Large-Volume Injection and Assessment of Reference Standards for n-Alkane δD and δC Analysis via Gas Chromatography Isotope Ratio Mass Spectrometry.

Rationale: Compound-specific stable isotope analysis of hydrogen (δD) and carbon (δC) in organic compounds is a valuable tool in biogeochemical research. A key limitation of this method is the relatively large amount of sample required to achieve desirable precision.

Methods: We developed a large-volume (20 μL) injection method that allows for high throughput analysis of less concentrated samples and tested it for δC and δD measurements of n-alkanes.

Analytical improvements and assessment of long-term performance of the oxidation-denitrifier method.

Unlabelled: The analysis of the nitrogen (N) isotopic composition of organic matter bound to fossil biomineral structures (BB-δ N) using the oxidation-denitrifier (O-D) method provides a novel tool to study past changes in N cycling processes.

Methods: We report a set of methodological improvements to the O-D method, including (a) a method for sealing the reaction vials in which the oxidation of organic N to NO takes place, (b) a recipe for bypassing the pH adjustment step before the bacterial conversion of NO to N O, and (c) a method for storing recrystallized dipotassium peroxodisulfate (K S O ) under Ar atmosphere.

Results: The new sealing method eliminates the occasional contamination and vial breakage that occurred previously while increasing sample throughput.

Distinct nitrogen isotopic compositions of healthy and cancerous tissue in mice brain and head&neck micro-biopsies.

Background: Cancerous cells can recycle metabolic ammonium for their growth. As this ammonium has a low nitrogen isotope ratio (N/N), its recycling may cause cancer tissue to have lower N/N than surrounding healthy tissue. We investigated whether, within a given tissue type in individual mice, tumoral and healthy tissues could be distinguished based on their N/N.

Ambient and laboratory observations of organic ammonium salts in PM.

Ambient measurements of PM aerosol chemical composition at Cabauw, the Netherlands, implicate higher ammonium concentrations than explained by the formation of inorganic ammonium salts. This additional particulate ammonium is called excess ammonium (e). Height profiles over the Cabauw Experimental Site for Atmospheric Research (CESAR) tower, of combined ground based and airborne aerosol mass spectrometric (AMS) measurements on a Zeppelin airship show higher concentrations of e at higher altitudes compared to the ground.