Tips and traps in the C-14 bio-AMS preparation laboratory

Maintaining a contamination free sample preparation lab for biological C-14 AMS requires the same or more diligence as a radiocarbon dating prep lab. Isotope ratios of materials routinely range over 4-8 orders of magnitude in a single experiment, dosing solutions contain thousands of DPM and gels us ed to separate proteins possess C-14 ratios of 1 amol C-14/mg C. Radiocarbo n contamination is a legacy of earlier tracer work in most biological labor atories, even if they were never hot labs. Removable surface contamination can be found and monitored using swipes. Contamination can be found on any surface routinely touched: door knobs, light switches, drawer handles, wate r faucets. In general, all surfaces routinely touched need to be covered wi th paper, foil or plastic that can be changed frequently. Shared air suppli es can also present problems by distributing hot aerosols throughout a buil ding. Aerosols can be monitored for C-14 content using graphitized coal or fullerene soot mixed with metal powder as an absorber. The monitors can be set out in work spaces for 1-2 weeks and measured by AMS with regular sampl es. Frequent air changes help minimize aerosol contamination in many cases. Cross-contamination of samples can be minimized by using disposable plasti c or glassware in the prep lab, isolating samples from the air when possibl e and using positive displacement pipettors. (C) 2000 Elsevier Science B.V. All rights reserved.