Optimizing the analyte introduction for 14C laser ablation-AMS†
Recently a novel approach enabling spatially resolved analyses of radiocarbon (14C) in carbonates has been introduced, combining laser ablation with accelerator mass spectrometry (LA-AMS). Here, we present a comprehensive study to find optimum working conditions for LA-AMS. The stepwise optimization and characterization process comprises (i) finding a suitable laser source for the ablation of carbonates with highest CaCO3 to Cgas (i.e. CO2 or CO) conversion rate, (ii) studying different capillaries with different gas flow resistance that interface the LA-cell with the ion source of the AMS system, and (iii) determining the exchange rate of the LA cell and the width of a stalagmite's growth stop under real measurement conditions. Three laser sources (Nd:YAG@266 nm; Nd:YAG@213 nm; ArF excimer@193 nm) were tested at different fluences (3 and 23 J cm−2) for their Cgas-conversion efficiencies. Highest Cgas-conversion efficiencies of (70 ± 4)% were found with an ArF excimer laser, independently of laser fluence. The characterization of the system using different capillaries showed that gas flow rates applied in LA-AMS are more than a factor of five higher than for regular 14C AMS gas measurements, which probably results in reduced ionization efficiencies of the LA-AMS setup. An exchange rate of 10 min−1 is determined for the LA-cell design applied in this study by matching a 14C dataset derived by LA-AMS with modeled data (χ2-fit). Additionally, the model allowed to estimate the width of a growth stop in a stalagmite sample to be on the order of 0.25 mm.
- This article is part of the themed collection: Young Analytical Scientists