Megabore capillary columns

Gas chromatograph equipped with a thermionic specific detector (TSD) DB-5 Megabore capillary column, 30 m x 0.53-mm i.d. 

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. 

Seto Y, Tsunoda N, Ohta H, et al. 1993. Determination of blood cyanide by headspace gas chromatography with nitrogen phosphorus detection and using a megabore capillary column. Analytica ChimicaActa 276 247-259. 

The design of an SFE-GC system with quantitative transfer of extraction effluent to a megabore capillary column."... 

Megabore capillary columns (0.53 mm ID or larger) are typically used at a flow rate of 8 to 15 mL/min. Desorption is slower at such flow rates, and... 

Capillary columns are available from several manufacturers in a wide range of column internal diameters (O.l-l.Omm), column lengths (5-50 m), and stationary phase film thicknesses (0.1-5.0 pm). Generally, sample capacity increases but the efficiency decreases as the internal diameter or film thickness increases. The larger bore capillary columns with internal diameters between 0.53 and 1.00 mm are termed wide bore or megabore capillary columns and these have similar capacities, but greater efficiencies, than packed columns (see Table 2). 

During the desorption phase, when the GC carrier gas passes through the trap, the optimal flow rate is determined by the GCcolunm used. The P T system described in this chapter was built for a megabore capillary column with an optimal gas flow of=8mL/min. However, as mass spectrometers become increasingly robust and suitable for field work, packed traps have been developed for the lower carrier gas flow rates (l-2mL/min) which these... 

In the following example, a soil sample (5 g) was spiked with approximately 1 mg/kg of gasoline, and extracted with 5 mL of methanol. A 100-p.L aliquot of the extract was added to water and purged onto a Tenax trap. The trap was desorbed onto a megabore capillary column for the separation and detection was accomplished by a PID and FID in series. The instrument conditions for this separation are listed in Table 15.10. 

The phthalate esters can also be determined by GCECD after an appropriate solvent extraction from aqueous or solid samples. USEPA Method 8061 lists 16 phthalate esters (13). Solid-phase extraction using C18 membrane disks can be used for aqueous samples, but the pH must be maintained between 5 and 7 to prevent hydrolysis of the phthalate esters. Solids or soils can be extracted by sonication or Soxhlet extraction using 1-1 methylene chloride-acetone. GPC or the Florisil cleanup may be necessary. Extreme care must be taken not to contaminate samples with phthalate esters that are ubiquitous in the laboratory. The solvent needs to be exchanged to hexane. Two megabore capillary columns that are connected by a Y in parallel are recommended for separation. Detection is accomplished by dual ECDs. The conditions for the GC are listed in Table 15.13. 

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