Polytetrafluoroethylene blanks

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. 

For reproducible analysis, it is important that equilibrium between the phases should first be established. This equilibrium is influenced by the conditioning time and temperature. The removal of the sample for the GC analysis can be by means of overpressure or underpressure, although care must be taken that the temperature not only of the sample vessel but also of the metering device is kept constant. The HS vessels (vials) are closed with a PTFE (polytetrafluoroethylene) or aluminum-coated silicone septum. The septum itself is protected from the overpressure of the interior space by an aluminum cap. Before each analysis, a blank determination with an empty HS vial is carried out to detect whether any constituents of the materials of the septum or vial are being emitted. 

These nebulizers and their components are typically constructed from polymer materials, such as polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), or poly-vinylfluoride (PVF), although some designs are available in borosilicate glass or quartz. The excellent corrosion resistance of the polymer nebulizers means they have naturally low blank levels. This characteristic, together with their ability to handle small sample volumes found in applications such as vapor phase decomposition (VPD), makes them an ideal choice for semiconductor laboratories that are carrying out ultratrace element analysis. - A microflow concentric nebulizer made from PFA is shown in Figure 3.8, and a typical spray pattern of the nebulization process is shown in Figure 3.9. 

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