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Accessories

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4. 4. In the same dialog box you can set the Inject Time (in

minutes) to the amount of time you want helium to go

through the loop onto the tube. This time will be based

on the method used for your analysis.

Enter an injection time between 0.1 and 9.9 minutes.

5. Set up the rest of your method parameters or if these

parameters are already setup, run your samples.

General IS Operating Information

Generally, the internal standard gas is expensive, and during the set

up most of the operational time of the ATD/TD a lot of gas can be

lost through the vent. As shown in Figure 58, you should connect the

reference gas to the standard injection accessory via a restrictor tube

(not supplied), and set the vent flow as low as possible (e.g., 1 mL/

min).

It is important to remember that repeatable standard addition will

occur if the pressure and temperature of the sample loop are held

constant. It is better to restrict the pressure input to the loop, not the

output, so that the output is as close as possible to atmospheric

pressure at all times.

Selecting an Internal Standard

When you are selecting an internal standard, there are a few

considerations. The volatility and boiling point of an internal

standard should be within the range of the analytes of interest. The

concentration should also be within the range of the compounds of

interest.

Additionally, the compound you select should be well separated

from your sample components, so that the internal standard does not

interfere or co-elute with your sample compounds.

Example: If you are analyzing benzene, toluene, and xylene,

deuterated toluene (toluene-D8) can be used. Toluene-D8 is

chemically almost the same compound as toluene, except the

hydrogen atoms have been replaced with deuterium atoms, which

adds 8 amu to the total mass of the molecule. This makes the internal

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ATD Tools 5928 Guía de usuario Pagina 202