ASTM E516 Testing Thermal Conductivity Detectors Used in Gas Chromatography
11. Standard Values
11.1 Detector characteristics measured at optimum conditions and at the current recommended by the manufacturer may be expected to fall within the typical range of values listed in Table 2 which also indicates the way these values should be expressed. All data refer to n-butane as the test substance.
12. Data Handling
12.1 All manufacturers supply an integral electrometer to allow the small electrical current changes to be coupled to recorders/integrators/computers. The preferred system will incorporate one of the newer integrators or computers that converts an electrical signal into clearly defined peak area counts in units such as microvolt-seconds. These data can then be readily used to calculate the linear range.
12.1.1 Another method uses peak height measurements. This method yields data that are very dependent on column performance and therefore not recommended.
12.1.2 Regardless of which method is used to calculate linear range, peak height is the only acceptable method for determining minimum detectability.
12.2 Calibration - It is essential to calibrate the measuring system to ensure that the nominal specifications are acceptable and particularly to verify the range over which the output of the device, whether peak area or peak height, is linear with respect to input signal. Failure to perform this calibration may introduce substantial errors into the results. Methods for calibration will vary for different manufacturers' devices but may include accurate constant voltage supplies or pulse generating equipment. The instruction manual should be studied and thoroughly understood before attempting to use electronic integration for peak area or peak height measurements.
13. Keywords
13.1 flame ionization detector (FID); flame photometric detectors (FPD); gas chromatography (GC); packed columns; supercritical fluid chromatography; thermal conductivity detectors
