Headspace autosampler vial

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. 

The unit shown has an automated robotic headspace autosampler for the analysis of the headspace of 50 samples in small glass vials. 

HT Headspace Autosampler (also 7050 with 50 sample vial positions)... 

The MHE procedure is carried out in a series of consecutive runs from one and the same sample vial. Immediately after the first headspace analysis, the vial is depressurized to the atmosphere and incubated with the same method again for the next analysis. This step can also be accomplished by many types of headspace autosamplers. In case of a headspace syringe autosampler, an optional MHE device is required, which is used to depressurize the vial (Vulpius and Bal-tensperger, 2009). With this stepwise procedure Eq. (2.10) can be rewritten in Eq. (2.11) by replacing the concentration with peak areas (with i the number of injections, A the peak area after i injections and the peak area of the first injection),... 

After the sample is prepared for analysis with internal standard(s), chill the sample and transfer to an appropriate autosampler vial with minimal headspace. The remainder of the sample should be re-chilled immediately and protected from evaporation for further analyses, if necessary. The autosampler vials should be chilled until ready for analyses. 

TCA, was used as an internal standard. The extraction fiber of the SPME, coated with polymethylsiloxane, was exposed for 25 minutes in the headspace of the sample vial, and then injected into the injection port of the GC-MS by a Varian 8200 CX autosampler. Limit of quantification of this method was 5 ng/L. The method was linear from 5 to 250 ng/L with an overall coefficient of variation for replicate analyses of less than 13%. 

SPME is a patented sample preparation method for GC applications (32-36). The solvent-free technique was developed in 1989 by Janusz Pawliszyn (http. /Avww.science.uwaterloo.ca/ -janusz/spme.html) at the University of Waterloo in Ontario, Canada, and a manual device made by Supelco, Inc. has been available since 1993. In 1996, Varian Associates, Inc., constructed the first SPME autosampler. SPME involves exposing a fused silica fiber that has been coated with a non-volatile polymer to a sample or its headspace. The absorbed analytes are thermally desorbed in the injector of a gas chromatograph for separation and quantification. The fiber is mounted in a syringe-like holder which protects the fiber during storage and I netration of septa on the sample vial and in the GC injector. This device is operated like an ordinary GC syringe for sampling and injection. The extraction principle can be described as an equilibrium process in which the analyte partitions between the fiber and the aqueous phase. 

The Fox e-nose used for determination of rancidity in cookies was ALPHA MOS Fox 4,000 system (Fig. 1). 5 g of cookie samples were heated at 50 °C inside a controlled thermostat-sampling chamber for a headspace generation time of 20 min and 2 ml of VOCs were injected to the Fox system with an autosampler HS100 from 10 ml sealed vials by means of a carrier gas (TOC grade synthetic air) at a flow rate of 2 ml/min. The gas sampling syringe was heated at 60 °C. Post injection, a valve was... 

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). 

Current autosamplers work with two different techniques. The first one employs sample loops in order to fill these loops with headspace gas, the closed vial is ptressutized to a pressure level above that present in the vial the pressurized headspace is then temporarily connected to the sample loop, causing the headspace gas to expand through the sample loop and into the atmosphere once the sample loop is filled, a valve is changed and its contents are transferred to the chromatographic column. This type of sampling has been commonly used for gas sampling in other areas, such as the petrol industry. 

Autosampler Tekmar AQUATek 70 Aqueous samples were filled into 40 mL vials without headspace 25 mL automatically transferred to the frit sparge glass vessel... 

With an autosampler the available vial size is dictated by what vials will fit in the trays of the autosampler. For our systems this included a 2-ml vial and a 12-ml vial. When possible, the sample volume should be adjusted to minimize the headspace, leaving just enough room to deploy the SPME fiber. For the 12-ml vials, this results in a sample size of 5 to 6 g of rice occupying approximately two-thirds of the volume. For the 2-ml vials, the sample is limited to 0.75 g of... 

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