ARTEMIS, THE 14C AMS FACILITY OF THE LMC14 NATIONAL LABORATORY: A STATUS REPORT ON QUALITY CONTROL AND MICROSAMPLE PROCEDURES

ABSTRACT Quality control procedures have been developed at the Laboratoire de Mesure du Carbone 14 (LMC14) national laboratory throughout the years of operation. Routine procedures are applied to sample preparation depending on their composition and their size. The tuning of the ARTEMIS AMS facility, hosted by the LMC14 laboratory, uses an accurate procedure. A batch of unknown samples is measured with accompanying samples (primary and secondary standards and blanks), which give a powerful set of data to control the quality of each measurement. A homemade database has been created to store the sample information and study the evolution of the accompanying samples. The LMC14 laboratory participated in the Sixth International Radiocarbon Intercomparison, SIRI. The results are presented here, with statistical tests to assess the quality of the preparations and measurements done at the LMC14 national laboratory. To obtain a reliable radiocarbon (14C) age by AMS, 1 mg of sample is required in routine analysis. Recently, the LMC14 developed a new procedure dedicated to microsamples, allowing the size of samples to be reduced and contributing to opening 14C dating to materials that were previously unreachable. This new procedure has been successfully tested on valuable Cultural Heritage samples: lead white mural paintings.

Is the Consensus Value of ANU Sucrose (IAEA C-6) Too High?

Primary and secondary standards are essential in radiocarbon analyses for the purpose of reporting and comparing data among laboratories, as well as for internal laboratory data quality control. ANU sucrose is one of the IAEA-certified 14C standards (C-6) with a consensus value of 1.5061 ± 0.0011 fraction modern (Fm). All of our measurements of ANU sucrose (n = 351) as a secondary standard over the last 7 yr result in an average value of 1.5016 ± 0.0005 Fm (2-σ standard error). After applying the same outlier tests used for IAEA reference standards, a weighted average value of 1.5016 ± 0.0002 Fm (n = 294) was calculated. This value is significantly lower than the IAEA C-6 consensus value (t test with unequal variance; p = 0.023). In contrast, our measurements of other secondary standards over the same time period are in excellent agreement with their respective consensus values. Since ANU is the only secondary standard measured in our lab that does not agree with the consensus values, and we have measured a larger number analyses compared to what went into the definition of the consensus value, we suggest that the consensus value of ANU sucrose might be too high by ∼0.0045 ± 0.0011 Fm. Given that some labs routinely use ANU sucrose as a primary standard, our results suggest that revisiting the consensus value of ANU sucrose may be necessary.

Point Status of lipid and lipoprotein standardization

Cholesterol and triglyceride standardization procedures have been used extensively and continuously since the 1950s. Definitive and Reference Methods, as well as primary and secondary standards, have been developed and maintained as the basis for evaluating the accuracy of results by various methods in many laboratories. But, although standardization efforts for apolipoprotein A-I and B measurements have been reported in detail in the scientific literature, much less has been reported in the area of total and lipoprotein cholesterol and triglyceride standardization efforts. Standardized cholesterol and triglyceride concentrations, determined in multiple large epidemiological and clinical studies, have been instrumental to the National Cholesterol Education Program panels that have assessed the lipoprotein values associated with risk of coronary disease, and have determined the cutpoints that are now used extensively by physicians to guide diagnosis and treatment of individual patients.