PTFE columns

Fig. 5.34. GC separation of metal fluorides. Peaks 1 = fluorine plus reaction products 2 = impurity in rhenium 3 = WF6 4 = ReF6 5 = OsF6 6 = ReOFj. Conditions PTFE column, 22 ft. X 1/4 in. O.D., 15% Kel-F No. 10 oil on Chromosorb T (40-60 mesh) helium flow-rate, 28 ml/min temperature, 75°C. (Reproduced from Anal. Chem., 38 (1966) 1860, by courtesy of R.S. Juvet and the American Chemical Society.)...

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

A sensitivity of 10 10 g of beryllium in a 50-/ul sample was reported for a PTFE column packed with 5% of SE-52 on Gas-Chrom Z and an ECD. The average recovery from the samples of all types was 93.5% and no interference of common cations and anions was observed. 

Foreman et al. [631] compared the direct method of the chelate formation with the preliminary ashing method for the analysis of beryllium in rat urine. A detailed study showed that both of the methods are satisfactory, whereas testing of column material and packings showed the best results for a PTFE column packed with SE-52. Down to 1 ng/ml of the element could be detected in urine with the use of an ECD and EDTA as a masking reagent and a 0.05 M benzene solution of trifluoroacetylacetone. 

Beryllium in lunar, meteorite and terrestrial samples was determined successfully by Eisentraut et al. [632]. The sample was pulverized and fused with sodium carbonate, dissolved in dilute hydrochloric acid and transferred into a polyethylene bottle. After adjusting the pH to about 4, it was further adjusted to 5.0 with acetate buffer, both EDTA and trifluoroacetylacetone in benzene were added and the mixture was heated briefly at 95°C. A PTFE column packed with 10% of SE-30 on Gas-Chrom Z was used and a sensitivity of 4 10"14 g of beryllium was reported for the measurement of peak heights with the use of a tritium-foil ECD. 

Chromium was measured in steels with high and low contents of carbon by Ross and Sievers [633]. A small amount of the sample (2 —4 mg) was allowed to react directly with trifluoroacetylacetone in the presence of nitric acid. If an undissolved residue occurred, it was dissolved in 70% nitric acid, evaporated to dryness and the procedure was repeated. The resulting red solution was extracted with benzene and excess of the chelating agent was removed by extraction with dilute sodium hydroxide solution. A PTFE column packed with 15% of SE-52 on Anakrom ABS and an ECD were used. The results showed a relative error of 1.4-1.7%. 

Iron was determined in ores by Sievers et al. [644] with the use of the same chelating agent. Less than 1 mg of the sample was treated with the reagent in a sealed capillary, which was then crushed in a modified injection port of a gas chromatograph. A PTFE column packed with 10% of SE-30 on Gas-Chrom Z and a TCD were used. Quantitative data obtained by GC accorded well with those obtained by other methods. 

HSCCC-thermospray (TSP) MS was initiated using an analytical HSCCC apparatus of a 5-cm revolution radius, equipped with a 0.85-mm-inner diameter (i.d.) polytetrafluoroethylene (PTFE) column at 2000 rpm [6-8]. Directly interfacing HSCCC to the MS produced, however, a problem in that the high back-pressure generated by the TSP vaporizer often damaged the HSCCC column. To overcome this problem, an additional high-performance liquid chromatography... 

Figure 8.21 Loose-lined modified PTFE column.

A major requirement for column tubes in HPLC is constancy of the column diameter when changing the pressure drop along them. If this is not so, the stability of the packing is affected on changing the pressure drop, which destroys the column efficiency. All available polymeric tubes, such as PTFE, nylon or plastic tubes, show a definite pressure dependence of the tube diameter. Apart from this, polymeric materials, except PTFE, are easily attacked by organic solvents. For these reasons polymeric materials are unsuitable as column tube materials in HPLC. Recently, however, the application of a radial compressed PTFE column for preparative LC was reported (Waters Assoc.). 

A major step in the miniaturization of HPLC columns was done early in 1967 by Horvath and coworkers, when investigating the parameters that influence the separation of nucleotides in a 1 mm I.D. column. These columns were then named microbore columns. A further step in the miniaturization process was done in 1973, by Ishii and coworkers, by separating polynuclear aromatic hydrocarbons (PAHs) in a 0.5 mm I.D. polytetrafluoroethylene (PTFE) column. The term micro-LC was then introduced to differentiate this technique from HPLC, which uses larger-bore columns.Shortly after, Scott and Kucera published several articles deahng with microbore (1 mm I.D. columns) LC. In spite of the fast development in its early days (late 1960s and early 1970s), the miniaturization of HPLC followed a slow progress until recently, with... 

The thermopile was mounted in a PTFE disc, and soldered to PTFE-insulated leads which were connected to the input terminals of the amplifier. The thermopile was thus contained between two further discs each having a groove that allows the mobile Aiase to flow over one set of junctions. The three PTFE columns were situated between two steel flanges containing cavities for centering the columns. 

Li Lorenzo- carried out a quantitative gas chromatographic analysis of mixtures of boron trichloride, boron and boron nitride i,e, the gas products of partial decomposition of boron trichloride in a nitrogen plasma jet. The gaseous products of partial decomposition of boron trichloride in the plasma jet were analysed on a PTFE column (2 metres x 5mm) packed with 10% of Kel-F3 on Teflon 6 and operated at 40°C, with helium (containing approximately 1% of boron trichloride to prevent irreversible absorption of the small... 

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