Reversed-phase liquid chromatography food additives analysis

The reaction of sulfite with formaldehyde to form hydroxymethylsulfonate (HMS), which is very stable under the controlled conditions of this assay, was used as the first step in an analytical procedure to determine food-borne sulfite. The effect of mobile-phase pH on the stability of HMS during high-performance liquid chromatography was studied. It was found that on-column HMS dissociation to formaldehyde and bisulfite increased with the pH of the mobile phase therefore the relatively low pH 4.7, at which the dissociation of HMS was approximately 2%, was selected for the analysis. In addition, the release of sulfite from its reversibly bound forms in wine and other foods was examined as a function of the pH of the extraction medium by following the appearance of HMS formed from the reaction of the freed sulfite with formaldehyde. The rate of dissociation of the reversibly bound sulfite was relatively slow at pH 3 but very rapid at pH 7. 

Zhao, Y. G., X. H. Chen, S. S. Yao, S. D. Pan, X. P. Li, and M. C. Jin. 2012. Analysis of nine food additives in red wine by ion-suppression reversed-phase high-performance liquid chromatography using trifluoroacetic acid and ammonium acetate as ion-suppressors. Anal. Sci. 28 967-971. 

The synthetic colorants Quinoline Yellow and Sunset Yellow are determined individually or simultaneously with other food additives by several methods, mainly spectrophotometry and chromatography. At present, the most used technique for synthetic colorants determination is liquid chromatography. The most popular reported HPLC modes applied for synthetic colorants analysis are reversed-phase chromatography (RPC), ion pair chromatography (IPC), and ion chromatography (IC). In recent years, electrochemical techniques have attracted wide attention due to their characteristics such as low operational cost, rapid and sensitive detection, selectivity, and reproducibility. 

Liquid chromatography coupled to electrospray ionization mass spectrometry (LC-ESI-MS) was introduced in the 1980s [1]. Today it has become a standard method for separation and characterization of nonvolatile compounds. Reversed-phase high-performance liquid chromatography (RP-HPLC) coupled to ESI-MS is the method of choice for peptide and protein analysis, but also used for the characterization of contaminants, therapeutic drugs, and food additives [2-5], More than 75% of HPLC analyses are run on RP stationary phases, and a wide range of columns are available with various substituents of the silica matrix, base deactivation, endcapping, and column dimensions. 

---