ANALYTICAL FACILITIES AT THE DEPARTMENT OF GEOLOGICAL MAPPING
Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) Laboratory

Dirk Frei and Jørgen Kystol

Inductively Coupled Plasma Mass Spectrometry is a highly sensitive technique for the fast, precise and accurate determination of trace element concentrations in a wide variety of liquid and solid materials. For ICP-MS analysis, samples are dispersed into a stream of argon gas and carried to an inductively coupled plasma where they are ionised. The ions are then separated according to their mass and charge ratio using a mass spectrometer and subsequently counted. For liquids, for example water samples and solid samples brought into solution, this is achieved by spraying the sample into the argon carrier gas using a nebulizer (Solution-ICP-MS)
Solid samples are held in a cell flushed with argon while sub-micron particles are ablated from the surface using a laser (Laser Ablation ICP-MS or LA-ICP-MS) . Our laboratory operates a PerkinElmer 6100 DRC Quadrupole ICP-MS, combining the efficient ionization of a high-temperature argon plasma with the high sensitivity and rapid scanning capabilities of a quadrupole mass spectrometer.

Liquid samples (Solution-ICP-MS) are introduced via a Meinhard nebulizer combined with a peristaltic pump and an autosampler. Currently about 40 elements (elements ≥ mass 45, i.e. transition elements, HFSE, LILE, REE and actinides) are determined routinely in any sample that can be put into aqueous solution. Detection limits and analytical precision vary widely between sample type and elements to be analysed, but range from <100 ppb to <1 ppt, and relative analytical precision is typically ~2 to 5% (one standard deviation).

For the introduction of solid samples (LA-ICP-MS) the laboratory is equipped with a Cetac LSX 200 laser ablation unit based on a solid-state Nd-YAG laser emitting at a wavelength of 266 nm. The LA-ICP-MS is capable of analysing a wide variety of solid phases and for a wide range of elements.
It is difficult to generalise about spatial resolution, detection limits, precision and accuracy because these are all inter-related and are also strongly dependent on instrument operating conditions (such as laser beam diameter, laser power, elements investigated, background levels etc.).
Therefore, all potential users should discuss their analytical requirements with the facility staff prior to initiating a project.
For typical operating conditions, using a 30 µm spot size with a 60–100 microns deep ablation pit and about 20 elements greater than mass 85 (Rb) analysed simultaneously, detection limits are usually about 1–10 ppm. For elements below mass 85 there are analytical restrictions because of interferences and generally higher background count rates, leading to higher detection limits (about tens of ppm). Isotope ratios can be determined by LA-ICP-MS with sufficient precision for certain applications such as environmental lead source tracing and detrial zircon lead-lead geochronology.

For all inquiries and for additional information about the ICP-MS laboratory contact Dirk Frei (email: df@geus.dk; Tel: 0045-38142263), Jørgen Kystol (email: jk@geus.dk; Tel: 0045-38142675) or Lotte Melchior Larsen (email: lml@geus.dk; Tel: 0045-38142252).