Stable Isotope Mass Spectrometer

The laboratory houses a Micromass PRISM III stable-isotope mass spectrometer which is used for the analysis of the isotopic ratios of ¹³ C/ ¹² C , ¹⁸ O/ ¹⁶ O , ¹⁵ N/ ¹⁴ N , D/H, ³⁴ S/ ³² S , ³⁰ Si/ ²⁸ Si , ³⁷ Cl/ ³⁵ Cl.

The instrument contains a number of on-line sample preparation systems which enable analysis of a wide variety of geological and biological materials. The preparation devices are:

• Manifold of 10 automated tube crackers for the conventional (dual-inlet) analysis of prepared gas samples
• Multiprep system for the analysis of 18 O/ 16 O and D/H in water samples (by CO ² /H ² O and H ² /H ² O equilibration) and of ¹³ C/ ¹² C and ¹⁸ O/ ¹⁶ O in individual carbonate samples. As the samples are processed in separate vials, it is possible to collect the sample residue for additional analyses.
• Carlo Erba 1500 elemental analyser and gas chromatograph for the continuous-flow analysis of ¹³ C/ ¹² C, ¹⁵ N/ ¹⁴ N, ¹⁸ O/ ¹⁶ O and ³⁴ S/ ³² S in combustible samples.
• micro-gas preparation system and gas chromatograph for the isotopic analysis of gas samples, including breath gases, and for DIC in water.

Contacts

Allan Chivas
Tel: 61 2 4221 3263 (office)
Fax: 61 2 4221 4250
Email: toschi@uow.edu.au

David Wheeler
Tel: 61 2 4221 4586 (office)
Fax: 61 2 4221 4250
Lab: 61 2 4221 5903
Email: dwheeler@uow.edu.au

Pricing

The cost of analyses for external customers is $66 per analysis (plus GST if applicable). There is a lower cost for contributing members of the original RIEF consortium, or if analyses from part of a collaborative research endeavour. University of Wollongong clients are charged $27.00 per analysis (GST not applicable). This includes staff, postgraduate students, and Bachelor (Hons) & B. Env.Science 4th year students. The lower rate may also apply to post-graduate students from other universities who come to the University of Wollongong and prepare and analyse their own samples.

Methods

The following are brief summaries of the analytical methods used.

Manifold

Tubes are loaded into one of the ten automatic tube crackers attached to the manifold. The sample tubes are sequentially cracked and the gas passed to the sample side of the dual inlet. It is then analysed against the working gas. Small samples of most gasses can be frozen across into the liquid nitrogen cold-finger. Calibration can be achieved by analysis of gas prepared from standard reference materials, however it is more common to calibrate the working gas using another preparation system, usually the Multiprep.

Carbonates

Carbonates are analysed using a Micromass Multiprep device. Samples are loaded into 1mL Weaton V-vials which are sealed with Kel-F and silicone septa and placed in a heated block maintained at 90oC. A double-bore needle is pushed through the septa and into the vial, the vial is evacuated and then pure phosphoric acid (103%) is dispensed onto the sample. The evolved CO2 is passed through the water trap and cryogenically collected in the external cold finger. After all the gas has been collected it is released into the sample side of the dual inlet and is analysed against the working gas. Calibration is performed against an internal laboratory standard, NBS18 and NBS19. The routine minamum sample size is about 30mg of calcium carbonate, although it is possible to analyse samples as small as 20mg.

Oxygen in Water

Sample aliquots (200mL)are loaded into 1mL Weaton V-vials. Using a glove bag, the vials are filled with CO2 and then sealed with Kel-F and silicone septa and placed in a heated block maintained at 40oC. The samples are equilibrated for 5h. prior to analysis to ensure that the d18O of the CO2is identical to that of the water. During analysis the needle is pushed into the silicone septum and the transfer capillary is evacuated. Then the needle is pushed through both septa to sample the CO2 in the headspace above the water. The CO2is passed through the water trap and into the sample side of the dual inlet and is analysed against the working gas. Calibration is performed against internal laboratory standards and V-SMOW, GISP and SLAP (as appropriate).

Hydrogen in Water

Sample aliquots (200mL)are loaded into 1mL Weaton V-vials with a few 'hokko beads'. The vials are sealed with Kel-F and silicone septa and placed in a heated block maintained at 40oC. The needle is pushed through the septa, the vial is evacuated and then filled with hydrogen, and the needle removed. After equilibrating for 2h. to ensure that the dD of the H2 is identical to that of the water the needle is re-inserted to sample the hydrogen in the headspace above the water. The hydrogen is passed through the water trap and into the sample side of the dual inlet and is analysed against the working gas. Calibration is performed against internal laboratory standards and V-SMOW, GISP and SLAP (as appropriate).

Carbon or Nitrogen in Combustible organic samples

Aliquots of powdered sample are weighed into tin cups and the cups are crushed to exclude air. The autoloader drops the cups into the combustion tube which is heated to 1050oC while oxygen is injected into the helium carrier gas. The tin and sample flash combust and the product gasses are passed over catalysts and high purity copper. This ensures that all carbon is present as CO2 and all nitrogen as N2. Water is removed by a magnesium perchlorate trap. For nitrogen analyses the CO2 is removed by a 'Carbasorb' trap.

The product gas is carried to the mass spectrometer for measurment of the 13C/12C ratio relative to a reference gas. Calibration is achieved by including standard reference materials in the run at regular intervals