Static headspace gas chromatographic

Leermakers, M., H.L. Nguyen, S. Kurunczi, B. Vanneste, S. Galletti, and W. Baeyens. 2003. Determination of methylmercury in environmental samples using static headspace gas chromatograph and atomic fluorescence detection after aqueous phase ethylation. Anal. Bioanal. Chem. 377 327-333. 

Ulberth, F. and Roubicek, D. (1993) Evaluation of a static headspace gas chromatographic method for the determination of lipid peroxides. Food Chemistry, 46, 137-41. 

Cruwys, J.A. et al.. Development of a static headspace gas chromatographic procedure for the routine analysis of volatile fatty adds in wastewaters, /. Chromatogr. A, 945,195, 2002. 

External standard calibration in static headspace gas chromatography is best for analytes in liquid samples where the analytes are soluble in the matrix and the matrix has no effect on the analyte response. In these type of calibration is important to match the standard and sample matrix as closely as possible and to demonstrate equivalence in the response between the standards and the samples. The main difficulty with external standard calibration is that is does not compensate for any variability due to the gas chromatograph injection or due to variation in the analyte matrix. 

The TICs of the headspace volatiles of Ethiopia coffee bean (L23) adsorbed on the SPME fiber under static and dynamic conditions under the same GCMS conditions are shown in Fig. 3. The DH-SPME sampling resulted in acceptable peak intensity and a chromatographic profile, and the ratios of components adsorbed were different from those obtained by the SH-SPME sampling. The amount of peak area of 47 volatile compounds trapped under the dynamic condition was about 1.8 times that of volatiles trapped under the static condition (Table 1). Also, minor compounds reported as potent odorants of coffee, such as 4-hydroxy-2,5-dimethyl-3(2//)-furanone, 2-methoxyphenol, 4-ethenyl-2-methoxyphenol, and 2-ethyl-3,5-dimethylpyr-azine, were found to be present in higher concentrations in the dynamic headspace than in the static headspace. This chromatographic difference was considered to have resulted from additional volatilization of compounds induced by flowing inert gas above the sample [10]. 

Static headspace gas chromatography (SHGC) was used to study the effects of saliva volume on the retention of the five aroma compounds by the emulsion. Emulsion to saliva ratios included 100 0, 80 20, 60 40, and 40 60. The 2mL of the samples was transferred to 10-mL headspace vials, which were then incubated at 37°C and agitated at 750 rpm for 6 min, using an automated headspace unit (Combipal-CTC Analytics JVA Analytical Ltd., Dublin, Ireland). One milliliter of the headspace was injected and analyzed by using a gas chromatograph (GC Varian CP-3800 JVA Analytical Ltd.) equipped with a flame ionization detector (FID). The injector and detector... 

Static headspace GC/MS. The partitioning of volatile and semivolatile compounds between two phases in a sealed container. An aliquot of the headspace gas generated is injected onto a gas chromatographic column. This is followed by mass spectrometric analysis of compounds eluting from the gas chromatograph. 

Cummins, T.M., Robbins, G.A., Henebry, B.J., Goad, C.R., Gilbert, E.J., Miller, M.E., and Stuart, J.D. A water extraction, static headspace sampling, gas chromatographic method to determine MTBE in heating oil and diesel fuel. Environ. Sci. Technol, 35(6) 1202-1208, 2001. 

Static mode the sample (liquid or solid matrix) is placed in a glass phial capped with a septum such that the sample occupies only part of the phial s volume. After thermodynamic equilibrium between the phases has been reached (1/2 to 1 h), a sample of the vapour at equilibrium is taken (Fig. 20.4). Under these conditions, the quantity of each volatile compound present in the headspace above the sample is proportional to its concentration in the matrix. The relationship between the amount of sample injected into the gas chromatograph and its concentration in the matrix can be obtained by calibration (using internal or external standards). 

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... 

Static headspace extraction is also known as equilibrium headspace extraction or simply as headspace. It is one of the most common techniques for the quantitative and qualitative analysis of volatile organic compounds from a variety of matrices. This technique has been available for over 30 years [9], so the instrumentation is both mature and reliable. With the current availability of computer-controlled instrumentation, automated analysis with accurate control of all instrument parameters has become routine. The method of extraction is straightforward A sample, either solid or liquid, is placed in a headspace autosampler (HSAS) vial, typically 10 or 20 mL, and the volatile analytes diffuse into the headspace of the vial as shown in Figure 4.1. Once the concentration of the analyte in the headspace of the vial reaches equilibrium with the concentration in the sample matrix, a portion of the headspace is swept into a gas chromatograph for analysis. This can be done by either manual injection as shown in Figure 4.1 or by use of an autosampler. 

There are many techniques available for the preparation of volatile analytes prior to instrumental analysis. In this chapter the major techniques, leading primarily to gas chromatographic analysis, have been explored. It is seen that the classical techniques purge and trap, static headspace extraction, and liquid-liquid extraction still have important roles in chemical analysis of all sample types. New techniques, such as SPME and membrane extraction, offer promise as the needs for automation, field sampling, and solvent reduction increase. For whatever problems may confront the analyst, there is an appropriate technique available the main analytical difficulty may lie in choosing the most appropriate one. 

Gas Chromatographic Methods. Gas chromatographic methods may be used for measuring volatile oxidation products. Static headspace, dynamic headspace, or direct injection methods may be employed. Specific aldehydes may be measured as indicators for oxidative stability of oils and fats. Thus, propanal is an and as indicator for stability of omega-3 fatty acids, whereas hexanal is best for following the oxidative stability of omega-6 fatty acids. 

The basic set-up for headspace analysis comprises an HS element — the characteristics of which depend on the particular mode used for pretreatment and a gas chromatograph or, less often, an alternative detector for measurement. Static and dynamic headspace (purge and trap included) differ in the type of equipment required multiple headspace uses the same automated device as static headspace. 

Soil spiked with trichloroethylene and toluene was analysed using a gas chromatograph equipped with a PT concentrator that was found to be replaceable by a headspace unit in order to simplify the overall assembly. The headspace analysis of soil samples was found to be restricted by incomplete desorption of the contaminants in soil-water mixtures this shortcoming, however, was effectively overcome by the addition of methanol. Henry s law constants for volatile organics in methanol must previously be determined if the method is to be applied to soils [142]. A comparison of the performance of static and dynamic (PT) headspace modes in the determination of nine VOCs in five different soils revealed poor PT recoveries in relation to those of static headspace (which ranged from 68 to 88%) the latter, however, required longer development times [143],... 

The detection of low level concentrations of volatile petroleum hydrocarbons in either soil or water can be performed by static headspace analysis. In this technique, the gas phase in thermodynamic equilibrium with the matrix is analysed. The soil is placed in a headspace vial to which water and soluble salts such as sodium chloride are added to aid the transfer of hydrocarbons into the headspace. Internal standards and surrogate spikes can also be introduced. The vial is heated and an aliquot of the static headspace vapour is directly injected onto the column of the gas chromatograph. The advantages of this technique for volatiles such as gasoline range organics are less sample handling which minimises losses, no introduction of solvents which can interfere with the compounds of interest (MTBE), and the technique can be easily automated. 

ISO/CD 22155 Soil quality - Gas chromatographic determination of volatile aromatic and halogenated hydrocarbons - Static headspace method. 

Gas chromatographic (GC) methods have been used for determining volatile oxidation products. Static headspace, dynamic headspace or direct injection methods are the three commonly used approaches. These methods were compared in an analysis of volatile compounds in an oxidized soybean oil. It was found that each method produced significantly different GC profiles (Frankel 1985). The dynamic headspace and direct injection methods gave similar results, but the static headspace is more sensitive to low molecular weight compounds. Lee and co-workers (1995) developed a dynamic headspace procedure for isolating and analyzing the volatiles from oxidized soybean oil, and equations were derived from theoretical considerations that allowed the actual concentration of each flavor component to be calculated. 

For GC analysis, HS is a preconcentration technique particularly suitable for the sampling of volatile organic compounds in air, water, and solids. Few reports have been published on the use of static headspace in the analysis of free amines in aqueous samples because of the high polarity and solubility in water of these compounds." In one experiment," static headspace preconcentration was developed for the gas chromatographic analysis of aliphatic amines in aqueous samples. A liquid-gas ratio of 1, an incubation temperature of 80°C (15 min), a pH of 13.7, and a mixture of salts (NaCl and K2SO4) at saturation concentration gave a maximal headspace amine concentration (Table 11.4). 

Various gas chromatographic (GC) methods, such as direct injection, dynamic headspace, and static headspace, have been used for the analysis of volatile products, resulting from the oxidative deterioration of vegetable oils. Though advantages and disadvantages are apparent with each GC method, for routine analyses, static headspace is the method of choice because it is rapid and requires no cleaning between samples. ... 

The different headspace sampling techniques can be classified into one-step procedures, such as static headspace, where an aliquot of the vapor phase is transferred in a closed container directly to the gas chromatograph, and two-step procedures, where the volatile analytes are transferred from the matrix of the headspace to a "trap" where they are released... 

Static headsp>ace extraction, also known as equilibrium headsp>ace extraction, is one of the techniques used for qualitative and quantitative analysis of volatile substances in the forensic field, in this technique the sample is placed in a closed vial, the volatile analytes disseminate into the headspace of the vial (figure 1), once equilibrium is reached between the analyte concentration in the headspace and the analyte concentration in the sample, a portion of the headspace is taken and injected into the gas chromatograph this can be done manually or with an autosampler, this process will be usually carried out at a pressure and temperature above ambient conditions (Slack et al., 2003). 

The equipment for static headspace extraction consists of a container, where equilibrium takes place, a device that heats the container at a constant temperature and an injection device, which transfers a portion of the headspace gas to the gas chromatograph. The container is a glass vial of between 5 ml and 25 ml capacity, which is sealed with a septum coated with polytetrafluoroethylene (PTFE) and an aluminum cap, using a crimp. Injection... 

Solid-phase microextraction (SPME) is a static head-space method similar to the carbon strip method however, it does not require a solvent desorption stage. Volatiles are extracted from the headspace by absorption into an absorbent polymer such as poly-dimethylsiloxane (ASTM method E2154). The absorbent polymer is coated onto a quartz fiber that is housed within a needle similar to a syringe needle. The coated fiber is exposed beyond the tip of the needle in the headspace above the fire debris. As with the carbon strip method, the fiber debris sample can be heated to increase the concentration of volatiles in the headspace. Volatiles are absorbed within the polymer with exposure times for routine screening being within the range 5-15 min. The fiber is retracted within the needle and can then be directly inserted into the injector of a gas chromatograph where the volatiles are thermally desorbed from the polymer onto the column. SPME fibers can be reused but appropriate blanks need to be run to ensure that the fiber is clean. 

The coupling of a pervaporator to a gas chromatograph is one of the most promising uses of pervaporation and is worth a more detailed discussion, because of the advantages that pervaporation presents as compared with both static and dynamic headspace sampling techniques. In the static approach, the sample is placed in a closed chamber and heated until the volatile compoimds in the headspace reach the equilibrium with the sample. Then, part of... 

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