Assessing the performance of international laboratories analysing the stable isotope composition (δ N, δ O, δ O) of nitrate in environmental waters.

Rationale: Stable-isotope analyses of nitrate (NO ) in various water sources are crucial for understanding nitrogen pollution and its impact on aquatic ecosystems. We evaluated the accuracy and precision of stable-isotope analyses of nitrate conducted by international laboratories.

Methods: Six samples with nitrate (2 mg L NO -N) were sent to 47 laboratories.

Automated rapid triple-isotope (N, O, O) analyses of nitrate by Ti(III) reduction and NO laser spectrometry.

The nitrogen and oxygen (N, O, O) stable isotopic compositions of nitrate () are crucial tracers of nutrient N sources and dynamics in aquatic and atmospheric systems. Methods to reduce aqueous to NO gas (microbial or Cd method) before N and O isotope analyses require multi-step conversion or toxic chemicals, and O in NO cannot be disentangled by IRMS due to isobaric interferences. This technical note describes the automation of the stable-isotope analyses of nitrate by coupling the new Ti method with a headspace autosampler and an NO triple-isotope laser analyzer based on off-axis integrated cavity output spectroscopy.

Nitrate isotopes reveal N-cycled waters in a spring-fed agricultural catchment.

Nitrate stable isotopes provide information about nitrate contamination and cycling by microbial processes. The Fischa-Dagnitz (Austria) spring and river system in the agricultural catchment of the Vienna basin shows minor annual variance in nitrate concentrations. We measured nitrate isotopes (N, O) in the source spring and river up to the confluence with the Danube River (2019-2020) with chemical and water isotopes to assess mixing and nitrate transformation processes.

Assessment of rapid low-cost isotope (δ N, δ O) analyses of nitrate in fruit extracts by Ti(III) reduction to differentiate organic from conventional production.

Rationale: The isotopic composition (δ N, δ O) of nitrate in fruits and vegetables differentiates organic from conventional food production practices. Organic systems do not use synthetic nitrate fertilizers high in O and low in N and thereby help reveal producers' fertilization claims. Isotope analyses of nitrate extracted from fruits and vegetables are done by bacterial reduction which is costly and by specialized laboratories.

Progress and challenges in dual- and triple-isotope (δ O, δ H, Δ O) analyses of environmental waters: An international assessment of laboratory performance.

Rationale: Stable isotope analyses of environmental waters (δ H, δ O) are an important assay in hydrology and environmental research with rising interest in δ O, which requires ultra-precise assays. We evaluated isotope analyses of six test water samples for 281 laboratory submissions measuring δ H and δ O along with a subset analyzing δ O and Δ O by laser spectrometry and isotope ratio mass spectrometry (IRMS).

Methods: Six test waters were distributed to laboratories spanning a wide δ range of natural waters for δ H, δ O and δ O and Δ O.

A Ti(III) reduction method for one-step conversion of seawater and freshwater nitrate into N O for stable isotopic analysis of N/ N, O/ O and O/ O.

Rationale: The nitrogen and oxygen (δ N, δ O, and δ O values) isotopic compositions of nitrate (NO ) are crucial tracers of nutrient nitrogen (N) sources and dynamics in aquatic systems. Current methods such as bacterial denitrification or Cd-azide reduction require laborious multi-step conversions or toxic chemicals to reduce NO to N O for N and O isotopic analyses by isotope ratio mass spectrometry (IRMS). Furthermore, the O composition of N O cannot be directly disentangled using IRMS because O contributes to mass 45 ( N).

Seeking excellence: An evaluation of 235 international laboratories conducting water isotope analyses by isotope-ratio and laser-absorption spectrometry.

Rationale: Water stable isotope ratios (δ H and δ O values) are widely used tracers in environmental studies; hence, accurate and precise assays are required for providing sound scientific information. We tested the analytical performance of 235 international laboratories conducting water isotope analyses using dual-inlet and continuous-flow isotope ratio mass spectrometers and laser spectrometers through a water isotope inter-comparison test.

Methods: Eight test water samples were distributed by the IAEA to international stable isotope laboratories.

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.

Measurement of extremely (2) H-enriched water samples by laser spectrometry: application to batch electrolytic concentration of environmental tritium samples.

Rationale: Natural water samples artificially or experimentally enriched in deuterium ((2) H) at concentrations up to 10,000 ppm are required for various medical, environmental and hydrological tracer applications, but are difficult to measure using conventional stable isotope ratio mass spectrometry.

Methods: Here we demonstrate that off-axis integrated cavity output (OA-ICOS) laser spectrometry, along with (2) H-enriched laboratory calibration standards and appropriate analysis templates, allows for low-cost, fast, and accurate determinations of water samples having δ(2) HVSMOW-SLAP values up to at least 57,000 ‰ (~9000 ppm) at a processing rate of 60 samples per day.

Results: As one practical application, extremely (2) H-enriched samples were measured by laser spectrometry and compared to the traditional (3) H Spike-Proxy method in order to determine tritium enrichment factors in the batch electrolysis of environmental waters.