ASTM E594 for Testing FIDs Used in Gas or Supercritical Fluid Chromatography
6. Noise and Drift
6.1 Methods of Measurement:
6.1.1 With the attenuator set at maximum sensitivity (minimum attenuation), adjust the detector output with the "zero" control to near mid-scale on the recorder. Allow at least 1/2 h of baseline to be recorded. Draw two parallel lines to form an envelope that encloses the random excursions of a frequency of approximately 1 cycle per minute or more. Measure the distance between the parallel lines at any particular time. Express the value as amperes of noise.
6.1.2 Measure the net change in amperes of the lower line of the envelope over 1/2 h and multiply by two. Express as amperes per hour drift.
NOTE 1 - This method covers most cases of baseline drift. Occasionally, with sinusoidal baseline oscillations of lower frequency, a longer measurement time should be used. This time must then be stated and the drift value normalized to 1 h.
6.1.3 In specifications giving the measured noise and drift of the FID, specify the test conditions in accordance with 7.2.4.
