Silicone stationary phases conditioning

Chromatographic Resolution. To optimize column-coating conditions and operating parameters glass capillary columns coated with various silicone-based stationary phases were tested with difficult-to-separate groups of PAH standards and Complex samples. The SE5 -coated columns performed excellently with respect to separation efficiency, column bleed and long-term stability. Other observers have had similar results with this... 

Figure 8.12 Chromatography of anthracene derivatives with different detection modes (A) laser-induced fluorescence (B) UV absorbance. Conditions capillary, 115.1 cm X 10 /un I.D. with 1.27-/im coating stationary phase, silicone acrylate/ethylhexyl acrylate Vy Vm = 0.65 mobile phase, acetonitrile detection, (A) laser-induced fluorescence (AeX 325 nm, Aem 380 nm), pressure 13.8 bar, (B) UV (258 nm), pressure 13.0 bar. Peaks 1, salicylate 2, anthracene-methanol 3, anthracenecarbonitrile 4, anthracene 5, fluoranthracene 6,1,2-benzanthracene 7, 9-phenylanthracene. (Reprinted from Ref. 11 with permission.)...

Different chromatographic conditions, sometimes very unusual ones, have been tested for the analysis of TFA-methyl ester derivatives. Hagen and Black [208] applied Carbo-wax 20M as the stationary phase, injected the sample at room temperature, and within 2—3 min increased the temperature to 270°C they detected in the chromatogram even Lys, Arg, Trp and His, thus succeeding where other workers failed, especially as far as His is concerned. The best separation of TFA-methyl esters of amino acids was obtained on a glass column (3.25 m X 2.5 mm I.D.) packed with Diatoport S coated with 2.5% of a mixed silicone phase (XE-60—QF-1—MS-200,46 27 27), both with a temperature programme and under isothermal conditions [211]. 

Procedure (See Chromatography, Appendix IIA.) Use a gas chromatograph equipped with a flame-ionization detector and a 4-m x 2-mm (id) stainless-steel column, or equivalent, packed with 15%, by weight, methyl trifluoropropyl silicone (DCFS 1265, or QF-1, or OV-210, or SP-2401) stationary phase on 80- to 100-mesh Gas Chrom R, or the equivalent. Condition a newly packed column at 120° and with a 30-mL/ min helium flow for at least 2 h (preferably overnight) before it is attached to the detector. For analysis, maintain the column isothermally at 105° the injection port and detector at 250° the carrier gas flow rate at 11 mL/min with fuel gas flows optimized for the gas chromatograph and detector in use. Change the experimental conditions as necessary for optimal resolution and sensitivity. The signal-to-noise ratio should be at least 10 1. 

The various triacylglycerol (TAG) components of coconut oil may be separated and quantified by gas chromatography with the use of stable silicon gum stationary phase under temperature-programed conditions and identified by reference to standard TAG solutions. The carbon number of a TAG component is the sum of carbon atoms of the fatty acids attached to the glycerol moiety. For example, the carbon numbers of trilaurin and oleodistearin are 36 and 54, respectively. The relative amounts of each TAG in a sample of fat serves to establish its identity. For coconut oil, this test may also serve to distinguish it from other lauric oils (see Table 4 and Figure 5). 

The operating conditions are slightly different from those given in method 6.2.16. A glass column (length 180-200 cm and 2-4 cm diameter) is filled with diatomaceous earth, acid-washed, silanized and impregnated with 2-5% of a suitable stationary phase, e.g. polysiloxane, methyl silicone (e.g. SE 30) or 50% phenylmethyl silicone (e.g. OV 17). The column temperature should be 230-240 °C and the rate of the carrier gas 30-50 ml of N2/min. 

You need to adjust your gas chromatograph to the proper conditions for the analysis. We recommend that you prepare and analyze the reference mixture listed in the Procedure section. Most chromatographs will be able to separate this mixture cleanly with the possible exception of the xylenes. One possible set of conditions for a Gow-Mac model 69-350 chromatograph is the following coliunn temperature, 110-115°C injection port temperature, 110-115°C carrier gas flow rate, 40-50 mL/min column length, approximately 12 ft. The column should be packed with a nonpolar stationary phase similar to silicone oil (SE-30) on Chromosorb W or with some other stationary phase that separates components principally according to boiling point. 

As stationary phase for the resolution of fatty acid mixtures polar (polyesters of short chain dicarbonic acids and low molecular diols) and unpolar (hydrocarbons, silicones) substances can be used. Gas-chromatography under standardized conditions permits the tentative identification of separated fatty acids from the time elapsing between application of the sample and the emergence of the acid in question. Figure 6 shows the separation of serum fatty acid methyl esters using a polar stationary phase. 

They used silicone SE-30 as stationary phase (10%) on Chromosorb W at 140°C (injection block temperature 220°C)using helium as carrier gas. Under these conditions they separated benzene, toluene. 

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