Headspace vapor

Certainly, the precision and accuracy of the PTV techniques are generally superior to those of the classical hot split and splitless techniques and approach those obtained by cold on-column Injection [ 34,36,37, -54-57,62,64]. However, less is known concerning optimization of PTV injection and probably more parameters have to be considered than for cold on-column injection. The latter is, consequently, the preferred injection technique for most samples, except those contaminated by larg< amounts of involatile Impurities and for headspace vapors. 

Bromomethane may be isolated from biological materials either by extraction into an organic solvent, or simply by collecting headspace vapors. Table 6-1 summarizes several methods used by researchers for measuring parent bromomethane in blood or tissues. Detection limits are sufficiently low that levels in blood or tissue associated with health effects can easily be measured. However, as discussed in Section 2.3.4, parent bromomethane is cleared from blood and tissues quite rapidly, so detection of bromomethane exposure in humans is typically performed by measuring serum bromide levels instead. Several methods for measuring bromide ion in serum are also presented in Table 6-1. These methods are also sufficiently sensitive that detection limits (0.5-2.5 ppm) are lower than typical levels of bromide in serum of unexposed people (5-15 ppm), and increases due to bromomethane exposure can easily be measured (Alexeeff and Kilgore 1983). 

Collect headspace vapor of HBr from plasma treated with dimethyl sulfate at 85°C Extract in 18% trichloroacetic acid derivatize to 1,2-dibromo-cylcohexanone Digest in KOH. Convert to bromate, then to tetrabromorosaniline... 

Source Component of high octane gasoline (quoted, Verschueren, 1983). Harley et al. (2000) analyzed the headspace vapors of three grades of unleaded gasoline where ethanol was added to... 

Harley, R.A. and Coulter Burke, S.C. Relating liquid fuel and headspace vapor composition for California reformulated gasoline samples containing ethanol. Environ. Sci Technol, 34(19) 4088M094, 2000. 

Analysis of a group of smokeless powders of known composition showed that the main components of their headspace vapor were acetone, toluene and limo-nene the concentration of nitroglycerin (NG) was relatively low. A series of... 

Blood Mix sample with internal standard add salt solntion eqnilibrate aspirate headspace vapor and inject to GC GC/MS 50 pg (tolnene) NR Kimnra et al. 1991... 

As discussed previously, military-grade TNT is not a pure material, containing additional nitroaromatic constituents at concentrations of up to several percent by mass [4], Some of these explosive-related compounds (ERCs) have been shown to be significant contributors to the chemical fingerprint of a landmine [5, 7], Of the ERCs found in TNT, those that are most prevalent in the headspace vapor of TNT include 2,4-DNT, 2,6-DNT, 1,3-dinitrobenzene (1,3-DNB), and... 

The spectra in Figure 11.4 were recorded from headspace vapor either at room temperature (TNT, PETN) or elevated temperature (about 50°C for RDX). For TNT this corresponds to a saturated headspace vapor pressure of less than 10 ppb. At these levels strong signal is observed with relatively weak signal from room air. Explosives compounds that have been detected by the MS detector with high sensitivity include TNT, ADNT, DNT, NT, TNB, DNB, DMNB, RDX, HMX, EGDN, NG, PETN, and TATP. (see Explosive Definitions, page 329). 

Figure 11.5 shows an example of detection of TNT headspace vapor at room temperature in MS mode and in MS/MS mode. In the latter example, the detector is programmed to trigger an excitation waveform when an ion signal at m/z 227 (TNT) is observed. The observation of fragment ions at m/z 210 and 197 is positive identification of TNT. 

Considerable effort has been made to examine the volatiles and trace components that contribute to food flavors. Sone early techniques for measuring the volatile components in food products by gas chromatography consisted of analyzing headspace vapors to detect vegetable and fruit aromas (5) and volatiles associated with other food materials ( ). AlTo, sample enrichment has been used in the analysis of Tome food products. However, these techniques require steam distillation or extraction and concentration, or both, before the volatile mixture can be introduced into a gas chromatograph (, 9, 10). Besides being... 

Leggett et al (Refs 22 23) used a similar technique, except that their apparatus was static . TNT samples were placed in a 125ml vial equipped with silicone rubber septum cap. The vial was thermostatted and the sample and its vapor were allowed to equilibrate for 2—4 weeks. Vapor was withdrawn from the head-space with a stainless steel syringe and injected into a gas chromatograph. The concn of TNT in the headspace vapor was determined by manual triangulation of the peak, giving peak area/ volume, and dividing by the detector response factor (peak area/mass), as determined by injection of known quantities of TNT dissolved in benzene... 

Automatic headspace samplers are available from manufacturers of gas chromatographs. These devices are based on the technique of sampling an amount of vapor above the sample itself. Samples are sealed, neat or in a suitable solvent, in containers, and hold at a preset temperature in a thermostatted liquid bath. The headspace vapor results as a partition equilibrium is established between the liquid or solid and the gaseous phase of the volatiles. As each sample is presented to the analyzer, the vessel is punctured and a portion of the headspace gas is withdrawn by a pneumatic injection technique and forced into the column. The main application for those samplers is in the routine analysis of low-boiling fractions in samples containing nonvolatile solids or high-boiling components. Some of the more popular applications today are ... 

Bi of1ui dsa Dilute with water, sealed vial, collection of headspace vapors GC/ECD No data No data Suitheimer et al.1982... 

The volatilization and leaching of various forms of mercury (elemental, mercuric sulfide, mercuric oxide, and mercurous oxide) from soils or wastes was examined using the headspace method for volatilization and the Resource and Conservation Recovery Act (RCRA) leaching protocols for leaching through soil to determine if the leachates exceeded the RCRA limit of 200 g/L (ppb) (Willett et al. 1992). With the exception of mercuric sulfide, the other forms of mercury increased in concentrations in the headspace vapor and in the leachate as the soil concentrations increased, although the elemental mercury... 

Peck, R.L., S.F. Osman, and J.F. Barson Cigar butt aroma. I. A preliminary study of cigar butt headspace vapors Tob. Sci. 13 (1969) 38-39. 

Roemer, E. and U. Hackenberg Mouse skin bioassay of smoke condensates from cigarettes containing different levels of cocoa Food Addit. Contam. 7 (1990) 563-569. Roeraade, J. and C.R. Enzell Tobacco chemistry. 14. Sampling, concentration, and examination of tobacco headspace vapors J. Agr. Food Chem. 20 (1972) 1035-1039. 

The volatility of elemental mercury was demonstrated by analysis of headspace vapor in sample bottles containing oil and solvents spiked with elemental mercury. The amount of mercury that partitions to bottle headspace depended on temperature and on liquid phase composition, as expected. Based on these results, one would expect significant variation in the rate of mercury evaporation depending on oil composition. 

Mix sample with Internal GC/MS standard add salt solution equilibrate aspirate headspace vapor and Inject to GC... 

Hobbs J. R. and Conde E. P, A simple inexpensive thermal desorption method for the trace analysis of headspace vapors from explosives and organic nitro-Compounds, Proceedings of Interernational Symposium on Forensic Aspects Trace Evidence, FBI Quantico, VA, June 24-28, 1991, 269. Avail. NTIS PB94-145877. 

---