Headspace chromatography, measurement

Using a similar experimental set-up as for the determination of Abraham s solvation parameters, the activity coefficient of solutes at infinite dilution y" cm be determined from their retention times using gas-liquid chromatography [12, 67-72], Alternatively, the diluter technique is applied [67, 73] for which an inert gas transports the solute from the headspace (which is in equilibrium with the ionic liquid matrix) to a GC-column. The continuous decrease of the concentration in the headspace is measured as a function of time, generating an exponential function from which y°° is calculated. 

For a volatile solute, the vapor pressure can be measured. This can be done as a function of the solute concentration at constant surfactant concentration. The activity of the solute is P/P° where P° is the vapor pressure of the pure solute. Two sets of data are required, the activity (or vapor pressure) of the solute in water and the activity (or vapor pressure) of the solute in aqueous surfactant solution. The horizontal distance between these two curves is a direct measure of the solubilized solute. The experimental techniques used for this purpose are headspace chromatography as used by Hayase and Hayano and Spink and Colgan, ° or the final equilibrium pressure over a solution containing a known quantity of volatile liquid can be measured. The latter method has been developed by Tucker and Christian. This method has the added advantage of providing an easy... 

Hussam, A., Carr, P. W. (1985) A study of a rapid and precise methodology for the measurement of vapor-liquid equilibria by headspace gas chromatography. Anal. Chem. 57, 793-801. 

For those aldehydes and ketones which are volatile enough, gas chromatography of the headspace gases can be used, and this has been used to measure acetone, butyraldehyde, and 2-butanone in oceanic waters. In a gas chromatography-mass spectrometry analysis of a single sample of volatile materials concentrated from inshore waters onto Tenax GC, MacKinnon [ 139] reported tentative identification of methyl isopropyl ketone, bromoform, 4-methyl-2-pentanone, 2-hexanone, and 2-hexanal. 

Chai, X.S. and Zhu, J.Y. Simultaneous measurements of solute concentration and Hetrry s constant trsing mrrltiple headspace extraction gas chromatography, Anal. Chem., 70(16) 3481-3487, 1998a. 

Figure 1.6 ICH Class 2 solvents measured using GC. Purification of pravastatin sodium by preparative liquid chromatography. Reprinted from [15], copyright 2004, with permission from Elsevier. (Column 30 m X 0.53 mm i.d. 3 pm OVI-G43 (Supelco) carrier gas helium at 5 ml/min injection in split mode total flow 25 ml/min injector temperature 140 C flame ionization detector temperature 25C C and oven temperature 40°C for 20 min, to 240°C at 10°C/min, maintain at 240 C for 20 min. The components are 1 methanol, 3 acetonitrile, 4 dichloromethane, 5 hexane, 6 cw-l,2-dichloroeth-ylene, 7 nitromethane, 8 chloroform, 9 cyclohexane, 13 1,2-dimethoxyethane, 15 1,1,2-trichloroethyl-ene, 16 methylcyclohexane, 17 1,4-dioxane, 18 pyridine, 19 toluene, 20 2-hexanone, 21 chlorobenzene, 22 ethylbenzene, 23 m-xylene, 24p-xylene, 25 o-xylene, and 26 tetralin. The solvents are dissolved in DMF and heated at 80X for 60 min, and a sample of the headspace is injected.)...

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... 

ERH may be estimated by measuring the relative humidity of the headspace over a food in a small, sealed container hygrometrically, psychro-metrically or directly by measuring the moisture content of the air by gas chromatography. ERH can be estimated by moisture-related colour changes in paper impregnated with cobalt thiocyanate (Co(SCN)2) and compared to standards of known aw. 

Gas chromatography/olfactometry (GCO) methods have been developed as screening procedures to detect potent odorants in food extracts. The FD-factors or CHARM values determined in food extracts are not consequently an exact measure for the contribution of a single odorant to the overall food flavor for the following reasons. During GCO the complete amount of every odorant present in the extract is volatilized. However, the amount of an odorant present in the headspace above the food depends on its volatility from the food matrix. Furthermore, by AEDA or CHARM analysis the odorants are ranked according to their odor thresholds in air, whereas in a food the relative contribution of an odorant is strongly affected by its odor threshold in the food matrix. The importance of odor thresholds in aroma research has been recently emphazised by Teranishi et al. [58],... 

Sorption The method allows a direct measurement of S from the equilibrium between gas and polymer. The volume of gas taken up by the polymer can be measured gravimetrically, manometrically or using a gas specific detector. Headspace gas chromatography is an useful technique for this. The S values then come from ... 

Frankel, E.N., Hu, M L., Tappel, A.L. 1989. Rapid headspace gas chromatography of hexanal as a measure of lipid peroxidation in biological samples. Lipids. 24, 976-981. 

Li, J., Carr, P.W. (1993) Measurement of water-hexadecane partition coefficients by headspace gas chromatography and calculation of limiting activity coefficients in water. Anal Chem. 65, 1443-1450. 

The hydrolysis of Alq3 was characterized with a gas chromatography and mass spectroscopy (GC-MS) apparatus modified with a headspace accessory designed to study volatile products evolved from solid materials (illustrated in Fig. 3.2, inset).41 Powder or film (deposited on foil) samples of Alq3 were held in a constant-temperature injection port for a given time, and the eluents at the end of the heating period were fed to the GC column. The relative areas of water and Hq peaks were used to measure the conversion (a typical trace is shown in Fig. 3.2). The prepurified Alq3 samples were allowed to absorb an equilibrium amount of water from the atmosphere, which occurred in about 3 min for the samples used.16... 

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