Megabore columns

Capillary Columns Capillary, or open tubular columns are constructed from fused silica coated with a protective polymer. Columns may be up to 100 m in length with an internal diameter of approximately 150-300 )J,m (Figure 12.17). Larger bore columns of 530 )J,m, called megabore columns, also are available. 

The signal was recorded on a Hewlett Packard Integrator Model 3393A Integrator. Samples were injected onto a 30 m megabore column coated with 1.5 micron DB-5 purchased from J W Scientific. The flow of nitrogen carrier gas was maintained at 30 cc/min. The column was equilibrated at 150°C. On injection of the sample, this temperature was maintained for five minutes followed by a programmed increase at a rate of 8°C/min. to a maximum of 300°C, which was maintained for 30 minutes. 

Packed column port with a megabore column adapter... 

Fused-silica megabore column, DB17, 15 m x 0.53-mm i.d., 1-p.m fllm thickness, (50% phenyl)-methylpolysiloxane... 

Instead of the packed column mentioned in Section 6.3, a megabore column may also be used for gas-chromatographic determination. The operating conditions are as follows ... 

The methyl-[14C]-dimethyltin chloride was used to compare the performance of packed and megabore capillary columns in a gas chromatographic analysis for separating mixtures of a carbon-14 labelled trimethyllead chloride, tetramethyltin, dimethyltin dichloride and methyltin trichloride. The megabore column was able to separate all four methyltin compounds quickly, i.e., before the tetramethyltin decomposed into trimethyltin chloride and dimethyltin dichloride (equation 47), a reaction which did occur on the packed columns. Thus, the megabore column enabled the determination of the precise distribution of the various methyltin compounds in an environmental sample. The packed columns, on the other hand, could not separate dimethyltin dichloride and the methyltin trichloride and allowed significant decomposition of the tetramethyltin during the 15 minutes the analysis required. 

Mclnnis and Dobbs179 showed that both a DB-5 megabore capillary-GC column and a packed (20% SP2100 on 60-80 mesh Supelcoport) GC column could be used for the analysis of C-14 labelled chlorotrimethylplumbane. Analysis times using the DB-5 megabore column were approximately one-half those required on the packed column. 

Direct vaporisation injection. For packed columns and megabore columns of 530 pm, which typically use a flow rate of 10 ml/min, direct vaporisation is a simple way to introduce the sample. All models of this type of injector are a variation of a simple assembly which uses a metal tube with a glass sleeve or insert. The glass insert is swept by the carrier gas and heated to the vaporisation temperature for the analytes undergoing chromatography. One end of the injector contains a septum made of silicone rubber that allows the syringe needle to pass through it into the system. The other end of the injector is connected to the head of the column (Fig. 2.4). The entire sample is injected into the column in a few seconds. 

For most of the columns listed in Table D 1.2.1, various dimensions are available for each of the column types. Generally, a column with an i.d. from 0.20 to 0.32 mm is regarded as a capillary column. A column with an i.d. of 0.45 or 0.53 mm is called a megabore column. Both capillary and megabore columns are commonly used in FAME analysis. There are advantages and disadvantages for both capillary and megabore columns. Capillary columns have better resolution but less sample capacity,... 

New developments in the gas chromatographic columns are of special interest to the flavor chemist. These include the availability of improved polar phases, columns of "non-standard dimensions (i.e. "microbore" and "megabore" columns), and columns with "super-thick" (i.e. 3 to 5 urn) films of stationary phase. 

Guthrie, R. Lautamo, and L. Plotczyk for data on the Megabore column, and for access to the chromatograms shown In Figures 8 and 9. 

Fig. 8. Water pollutants (Table 1) by Megabore columns. Operating conditions hydrogen carrier gas 8.0 mVmin temperature — 30 °C for 3 min, 5°/min to 120 °C chart speed 0.5 cm/min.

The most useful and effective interfaces between HS devices and megabore columns are probably the low-dead volume (LDV) interface and the PT-LDV injector. The former... 

Recently, 530-p.m capillaries, sometimes called megabore columns, have appeared on the market. These columns will tolerate sample sizes that are similar to those for packed columns. The performance characteristics of megabore open tubular columns are not as good as those of smaller diameter columns but are significantly better than those of packed columns. 

Commercial columns are available with stationary phases that vary in thickness from 0.1 to 5 /rm. Film thickness primarily affects the retentive character and the capacity of a column, as discussed in Section 30E-6. Thick films are used with highly volatile analytes because such films retain solutes for a longer time, thus providing a greater time for separation to take place. Thin films are useful for separating species of low volatility in a reasonable length of time. For most applications with 0.25- or 0.32-mm columns, a film thickness of 0.25 xm is recommended. With megabore columns, 1- to 1.5- JLm films are often used. Today, columns with S-pm films are marketed. 

Megabore columns are open tubular columns that have a greater inside diameter (530 (xm) than typical open tubular columns (150 to 320 p,m). 

Figure 3. Comparison of packed and Megabore columns, EPA Method 602. FID, and identical injections in both cases. Top, 6 ft x 1/8 in stainless steel column packed with 5% AT-1200 + 1.75% Bentone 34 on 100/120 Chromosorb WAW 50°C (4 min), 8°/min to 100°C 20 min hold. Helium carrier at 50 mL/min. Bottom, 30 m x 530 urn Megabore column, coated with a 1 um film of DB-Wax 45°C (2 min), 8°/min to 100°C. Helium carrier at 30 mL/min. Solutes 1) benzene 2) toluene 3) ethylbenzene 4) chlorobenzene 5) 1,3-dichlorobenzene 6) 1,4-dichlorobenzene 7) 1,2-...

For the determination of all of the OCPs, a megabore column was not found to be suitable due to the poor chromatographic separation between determinands and between... 

A GLC analysis (Megabore Column (DB5)) shows a conversion of 95%. The remaining bromide 1 Is converted to the iodide 2 during the formation of the zinc organometallic (next reaction step). 

DAI-GC with flame ionization detection (FID) has also been reported for the analysis of MTBE in water by Potter et al. [27]. By injection of 1-5 p.L aqueous sample into a 165 °C hot injector and using a 6% cyanopropylphenyl 94% dimethylpolysiloxane megabore column, detection limits of 50 xg/L for MTBE and its degradation product TBA were obtained. However, in general, the limited sensitivity and selectivity of FID will often not suffice for environmental analysis. 

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