Troubleshooting a failed ASTM Drift and Noise Test for the Agilent RID

This Information Applies To: Agilent Refractive Index Detectors, G1362A and G7162A/B

Issue:

The ASTM Drift and Noise Test for Agilent RID modules available within Agilent Lab Advisor Software fails. This article will help you identify potential causes of the test failure and how to resolve them.

Resolution: 

If you encounter a general RID baseline drift or a high noise that causes your ASTM Drift and Noise Test to fail, this may be due to:

• A thermally unstable system or lab (HPLC below air conditioning, exposed to sunlight, heater radiation, air currents, etc.), please also check this article on general RID recommendations.
• Solvent properties that change with time (baseline drifts may occur if the amount of water in organic solvents changes, hence affecting the reference cell).
  • In this case, flush out the contamination, using only stabilized solvents.
  • Clean the parts in flow path and allow the system to be flushed out and equilibrated: After flushing and cleaning the instrument, purge sample and reference cell from the same water bottle with pure HPLC-grade water overnight. You may use the recycling function. Repeat the test in the morning.
• Ensure that the diodes are balanced.
• Verify that the degasser is running and works properly.
• There can also be issues with the system pressure or the temperature control (column oven, RID heater) that can affect the RID signal.
• Ensure that the rest of the system works properly (pump leak tight, system pressure tight).

An acceptable noise should look comparable to the following graph (Figure 1): 

Figure 1. RI Signal during the ASTM Drift and Noise Test

The Noise is calculated according to the ASTM method as shown in Figure 2:

 
Figure 2: RI Signal Noise calculation
1. Noise = maximum peak - minimum peak, 2. Wander,  3. Time.

The time range for each cycle, dt, is typically set to 0.5 minutes in the test. The noise is calculated as the difference between minimum and maximum in these time intervals. The wander value, although not appearing in the test results, is determined as the peak-to-peak noise of the mid-data values in the ASTM noise cycles. The drift is calculated as the slope of a linear regression over the whole measurement.

Learn how to effectively troubleshoot your Agilent LC System: Agilent 1290 Infinity LC Systems with OpenLAB CDS ChemStation Edition e-learning path on Agilent University