GDMS vs ICP-MS vs ICP-OES vs XRF: A Comparison Guide

Why Elemental Analysis Method Selection Matters

Elemental analysis – determining which elements are present in a material and at what concentration – is required across semiconductor, metals, pharmaceutical, environmental, and failure analysis applications. Four techniques dominate: glow discharge mass spectrometry (GDMS), inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma optical emission spectrometry (ICP-OES), and X-ray fluorescence (XRF). Each has a different concentration range, sample form requirement, element coverage, and cost. Selecting the wrong technique produces data that cannot answer the question being asked or costs more than necessary.

The selection decision is driven by three factors: the concentration range of interest (parts per trillion to percent), the sample form (solid, solution, or bulk), and the elements of interest. There is no single technique that is best for all combinations – the guide below maps each technique to its strengths and practical applications.

Technique Overviews

GDMS – Glow Discharge Mass Spectrometry

GDMS sputters a solid sample surface with a glow discharge plasma, atomizing and ionizing the surface material. The ions are analyzed by a mass spectrometer, providing elemental concentrations directly from the solid without dissolution. Detection limits are in the parts per billion (ppb) to parts per trillion (ppt) range for most elements. GDMS covers nearly the entire periodic table simultaneously from a single analysis and requires no sample dissolution, eliminating the risk of contamination during acid digestion. It is the technique of choice for ultra-high purity metals (semiconductor-grade silicon, germanium, III-V compound semiconductors), where trace impurities at the ppb level affect electrical properties.

ICP-MS – Inductively Coupled Plasma Mass Spectrometry

ICP-MS dissolves the sample and introduces a solution into an argon plasma at approximately 6,000-8,000 K, atomizing and ionizing all elements. Ions are extracted into a mass spectrometer and measured. Detection limits are in the parts per trillion (ppt) to parts per quadrillion range for most elements – the most sensitive technique for solution analysis. ICP-MS covers the full mass range (Li to U) in a single analysis. It is the standard method for trace metals in environmental water (EPA 200.8), pharmaceutical elemental impurities (USP <232>/<233>), and ultra-low impurity analysis in semiconductor process chemicals and ultrapure water.

ICP-OES – Inductively Coupled Plasma Optical Emission Spectrometry

ICP-OES uses the same plasma ionization as ICP-MS but detects light emitted by excited atoms at element-specific wavelengths rather than mass. Detection limits are in the parts per billion range – less sensitive than ICP-MS but sufficient for most environmental, metallurgical, and industrial applications. ICP-OES handles high-matrix samples and high analyte concentrations better than ICP-MS and has lower instrument and operating cost. It is the workhorse for metals analysis in environmental samples (EPA 200.7), alloy chemistry verification (ASTM E1086), and mineral and ore analysis.

XRF – X-Ray Fluorescence

XRF irradiates the sample surface with X-rays that eject inner-shell electrons from atoms; the resulting fluorescent X-rays at element-specific energies are detected and quantified. XRF is a direct solid analysis technique – no dissolution is needed. Detection limits are in the parts per million (ppm) range for most elements, which is far less sensitive than ICP techniques but entirely adequate for bulk chemistry applications. XRF is fast (seconds to minutes per analysis), non-destructive, and handles samples from powders to solid blocks. Wavelength dispersive XRF (WDXRF) provides higher resolution and accuracy than energy dispersive XRF (EDXRF); handheld EDXRF provides rapid field screening.

Comparison by Application

Semiconductor and Ultra-High-Purity Metals

GDMS is the preferred method for direct solid analysis of high-purity metals and semiconductors at ppb concentrations. It avoids the contamination risk of dissolution and directly samples the bulk solid. ICP-MS on acid-digested or dissolved samples achieves comparable detection limits but introduces contamination risk during sample preparation that can exceed the analyte concentration being measured. For semiconductor wafer surface contaminants in vapor phase decomposition (VPD) solutions, ICP-MS achieves the required sensitivity at concentrations too low for GDMS on a bulk solid.

Environmental Water and Soil

ICP-MS per EPA 200.8 covers most regulated trace metals in drinking water, wastewater, and soil digests at EPA action levels, which are in the ppb to ppt range for lead, mercury, arsenic, and cadmium. ICP-OES per EPA 200.7 covers metals at higher concentrations – calcium, magnesium, iron, manganese, sodium – and the bulk of environmental metals work. XRF is used for soil screening and field analysis but does not meet EPA quantitative reporting requirements for most regulated metals in water.

Metals and Alloy Chemistry Verification

XRF (WDXRF) is the standard for alloy chemistry verification per ASTM E1086 (stainless steel by XRF) and ASTM E572 – fast, non-destructive, accurate to the 0.01% level. ICP-OES is used when dissolution is practical and higher accuracy is needed for minor and trace alloying elements, or when XRF matrix effects are problematic for complex alloy systems. GDMS is used when trace impurities below 10 ppm must be quantified in high-purity metals or when near-full-periodic-table coverage is needed simultaneously.

Pharmaceutical Elemental Impurities

USP <232> defines elemental impurity limits in drug products; USP <233> defines the analytical procedures – ICP-MS and ICP-OES are the specified methods. ICP-MS is required for elements with oral PDE values below 100 micrograms per day (cadmium, lead, arsenic, mercury, iridium, osmium, ruthenium, rhodium, palladium, platinum). ICP-OES is acceptable for higher-PDE elements. XRF is not a USP <233> specified method for pharmaceutical elemental impurities but is used for raw material screening.

Industry Specifications

• Semiconductor Purity: SEMI MF1569 (GDMS for silicon), ASTM F1699 (trace impurities in metals), SEMI C1 series (chemical purity)
• Environmental Analysis: EPA 200.7 (ICP-OES), EPA 200.8 (ICP-MS), EPA 6010 (ICP-OES in SW-846), EPA 6020 (ICP-MS in SW-846)
• Pharmaceutical: USP <232> (elemental impurity limits), USP <233> (procedures – ICP-MS and ICP-OES), ICH Q3D
• Metals and Alloys: ASTM E1086 (XRF for stainless steel), ASTM E572, ASTM E1613 (ICP for lead)
• Geological and Mineral: ASTM D2369, ISO 11885 (ICP-OES water and extracts)
• XRF Standards: ASTM E1621 (XRF general practice), ISO 12677 (XRF for refractories)

Conclusion

No single technique covers all elemental analysis needs. GDMS is the method for direct solid analysis at ppb sensitivity with full periodic table coverage – the choice for ultra-high-purity metals and semiconductors. ICP-MS in solution achieves ppt detection limits for dissolved samples – the choice for pharmaceutical elemental impurities, ultra-trace environmental metals, and semiconductor process chemicals. ICP-OES covers the ppb range in solution more economically – the workhorse for environmental metals, alloy verification by dissolution, and industrial applications. XRF provides direct solid analysis at ppm sensitivity with no sample preparation – the choice for rapid bulk chemistry screening, alloy verification, and field use.

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