High‐precision measurement of phenylalanine δ¹⁵N values for environmental samples: A new approach coupling high‐pressure liquid chromatography purification and elemental analyzer isotope ratio mass spectrometry

Abstract

These results demonstrate that offline HPLC represents a viable alternative to traditional GC/C/IMRS for δ(15)N(AA) measurement. HPLC/EA-IRMS is more precise and widely available, and therefore useful in applications requiring increased precision for data interpretation (e.g. δ(15)N paleoproxies).

Isolation of underivatized amino acids by ion-pair high performance liquid chromatography for precise measurement of nitrogen isotopic composition of amino acids: Development of comprehensive LC × GC/C/IRMS method

“…Please see other non-protein type amino acids shown in Fig. 3 chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) [14]. Here, we report the development and validation of a method for underivatized amino acid separation by the ion-pair LC procedure.…”

Errors associated with compound specific δ15N analysis of amino acids in preserved fish samples purified by high pressure liquid chromatography

“…A program was set up for the fraction collector to collect AAs of interest in 7 ml glass tubes at specific times based on elution times from previous runs. A steep gradient in δ 15 N can occur across the peak of an eluting AA (Hare et al 1991;Broek et al 2013). Therefore, the quality of all collections was assessed by comparing the chromatogram with set collection times, and only AAs where ≥ 99% of the peak areas fit within the collection windows were accepted.…”

“…This approach assumes that analytical and methodological errors are similar for CSIA-AA and bulk SIA. However, Elemental Analyzer -Isotope Ratio Mass Spectrometry (EA-IRMS) used in bulk SIA typically operates with an analytical precision (0.1 -0.2 ‰) that is substantially higher than what is reported in CSIA-AA studies (0.4 -1.0 ‰; Bradley et al 2016;Broek and McCarthy 2014;Broek et al 2013;Chikaraishi et al 2015;Hetherington et al 2017;Nuche-Pascual et al 2018;Ogawa et al 2013;Ruiz-Cooley et al 2017;Vane et al 2018;Vokhshoori et al 2019). This lower precision is the result of a lengthy and time-consuming analytical process inherent to the Gas Chromatography-Combustion-IRMS (GC-C-IRMS) used for almost all CSIA-AA work.…”

“…This lower precision is the result of a lengthy and time-consuming analytical process inherent to the Gas Chromatography-Combustion-IRMS (GC-C-IRMS) used for almost all CSIA-AA work. For CSIA-AA, AAs first undergo derivatization that causes significant and inconsistent fractionation of N isotopes and is followed by an instrumentally long and complex sequence prior to the δ 15 N measurement (Broek et al 2013;Broek and McCarthy 2014). Ultimately, the propagation of errors limits the precision of TP estimates.…”

“…Ultimately, the propagation of errors limits the precision of TP estimates. As an alternative to GC-C-IRMS, Broek et al (2013) developed a method using High Pressure Liquid Chromatography (HPLC) for AA purification followed by offline EA-IRMS for δ 15 N measurement in Phe. Broek and McCarthy (2014) later optimized the method for Glu and Phe.…”