The Differential Refractive Index Detector (RID) is a commonly used universal detector. In previous articles, we covered the principles and considerations of the differential refractive index detector:
Today, we will once again share with you some key points to pay special attention to when using the differential refractive index detector (RID), as well as potential troubleshooting for challenging situations. Without further ado, let’s dive into the valuable insights. Get your notebooks ready to jot down the key takeaways!
01 Rinsing Equilibrium Issue
Before usage, flush the reference cell with the mobile phase. The RID requires a relatively extended period to cleanse the reference cell. Rinse until the baseline stabilizes. After that, close the rinsing valve, and the instrument will transition into a ready state, allowing for proper sample introduction
02 Column Temperature Issue
The RID is highly sensitive to temperature. The set temperature for the RID should be at least 5 degrees Celsius higher than room temperature, with a recommendation of 10 degrees Celsius higher. Inadequate temperature stability could potentially impact baseline variations.
03 Bubble Issue
Due to the principle of the RID, bubbles passing through the sample cell can significantly affect the baseline.
04 Possible Reasons for RID Not Being Ready
a) The reference cell is not fully equilibrated; rinse the reference cell.
b) Air bubbles are present in the mobile phase.
c) The photodiode balance value exceeds the set range; adjust the photodiode optical balance.
05 Ensuring Testing Stability
The refractive index of a solvent can significantly change due to factors such as temperature, dissolved air content, and pressure variations. These changes manifest as variations in the signal of the refractive index detector (baseline drift, fluctuations, noise).
To ensure stable analysis, it’s crucial to maintain the solvent’s condition using the following methods:
a) Operate in an environment with minimal room temperature fluctuations.
b) De-gas the mobile phase to reduce the amount of dissolved gases in the solvent.
c) Increase the internal diameter of the tubing on the detector outlet side to reduce back pressure.
d) For solvents prone to changes over time (e.g., THF), use solvents containing stabilizers.
e) The testing laboratory environment should be free from vibrations, direct sunlight, and direct air conditioning drafts.
06 Post-Usage Considerations
The most common issues that can occur with an RID are contamination and blockage in the flow cell. When analyzing samples with higher concentrations, it’s essential to thoroughly clean the flow cell to prevent sample residue.
If buffer solutions are used in the mobile phase, after analysis, perform repeated rinsing with water to replace the sample and reference paths with water. Drying of buffer solutions can lead to crystallization, causing signal problems in the flow cell and blockages in the paths. Additionally, crystallization can damage the sealing ring of the solenoid valve, leading to malfunctions.
07 Causes and Troubleshooting Methods for Abnormal Baseline in RID Detector
As presented in the table below, the editor has compiled a list of causes and troubleshooting methods for abnormal baselines in the RID detector.