Stable Isotope Ratio Mass Spectrometer (SIRMS) Laboratory

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The Stable Isotope Ratio Mass Spectrometer (SIRMS) Laboratory is the main analytical facility in the Department of Atmospheric and Environmental Sciences dedicated to global paleoclimatological and paleoenvironmental research. Since beginning routine operation in October 1996, thousands of samples of coral, foraminifera, plants, sediment, soil, and water have been analyzed.

The heart of the facility is a Isoprime Optima gas-source triple-collector mass spectrometer equipped with a dual inlet.

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There are two units interfaced with the mass spectrometer, the MultiPrep automated sample preparation device and a Carlo Erba NA 1500 Series II NC elemental analyzer.

MultiPrep: The MultiPrep automated sample preparation device is used to digest powdered biogenic or mineral carbonate material with phosphoric acid or to equilibrate water samples with carbon dioxide or hydrogen. This single device takes the place of two older automated sample preparation devices made by Micromass, the Isocarb carbonate preparation device and the Isoprep 18 water equilibration device. The MultiPrep is adapted from a Gilson 222 XL liquid handler. Powdered carbonate material or water is placed in small septum-capped glass chromatography V-vials that are loaded into a heated rack controlled to ± 0.1 °C. A needle sequentially punctures each vial's septum, injecting either 100% phosphoric acid into vials containing carbonate material, or carbon dioxide or hydrogen into vials containing water samples. The carbon dioxide that is evolved during acid digestion of the carbonate material, or the carbon dioxide or hydrogen that has equilibrated with the water sample, enters a side port in the same needle and passes through a water trap prior to being frozen into cold fingers in the mass spectrometer's dual inlet.

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The evolved carbon dioxide or equilibrated carbon dioxide or hydrogen is analyzed by comparing its stable isotopic composition to that of reference carbon dioxide or hydrogen repeatedly during a 7-minute analysis. An average difference in isotopic composition between the sample and the working reference gas is determined using the following general equation:

[(Rsample-Rstandard)/(Rstandard)] x 1000 = deltasample-standard

where Rsample = ratio of the heavy isotope of interest to the light isotope of interest in the sample,

Rstandard = the same ratio in the working reference gas, and

deltasample-standard = the difference in isotopic composition of the sample relative to that of the reference, expressed in parts per thousand (per mil)

Through careful calibration, Rstandard of the working reference gas is known with respect to an internationally accepted standard, and hence Rsample can be determined relative to the same international standard. As an example, the carbon isotopic composition of a coral aragonite sample can be expressed as

[(13C/12Ccoral-13C/12Cref)/(13C/12Cref)] x 1000 = delta13Ccoral , expressed in per mil

As long as the (13C/12C) of the reference carbon dioxide is known with respect to an international standard such as Vienna Pee Dee Belemnite (VPDB), the delta13C of the coral can be expressed relative to VPDB.

A variety of solid, liquid, and gaseous reference standards may be found at the following two sites:

National Institute of Science and Technology

International Atomic Energy Agency

Elemental analyzer: The Carlo Erba NA 1500 Series II NC elemental analyzer is used to combust solid and viscous liquid samples containing organic matter. The samples are placed in tin foil capsules that are crimped to a bead and placed in a sample carousel. The carousel sequentially drops each capsule into a slide which, in turn, drops the capsule into a vertical furnace tube to be combusted. The capsule and sample are flash-combusted in a stream of oxygen at 1800°C. Evolved gases are carried in a stream of helium through an oxidizing furnace tube at 1025°C, a reducing furnace tube at 650°C, and a water trap at ambient temperature. The emerging anhydrous carbon dioxide and nitrogen pass through a 2-meter long packed chromatography column at 40°C which separates the gases from each other due to their different affinities for the column's exchange medium, with nitrogen eluting from the column before carbon dioxide. The gases are then carried in the helium stream to the mass spectrometer where they are analyzed by "continuous flow." The elemental carbon and nitrogen composition of the sample may be determined by comparison to the elemental composition of standards, while the carbon and nitrogen isotopic composition of the sample may be determined by comparison to the isotopic composition of a pulse of working reference carbon dioxide and/or nitrogen injected early during the 7-minute analysis. A Micromass Diluter facilitates the isotopic analysis of samples with high C/N ratios by diluting the amount of carbon dioxide produced by the combustion of the sample with helium so that the response of the mass spectrometer to the sample carbon dioxide pulse is more closely similar to the smaller sample nitrogen pulse than it would be if the Diluter were not employed. The elemental carbon and nitrogen composition of samples may also be determined utilizing the elemental analyzer alone, employing the unit's thermoconductivity detector.

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Well-characterized synthetic and natural internal working standards, calibrated by comparison to international standards, are analyzed at regular intervals during both dual-inlet and continuous-flow autoruns.

Ancillary instrumentation in the SIRMS facility includes:

A Dell OptiPlex 466/Le computer used to run the proprietary OS/2-based dual-inlet and continuous-flow software, a Dell UltraScan monitor (subsequently replaced by a Sylvania F74 monitor), an Epson LQ-570+ printer, and a MultiTech Systems MultiModem ZDX MT932 FAX/modem used for remote diagnostics.

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A FTS Systems FC100D10 immersion cooler, the probe of which is an integral part of the water trap in the MultiPrep device.

A Peak Scientific 8/24 oil-lubricated air compressor (very similar to the Werther International P50/24AL oil-lubricated compressor), supplying compressed air dried by an Arrow Pneumatics A-10 dryer to various pneumatic valves and air-actuated components in the mass spectrometer and elemental analyzer.

A Powerware 9170+ single-phase uninterruptible power supply provides backup power to the mass spectrometer, sample preparation device, and the elemental analyzer in the event of a power outage.

A large floor-standing Carrier air conditioner.

Other equipment in the SIRMS facility includes:

A Sartorius M2P microbalance for accurate weighing of samples to ±1 microgram.

A Fisher Scientific Isotemp 650G drying oven.

A large GE refrigerator/freezer.

A Thermolyne Thermo 30 dewar for containing 30 liters of liquid nitrogen used to cool cold fingers during dual-inlet analyses.

Two MVE Dura-Tech dewars each holding 230 liters of liquid nitrogen.

The SIRMS facility is managed by Stephen S. Howe, Research Geochemist and Instrumentation Support Specialist, in the Department of Atmospheric and Environmental Sciences, University at Albany, SUNY.

The SIRMS facility occasionally accepts samples for analysis on a contract basis. Contact Stephen S. Howe at this email for a price schedule and for instrument availability.

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