GC Retention Behaviour

Packed column GC was routinely employed in the past for the analysis of chemical warfare agents, but with the advent of fused silica capillaries this technology has been used less frequently. Capillary column GC has become the most frequently employed analytical separation method for the screening of samples contaminated with chemical warfare agents. Separation of chemical warfare agents may be achieved with fused silica columns coated with poly-

Table 1 Common chemical warfare agents

Full name (trival name(s))

ChemicalAbstracts no.

(a) Nerve (reacts irreversibly with cholinesterase; this results in acetylcholine accumulation, continual stimulation of the body's nervous system and eventual death)

o-Isopropyl methylphosphonofluoridate (sarin, GB)

o-Pinacolyl methylphosphonofluoridate (soman, GD)

o-Cyclohexyl methylphosphonofluoridate (GF)

o-Ethyl n,n-dimethylphosphoramidocyanidate (tabun, GA)

o-Ethyl s-2-diisopropylaminoethyl methylphosphonothiolate (VX)

107-44-8

96-64-0

329-99-7

77-81-6

50782-69-9

(b) Blister (affects the lungs, eyes and produces skin blistering) Bis(2-chloroethyl)sulfide (mustard, H) Bis(2-chloroethylthio)ethane (sesquimustard, Q) Bis(2-chloroethylthioethyl)ether (T) Tris(2-chloroethyl)amine (HN-3) 2-Chlorovinyldichloroarsine (lewisite, L)

505-60-2

3563-36-8

63918-89-8

555-77-1

541-25-3

(c) Choking (affects respiratory tract and lungs) Chlorine

Carbonyl dichloride (phosgene, CG)

7782-50-5 75-44-5

(d) Vomiting(causes acute pain, nausea and vomiting in victims) Diphenylarsinous chloride (DA) 10-Chloro-5,10-dihydrophenarsazine (adamsite, DM) Diphenylarsinous cyanide (DC)

712-48-1 578-94-9 23525-22-6

(e) Blood (prevents transfer of oxygen to the body's tissues) Hydrogen cyanide (HCN, AC)

74-90-8

(F) Tear (Causes tearing and irritation of the skin) [(2-chlorophenyl)methylene]propanedinitrile (CS) 2-Chloro-1-phenylethanone (CN) Dibenz[b,f][1,4]oxazepin (CR)

2698-41-1

532-27-4

257-07-8

(g) Incapacitating (prevents normal activity by producing mental or physiological effects) 3-Quinuclidinyl benzilate (BZ)

6581-06-2

Nerve agents ch3ch2o-P —CN N(CH3)2 Tabun (GA)

Sarin (GD)

0 II

1

ch3ch2o-p—

ch3

ch3

SCH2CH2N[CH(CH3)2]2

SCH2CH2N[CH(CH3)2]2

Blister agents cich2ch2—s—ch2ch2ci

Mustard (H)

N—(ch2ch2ci)3 Nitrogen mustard (HN-3)

Figure 1 Structures of common chemical warfare agents.

siloxane or other Rlms and retention index data relative to n-alkanes and n-alkylbis(trifiuoromethyl)phos-phine sulRdes (M-series) have been reported for many chemical warfare agents and related compounds under temperature programming conditions. Retention indices relative to n-alkanes have been reported for 100% dimethyl-polysiloxane (e.g. J&W DB-1), (95%)-methyl-(5%)-diphenyl-polysiloxane (e.g. J&W DB-5), (86%)-dimethyl-(14%)-cyanopropylphenyl-polysiloxane (e.g. J&W DB-1701) and other films. In general, the best separations have been achieved with a moderately polar film such as (86%)-dimethyl-(14%)-cyanopropylphenyl-polysiloxane. Table 2 lists typical retention index data for several common chemical warfare agents on three different liquid phases under temperature programming conditions.

The use of retention indices relative to n-alkanes by the OPCW during on-site inspections is anticipated in the near future to differentiate between controlled compounds that exhibit similar electron impact mass spectrometric (EI-MS) data during GC-MS analysis,

Table 2 GC retention index data for common chemical warfare agents (relative to n-alkanes)

Compound name GC retention indexa

DB-1

DB-5

DB-1701

O-Isopropyl methylphosphono-

fluoridate (sarin, GB)

792

824

966

O-Pinacolyl methylphosphono-

1008

1045

1188

fluoridate (soman, GD)b

1013

1049

1193

O-Ethyl A/,A/-dimethylphosphor-

amidocyanidate (tabun, GA)

1078

1132

1340

O-Ethyl S-2-diisopropylamino-

ethyl methylphosphono-

thiolate (VX)

1664

1710

1881

Bis(2-chloroethyl)sulfide

(mustard, H)

1124

1173

1326

Bis(2-chloroethylthio)ethane

(sesquimustard, Q)

1623

1689

1923

Bis(2-chloroethylthioethyl)-

ether (T)

1910

1983

2241

aGC retention indices determined with three J&W 0.25 ^m films with the following temperature program: 50°C (2 min), then 10°Cmin~1 to 300°C (5 min). ^Retention data for both enantiomer pairs.

aGC retention indices determined with three J&W 0.25 ^m films with the following temperature program: 50°C (2 min), then 10°Cmin~1 to 300°C (5 min). ^Retention data for both enantiomer pairs.

thioethyl)ether (T) by weight, while HQ is usually 75% distilled mustard and 25% sesquimustard (Q) by weight. HS is crude mustard-containing 15% carbon tetrachloride. Munitions grade samples typically contain additional sample components that may provide synthetic procedure or source information. These samples contained several other sulfur-containing impurities, including 1,4-thioxane, 1,4-dithiane (two common mustard degradation products) and several longer chain blister agents (chromatographic peaks 8, 9 and 10 in Figure 2).

Figure 3 illustrates the application of capillary GC-FID for the characterization of tabun and related impurities in a munitions grade sample used for military chemical agent detector evaluation. The volatile organic content of this munitions grade tabun was estimated on the basis of the FID response of the individual components. Tabun accounted for 81% of the sample. The impurities, isopropyl N,N-dimethylphosphoramidocyanidate (isopropyl analogue of tabun), ethyl N,N,N',N'-tetramethylphosphoro-diamidate, N,N,N',N'-tetramethylphosphorodiamidic cyanide and the cluster of pyrophosphates, represented approximately 5%, 4%, 2% and 5%.

but different GC retention behaviour. Application of GC retention indices during the analysis of VX-con-taminated samples is likely since the EI-MS data for VX and a number of VX-related compounds are remarkably similar. The EI data for these compounds lack a molecular ion and contain a base ion at m/z 114 due to (CH2N(iPr)2) + and additional ions related to the - SC2H4N(iPr)2 substituent.

Chiral stationary phases have been developed for the resolution of stereoisomers of several chiral nerve agents, most notably soman. The use of multiple columns of differing polarity during one analysis has also been successfully employed during chemical warfare agent analysis and the term 'retention spectrometry' was coined to describe this technique.

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