Stable Isotrope | AMS Prep Laboratory | Technical Developments at UCI

Target preparation for accelerator mass spectrometer (AMS) dating is available as part of the Keck-CCAMS facility. At present, we can combust organic material, acidify carbonates, and perform simple sample processing and purification procedures – such as acid- and base-hydrolyses, preparation of cellulose, purification of CO2 from air, and molecular weight separation of macromolecules by centrifuge filtration. We also have the capability (on pre-existing UC Irvine preparation laboratory) to separate organic compound classes, ie., lipids using methylene chloride/methanol extraction, and sugars and amino acids using column chromatography. We have run over 5000 research unknowns plus 3000 standards, blanks and test samples supplied from our three sample preparation laboratories from October 2002 to June 2004 and we are currently measuring about 500 unknowns per month.

The AMS pretreatment-laboratory became full operated in the end of 2002. It is equipped for routine processing of low-level samples with a background of >55,000 years on processed graphite. We also can generate graphitize samples from 1mgC to 25μgC. Improvements to graphitize ultra-small samples are ongoing and we do expect to drop the sample size furthermore.

This laboratory is devoted to: (1) improving the precision and accuracy of the AMS measurements, (2) teaching collaborators and their students how to make their own samples, (3) preparation of recharge samples, and (4) preparation of samples in support of funded research by Southon and G. dos Santos. Samples are processed for collaborative research with UC and non-UC PIs, and limited analytical services (commercial sample preparation and measurement) are available. See price list for more info.

Radiocarbon sample preparation

The goal of target preparation is to produce graphite samples from carbonaceous raw materials after removing any contamination not associated with the sample itself.

Submitted samples are chemically and/or physically pre-treated, when necessary, to remove any unwanted material before conversion to carbon dioxide (by combustion or acid hydrolysis) and then to graphite cathodes.

Pre-treatments

Organic Samples (Acid/Base/Acid) – This procedure involves a first removal of any visually obvious contamination, followed by an acid wash (HCl), repeated base washes (NaOH), a final HCl¯ treatment, and rinsing with deionized water. Carbonates samples are leached in dilute HCl to remove secondary carbonate. Many other procedures can also be applied if necessary to isolate the sample from the matrix. Please contact us for more information.

Carbon dioxide production and isolation

For organic materials, this is done by combustion at 900°C in evacuated sealed quartz tubes in the presence of CuO oxidizer and silver wire.  For carbonates we use acid hydrolysis procedure, with 85% phosphoric acid in disposable septum-sealed reactors (Vacutainer blood collection vials).

Graphite Reduction

Following cryogenic purification, the carbon dioxide is reduced to graphite in a reaction at 560°C with hydrogen, and iron powder catalyst.

Our two graphitization lines have 12H2/Fe reduction reactors each, allowing us to prepare 48 samples a day. Mg(ClO4)2 is used for reaction water removal and the progress of the reaction is monitored using a pressure transducer. Samples prepared on these lines have demonstrated 0.3% precision and 55,000 year backgrounds.

AMS Analysis

All graphite targets measured will receive a unique UC IrvineAMS# whether prepared in-house or received from outside submitters. Please use this number when listing 14C results in publications.

We will report the date provided by the AMS facility, but data interpretation is left up to the submitter except for collaborative projects.

IMPORTANT:

The Keck-CCAMS facility highly encourage submitters who a) have funded cycle carbon projects and b) develop processing capabilities for large numbers of samples in their own laboratories. This accomplishes three goals: (1) it reduces the burden on sample preparation labs at UC Irvine, ensuring timely sample turnaround; (2) it ensures that the science performed has undergone intensive peer review for excellence and relevance to carbon cycling and; (3) it lowers per-sample costs. The reliance on investigator sample preparation requires that researchers receive training in AMS sample preparation. To reach these goals, we will offer an annual summer course, including hands-on experience, to graduate students and postgraduate researchers to facilitate training and expand future collaborations. Any person interested, please contact us.