Appendix Carbowax

For routine separations, there are about a dozen useful phases for capillary columns. The best general-purpose columns are the dimethylpolysiloxane (DB-1 or equivalent) and the 5% phenyl, 95% dimethylpolysiloxane (DB-5 or equivalent). These relatively nonpolar columns are recommended because they provide adequate resolution and are less prone to bleed than the more polar phases. If a DB-1, DB-5, or equivalent capillary column does not give the necessary resolution, try a more polar phase such as DB-23, CP-Sil88, or Carbowax 20M, providing the maximum operating temperature of the column is high enough for the sample of interest. See Appendix 3 for fused silica capillary columns from various suppliers. 

Procedure (See Chromatography, Appendix IIA) Use a gas chromatograph equipped with an electrolytic conductivity detector operated in the halogen mode and fitted either with a capillary injector operated in the splitless mode or with a purged, packed injector with a glass insert. Use a 30-m x 0.53-mm (id), fused-silica column, or equivalent, coated with l-(xm Supelcowax 10 or an equivalent bonded carbowax column fitted with a 50-cm retention gap of 0.53-mm, deactivated, fused silica, or equivalent. Set the column temperature to 170° for 5 min, raise the temperature at a rate of 5°/min to 250°, and hold it at that temperature for 10 min. Maintain the injector temperature at 225°. Use helium as the carrier gas at a flow rate of 8 mL/min. 

Procedure (See Chromatography, Appendix IIA.) Use a suitable gas chromatograph equipped with a hydrogen flame-ionization detector, and a silanized 1-m x 4-mm (id) glass column, or equivalent, packed with 90- to 100-mesh Anakrom ABS, or equivalent, containing 7.5% Carbowax 20M and 2% potassium hydroxide, or equivalent. Maintain the column at 190° (isothermal). Set the injection point temperature to 200° and the detector temperature to 250°. Use nitrogen as the carrier gas, with a flow rate of 50 mL/min. 

Assay (See Chromatography, Appendix BA.) Inject a 10-p,L portion of sample into a suitable gas chromatograph in which the detector is the thermal conductivity type and the column is 1-m x 8-mm (id) stainless steel tubing (Perkin Elmer Instruments, or equivalent) packed with 4% Carbowax compound 20 M on 40- to 60-mesh Chromosorb T, or equivalent materials. The carrier gas is helium flowing at 75 mL/ min. The injection port temperature is 240° the column temperature is 120° to 200°, programmed at a rate of 5°/min and the block temperature is 250°. Under the conditions described, the approximate retention time for Propylene Glycol is 5.7 min, and 8.2, 9.0, and 10.2 min for the three isomers of... 

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