (section 1.5). Solids are solubilized by gentle refluxing with nitric and hydrochloric acids (section 2.1). |
| Silver | Low recoveries are possible without the chloride complex, so digest before analysis (section 1.7). |
| Barium | Free sulfate can limit solubility (section 1.8). |
| Volatile organo-mercury | Not suitable for the digestion procedure (section 1.6). |
For digestion options in more depth, see ICP-MS sample preparation and acid digestion methods.
Reading a lab report: the quality-control samples
Method 200.8 defines a standard set of quality-control samples. A report from an ICP-MS run that follows the method should be able to point to each of them:
- calibration blank
- laboratory reagent blank
- laboratory fortified blank
- laboratory fortified matrix
- laboratory duplicates
- internal standards, used to correct drift and matrix effects
Asking which of these were run, and what they showed, is a practical way to audit a data package or compare labs. It also shows why consumables matter to the result: acid-preserved samples, blanks and calibration and internal standard solutions are all part of how the method gets its answer.
Detection limits are not a promise
Method 200.8 defines the instrument detection limit (IDL) as three times the standard deviation of ten replicate calibration-blank measurements. Its Table 1 IDLs are described as a guide to instrumental limits typical of a system optimized for multielement determinations. Actual method detection limits and linear ranges depend on the sample matrix, instrumentation and selected operating conditions. A vendor figure or a table value is therefore a starting point, not a guarantee for your samples. The same distinction between detection and quantitation is covered in limit of detection versus limit of quantitation.
Related techniques
ICP-MS is often considered alongside ICP optical emission spectrometry (ICP-OES) and atomic absorption. For a side-by-side view, see ICP-MS vs ICP-OES and atomic absorption spectroscopy. For how Method 200.8 relates to other EPA methods, see EPA Method 200.8 vs 200.7 vs 6020.
Where it matters for labs and equipment decisions
- Staffing. Method 200.8 says it should be used by analysts experienced in ICP-MS and in interpreting spectral and matrix interferences, and recommends a minimum of six months of experience with commercial instrumentation.
- Compliance work. For compliance programs, the method points to 40 CFR Part 136 Table 1B (NPDES) and Part 141 section 141.23 (drinking water), along with the latest Federal Register announcements.
- Solid and wipe samples. EPA’s Selected Analytical Methods (SAM) listing names SW-846 Method 6020B (ICP-MS), revision 2, July 2014, for solid and wipe samples for compounds containing arsenic, osmium, thallium and vanadium, and for titanium as total metal.
Common misunderstandings
- “ICP-MS can analyse any sample as received.” Method 200.8 limits dissolved solids and turbidity for direct analysis and requires digestion for many sample types.
- “A published detection limit applies to every sample.” The method says actual limits depend on matrix, instrument and operating conditions.
- “The mass spectrometer removes interferences by itself.” The method requires explicit correction for isobaric and polyatomic interferences, and for drift and matrix effects.
- “Spectroscopy and spectrometry are different methods.” Both spellings are searched for the same technique; EPA Method 200.8 uses “spectrometry”.
FAQ
What does ICP-MS measure?
It measures trace elements in a sample solution by ionizing them in a plasma and separating the ions by mass-to-charge ratio. Method 200.8 lists 21 elements for water, waste and soil samples.
How does the sample get into the plasma?
By pneumatic nebulization of the solution into a radiofrequency plasma, where it is desolvated, atomized and ionized.
Does every sample need digestion?
No. Acid-preserved drinking water with turbidity below 1 NTU can be analysed directly, except for silver. Soils, sludges, sediments and particulates need digestion or extraction.
How is a detection limit defined?
Method 200.8 defines the instrument detection limit as three times the standard deviation of ten replicate calibration-blank measurements. Method detection limits depend on the matrix and operating conditions.
Sources
- U.S. EPA, Method 200.8, Revision 5.4 (1994), “Determination of Trace Elements in Waters and Wastes by Inductively Coupled Plasma-Mass Spectrometry,” https://www.epa.gov/sites/default/files/2015-06/documents/epa-200.8.pdf (checked 2026-10-29).
- U.S. EPA Selected Analytical Methods, “EPA Method 6020B (SW-846): Inductively Coupled Plasma-Mass Spectrometry,” https://www.epa.gov/esam/epa-method-6020b-sw-846-inductively-coupled-plasma-mass-spectrometry (checked 2026-10-29).
