Carrier gas linear velocity

Always adjust the carrier gas linear velocity to 20-40 cm/sec before heating the capillary column. Neglecting to supply carrier gas while heating a capillary column will destroy it. Avoid injecting samples containing inor-... 

An important parameter when considering GC resolution of the sample components is the carrier gas linear velocity (flow rate, F), which can be determined by injecting 5-50 /A of argon or butane and measuring the time from injection to detection by the mass spectrometer. An optimum linear velocity using helium as a carrier gas is approximately 30 cm/sec and... 

The enantiomeric excess was determined to be >99% by capillary GLC analysis (30 ra x 32 tim WCOT column coated with Carbowax 20 M, hydrogen carrier gas, linear velocity ca. 94 cra/s, oven temperature 225°C) of the imide derived from the Mosher acid chloride. ... 

Capillary column Fused silica capillary column, such as RTX-5, DB-5, SPB-5, or equivalent, 15 m x 0.53 mm ID x 1.5 pm film (direct injection) at 40° to 240°C at H2 carrier gas linear velocity 80 cm/s (or flow rate 10 mL/min). A longer column 30 m with smaller ID and lesser film thickness may be used with spht injection. Temperature and carrier gas flow conditions may be set accordingly. 

Equation [3] reveals that the column temperature (because this influences k), carrier gas linear velocity (which will change the plate duration (the Purnell criterion) H/u), and column selectivity (affects k ol/ol — 1) are important considerations for reducing analysis time. 

When compared to conventional GG, the primary objective of fast GC is to maintain suf cient resolving power in a shorter time, by using adequate columns and instrumentation in combination with optimized run conditions to provide 3 10 times faster analysis times [46-48]. The technique can be accomplished by manipulating a number of analysis parameters, such as column length, column internal diameter [ID], stationary phase, Im thickness, carrier gas, linear velocity. 

Capillary-column dimensions and the average carrier-gas linear velocity exert a strong influence on peak resolution and the speed of analysis. Chromatogra-phers can control a separation s characteristics by choosing these parameters as required to meet specific performance goals. In order to simplify the discussion and to provide a clear separation of the variables inflnences, we will hold the column temperature constant when considering the effects of changing the physical column parameters. The influence of colunm temperature is addressed later in this chapter. 

Decreasing the column length while keeping the average carrier gas linear velocity constant will decrease retention times in the same proportions. As for the peak resolution, the resolution equation can be written in terms of the column length, and the plate height and retention factor of the second of a pair of peaks in this way ... 

FIGURE 4.7 Plot of resolution versus average carrier gas linear velocity. The lines represent resolution calculated from theory, and the points represent the measured values for the following pairs of peaks A = w-undecane, 2,4-DMA B = 1-octanol, n-undecane C = 2,4-DMA, n-dodecane D = n-dodecane, naphthalene. For conditions, see Figure 4.5. [Reprinted from LC/GC Magazine with permission of Advanstar Publications (7).]... 

The optimization of gas chromatographic temperature programs is similar to optimization of isothermal temperature or carrier-gas linear velocity criteria that... 

The unretained peak time can be related to the pressure drop, column dimensions, and carrier-gas viscosity by combining the—hopefully—familiar relationship between column length, unretained peak time, and average carrier-gas linear velocity tM = Liu with liquation 4.10 to yield... 

This deceptively simple expression incorporates all the variables mentioned previously, plus temperature and pressure programs as discrete time-based functions. Combining Equations 4.18, 4.17, and 4.13 allows us to express the pro-grammed-temperature elution process in terms of the thermodynamic coefficients, the average carrier-gas linear velocity as a function of the program time, and the column phase ratio ... 

The column outlet flow-rate corrected to room temperature and pressure for example, the flow-rate as measured by a flow metre. can be calculated from the average carrier gas linear velocity and the column dimensions. 

The speed at which the carrier gas moves through the column, usually expressed as the average carrier gas linear velocity (w vg). 

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