eichrom

Expertise in Sample Preparation

Application Note: 502

Determination of Thorium
in High Purity Aluminum by ICP-MS

Abstract:
A combined matrix removal by on-line solid phase extraction and ICP-MS method has beendeveloped for the determination of thorium in high purity aluminum. The sample solution
prepared as 3M HNO3 solution was loaded onto a column packed with TEVA Resin (Eichrom
Technologies, Inc, Darien, IL, USA.) Thorium is retained on the column and then eluted by 1M
HCl solution. The effluent was directly introduced into the nebulizer of an ICP-MS instrument
and thorium was measured continuously at a mass number of 232. Thorium at ppb or sub ppb
levels in high purity aluminum reference materials provided by the Japan Society of AnalyticalChemistry was determined accurately and precisely.

Introduction.
Thorium in nature consists of almost 100% 232Th, which is a radioisotope with a very long halflife (1.4 x 1010 years.) The alpha particles emitted by even a very small amount of thorium in alarge scale integrated circuit (LSI) materials induces
soft errors in the CPU of a computer and the strict
control of its concentration in LSI materials at ppblevels (or less) is important. Inductively coupledplasma mass spectrometry (ICP-MS) is a suitable
analytical technique for measuring this level ofthorium. Because this technique is susceptible tomatrix interferences, it is absolutely necessary toseparate the thorium analyte away from other matrix
components prior to injection into the plasma toensure accurate measurement of thorium values.
TEVA Resin from Eichrom Technologies is a
specialty chromatographic material that has a very
high affinity for tetravalent thorium from nitric acidsolutions and a low affinity for most mono-, di- andtri-valent metal ions, including aluminum (see figure2&3.) The retention of Th is quite low from HClFigure 1solutions and could be used to elute thorium sorbed
on to the column. This resin was used to remove
matrix components of the samples for thorium analysis prior to injection in the ICP-MSinstrument.

Experimental:
Aluminum samples (20 – 200 mg) were dissolved in 3 mL each of HNO3 and HCl with heating
followed by evaporation to near dryness. The residue was treated with 3 mL each of HNO3 andHCl, followed by 3 mL of HNO3 and finally, the residue was taken up in 5 mL of 3M HNO3.
01/03/2006

Application Note: 502
A flow injection system was used to accomplish the matrix elimination on-line. The separation
column was prepared by packing 3 g of TEVA Resin in a 4.6 x 50 mm PEEK column. The
column was conditioned with 3M HNO3 for 1 minute at a flow rate of 3 mL/min. Samples
prepared as above were passed through thePlasma Conditions
column at 3 mL/min flow rate to sorb thorium onRf power
1kw
the TEVA Resin column. Following a 2 minute
Nebulizer gas flow 1.0 L/minrinse with 3M HNO3 to remove aluminum, thePlasma gas flow
16.0 L/minthorium was eluted with 1M HCl in a reverse
Auxiliary gas flow 1.0 L/mindirection flow. The column effluent was
Sampling conditions
Sampling depth
10 mm
introduced directly into the nebulizer of the ICPSampling
cone
Copper, 0.80 mm orifice
MS system (Seiko, SPQ9000, Tokyo, Japan.) The
Skimmer cone
Copper, 0.40 mm orifice
operating conditions for the ICP-MS are shown in Table 1. ICP-MS Operating Conditions
Table 1.

Results
SampleJAC0021

JAC0022

JAC0023

Size(g)0.02680.02600.0279Mean:
0.08080.08460.0811Mean:
0.31200.2726
0.27970.26080.31810.2762Mean:

Th found(ng/g)
10.7
11.3
10.7
10.9 ± 0.35
1.4
1.4
1.7
1.5 ± 0.2
0.099
0.073
0.089
0.084
0.091
0.080
0.086 ± 0.009

Certifiedvalue (ng/g)

9.7 ± 1.7

1.7 ± 0.4

Various high purity aluminum referencematerials supplied by the Japan Society for
Analytical Chemistry were analyzed forthorium content using the method describedabove. These results are summarized intable 2. Each analytical value is in good
agreement with the corresponding certified
value and precision is excellent.
The sample throughput is five samples perhour when a 10 mL sample is used and thedetection limit of 8 pg was achieved (3σ ofbackground noise.)0.086 ± 0.037

Table 2 Determination of thorium in high purity aluminum reference materials.

Reference:Seki, T. & Oguma, K., J. Flow Injection Anal. Vol. 18, No. 2, (2001) 140-143.

eichrom
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Suite 106
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+1-630-963-0320 (tel)info@eichrom.com

01/03/2006

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