Ammonium Fluoride as Suitable Additive for HILIC-Based LC-HRMS Metabolomics

Hydrophilic Interaction Liquid Chromatography (HILIC) chromatography is widely applied in metabolomics as a complementary strategy to reverse phase chromatography. Nevertheless, it still faces several issues in terms of peak shape and compounds ionization, limiting the automatic de-convolution and data semi-quantification performed through dedicated software. A way to improve the chromatographic and ionization performance of a HILIC method is to modify the electrostatic interactions of the analytes with both mobile and stationary phases. In this study, using a ZIC-HILIC chromatographic phase, we evaluated the performance of ammonium fluoride (AF) as additive salt, comparing its performance to ammonium acetate (AA). Three comparative criteria were selected: (1) identification and peak quality of 34 standards following a metabolomics-specific evaluation approach, (2) an intraday repeatability test with real samples and (3) performing two real metabolomics fingerprints with the AF method to evaluate its inter-day repeatability. The AF method showed not only higher ionization efficiency and signal-to-noise ratio but also better repeatability and robustness than the AA approach. A tips and tricks section is then added, aiming at improving method replicability for further users. In conclusion, ammonium fluoride as additive salt presents several advantages and might be considered as a step forward in the application of robust HILIC methods in metabolomics.

Part B. Retention parameters in gas chromatograpy

The paper presents a revision of terms in the IUPAC "Nomenclature for Chromatography", Pure and Applied Chemistry, 65, 819-872, 1993. The terms revised pertain to hold-up volumes in gas, liquid, and supercritical-fluid chromatography, as well as to basic retention parameters, especially in gas chromatography. A number of related and derived definitions are described, including definitions of the terms "chromatographic process" and "chromatographic phase system". A number of the original terms were found to be misleading or superfluous, including such terms as corrected retention time, net retention time, total retention volume (time), and specific retention volume at 0 °C, and their use is strongly discouraged In Part A, the concept of the hold-up volume in chromatography is discussed. The paper also compares methods described in the literature to determine the hold-up volume. In Part B, retention parameters in gas chromatography are discussed with the aim of (i) emphasizing the physical meaning of the terms and (ii) specifying the temperatures and pressures for the terms for gas volumes and flow rates. The appendix presents revised recommendations for the terminology of some items, as well as those that are not recommended.