ICP-MS Facilities in the USGS Geologic Discipline

Solution ICP-MS Laboratory

ELAN® 6000 ICP-MS system in Solutions Laboratory


Cetac USN5000+ Desolvation system with PerkinElmer AS-91 Autosampler The solution ICP-MS Laboratory uses a dedicated quadrupole ICP-MS instrument to perform analyses on a wide variety of sample types. Several standard sample preparation procedures are available for routine matrix types, including soils, rocks, and biological specimens. Specialized techniques, such as the use of desolvation systems, are used to minimize interferences during sample analysis.

• Water samples are typically analyzed without sample preparation if they have been filtered and acidified during collection. Water samples containing particulates must be filtered before analysis via ICP-MS. Typically all samples are acidified before analysis to ensure stability and comparability with calibration standards.
• Sediment, soil and rock samples for total elemental analysis are digested using a 4-acid digestion procedure in order to dissolve most silicate minerals. This digestion is carried out in open vessels on a hot-plate, so if volatile elements are of interest, another digestion procedure such as microwave digestion should be used.
• Geological samples for rare-earth-element (REE) analysis are typically prepared using a sodium peroxide sinter method. In this method the ground sample is mixed with sodium peroxide in a carbon crucible and placed in a muffle furnace. The resulting sinter is leached with water and acidified with nitric acid before analysis.
• Biological and organic samples are generally digested using a closed-vessel microwave digestion procedure that is appropriate to the matrix of the sample. The high temperature and pressures reached in the microwave digestion system can dissolve most biological samples, including fatty tissues. This is also the best method for digesting organic samples, including crude oils.

Sample Preparation Techniques

4-Acid Digestion

4-Acid Digestion of geological samples. Sample decomposition using this multi-acid digestion technique is suited to dissolve certain rock types, soils, and sediments. This method uses a combination of nitric, hydrochloric, hydrofluoric and perchloric acids. As with any technique there are going to be exceptions. The method does not fully dissolve refractory or resistant minerals and some secondary minerals. Examples of incomplete digestion are as follows: Ba in barite, Cr in chromite, Ti in rutile, Sn in cassiterite, Al in corundum, and rare earth elements in monazite. Samples that contain elements in high concentrations where normally the element is a trace constituent will have to be diluted (i.e., Mg in dolomite, Pb in galena, Zn in sphalerite, Cu in chalcopyrite). This dilution increases the lower reporting limits.

Sodium Peroxide Sinter

Samples being prepared via Na₂O₂ sinter method.For the determination of the rare earth elements (REE) La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb in geologic materials, the REE are made soluble in the sample material by sintering with sodium peroxide (Na₂O₂), leaching with water, and acidifying with nitric acid. Lutetium is added as an internal standard for oxide correction. Rhodium and Iridium are added on line as internal standards to correct for matrix effects and instrumental drift.

Microwave Digestion

Multiwave 3000 Microwave digestion system and Teflon vessels.

For biological or organic samples, difficult to digest samples, or for samples where the volatile elements need to be preserved, microwave digestion is a preferred sample preparation technique. Using a specially-designed laboratory microwave digestion system, the temperature and pressure inside the vessels can be precisely controlled. This provides reproducible results and a high degree of reliability and safety. In this technique, small amounts (< 0.5 gram) of sample are digested with small amounts of high-purity acids and/or peroxide in closed Teflon vessels. The temperature and pressure are controlled automatically using a computer interface. Once the digestion is complete, the samples are allowed to cool and are then diluted with high-purity water.

More details on the methodologies used by the laboratory can be found in the following document: http://pubs.usgs.gov/of/2002/ofr-02-0223/.

For further information contact Ruth Wolf (rwolf).

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