Evaluation of δ¹³C and δ¹⁵N Uncertainties Associated with the Compound-Specific Isotope Analysis of Geoporphyrins

Abstract

Compound-specific isotope analyses of geoporphyrins, which are derivatives of chloropigments possessed by phototrophs, provide essential records of the biogeochemical cycle of past aquatic environments. Here, we evaluated uncertainties in carbon and nitrogen isotopic compositions (δ13C and δ15N) associated with high-performance liquid chromatography (HPLC) purification and isotopic measurements of geoporphyrins. Evaluation of total blank carbon and nitrogen for the HPLC and our sensitivity-improved elemental analyzer/isotope ratio mass spectrometer (nano-EA/IRMS) analysis confirmed that blank carbon can be corrected and that blank nitrogen is negligible compared to the mass of geoporphyrins required for the isotopic measurement. While geoporphyrins exhibited substantial in-peak carbon and nitrogen isotopic fractionations, no systematic changes in δ13C and δ15N values were observed during reversed- and normal-phase HPLC isolation of Ni- and VO-porphyrin standards, with the changes in δ13C and δ15N values being within ±0.6‰ and ±1.2‰ (2σ), respectively. These values are comparable to the instrumental precision of the nano-EA/IRMS system (±1.3‰ for 0.70 μgC and ±1.1‰ for 0.08 μgN, 2σ), confirming that no substantial artifact in the δ13C and δ15N values would be expected during the reversed- and normal-phase HPLC purification. The sensitivity and precision of our method enable us to determine δ13C and δ15N values of both major and minor geoporphyrins found in ancient sediments, which would provide detailed information on the photosynthetic primary producers and the carbon and nitrogen cycles in the past.

Redox-Controlled Ammonium Storage and Overturn in Ediacaran Oceans

“…This number represents the average of analytical errors (1 sigma) of various inhouse synthesized maleimide injections (also see Chikaraishi et al, 2008). The δ 15 N values of these maleimides were independently determined at JAMSTEC on an EA/IRMS (described in Isaji et al, 2020) that was calibrated with IAEA authentic standards. Methyl-isobutyl-maleimides were below the limit of reliable analysis.…”

A method for stable carbon isotope measurement of underivatized individual amino acids by multi‐dimensional high‐performance liquid chromatography and elemental analyzer/isotope ratio mass spectrometry

“…The isotopic compositions and quantities of carbon were determined using a nano‐EA/IRMS system consisting of a modified elemental analyzer (Flash EA1112, ThermoFinnigan, San Jose, CA, USA), a continuous flow interface (ConFloIII, ThermoFinnigan) and an isotope ratio mass spectrometer (Delta plus XP, ThermoFinnigan), following the protocol reported by Ogawa et al 27 An aliquot of the AA was transferred into tin capsules. All the tin capsules were solvent rinsed (dichloromethane and methanol, 1:1, v/v) to remove contaminants from the surface 28 . The AA samples were transferred to the capsules and dried at 95°C on a hot plate before analysis.…”

Organic matter in carbonaceous chondrite lithologies of Almahata Sitta: Incorporation of previously unsampled carbonaceous chondrite lithologies into ureilitic regolith

“…For the measurements of total carbon and nitrogen contents and their isotopic compositions, we used an automated EA/IRMS system (Flash EA1112 elemental analyzer/Conflo III interface/Delta Plus XP isotoperatio mass spectrometer, Thermo Finnigan Co., Bremen) at Japan Agency for Marine-Earth Science and Technology (JAMSTEC), which was modified to improve the sensitivity for small sample analysis (>100 ngN, >500 ngC; Ogawa et al 2010;Isaji et al 2020). This analysis was conducted at the same time by the same methods as our previous measurement of the carbonaceous clast in the Zag meteorite (Kebukawa et al 2020).…”