Ultratrace-3 is a combination of our 1H package (INAA and multi-acid digestion ICP) combined with ICP-MS on the same solution we use for ICP. Some elements reported by ICP-MS are duplicated by INAA and indicate the degree of dissolution as certain elements reside in very resistate phases like zircon, monazite, sphene, xenotine, chromite, barite, etc., which can’t be totally dissolved with any acids. To ensure complete dissolution we suggest our Code 4 group packages. 

INAA

INAA (Instrumental Neutron Activation Analysis) is an analytical technique dependent on measuring gamma radiation induced in the sample by irradiation with neutrons. The primary source of neutrons for irradiation is usually a nuclear reactor. Each activated element emits a “fingerprint” of gamma radiation which can be measured and quantified. Routine multi-element analyses by INAA are performed on practically any material from the smallest sample which can be weighed accurately to very large samples.

A 30g aliquot, if available, is encapsulated in a polyethylene vial and irradiated along with flux wires at a thermal neutron flux of 7 x 10 12 ncm-2 s-1. After a 7-day period to allow Na-24 to decay the samples are counted on a high purity Ge detector with resolution of better than 1.7 KeV for the 1332 KeV Co-60 photopeak. Using the flux wires and control standards, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. For values exceeding the upper limits, assays are recommended. One standard is run for every 11 samples. One blank is analyzed per work order. Duplicates are analyzed when sample material is available.

“Near Total” Digestion – ICP

A 0.25g sample is digested with four acids beginning with hydrofluoric, followed by a mixture of nitric and perchloric acids, heated using precise programmer controlled heating in several ramping and holdingcycles which takes the samples to incipient dryness. After incipient dryness is attained, samples are brought back into solution using aqua regia.

With this digestion, certain phases may be only partially solubilized. These phases include zircon, monazite, sphene, gahnite, chromite, cassiterite, rutile and barite. Ag greater than 100 ppm and Pb greater than 5000 ppm should be assayed as high levels may not be solubilized. Only sulphide sulfur will be solubilized.

The samples are then analyzed using an ICP. QC for the digestion is 14% for each batch, 5 method reagent blanks, 10 in-house controls, 10 samples duplicates, and 8 certified reference materials. An additional 13% QC is performed as part of the instrumental analysis to ensure quality in the areas of instrumental drift.

“Near Total” Digestion – ICP-MS

The multi-acid digest solution above is diluted and then run by ICP-MS for additional elements.  One blank is run for every 40 samples. In-house control is run every 20 samples. Digested standards are run every 80 samples. After every 15 samples, a digestion duplicate is analyzed. Instrument is recalibrated every 80 samples.

Elements and Detection Limits (ppm)

Notes: Extraction of each element by 4-Acid Digestion is dependent on mineralogy.
Unaltered silicates and resistate minerals may not be dissolved.
* Element reported by multiple techniques if one or more techniques may not be total.
+ Sulphide sulphur and soluble sulphates are extracted.

Reference:
Hoffman, E.L., 1992. Instrumental Neutron Activation in Geoanalysis. Journal of Geochemical Exploration, volume 44, pp. 297-319.