Carbowax™ retention

The purity of the product is greater than 99% as determined by gas chromatographic analysis using a 6-m. column of 30% Carbowax 20M on 60-80 Chromosorb W. The major impurity (<1%) was shown to be 3-heptanol by comparison of gas chromatographic retention times and mass spectral fragmentation patterns with those of an authentic sample. 

For the AOAC beer samples, a 2 m x 2 mm glass column packed with 8.57o Carbowax 20 M + 0.857, NaOH on 100/120 mesh Chromosorb G was used at 130 C and a helium flow rate of 20 cc/min. Retention times of NDMA and NDPA were 4.5 and 12.2 min, respectively. For the ASBC collaborative study, a 1 m x 2 mm glass column containing 67, Carbowax 20 M-TPA on 100/120 mesh Chromosorb G was operated at 90 C with 20 cc/min helium flow rate. Retention times were 3.6 and 11.3 min for NDMA and NDPA, respectively. For determination of nitrosamines in amines, a 2 m X 2 mm, 107, Carbowax 20 M-TPA on 100/120 mesh Chromosorb G column was operated at 190 C with a carrier gas flow rate of 20 cc/min. Retention times were NPYR, 6.6 min NMOR, 7.4 min. 

In practice, it is more difficult to optimize resolution as a function of the relative retentlvity than to optimize retention. Thus, unless the mixture is very complex or contains components that are particularly difficult to separate it may be possible to optimize a particular separation using the linear equation (1.72) as demonstrated by Bttre [177]. Figure 1.13 illustrates the relative change in peak position for a polarity test mixture with two identical, serially coupled open tubular columns, coated with a poly(dimethylslloxane) and Carbowax 20 M stationary phases, as a function of their relative retentlvity on the second column. The linear relationship predicted by equation (1.72) effectively predicts the relative peak positions and indicates that a nearly... 

Carbowax 4000, gas-liquid phase adsorption contributes only Moderately to the retention of all solutes, decreasing rapidly with increasing liquid phase loading. At low phase loadings adsorption at the gas-liquid interface nay contribute between 3 and 42% to the retention of the solutes investigated... 

Halogenated hydrocarbons in different waters were identified by comparison with a standard solution. A chromatogram of a standard pentane solution of various volatile organochlorine compounds including trihaloforms is shown in Fig. 9.1. Retention times were measured on two columns with different stationary phases (SE-52 and Carbowax 400). 

Triprolidine hydrochloride has been separated from other antihistamines with a 1.52m x 2.4 mm i.d. column packed with 2% carbowax 20M + 10% KOH on 60/80 mesh Chromosorb W. Retention time of 32 minutes was obtained with a column temperature of 190°C. Triprolidine hydrochloride was probably eluted as the free base.21... 

The fractions from this distillation may be analyzed by gas chromatography employing a column packed with Carbowax 20M suspended on Chromosorb P. The retention times for the various components (minutes) are pentane, 1.6 3-methyl-2-butanone, 4.2 3-methyl-l-buten-2-yl triflate, 6.7 and 3-methyl-2-buten-2-yl triflate, 9.5. 

Gas chromatographic analyses are obtained at about 120° with a 2 m. X 7 mm. column packed with a suspension of 5% (by weight) of silver nitrate and 15% (by weight) of Carbowax 6000 (polyethylene glycol) on either Chromosorb P or Celite 545. With this column the relative retention times of the various possible components in the reaction mixture are cyclododecane, 1.00 trans,trans,trans-, S,9-cyc ododec tnene, 1.20 trans-cyclo-dodecene, 1.13 m-cyclododecene, 1.33 ci5,iraw5-l,5-cyclodode-cadiene, 1.51 m, m 5-/raw5-l,5,9-cyclododecatriene, 1.72. The reaction should be stopped when the rate of reduction of cis,trans-1,5-cyclododecadiene to cw-cyclododecene has become approximately equal to the rate of conversion of the as-monoolefin to cyclododecane. 

The product may be analyzed by use of a gas chromatography column packed with either LAC-728 (diethylene glycol succinate) or Carbowax 20M suspended on Chromosorb P. Using a 2.5-m. LAC-728 column heated to 100°, the submitters found retention times of 9.4 and 13.0 minutes for cyclohexyl methyl ketone and cyclohexyldimethylcarbinol. Less than 1% of the carbinol by-product was present. 

Diethyl succinate is the sole product of the reduction, rhc yield reflects the efficiency of the workup. The distilled ])ro(luct gives a single sharp peak on gas chromatography employ-itig a column packed with Carbowax 20M suspended on Chromo-sorl) P. On this column the checkers found the retention times of diethyl succinate to be 38.8 minutes and 43.0 minutes, respectively. 

Gas chromatographic analysis (10% Carbowax 20 M on 80-100 mesh Chromosorb W, 2.5 m x 2 mm, column temperature 180°C, injection temperature 230°C, flow rate 10 mL/min, retention time 10 min) of the corresponding dimethyl ester, formed with ethereal diazomethane, indicated a purity of greater than 99%. 

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 very polar phase such as carbowax is generally only used for samples requiring a high degree of polar discrimination for adequate separation or retention. An example of this is in the analysis of fatty acids with differing degrees of unsaturation. On a non-polar column such as BPX-5, a series of C-18 acids such as stearic, oleic, linoleic and linolenic acids, which contain respectively 0, 1,2 and 3 double bonds, overlaps extensively. However, on polar columns such as carbowax they are separated. 

The trifluoroacetates of 1-hexanol and 1-heptanol had retention times of 3.0 and 5.1 minutes, respectively, on Carbowax at 80°C. The trifluoroacetates of 1-undecanol, nonane-1,9-diol, and decane-1,10-diol had retention times of 4.0, 5.1, and 7.6 minutes on Apiezon at 170°C. Peaks were well formed and did not have the characteristic tail of alcohol peaks. The reduction-trifluoroacetylation treatment of 5-ketohexanoic... 

A gas chromatographic analysis of the product by the submitters using a 1.8-m. column packed with 20% Carbowax 20 M suspended on Chromosorb P and operated at 150° with a flow rate of 30 ml. per minute showed a peak for the major component having a retention time of 16 minutes and two minor peaks having retention times of 4 and 7 minutes, with relative areas amounting to 6% and 2% of the major peak, respectively. The stereochemical purity of the product was shown to be >95% cis by the submitters by gas chromatographic analysis using a 50-ft. capillary column... 

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. 

The submitters obtained 8.3-9.1 g (86-94%) boiling at 85-107°C, 0.4 mm. The reported bp of N,N-dimethyl-N -p-tolylformamidine is C (30 urn).3 A gas chromatographic analysis of the product using a 1/4 x 10 column packed with 5% carbowax 20 M supported on 80-100 mesh chromosorb N exhibited a single peak with a retention time of 4.8 min at an oven temperature of 220 C with a flow rate of 60 cc/mln. The checkers redistilled the product to obtain colorless material, bp 69.5°C (0.2 mm), which was analyzed. Anal. Calcd for... 

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. 

The retention index of a compound obtained on a given stationary phase under given experimental conditions constitutes worthwhile information. However, if several indices of the same compound obtained on different stationary phases are available, better identification of this compound can be made. Because of the excellent reproducibility of retention times on modern chromatographs, this method is reliable for known control compounds. While obtaining retention indices does not constitute absolute identification of a compound, this method can be quite useful to identify unknowns if the proper retention indices tables are available on the most common stationary phases (Squalane, Apiezon, SE30, Carbowax 20M). However, the use of retention indices is now of lesser interest because of capillary columns that involve new stationary phases. This limits the information that can be obtained from the retention indices. Hyphenated techniques are currently more popular. They represent excellent methods for compound identification but depend on instruments that are more complex and more expensive. 

C. (a) In Table 24-3.2-pentanone has a retention index of 987 on a polyethylene glycol) column (also called Carbowax). Between which two straight-chain hydrocarbons is 2-pentanone eluted ... 

The checkers employed a 5-ft. 20% Carbowax 20 M (terminated with terephthalic acid) on Chromosorb W (acid washed) column at 60°. Methyl isocyanide showed a retention volume of 300 cc. of helium Only traces of lower-boiling impurities were observed. 

A Carbowax 20M or 1500 gas chromatography column at a temperature of 180° may be used. Diamantane has a shorter retention time than tetrahydro-Binor-S. The checkers used a 10% OV101 GCQ column, 100/120, at 200° retention times are Binor-S, 11.5 minutes tetrahydro-Binor-S, 7.6 minutes diamantane, 6.2 minutes. 

Infrared spectra of individual fractions were determined by means of a Beckman IR-5 spectrophotometer equipped with a 5 X KBr lens-type beam condenser. Infrared spectra of selected reference compounds were obtained from samples which had been purified by chromatography. On the basis of identity of infrared spectra and retention data with those of authentic reference compounds, most of the peaks shown in Figures 1 and 2 were identified (15,16). To obtain information about minor components not detectable in the infrared spectra, mass spectra were obtained as components of an irradiated odor concentrate were eluted from a 10-foot, J/g-inch 5% Carbowax 20M column programmed from 20° to 160°C. at 1° per minute. These spectra were obtained on a modified model 14 Bendix Time-of-Flight mass spectrometer. Electron energy was set at 70 e.v., and spectra were scanned from m/e 14-200 in 6 seconds. 

The reaction may alternatively be carried out by boiling the benzaldehyde vigorously under reflux for 2 hours with a solution of 20 g of potassium hydroxide in 90 ml of water, and then working up the cooled reaction mixture as described above. Reaction is normally complete under these conditions the extent of the reaction may be determined by subjecting the crude ether extract, before the latter is washed with bisulphite solution, to g.l.c. analysis on a 1.5 m column of Chromosorb W with 10 per cent of Carbowax as the stationary phase, at 156 °C with a nitrogen flow rate of 40ml per minute. The retention times of benzaldehyde and benzyl alcohol are approximately 2.7 and 9.7 minutes respectively. 

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