Geochemical analysis

Room 5657, Oceanography Wing, LSC.  Part of the Dalhousie Geochronology Centre.

ICP-OES is different from ICP-MS.  An ICP-MS can measure the abundance of isotopes of elements at the parts per trillion level.  An ICP-OES cannot (expect in special circumstances) distinguish isotopes of a given element, and is limited to abundances greater than about 0.1 parts per million.  However, an ICP-OES can measure concentrations above 10 ppm, whereas the ICP-MS would require dilutions below those concentrations.

The precision of the measurement of an element in the solution depends on many things, but mostly:

1. how well its concentration is bracketed by the standards used to calibrate the measurement;
2. the presence of other elements that interfere with wavelengths that were used to measure an element;
3. other matrix effects (generally, the concentrations of all elements in the solution).

We generally can routinely obtain 5% precision at 1-sigma confidence on most elements in most solutions.  Better precision is definitely possible but require additional standards and methods (standard addition, internal standard, initial semi-quantitative analyses to determine the matrix, etc).  By June 2013, we have not yet analyzed enough halogens to establish the routine precision that we can obtain, but we will eventually.

Accuracy of the measurements depends on both the precision of the measurements and reliability of the standards.  We use different methods of QA and QC to ensure the ICP is well maintained and our standards are diluted as reliably as possible.  Standards (prepared gravimetrically) from over two or three orders of magnitude concentrations (e.g. 0.1 to 50 mg/ml) typically have linear regressions of 0.99999.

Please contact John Gosse before submitting solutions for measurement.  Samples should be prepared as solutions in 2% nitric acid with minimal matrix. We will do our best to mix a set of standards that match your matrix as closely as possible. A minimum of 7 ml is required per sample for low (5%) precision, and more sample solution is required for higher precision measurements.  We also have the capacity to run samples prepared in dilute HF.

The cost of ICP-OES measurements depends on a number of factors. The Prodigy uses (Liquid) Argon for coolant, the nebulizer, and camera and Nitrogen gas for the optics purge, which are the principal consumables.  Higher precision, complexity of the matrix, and elemental interferences will all increase labour and consumables (e.g. standards).  The lab is a non-profit lab, so costs generally reflect the cost of labour, operation, consumables, and maintenance. Please contact John Gosse for questions regarding costs for your samples.

While the ICP-OES is used mostly for Dalhousie Geochronology Centre sample analysis, we are interested in supporting the broader academic and research community in Nova Scotia.