High-Precision Measurement of N₂O Concentration in Ice Cores

Atmospheric nitrous oxide (N₂O) is a greenhouse gas and ozone-depleting substance whose emissions are substantially perturbed by current human activities. Although air trapped in polar ice cores can provide direct information about N₂O evolution, analytical precision was not previously sufficient for high temporal resolution studies. In this work, we present a highly improved analytical technique with which to study N₂O concentrations in ancient-air-trapped ice cores. We adopt a melt–refreezing method to extract air and use a gas chromatography–electron capture detector (GC–ECD) to determine N₂O concentrations. The GC conditions are optimized to improve the sensitivity for detecting N₂O. Retrapped N₂O in ice during the extraction procedure is precisely analyzed and corrected. We confirmed our results using data from the Styx Glacier ice core in Antarctica by comparing them with the results of a dry-extraction method. The precision estimated from the pooled standard deviation of replicated measurements of the Styx ice core was 1.5 ppb for ∼20 g of ice, a smaller sample of ice than was used in previous studies, showing a significant improvement in precision. Our preliminary results from the Styx Glacier ice core samples have the potential to define small N₂O variations (a few parts per billion) at centennial time scales

Controlled Supramolecular Assembly of Helical Silica Nanotube–Graphene Hybrids for Chiral Transcription and Separation

Chiral templating and enantioselective separations are demonstrated on graphene surfaces as directed by encapsulated silica nanotubes. Electrostatic assembly of helical silica nanotubes within graphene sheets results in a hybrid material with the electrochemical properties of graphene and the capability for chiral recognition. Control of the silica nanotube helicity within the graphene hybrid provides a means for directed chiral templating of guest molecules on the outer graphene surface as revealed in the chiral transcription of <i>N</i>¹,<i>N</i>³,<i>N</i>⁵-tri(4-pyridinyl)cyclohexane-1,3,5-tricarboxamide as well as polyallylamine into supramolecular templated assemblies. Changing the helicity of the internal nanotube also provides control over enantiomer selectivity as demonstrated by the chiral separation of racemic mixtures of phenylalanine, tryptophan, and alanine derivatives