Carbowax column

Hept-l-ene [592-76-7] M 98.2, b 93 /771mm, d 0.698, n 1.400. Distd from sodium, then carefully fractionally distd using an 18-in gauze-packed column. Can be purified by azeotropic distn with EtOH. Contained the 2- and 3-isomers as impurities. These can be removed by gas chromatography using a Carbowax column at 70°. 

In the second part of the work, 2-D chromatography using a Zoex system 2-D chromatography kit with a 15 m x 0.25 mm x 1 pm nonpolar DB-1 column coupled to a 1.5 m X 0.25 mm x 1 pm polar Carbowax column was used for LCO speciation. Figures 2.2 and 2.3 show 2-D chromatograms of FCC products from two catalysts compared at similar slurry oil yields. Figure 2.2 is from the product of the novel... 

Figure 11.5 shows the structures of some of the major components in peppermint oil. The use of the retention index system is illustrated in Figures 11.6 and 11.7 for peppermint oil run in comparison with n-alkane standards on both a weakly polar OV-5-type column and a polar carbowax column. 

A carbowax column is highly selective for polar compounds. As can be seen in Figure 11.7 the group of polar compounds including menthol and menthone is... 

A 25-m x 0.3-mm HP Ultra Silicone capillary column at 70°C with 30 psi helium head pressure was used for the chromatographic analysis retention times of 3-buten-l-ol and cyclobutanol are 1.19 min and 1.35 min, respectively. The submitters used a 3-m x 0.3-cm 20 M carbowax column at 90°C/8 psi hydrogen and they reported retention times of 13 m1n and 20 min for 3-buten-l-ol and cyclohutanol, respectively. 

A Beckman Model 4 GC was equipped with a carbowax column, temperature 180 C (inlet). A microliter injection was made and the oxidized beta-pinene peak was measured. The retention time for the oxidized beta-pinene peak is 5.5 minutes. The encapsulated orange terpenes were first dissolved in water before injection. 

Although these peak areas were sufficient to quantify quinaldic acid on Carbowax columns, residual water present in the extracts of the ion-exchange resins interfered in previous experiments using water-sensitive polydimethylsiloxane stationary phases. The change to a polyethylene glycol stationary phase eliminated the water interferences, and good linear calibration curves for methyl quinaldate were then obtained. 

Note. (1) The reaction may be monitored by observing the diminution of carbonyl absorption in the infrared spectrum of successive samples withdrawn from the organic phase, after allowing the dichloromethane to evaporate from a portion placed on a sodium chloride plate. Alternatively samples of the reaction medium may be analysed by g.l.c. using a 10 per cent Carbowax column on Chromosorb W held at 150 °C with a nitrogen carrier gas flow rate of 40ml/minute benzaldehyde has tR 2 minutes and phenyloxirane has tR 2.75 minutes. 

Heaton et al. have reported the supercritical fluid chromatography of taxicin I and taxicin II extracted by supercritical fluid extraction of Taxu baccata, the English yew tree [41]. They compared capillary- and packed- column SFC and concluded that packed-column SFC was better than capil4 lary-column SFC for quantitative analysis of these compounds. Capillary SFC was done on either a biphenyl or carbowax column with unmodified carbon dioxide as the mobile phase. The packed-column SFC was performed on a nitrile column with a mobile phase consisting of a methanol gradient with carbon dioxide. 

The Carbowax column is very sensitive to oxidation when the stationary phase is exposed to traces of water or air especially at temperatures above about 160°C. A new type of cross-linking has been reported to impart resistance to oxidative degradation of the stationary phase [5-7]. Two other phases which show promise are an oligo-(ethylene oxide)-substituted polysiloxane (glyme) and an 18-crown-6-substituted polysilox-ane [8]. The glyme column offers a polar phase with good operational conditions to a low of a least 20°C with the same selectivity of Carbowax. The crown polysiloxane selectivity is based on the interaction of the solute molecule with the cavity of the crown ether. 

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. 

See Chapter 12 for information about gas chromatography. A Carbowax column works best, although any other nonpolar phase such as silicone rubber should work as well. With a nonpolar column packing the products cU e expected to come out in the order of their boiling points. A typical set of operating conditions would be column temperature 100°C, He flow rate 35 mL/min, column size 5-mm dia x 2 m, scunple size 5 microliters, attenuation 16. 

These figures, which have significant differences, show the pyrograms of a cellulose pyrolysate obtained at 590° C, separated on a Carbowax column (Figure 5.2.10) or on a methyl 5% phenyl silicone column (Figure 5.2.11). 

As an example, a bidimensional separation was performed for a segment in a separation of a cellulose pyrolysate. Figure 5.2.13(A) shows the chromatogram of a pyrolysate obtained at 600° C from microcrystalline cellulose. The results were obtained on a 30 m X 0.32 mm Carbowax column with 0.5 pm film thickness as a first dimension separation in a bidimensional system similar to the one shown in Figure 5.2.12. 

Figure 5.2,13(A). The chromatogram of the pyrolysate obtained from microcrystalline cellulose at 60

A Py-GC study [7] with pyrolysis done at 500° C showed numerous peaks corresponding to the isoprene dimers, trimers. .. up to hexamers eluting in clusters of peaks. The separation was done on a methyl silicone 5% phenyl silicone type column with FID detection. The results from a Py-GC/MS study [8] where natural rubber was pyrolysed at 580° C in a Curie point Py-GC/MS on-line system showed similar results. The TIC trace of the pyrolysate with the separation done on a 60 m Carbowax column, 0.32 mm i.d., 0.25 pm film thickness, with the temperature gradient of the GC oven between 40°... 

The pyrolysate of cellulose acetate contains both volatiie and iess volatile compounds. In order to identify a wider range of compounds with different voiatilities by GC analysis, it is common to appiy two chromatographic conditions, one for the analysis of more volatile compounds and another for more polar and less volatile ones. The second technique may be associated with derivatizations. The results for the pyrolysis of a cellulose acetate sample at 590° C followed by GC/MS with the separation on a polar chromatographic column are shown in Figure 7.3.1. This particular separation was done on a 60 m Carbowax column with 0.32 mm i.d., 0.25 n film thickness. 

Figure 7.3.1. Total ion chromatogram forpyrolysed cellulose acetate separated on a Carbowax column. Peak corresponds to the identification given in Table 7.3.2.

Figure 7.3.3. Total ion chromatogram for pyrolysed CMC by on-line Py-GC/MS with separation on a Carbowax column.

Table 7.3.5. Peaks identified in the TIC of CMC pyroiysate separated on a Carbowax column.

Figure 7.4.1. Starch pyrolysate at 59(f C and separated on a Carbowax column. Peak identification (by mass spectra library search) is indicated in Table 7,4.1.

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