Septum headspace sampling vial

Prom the experimental point of view the static headspace sampling technique is very simple. The sample, either solid or liquid, is placed in a glass vial of appropriate size and closed with a Teflon-lined silicone septum. The 1 is carefully... 

In static headspace sampling [301,302] the polymer is heated in a septum-capped vial for a time sufficient for the solid and vapour phases to reach equilibrium (typically 2 hours). The headspace is then sampled (either manually or automatically) for GC analysis, often followed by FID or NPD detection. Headspace sampling is a very effective method for maintaining a clean chromatographic system. Changing equilibrium temperature and time, and the volumes present in the headspace vial can influence the sensitivity of the static headspace system. SHS-GC-MS is capable of analysing volatile compounds in full scan with ppb level... 

The SPME process, adapted for solid or viscous matrix, is shown in Figure 10.1. A fused silica fibre, coated with a polymer, is installed inside a stainless steel hollow needle. In the first step, the needle is introduced in the sample vial through the septum. The fibre is then exposed to the headspace above the sample and the organic analytes adsorb to the coating of the fibre. After a variable sampling time, the fibre is drawn into the needle and the needle is withdrawn from the sample vial. Finally, in the same way, the fibre is introduced into the chromatograph injector where the analytes are thermally desorbed. 

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 Vapor was withdrawn from the head-space with a stainless steel syringe and injected into a gas chromatograph.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... 

The actual sampling procedure, whether manual or automated, is as follows (1) The fiber sheath pierces the septum of the sample vial. (2) The fiber is extended from the sheath into either liquid sample or the headspace above liquid, solid, or semisolid samples. (3) Equilibration of analytes between the fiber and liquid or headspace occurs over a period of time. (4) The fiber is withdrawn into its sheath. (5) The sheath is withdrawn from the vial and inserted into a hot or cold injection port of a gas chromatograph. (6) The sample desorbs into the carrier gas stream." Store opened, but unused, cartridges in a plastic bag in a desiccator. 

Method 5021 describes the automated static-HS technique. Static HS has been introduced in this book from a theoretical viewpoint. A soil sample is placed in a tared septum-sealed vial at the time of sampling. A matrix modifier containing internal and/or surrogate standards is added. The sample vial is placed into an automated equilibrium headspace sampler. The vial s temperature is elevated to a fixed value that does not change over time and the contents of the vial is mixed by mechanical agitation. A measured volume of headspace is automatically introduced into a GC or a GC-MS. The method is automated and downtime is minimal. However, the cost of the automated system is appreciable. Contamination of the instru-... 

Headspace sampling. A syringe is inserted through a rubber septum (a rubber disk) in the cap of the vial to withdraw gas for analysis. 

The procedure described in this section is a modification of that described by Namera et al. (3), where ethylchloroformate is used for amphetamine derivatiza-tion in order to achieve high resolution of the various amphetamines. Blood or urine samples (0.5 mL),l mL of K2CO3, 0.5 g of NaCl, 20 p,L of ethylchloroformate, and 30 xL of the internal standard, are placed into a 10-mL vial and sealed rapidly with a silicon septum and a vial cap. The SPME needle is inserted into the vial and extraction fiber exposed in the headspace. The vial is then heated at 80°C for 15 min. The vial is rotated at 250 rpm during the SPME extraction. After extraction, the fiber is pulled back into the needle and the needle inserted into the injection port of the GCMS instrument. The fiber is exposed for 3 min in the injector. 

Figure 8.26(A) is an example of a valve type interface [329]. Helium carrier gas is provided to the headspace saiq)ler and is split into two flow paths. One path is flow-controlled and provides a constant flow of carrier gas which passes from the headspace unit through the heated transfer line to the gas chromatograph. The second flow path is pressure-regulated and, in the standby mode, the seunple loop and seuapling needle are flushed continuously by the helium flow. At a time determined by the operator, the sampling needle pierces the septum and helium pressurizes the headspace vial to any desired pressure. The headspace gas is then allowed to vent through the sample loop. Once filled, the sample loop is placed in series with the normal carrier gas flow and its contents are driv Bbhrough the heated...

The samples were placed in headspace vials. When saponification was performed, a few milliliters of NaOH solution were added to the sample. The vial was sealed with a headspace aluminum cap furnished with a Teflon-faced septum, immersed in a water bath maintained at 100 °C, and let equilibrate for 6 min before HSSPME. Afterward, the fiber was exposed to the headspace over the sample for 5-240 min, depending on the experiment. The sample was magnetically agitated during sampling. Once the exposition period was finished, the fiber was immediately inserted into the GC injector and the chromatographic analysis was carried out. Desorption time was set at 5 min. 

Here is a student procedure to measure nicotine in urine. A 1.00-mL sample of biological fluid was placed in a 12-mL vial containing 0.7 g Na2CO , powder. After 5.00 pig of the internal standard 5-aminoquinoline were injected, the vial was capped with a Teflon-coated silicone rubber septum. The vial was heated to 80°C for 20 min and then a solid-phase microextraction needle was passed through the septum and left in the headspace for 5.00 min. The fiber was retracted and inserted into a gas chromatograph. Volatile substances were desorbed from the fiber at 250°C for 9.5 min in the injection port while the column was at 60°C. The column temperature was then raised to 260°C at 25°C/min and eluate was monitored by electron ionization mass spectrometry with selected ion monitoring at m/z 84 for nicotine and m/z 144 for internal standard. Calibration data from replicate... 

Prepare sample (see Basic Protocol 1, step 1). Weigh 2 g of sample into a 6-ml headspace vial and seal with a Teflon/Buty 1 rubber septum, with the Teflon side facing the sample. 

To imitate water samples, trip blanks are prepared in volatile organic analysis (VOA) vials with septum caps lined with polytetrafluoroethylene (PTFE). The vials are filled without headspace with analyte-free water. For soil sampled according to the requirements of EPA Method 5035, field blanks may be vials with PTFE-lined septum caps, containing aliquots of methanol or analyte-free water. 

In this technique, an aliquot of sample (10 ml) is placed in a septum vial (20 ml) to a maximum of 50% capacity. The vial is spiked with surrogates and then heated for a moderate period ( 30 min) to create an equilibrium for volatile organic compounds between the air phase (headspace) and the water. The headspace is sampled (20—100 pi) with an airtight syringe and injected into a GC. Analytes are similar to... 

The liquid or solid sample is placed in a vial, which is sealed with a septum and heated to a predetermined temperature for a period of time. Equilibrium between the sample and vapor phase is then established and a portion of the volatiles in the gas phase (headspace) is subsequently injected onto the column. Several different methods have been used to transfer headspace volatiles into the GC, from manual withdrawal that uses a gas syringe, to sophisticated automatic sampling that involves transfer lines, and valves that lead directly onto the column. 

Static mode the sample (solid or liquid matrix) is placed in a glass vial capped with a septum such that the sample occupies only a part of the vial s volume. After thermodynamic equilibrium between the phases present (1/2 to 1 h), a sample of the vapour is taken. Under these conditions, the quantity of each volatile compound present in the headspace (volume above the liquid) will be proportional to its concentration in the matrix. After calibration (using methods of internal or external standards), it is possible to match the real concentrations in the sample with those of the vapours injected in the gas chromatograph (Figure 21.6). 

When SPME is applied to analysis of water samples, the sample is placed in a vial with a cap that contains a septum. In order to extract the analytes from the sample, the sheath is pushed through the septum and the plunger is lowered, forcing the hber into the vial, where it is immersed into the aqueous sample or its headspace. Then the SPME hber absorbs organic compounds from the phase that is in contact with it unhl equilibrium is achieved. 

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