A simple polymer electrolyte membrane system for enrichment of low-level tritium (H) in environmental water samples.

Tritium (H) is an essential tracer of the Earth's water cycle; yet widespread adoption of tritium in hydrologic studies remains a challenge because of analytical barriers to quantification and detection of H by electrolytic pre-concentration. Here, we propose a simple tritium electrolytic enrichment system based on the use of solid polymer electrolyte membranes (PEMs) that can be used to enrich H in 250-3000 mL environmental water samples to a 10-mL final volume. The IAEA PEM-H system reported here can produce high enrichment factors (>70-fold) and, importantly, removes some of the deterrents to conventional H enrichments methods, including the use of toxic electrolysis and neutralization chemicals, spike standards, a complex electrolysis apparatus that requires extensive cooling and temperature controls, and improves precision by eliminating the need for tracking recovery gravimetrics.

N and O isotope (δ N , δ N , δ O, δ O) analyses of dissolved NO and NO by the Cd-azide reduction method and N O laser spectrometry.

Rationale: The nitrogen and oxygen (δ N, δ O, δ O) isotopic compositions of NO and NO are important tracers of nutrient dynamics in soil, rain, groundwater and oceans. The Cd-azide method was used to convert NO or NO to N O for N and triple-O isotopic analyses by N O laser spectrometry. A protocol for laser-based headspace isotope analyses was compared with isotope ratio mass spectrometry.

Approaches for achieving long-term accuracy and precision of δ18O and δ2H for waters analyzed using laser absorption spectrometers.

The measurement of δ(2)H and δ(18)O in water samples by laser absorption spectroscopy (LAS) are adopted increasingly in hydrologic and environmental studies. Although LAS instrumentation is easy to use, its incorporation into laboratory operations is not as easy, owing to extensive offline data manipulation required for outlier detection, derivation and application of algorithms to correct for between-sample memory, correcting for linear and nonlinear instrumental drift, VSMOW-SLAP scale normalization, and in maintaining long-term QA/QC audits. Here we propose a series of standardized water-isotope LAS performance tests and routine sample analysis templates, recommended procedural guidelines, and new data processing software (LIMS for Lasers) that altogether enables new and current LAS users to achieve and sustain long-term δ(2)H and δ(18)O accuracy and precision for these important isotopic assays.

Lower groundwater ¹⁴C age by atmospheric CO₂ uptake during sampling and analysis.

Uptake of atmospheric CO₂ during sample collection and analysis, and consequent lowering of estimated ages, has rarely been considered in radiocarbon dating of groundwater. Using field and laboratory experiments, we show that atmospheric CO₂ can be easily and rapidly absorbed in hyperalkaline solutions used for the extraction of dissolved inorganic carbon, resulting in elevated ¹⁴C measurements. Kinetic isotope fractionation during atmospheric CO₂ uptake may also result in decrease of δ¹³C, leading to insufficient corrections for addition of dead carbon by geochemical processes.

A portable membrane contactor sampler for analysis of noble gases in groundwater.

To enable a wider use of dissolved noble gas concentrations and isotope ratios in groundwater studies, we have developed an efficient and portable sampling device using a commercially available membrane contactor. The device separates dissolved gases from a stream of water and collects them in a small copper tube (6 mm in diameter and 100 mm in length with two pinch-off clamps) for noble gas analysis by mass spectrometry. We have examined the performance of the sampler using a tank of homogeneous water prepared in the laboratory and by field testing.