The Chemical Weapons Convention (CWC) (1993) outlawed chemical warfare agent (CWA) use and specified that destruction of agent stockpiles should advance within set deadlines. Ongoing CWA-related research projects (for example, civil defense, agent destruction, and protection) require monitoring of airborne CWA concentrations at the lowest possible level and with accurate identification. The use of handheld devices in these situations is compromised by their lack of sensitivity and their tendency to give false positives. Thermal desorption (TD), combined with GC–MS, is the only technique offering sufficient sensitivity and specificity for identifying and measuring trace CWAs. This article discusses the analysis of a wide range of CWAs at current exposure limits and describes a number of recent beneficial developments in TD and associated analytical technologies for the identification and quantification of CWAs at these levels.

Chemical warfare is defined as "Warfare and associated military operations involving the employment of lethal and incapacitating munitions and agents, typically poisons, contaminants, and irritants." This definition only covers deliberate use of agents and excludes most of those used legally, such as herbicides, smoke, and flame. An exception to this is the use of riot-control agents during warfare, which is now forbidden (1,2).

Chemical warfare has been used since ancient times. The "modern" era of chemical weaponry began in World War I (WWI) with blister agents such as mustard gas and continued with the advances in synthetic organophosphate chemistry during the development of insecticides in the 1930s.

Since then, thousands of chemicals have been screened as weapons. The current list of chemical warfare agents (CWAs) is divided into five groups, based roughly on mode of action: nerve, blister, choking, blood, and lachrymatory.

Toxicity and Protection

Figure 1: Chemical structure of VX.

Typically, CWAs are liquids, or vapors dispersed as aerosols or gas. They can enter the body via the respiratory system or through skin contact. Nerve agents can kill within minutes of inhalation and in under an hour after skin contact. VX (Figure 1) and the Russian equivalent, RVX, are among the most toxic compounds in existence. A 1-L volume of VX can theoretically kill one million people, and less than one tenth of the volume of an average swimming pool could wipe out the entire human population (3). Moreover, VX persists on material, equipment, and terrain, remaining deadly for up to three weeks. Table I shows the maximum exposure limits for particular agents and illustrates their extreme toxicity.

Table I: Maximum limits of human exposure to select CW agents

It was quickly realized that the only real prospect for defense against chemical weapons was to ban their use. This prompted international action on a chemical disarmament regime under the 1925 Geneva Protocol. This protocol has limitations, however, including the inability to enforce policing and the fact that it does not forbid retaliation in the case of chemical attack. The Chemical Weapons Convention (CWC) addressed these shortfalls and has now been adopted by over 120 countries. The agreement involves not using or making (or encouraging others to make) chemical weapons. To prove this good intention, all parties agree to inspection of any site where agents might have been used. Another condition was the disposal of all large stockpiles by 2007. While this target was not met, international efforts to destroy agent stockpiles are proceeding at pace, with extensions until 2012 for substantial stockpiles and longer in other cases (4).

Russia and the U.S. possess more than 95% of the Cold War stockpiles of chemical arms. Albania, Libya, South Korea, and India have declared much smaller quantities, and Japan has started elimination of the CW stockpile abandoned in China after World War II.