Optimization of the Amount of Zinc in the Graphitization Reaction for Radiocarbon AMS Measurements at LAC-UFF

Radiocarbon ◽  
2016 ◽  
Vol 59 (3) ◽  
pp. 885-891 ◽  
Author(s):  
Kita D Macario ◽  
Fabiana M Oliveira ◽  
Vinicius N Moreira ◽  
Eduardo Q Alves ◽  
Carla Carvalho ◽  
...  
Keyword(s):  
Isotope Ratio ◽  
Isotope Fractionation ◽  
Reduction Method ◽  
Isotopic Fractionation ◽  
Isotope Ratio Mass Spectrometry ◽  
Methodological Research ◽  
Lower Variation ◽  
Zinc Reduction ◽  
Precision And Accuracy ◽  
Graphitization Temperature

AbstractThe Radiocarbon Laboratory of the Universidade Federal Fluminense, in Brazil, has been successfully applying the zinc reduction method for graphitization of carbon samples since the development of its early protocols in 2009. Successive methodological research aiming to improve and, ultimately, optimize the precision and accuracy of our results indicates that graphitization temperatures as low as 460°C promote erratic 13C isotopic fractionation, but an approximately constant fractionation of about –5‰ is achieved at 520°C. In this work, we present isotope ratio mass spectrometry (IRMS) δ13C results for 14C reference materials graphitized at 550°C with variable amounts of zinc. Based on the results obtained from the addition of 20, 35, and 50 mg of zinc, we conclude that a slightly lower variation in 13C isotope fractionation during graphitization is obtained with less zinc. Moreover, the average isotopic fractionation is not altered by increasing the graphitization temperature from 520°C to 550°C.

Ultra Small-Mass Graphitization by Sealed Tube Zinc Reduction Method for AMS 14C Measurements

Radiocarbon ◽  
2013 ◽  
Vol 55 (2) ◽  
pp. 608-616 ◽  
Author(s):  
Xiaomei Xu ◽  
Pan Gao ◽  
Eric G Salamanca
Keyword(s):  
Reduction Method ◽  
Isotopic Fractionation ◽  
Small Mass ◽  
Previous Method ◽  
University Of California ◽  
Fe Powder ◽  
Accuracy And Precision ◽  
On Line ◽  
Zinc Reduction ◽  
Graphitization Temperature

A modified sealed tube Zn reduction method based on Khosh et al. (2010) has been developed to graphitize ultra small-mass samples ranging from 4–15 μg carbon (C) for accelerator mass spectrometry (AMS) radiocarbon measurements. In this method, the reagent TiH2 is removed from the previous method while the amounts of Zn and Fe powder remain the same. The volume of the sealed reactor is further reduced by ∼40% to ∼0.75 cm3 and the graphitization temperature is lowered to 450 °C. Graphite targets produced by this method generally yield 12C+1 currents of about 0.5 μA per 1 μg C, similar to the small mass (15–100 μg C) sealed tube Zn reduction method previously reported by Khosh et al. (2010) when measured on the same AMS system at KCCAMS, University of California, Irvine. Change of Fe powder to Sigma-Aldrich (400-mesh) has yielded further improved backgrounds over Fe powder of Alfa Aesar (325-mesh). Modern C background from combustion and graphitization is estimated to be 0.2–0.8 μg C, and dead-C background to be 0.1–0.4 μg C. The accuracy and precision of ultra small-mass samples prepared by this method are size and 14C content dependent, but is usually ±4–5% for the smallest sample size of ∼4–5 μg C with modern 14C content. AMS on-line δ13C measurement that allows for correction of both graphitization and machine-induced isotopic fractionation is the key for applying the sealed tube Zn reduction method to ultra small-mass sample graphitization.

Isotope ratio analysis of carbon and nitrogen by elemental analyser continuous flow isotope ratio mass spectrometry (EA-CF-IRMS) without the use of a reference gas

2015 ◽  
Vol 30 (1) ◽  
pp. 310-314 ◽  
Author(s):  
L. J. Bay ◽  
S. H. Chan ◽  
T. Walczyk
Keyword(s):  
Mass Spectrometry ◽  
Continuous Flow ◽  
Isotope Ratio ◽  
Isotope Fractionation ◽  
Isotope Ratio Mass Spectrometry ◽  
Nitrogen Isotope ◽  
Ratio Analysis ◽  
New Approach ◽  
Carbon And Nitrogen ◽  
Isotope Ratio Analysis

A new approach to normalize carbon and nitrogen isotope ratios measured by EA-CF-IRMS without using a reference gas for correction of instrumental drifts and instrumental isotope fractionation.

scholarly journals Hydrogen isotope fractionation in the photolysis of formaldehyde

2008 ◽  
Vol 8 (5) ◽  
pp. 1353-1366 ◽  
Author(s):  
T. S. Rhee ◽  
C. A. M. Brenninkmeijer ◽  
T. Röckmann
Keyword(s):  
Isotope Ratio ◽  
Isotope Fractionation ◽  
Isotopic Fractionation ◽  
Photochemical Oxidation ◽  
Atmospheric Conditions ◽  
Isotopic Enrichment ◽  
Fractionation Factor ◽  
Removal Processes ◽  
Molecular Channel ◽  
Fractionation Factors

Abstract. Experiments investigating the isotopic fractionation in the formation of H2 by the photolysis of CH2O under tropospheric conditions are reported and discussed. The deuterium (D) depletion in the H2 produced is 500(±20)‰ with respect to the parent CH2O. We also observed that complete photolysis of CH2O under atmospheric conditions produces H2 that has virtually the same isotope ratio as that of the parent CH2O. These findings imply that there must be a very strong concomitant isotopic enrichment in the radical channel (CH2O+hν → CHO+H) as compared to the molecular channel (CH2O+hν → H2+CO) of the photolysis of CH2O in order to balance the relatively small isotopic fractionation in the competing reaction of CH2O with OH. Using a 1-box photochemistry model we calculated the isotopic fractionation factor for the radical channel to be 0.22(±0.08), which is equivalent to a 780(±80)‰ enrichment in D of the remaining CH2O. When CH2O is in photochemical steady state, the isotope ratio of the H2 produced is determined not only by the isotopic fractionation occurring during the photolytical production of H2 (αm) but also by overall fractionation for the removal processes of CH2O (αf), and is represented by the ratio of αm/αf. Applying the isotopic fractionation factors relevant to CH2O photolysis obtained in the present study to the troposphere, the ratio of αm/αf varies from ~0.8 to ~1.2 depending on the fraction of CH2O that reacts with OH and that produces H2. This range of αm/αf can render the H2 produced from the photochemical oxidation of CH4 to be enriched in D (with respect to the original CH4) by the factor of 1.2–1.3 as anticipated in the literature.

Development and characterization of a new in-house reference material for stable carbon and oxygen isotopes analyses

2021 ◽  
Author(s):  
Stefano Crivellari ◽  
Patricia Viana ◽  
Marilia Carvalho Campos ◽  
Henning Kuhnert ◽  
Alyne Barros ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Reference Material ◽  
Isotope Ratio ◽  
Isotope Ratio Mass Spectrometry ◽  
Scientific Production ◽  
Stable Carbon ◽  
Carbon And Oxygen Isotopes ◽  
Precision And Accuracy

The precision and accuracy of an isotope ratio mass spectrometry (IRMS) laboratory and the quality of its scientific production directly depend on the quality of its in-house reference material. However,...

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