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E1H - INAA + 4-Acid Digestion/ICP

A 30 g sample is analyzed by INAA and with a four acid digestion followed by ICP analysis.

 

INAA

INAA 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. 

A 30 g aliquot, if available, is encapsulated in a polyethylene vial and irradiated with flux wires and an internal standard (1 for 11 samples) at a thermal neutron flux of 7 x 1012 n cm-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, the decay-corrected activities are compared to a calibration developed from multiple certified international reference materials. The standard present is only a check on accuracy and is not used for calibration purposes. From 10-30 % of the samples are rechecked by re-measurement.  For values exceeding the upper limits, assays are recommended.

One standard is run for every 11 samples. One blank is analyzed per work order. Selected duplicates are analyzed when enough material is submitted.

"Near Total" Digestion - ICP Portion

A 0.25 g sample is digested with four acids beginning with hydrofluoric, followed by a mixture of nitric and perchloric acids. This is then heated using precise programmer controlled heating in several ramping and holding cycles 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 Agilent 735 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.

 

Code E1H (Au + 48)  Elements and Detection Limits (ppm)

Element

Detection Limit

Upper Limit

Reported

By

Element

Detection Limit

Upper Limit

Reported By

Ag †

0.3

10,000

ICP&INAA

Mn

1

100,000

ICP

Al

0.01%

50%

ICP

Mo †

1

10,000

ICP

As

0.5

10,000

INAA

Na

0.01%

50%

INAA

Au

2 ppb

30,000 ppb

INAA

Nd

5

10,000

INAA

Ba

50

500,000

INAA

Ni †

1

100,000

ICP&INAA

Be

1

10,000

ICP

P

0.001%

10%

ICP

Bi

2

10,000

ICP

Pb

3

5,000

ICP

Br

0.5

5000

INAA

Rb

15

10,000

INAA

Ca

0.01%

70%

ICP

S+

0.01%

20%

ICP

Cd

0.3

2,000

ICP

Sb

0.1

10,000

INAA

Ce

3

10,000

INAA

Sc

0.1

1000

INAA

Co

1

5,000

INAA

Se

3

10,000

INAA

Cr

2

100,000

INAA

Sm

0.1

10,000

INAA

Cs

1

10,000

INAA

Sn

0.02%

20%

INAA

Cu

1

10,000

ICP

Sr

1

10,000

ICP

Eu

0.2

10,000

INAA

Ta

0.5

10,000

INAA

Fe

0.01%

70%

INAA

Tb

0.5

10,000

INAA

Hf

1

5000

INAA

Th

0.2

10,000

INAA

Hg

1

10,000

INAA

Ti

0.01%

10%

ICP

Ir

5 ppb

10,000 ppb

INAA

U

0.5

10,000

INAA

0.01%

10%

ICP

V

2

10,000

ICP

La

0.5

10,000

INAA

W

1

10,000

INAA

Li

1

10,000

Y

1

1,000

ICP

Lu

0.05

10,000

INAA

Yb

0.2

10,000

INAA

Mg

0.01%

50%

ICP

Zn †

1

100,000

ICP&INAA

 

 

Notes:      
Extraction of each element by 4-Acid Digestion is dependent on mineralogy.

+ Sulphide sulphur and soluble sulphates are extracted.

† Element reported by multiple techniques if one or more techniques may not be total.

 Assays are recommended for values which exceed the upper limits.

 

Reference  :

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




Activation Laboratories Ltd. | 41 Bittern Street, Ancaster, Ontario, L9G 4V5, Canada | TF: +1.888.228.5227
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