Mechanism of chemical activation of sodium chloride in the presence of amino acids.

Sodium chloride has been shown to promote chlorination of glycerol during thermal processing. However, the detailed mechanism of this reaction is not well understood. Preliminary experiments have indicated that the reaction mixture should contain an amino acid and it should be dissolved thoroughly in water in order to induce chlorination. These observations are consistent with the process of dissociation of sodium chloride and its re-association with amino acid and eventual formation of the chlorinating agent in the form of the hydrochloride salt. Release of HCl from this salt can be manifested in chlorination and hydrolytic reactions occurring during thermal processing. The generation of HCl at room temperature from a mixture of sodium chloride and glycine was confirmed through spectrophotometric monitoring of the pH. Hydrolytic and chlorination reactions were demonstrated through monitoring of formation of HMF and chlorinated products under pyrolytic conditions using glucose or sucrose and amino acid mixtures.

Characterization of electron ionization mass spectral (EIMS) fragmentation patterns of chloropropanol esters of palmitic acid using isotope labeling technique.

Chloropropanol (CP) esters are a class of thermally-induced toxicants that are mainly formed in refined edible oils. The structural diversity of these esters presents significant analytical challenges which have often been overcome through analysis of their corresponding free alcohols after a hydrolysis step. Mass spectrometry-based methodologies incorporating characteristic fragmentation patterns of particular isomers of CP esters greatly facilitates their identification. The electron ionization mass spectra (EIMS) of various isomers of synthetic and commercially available (13)C- and (2)H-labeled CP ester standards of palmitic (C16) and other short chain fatty acids (C3 to C10) were generated and analyzed using GC/MS. Short chain CP esters were synthesized by reacting their respective acid anhydrides with the corresponding 3-chloro- and 2-chloro- propanediols in addition to 1,3-dichloro- and 1,2-dichloropropanols. Five fragmentation pathways were identified. Four of the five pathways, such as α-cleavage, McLafferty rearrangement, α-H rearrangement and cyclic acyloxonium ion formation, were characteristic of CP mono- and diesters. The remaining pathway generating chloronium ion was found only in dichlorinated isomers. The proposed fragmentation pathways for the palmitic acid esters were confirmed through the use of (13)C- and (2)H-labeled CP ester standards of palmitic acid, and the generality of identified fragmentation patterns was confirmed through the identification of equivalent ions in the mass spectra of short chain fatty acids (C3 to C16). Characteristic ions that were identified in this study retaining the chlorine atom in their structures can be considered as potential markers for the presence of CP esters.

Isotope labeling studies on the electron impact mass spectral fragmentation patterns of chloropropanol acetates.

Chloropropanol (CP) esters are part of an emerging group of process-induced toxicants that are considered as potential health hazards particularly in palm oil. Mass spectrometry-based methodologies for identification of CP esters in food are critical in overcoming the challenges associated with direct detection methods. In the present study, a convenient strategy was employed to generate all possible CP acetates through reacting acetic anhydride with either glycerol in the presence of a chloride source or the corresponding CPs, such as 3-chloro-, 1,3-dichloro-, 2-chloro-, and 1,2-dichloropropanols, allowing for the identification of the individual CP acetates and assignment of their mass spectral fragmentations. Mass spectral fragmentations were confirmed through the use of the isotopic signature of chlorine in addition to the isotope labeling experiments performed using isotopically labeled precursors, such as [¹³C-U3] glycerol, [¹³C-U4] acetic anhydride, [¹³C-2,2'] acetic anhydride, and [d5] 3-monochloropropane-1,2-diol (3-MCPD) as reactants. Such studies have indicated that all CP esters can undergo two general fragmentations under electron impact (EI) conditions, one generating the acylium ion at m/z 45 and the other generating a chlorinated cyclic acyloxonium ion at m/z 135.6. Considering the fact that such ions can also be generated from any fatty acid containing CP esters after undergoing McLafferty rearrangement, the ion at m/z 135.6 can therefore be considered as a universal marker for the presence of CP esters undergoing EI fragmentation. Furthermore, these studies have also indicated the formation of ions characteristic of CP diesters, monoesters, and dichloro esters.

Cyclic acyloxonium ions as diagnostic aids in the characterization of chloropropanol esters under electron impact (EI), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) conditions.

During mass spectrometric analysis of various lipids and lipid derivatives such as the chlorinated counterparts of triacylglycerols, the detailed structure of the characteristic and common ions formed under electron impact (EI), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) conditions by the loss of a single fatty acid remains ambiguous. These ions are designated in the literature as "diacylglyceride ions" and are frequently depicted with a molecular formula without showing any structural features and sometimes represented as cyclic acyloxonium ions. Characterization of these ions is of considerable importance due to their utility in structural identification of lipid derivatives. This study provides complementary evidence on the cyclic nature of "diacylglyceride ions" through the use of the simplest 3-monochloropropanediol diester as a model and the use of isotope labeling technique. Tandem MS/MS studies have indicated that the ion at m/z 135.6 generated from 1,2-bis(acetoyl)-3-chloropropane through the loss of an acetyl group was identical to the ion at m/z 135.6 generated from 4-chloromethyl-2,2-dimethyl-1,3-dioxolane, the latter being generated from a cyclic precursor through the loss of a methyl radical, keeping the dioxolane ring structure intact, thus confirming the cyclic nature of these ions. The corresponding cyclic oxonium ions generated from longer chain chloropropanol diesters, such as the ion at m/z 331.2 originating from 3-monochloropropanediol (3-MCPD) diesters containing palmitic acid(s), could serve as chemical markers for the presence chloropropanol esters.