People

The Environmental Biology Group Stable Isotope Facility (EBSIF) is operated by four people. Dr Hilary Stuart-Williams (Research Officer) maintains the mass spectrometers, develops techniques and manages the facility.Help with maintenance and sample processing comes from Dr Steve Clayton. Electronics expertise and experimental design come primarily from Dr S. Chin Wong (Research Officer), while fabrication and design detail are provided by Peter Groeneveld. Programming support is provided by HSW and SCW.

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Equipment

EBSIF runs four stable isotope ratio mass spectrometers (IRMS)and an elemental analyser. There are three continuous-flow (CF) IRMS (one with dual-inlet capabilities) and a dedicated dual-inlet machine. Two Micromass IsoChrom CFIRMS are responsible for the bulk of the carbon, nitrogen and oxygen analyses. A recently delivered Micromass IsoPrime IRMS is primarily for use in CF mode for hydrogen isotope analysis but also has a dual-inlet designed for high precision analysis of carbon dioxide. A VG SIRA 24 is maintained for high precision carbon dioxide analysis. This machine has been updated with modern software and has high vacuum provided by turbo and molecular drag pumps. Elemental analyses are performed on a Carlo Erba EA-1110 CHN-O analyser.

The mass spectrometers are housed in state-of-the-art laboratories with gases piped in at controlled rates, with continuous monitoring of flows and atmospheric concentrations.

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Who uses this facility?

EBSIF provides analytical facilities to the Environmental Biology group as well as other teams in RSBS and within ANU. We are also pleased to co-operate with outside workers from all over the world to analyse a variety of materials. People interested in using this service should contact Hilary Stuart-Williams or Sue Wood to discuss cost and availability. Cost varies widely depending on the nature of our relationship with the project, the number of samples and the materials to be analysed, et cetera. For some extra information see the sample preparation instruction sheet.

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Micromass IsoChroms

Two Isochroms are used in EBSIF, one for carbon and nitrogen isotopic analysis and the other for oxygen isotopic analysis. The carbon system uses a typical oxidizing combustion system, while the oxygen machine uses high temperature pyrolysis.

Micromass IsoChrom for carbon and nitrogen isotopic analysis

The IsoChrom is connected to an EA-1110 Elemental CHN-O Analyser and is dedicated to measuring carbon dioxide and nitrogen isotopes in organic samples. Usually we make runs of about 150 samples which are dropped from a rotary sample dropper. The organic sample is then combusted in a pulse of oxygen. The combustion gases (dominantly carbon dioxide, water and nitrogen) are separated in a GC column and pass in a helium gas stream to the mass spectrometer. The demands for the two gases are rather different: in order to reduce sample heterogeneity we like to measure about 1 mg of plant material for carbon, whilst we must accept much less nitrogen from low N plant samples. After the failure of the original turbo, high vacuum is now provided by an Alcatel turbo molecular pump with an external controller and safety cutout.

Micromass IsoChrom for oxygen isotopic analysis

The IsoChrom CFIRMS used for oxygen isotopic analysis is essentially a standard unit with a pyrolysis front-end that has recently been extensively modified. Previously we used a CE elemental analyser running at 1080 degrees C, but this has now been replaced by a two-column system designed by Chin Wong that typically runs at 1200 - 1400 degrees C and for oxygen analysis converts the sample almost quantitatively to carbon monoxide. Removing the EA meant that we had to provide a separate Shimadzu GC oven with a built in TCD. The GC column was built by ourselves (as are most of our columns) and consists of a 2 metre stainless steel tube packed with molecular sieve. We salvaged the rotary sample dropper from the EA and it is now actuated by our own system, triggered by the signals originally used for controlling the EA cycle. The system is under continuous development

Part of the new equipment surrounding the O-18 IsoChrom. Centre, top, is the rack of solenoids for the sample dropper. To its left is one of the helium mass flow controllers. A blue CO detector hangs down at the front.

The rear of the IsoChrom with the high temperature furnace controller. Not a click to be heard! Almost all furnace switching is ramped and solid-state.

The front of the IsoChrom with the Shimadzu GC/TCD on top and a mass flow controller for the helium carrier on top of that! The high temperature furnace is to the left of the mass spectrometer.

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Micromass IsoPrime

This machine was delivered and installed in September 2002. It was acquired primarily for hydrogen isotope research by continuous-flow analysis, but also has a micro-volume dual inlet for precision work on small gas samples - typically carbon dioxide. Our main plan for the machine is to use it to provide hydrogen isotope analyses for plants, complementing the extensive oxygen isotopic work that we have already done. We will examine the ways that hydrogen isotopic responses differ from the oxygen isotopic trends, including looking at hydrogen isotopes in Calvin Cycle products. The machine uses the same high temperature furnace front-end as the O-18 IsoChrom, but has its own pyrolysis column and Shimadzu GC/TCD unit. The software for the Isoprime runs under Windows NT, in comparison with the IsoChrom beside it which is running its software under OS/2 2.1. For people interested in CPU's the IsoPrime employs a Motorola 68000, as found in Macintosh computers. The mass spectrometer communicates with the PC over a serial link and through fibre optic cables.

The Micromass IsoPrime CFIRMS. Three rotary pumps and three turbos, with the dual-inlet system. The GC oven sits beside the rotaries with the high temperature furnace in the top right corner of the picture.

A detail of the top of the IsoPrime with the electromagnet, the dual-inlet system and the CF capillaries.

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VG SIRA 24

The VG SIRA 24 is a vintage dual-inlet, permanent magnet machine with two separate flight-tubes, sources and collector assemblies to permit the analysis of hydrogen and other gases. We have removed the hydrogen capability (blanking off the hydrogen analyser) and upgraded the pumping - the SIRA now uses an Alcatel turbo molecular pump to replace the main diffusion pump under the analyser, and an Alcatel molecular drag pump to provide high vacuum on the inlet side. The machine is controlled by custom written software running under Windows 98. Backing is provided by two rotaries - one provides high vacuum to the analyser continuously and backing to the inlet high vacuum when the inlet rotary is rough pumping. When rough pumping is completed the inlet roughing pump switches back to provide backing to inlet high vacuum. The drag pump is tolerant of poor backing and gulps of gas, while the software ensures that the valves are set so that the drag pump is always backed.

		The SIRA 24 is fully functional but has a period charm - the matching Avocado stools say it all. Notice the insertion of the turbo and drag controllers at the top of the rack with the vacuum system protection monitor.
	Windows based software running the SIRA, shown with high vacuum turned off and the backing pumps isolated.

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Carlo Erba EA-1110 CHN-O Elemental Analyser

This machine provides reliable elemental analyses of a continuous stream of samples. The EA uses a molecular sieve filled column similar to that in all our other machines. The most common analyses are for carbon and nitrogen content but we also run hydrogen on demand. Oxygen is more conveniently analysed on the IsoChrom that routinely runs oxygen isotopes.

The EA has a rotary sample dropper permitting single runs of nearly 150 samples.

Method development

In addition to equipment development, we are also interested in developing new methods for
stable isotope analyses. If you have an idea that you would like to try, contact one of us!

Many of our papers include method development, but the following are specifically devoted to new analytical techniques:

Farquhar G.D.,Henry B.K.,and Styles J.M.(1997). A rapid on-line technique for determination of oxygen isotope composition of nitrogen-containing organic matter and water. Rapid Communications in Mass Spectrometry, 11(14): 1554-1560

Gan, K.S, Wong, C.S. and Farquhar, G.D. (In press) Oxygen isotope analysis of plant water without extraction procedure. In Handbook of stable isotope analytical techniques. Volume 1 (Ed. Pierre A. de Groot), Elsevier

Stuart-Williams, H. Le Q. (In press) A new method for the isotopic examination of sub-milligram carbonate samples, using sulphamic acid (NH2.SO3H) at elevated temperatures In Handbook of stable isotope analytical techniques (Ed. Pierre A. de Groot.), Elsevier

Stuart-Williams, H. Le Q. and Schwarcz, H.P. (1995) Oxygen isotopic analysis of silver orthophosphate using a reaction with bromine. Geochim. Cosmochim. Acta 58, 3837-3841

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