Packed columns programmed techniques

Early work relied on the use of packed columns, but all modern GC analyses are accomplished using capillary columns with their higher theoretical plate counts and resolution and improved sensitivity. Although a variety of analytical columns have been employed for the GC of triazine compounds, the columns most often used are fused-silica capillary columns coated with 5% phenyl-95% methylpolysiloxane. These nonpolar columns in conjunction with the appropriate temperature and pressure programming and pressure pulse spiking techniques provide excellent separation and sensitivity for the triazine compounds. Typically, columns of 30 m x 0.25-mm i.d. and 0.25-qm film thickness are used of which numerous versions are commercially available (e.g., DB-5, HP-5, SP-5, CP-Sil 8 CB, etc.). Of course, the column selected must be considered in conjunction with the overall design and goals of the particular study. 

Diffusivity data are available only for a limited number of polymer-solvent systems. This paper describes research that has led to the development of the use of capillary column inverse gas chromatography (IGC) for the measurement of diffusion coefficients of solute molecules in polymers at infinite dilution. The work has resulted in a precise, rapid technique for the diffusion measurements that circumvents the many problems attendant to classical sorption methods and packed column IGC methods. Initial results of the program appeared in two recent publications (1,2)- Some of the material introduced in those papers is discussed here to present background for... 

Mass Spectrometry. Electron impact (El) mass spectrometry was done at NRL on the effluent from a 6 ft. OV-101 packed GC column programmed from 70 to 210°C. Field ionization mass spectrometry (FIMS) was performed by SRI International on contract to NRL. In this latter analysis, the fuel sample was frozen on a solids inlet probe prior to insertion into the mass spectrometer. The spectra accumulated for each mass during a temperature program were normally totaled for data presentation (6). Molecules boiling below 140°C are lost or depleted with this technique but such compounds comprise a very small fraction of JP-5 or DFM. Since the ionization efficiency for hydrocarbon classes is currently under study, the FIMS data are utilized primarily in a qualitative sense. 

This procedure is used after preliminary separation of the PEG from the surfactant by the extraction or ion exchange methods described above. Compounds are analyzed as either the trimethylsilyl or the acetate derivatives. Standard techniques for derivatization are used, as available in the literature of vendors such as Supelco. An ordinary packed-column GC apparatus is used, with flame ionization detection. The column is stainless steel, 2.7 x 600 mm, packed with 2% OV-17 on Chromosorb G-AW-DMCS. Helium carrier flow is at 50 cc/min. Injector and detector are at 370 C the column is programmed from 130 C to 300 C at d C/min. 

Various precolumn concentration procedures used in conjunction with thermal focusing are desirable for biochemical applications. Novotny and Farlow [65] developed a simple technique, where an off-line injection of a relatively large dilute sample onto a small precolumn results in effective concentration. In this procedure, a small volume of deactivated solid support is packed into the glass liner of an injection system. After the volatile solvent is removed, the liner is quickly introduced into the injection port, and the desorbed sample is trapped for several minutes in the cool column. Chromatograms obtained through the following temperature program-... 

Over the past decade, CEC has become incorporated into the research and development programs of many universities and industrial organizations. Progress has been made in the areas of column construction, column packing, general instrumentation, mobile phase optimization, applications, and method development. " The elucidation of the physicochemical and electrochemical properties of CEC systems and the determination of their influence on the entire analysis is ongoing and adds a fascinating dimension to the study of this technique. 

Because of the variety of columns and samples that can be analyzed by GC, several injection techniques have been developed. The packed inlet system is designed mainly for packed and wide-bore columns. However, an adapter can be used to enable capillary columns to be used. When injection is carried out in the on-column mode, glass wool can be used for packing the injector. For capillary GC, spht technique is most common, which is used for high concentration samples. This technique allows injection of samples virtually independent of the selection of solvent, at any column temperature, with httle risk of band broadening or disturbing solvent effects. The sphtless technique, on the other hand, is used for trace level analysis. The so-called cold injection techniques (on-column, temperature programed vaporization, cooled needle split) have also been recently developed. " " ... 

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