Phosgene as a derivatizing reagent prior to gas and liquid chromatography

Derivatisation reactions in the chromatographic analysis of chemical warfare agents and their degradation products

The analysis of chemical warfare agents and their degradation products is an important component of verification of compliance with the Chemical Weapons Convention. Gas and liquid chromatography, particularly combined with mass spectrometry, are the major techniques used to detect and identify chemicals of concern to the Convention. The more polar analytes, and some of the more reactive or highly volatile agents, are usually derivatised to facilitate chromatography, and to impart properties beneficial for detection. This review focuses on derivatisation reactions used in the chromatographic analysis of chemical warfare agents, their degradation products and metabolites.

Adduction of the chloroform metabolite phosgene to lysine residues of human histone H2B

Human exposure to trihalomethanes such as chloroform has been associated with both cancer and reproductive toxicity. While there is little evidence for chloroform mutagenicity or DNA adduct formation, in vivo studies in rats have demonstrated adduction to histones and other nuclear proteins. Histones play a key role in controlling DNA expression particularly through the acetylation of lysine residues in their N-termini. Therefore, we studied the reaction of phosgene, the major active metabolite of chloroform, with the N-terminus of human histone H2B (Hpep, Pro-Glu-Pro-Ala-Lys-Ser-Ala-Pro-Ala-Pro-Lys-Lys-Gly-Ser-Lys-Lys-Ala-Val-Thr-Lys-Ala-Gln-Lys) in a model chemical system. The aim of this study was to assess whether phosgene is able to form irreversible adducts with this peptide and to investigate which residues are most susceptible. Hpep was reacted with a range of phosgene concentrations (0.03-36 mM) at 37 degrees C, pH 7.4. The products of these reactions, analyzed by matrix-assisted laser desorption ionization MS, showed that up to three CO moieties could be adducted to the peptide. The singly and doubly adducted peptides were purified by HPLC and then hydrolyzed with trypsin to produce a series of fragments that were analyzed by HPLC-MS. The tryptic products showed that adduction occurred principally at lysine residues, and that all seven lysine residues of the peptide were subject to adduction. Collision-induced dissociation analysis using ion trap MS-MS of the tryptic fragment [Pro-Glu-Pro-Ala-Lys-Ser-Ala-Pro-Ala-Pro-Lys + CO] and of the full-length singly adducted peptide supported the role of lysine residues in adduction; the data also indicated that the N-terminal proline and the serine residues are susceptible. Addition of glutathione to the reaction mixture only partially attenuated adduct formation and allowed production of another adducted species, i.e., Hpep-CO-glutathione. The occurrence of such reactions to the N-termini of histones, if confirmed by in vivo studies, could help to explain the mechanism of chloroform carcinogenicity.

Chiral separation of beta-blockers after derivatization with (-)-alphamethoxy-alpha-(trifluoromethyl)phenylacetyl chloride by gas chromatography

Gas chromatographic method was investigated for the chiral separation of several beta-blockers(atenolol, betaxolol, bisoprolol, metoprolol and pindolol) using (-)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride as a chiral derivatizing agent for amino group. Prior to N-acylation, hydroxyl group was converted into O-silyl ethers by react with N-methyl-N-(trimethylsilyl)trifluoroacetamide. The reaction was selective and rapid and the diastereomeric derivatives were well separated by capillary gas chromatography. (R)-isomers were eluted faster than (S)-isomers when (-)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride was used as the chiral derivatizing agent. But in the opposite sequence when (+)-alpha-methoxy-alpha-(trifluoromethyl)phenylacetyl chloride was used. No racemization was found during the reaction.

In vitro adduct formation of phosgene with albumin and hemoglobin in human blood

The development of procedures for retrospective detection and quantitation of exposure to phosgene, based on adducts to hemoglobin and albumin, is described. Upon incubation of human blood with [(14)C]phosgene (0-750 microM), a significant part of radioactivity (0-13%) became associated with globin and albumin. Upon Pronase digestion of globin, one of the adducts was identified as the pentapeptide O=C-(V-L)-S-P-A, representing amino acid residues 1-5 of alpha-globin, with a hydantoin function between N-terminal valine and leucine. Micro-LC/tandem MS analyses of tryptic as well as V8 protease digests identified one of the adducts to albumin as a urea resulting from intramolecular bridging of lysine residues 195 and 199. The adducted tryptic fragment could be sensitively analyzed by means of micro-LC/tandem MS with multiple-reaction monitoring (MRM), enabling the detection in human blood of an in vitro exposure level of >/=1 microM phosgene.

Chromatographic analysis of chemical warfare agents

The usefulness and applications of the particular types of chromatography in the analysis of chemical warfare agents have been reviewed. A major problem in the chromatographic analysis of chemical warfare agents is the collection and preparation of the samples. The importance of this problem differs for the various types of chromatography. Significant differences occur in the way in which samples are collected from air, water, soil, vegetables or animal organisms. The analyses are characterized by the main groups of chemical warfare agents, e.g., organophosphorus, vesicants, irritants, etc. Account has been taken of the relationships between their properties and the possibilities of their chromatographic analysis. The advantages and disadvantages of particular types of chromatography in the analysis of the particular groups and individual agents have been considered. The detectability of particular chemical warfare agents has been assessed, together with the separating efficiency for their mixtures. Examples of applications of chromatographic systems and conditions of chromatographing are summarized in tables. It is concluded that chromatography is a very useful tool in the analysis of chemical warfare agents; GC and TLC have the most advantageous properties, HPLC being slightly inferior.