Problems:

Strategy:

Instrumentation:

Procedure:

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Chromitites are difficult to digest in acids, but acids are cleaner than flux chemicals.Low PGE abundances and high matrix concentration.PGE concentrations variable.

Molecular interferences of transition element argides (e.g. Cu Ar on Pd) are problematic.

Oxide interferences e.g. Rb O on Ru or Lu O on Ir should be of a lesser problemsince their abundances in chromitites are low.

Complete digestion of chromitites at high pressure and temperature in sealed quartz tubes toreplace Carius tubesExtraction of OsO with CCl

Ion exchange to separate matrix (either cation or anion exchange resin)

Measurement of Os with N-TIMS for isotope dilution and isotopic composition ( Os/ Os)Measurement of the remaining PGE and Re with ICPQMS or ICPSFMS.

CCl at room

temperature. The combined organic phases are heated with 4 mL HBr 48%(w/w) overnight at80°C. After discarding the CCl the HBr is dried down and microdistilled into 5µl HBr. The Os

is now ready for N-TIMS measurement.

There are two possibilities:Removing the matrix with an column (e.g. AG1X8). Most matrix elements passthe column directly. The PGE chloro complexes are eluted with HCl and HNO conc. Problems

are: the low recoveries of Pt and Ir, the need of large amounts of strong acids ( resin attack andblank), the control of oxidation state (Ir), Cr(VI) and Cu also elute with the PGEs.

Loading the sample solution directly onto a column (e.g. AG50WX8) andelution with 0.5 M HCl retains the matrix on the column and the chloro complexes pass throughthe column. Although some transition elements also elute with the sample they are reduced to anegligible amount. Only little dilute acid is needed thus blanks and the amounts of organics arelow. Problems occur when the column is overloaded with cations, thus the sample amountloaded is limited unlike the anion exchange columns.

In either case any Cr(VI) that formed during digestion needs to be reduced to Cr(III) with H O

since CrO behaves similar to the PGE chloro complexes.

Although most of the matrix was removed, traces of Cr remain.

6 5 4 0 1 0 5

8 5 1 6 1 0 1 1 7 5 1 6 1 9 1

1 8 7 1 8 8

2 -

OsO is volatile (BP ca. 105°C).

0.3 to 0.4 g of powdered or crushed chromitite sample with 5 mL HNO conc. 2 mL HCl conc.

and an appropriate amount of a mixed spike solution containing Ru, Pt, Re, Os and Ir in 50 mLquartz tubes goes completely into solution at 125 bar and 320°C in 3 to 5 hours. Only a colorlessresidue (leached silicates) remains. The digest is diluted to a final volume of 50 mL and is readyfor the ion exchange step.

After opening the HPA-S tubes OsO is extracted in 2x3 mL and 1x2 mL

Very sensitive in the high mass range. Problems occurred with the formation of Cr O H species

interfering with Ru, Pd and also Re. The following species have been identified:

CrO > CrO > CrO H interference with Ru

CrO H interference with Re

The isotope ratios Ru/ Ru and Pd/ Pd were severely, Re/ Re slightly disturbed.

Although less sensitive in the high mass range (Re, Ir and Pt) good results for all elements wereobtained due to low molecular interferences of the transition elements. Problems were memoriesin the MCN6000 system and drift effects. Recalibration and background corrections werenecessary more frequently.

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3

4

x x x

2 3

8 3

4 4

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2 2

4

Digestion:

Separation:

Os.

ELEMENT

HP4500 and MCN6000

Other PGE and Re.anion exchange

cation exchange

Measurement:

5 2 5 2 5 2 1 0 1

5 2 1 8 5

1 0 1 9 9 1 0 6 1 0 5 1 8 7 1 8 5

Thomas Meisel , Johann Moser and , Department of General and Analytical Chemistry

University of Leoben, Franz-Josef-Strasse 18, A-8700 Leoben/Austria, Anton Paar GmbH, A-8054 Austriae-mail: meisel unileoben.ac.at and johann.moser unileoben.ac.at

1 2 1

2

1Peter Kettisch

@ @

Determination of Osmium and Other Platinum Group Elementsin Chromitites by Acid Digestion and ICPMS

Goal: Development of a simple method for the determination of Ru, Pd, Os, Ir, Pt (PGE) and Re concentrations in chromitites

Final procedure for the digestion anddetermination of Ru, Pd, Re, Os, Ir and Ptin chromitite.

PGE isolation by anion exchange does notseparate them from remaining Cr(VI). Theisotopic composition of Pd and Ru aregreatly influenced if measured withoutmembrane desolvation.

Summary:

Chromitites go into solution completely.

Cation exchange resin is most effective for matrix separation.

Membrane desolvation is essential for ICPMS measurement.

Isotope dilution is reliable and simple.

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Only dilute and small amounts of acid isused for matrix separation. Desolvationmakes accurate isotope ratio determina-tion possible.

sample + spike

5mL HNO3, 2 mL HCl

digestion HPA-S

125 bar, 320°C

3-5 h

extract OsO4 N-TIMS

conc. low?

reduce volume

cation exchange

AG50Wx8

0.5 M HCl

conc. low?

reduce volume

ICPMS

HP4500+MCN6000

HBr

CCl4

yes

yes

anion exchange resin AG1x8

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0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 10 20 30 40 50

mL

rel.

un

its,

iso

top

era

tio

CrO2

101Ru-52CrO3H

108Pd/105Pd

105Pd

8M HNO3 13.5M HNO3 11M HCl 13.5M HNO3

after Rehkämper and Halliday (1997)

natural ratio

Finnigan MAT ELEMENT

cation exchange resin AG50Wx8

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 10 20 30 40 50

mL

rel.

un

its,

isoto

pe

rati

o

85Rb-CrO2

101Ru

108Pd/105Pd

105Pd

0.5 M HCl

natural ratio

HP 4500 + MCN6000

ELEMENT (Finnigan MAT)

RF 1300 W, low flow pneumaticnebulizer in selfaspiration. 1.0%

CeO /Ce. 1.4 Mcps Ce+ 1 4 0

HP4500MCN6000

(Hewlett Packard)(FMS-Cetac)

RF 1150W, 0.9 L/min carrier gasflow, MCN, PTFE spray chamber.

0.02% CeO /Ce, 0.4 Mcps Ce.+ 1 4 0

HPA-S (Perkin Elmer-Anton PAAR)high pressure asher

( ) ( )

( ) ( )

( )

( )S

S

N

NNM

SMS

N cN

S

AW

AW

ABRK

BRKAc ⋅⋅⋅

−⋅⋅⋅⋅−

=

MR ... measured isotope ratio

K ... mass discrimination correction factor

N ... sample mass

S ... spike mass

Nc ... concentration (w/w) of the natural iridium in the sample

Sc ... concentration (w/w) of the iridium in the spike

( )NA ... atomic abundance (mol/mol) of isotope A in the sample

( )SA ... atomic abundance (mol/mol) of isotope A in the spike

( )NB ... atomic abundance (mol/mol) of isotope B in the sample

( )SB ... atomic abundance (mol/mol) of isotope B in the spike

( )NAW ... atomic weight of the iridium in the sample

( )SAW ... atomic weight of the iridium in the spike

cS N S AW(S) AW(N) A(N) B(N) A(S) B(S) RM K

standard uncertainties 5.7 0.0001 0.0001 0.016 0.016 0.000058 0.000058 0.000058 0.000058 0.0008 0.0011

cS 111.5 117.2 111.5 111.5 111.5 111.5 111.5 111.5 111.5 111.5 111.5 111.5

N 0.32971 0.32971 0.32981 0.32971 0.32971 0.32971 0.32971 0.32971 0.32971 0.32971 0.32971 0.32971

S 0.67644 0.67644 0.67644 0.67654 0.67644 0.67644 0.67644 0.67644 0.67644 0.67644 0.67644 0.67644

AW(S) 191.00 191.00 191.00 191.00 191.01 191.00 191.00 191.00 191.00 191.00 191.00 191.00

AW(N) 192.21 192.21 192.21 192.21 192.21 192.23 192.21 192.21 192.21 192.21 192.21 192.21

A(N) 0.6236 0.6236 0.6236 0.6236 0.6236 0.6236 0.6236 0.6236 0.6236 0.6236 0.6236 0.6236

B(N) 0.3764 0.3764 0.3764 0.3764 0.3764 0.3764 0.3764 0.3765 0.3764 0.3764 0.3764 0.3764

A(S) 0.0184 0.0184 0.0184 0.0184 0.0184 0.0184 0.0184 0.0184 0.0185 0.0184 0.0184 0.0184

B(S) 0.9816 0.9816 0.9816 0.9816 0.9816 0.9816 0.9816 0.9816 0.9816 0.9816 0.9816 0.9816

RM 0.7025 0.7025 0.7025 0.7025 0.7025 0.7025 0.7025 0.7025 0.7025 0.7025 0.7033 0.7025

K 1 1 1 1 1 1 1 1 1 1 1 1.0011

cN 430 452.3 430.2 430.4 430.3 430.4 430.3 430.4 430.3 430.4 431.2 431.2

cN [ng/g] 430 430.4 430.4 430.4 430.4 430.4 430.4 430.4 430.4 430.4 430.4 430.4

differences 21.90 -0.13 0.06 -0.04 0.04 -0.07 0.05 -0.04 0.03 0.87 0.84

squares 479.55 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.75 0.70

sum of squares 481

square root 22

%RSD 5.1

Example for the calculation of combined standard uncertainty of theconcentration of iridium in a chromitite sample. The uncertainty associated withthe concentration of the spike has the greatest influence.