I am using Agilent Infinity II ELSD (G4260B) to develop a new analysis method and facing these problems.
1. Large baseline offset: When turning on the system (parameters as below), the signal was about 700 mV, even though I have spent a few days to wash as recommended as in the manual of Agilent.
- Column: XBridge C18, 150 x 4.6 mm, 3.5 µm, 25 °C
- Mobile phase: 100% Methanol (LC grade)
- Flow Rate: 1.0 mL/min
- Evaporator temperature: 60 °C
- Nebulizer temperature: 25 °C
- Evaporator gas flow: 1.6 SLM (nitrogen)
2. Baseline increases when using water in mobile phase: The parameters were the same as above except mobile phase was methanol - water. Whenever the percentage of water was higher than 20%, e.g. methanol - water (6:4, isocratic), the baseline began to increase steadily (approximately 3.5 mV/min or 210 mV/h). After a few hours, the baseline became straight because the signal had reached the upper limit (1250 mV). If changing mobile phase back to 100% methanol, the baseline would slowly decrease back to its previous value.
Does anyone know about or experience these problems? Please help me!
Thank you!
- Thành Nguyễn Tri wrote: "Baseline increases when using water in mobile phase".
Yes, it should change when the amount of less volatile liquid, water, is added to methanol. What you have observed is normal. That "offset" is due to the change in volativity due to your mobile phase changes. Water is far less volatile than Methanol and requires different nebulizer, heat and gas flow settings to work well. Each mobile phase must be evaluated to determine the best ELSD settings for use in your application. The signal to noise (S/N) level of a standard peak must be evaulated with each setting change to find the optimized conditions for use (To evaluate "noise", never rely on the "baseline" signal only! Often, as the baseline noise changes, so does the signal level, so monitoring the baseline is unreliable. S/N only of signal). Failure to optimize the ELSD to each mobile phase used may result in instability of signal and internal contamination. Once the settings are optimized, autozero the signal and monitor to determine ripple.
- You can not use one set of ELSD settings for all mobile phases.
- The ELSD is NOT a "Universal" detector.
- "Optimization" of the detector to the method must take place before any data is collected, and this takes time and detailed HPLC system knowledge of how the ELSD system works.
Please find a professional chromatographer with practical experience using HPLC and esp ELSD detectors in your area for to assist you. To use an ELSD, you must first receive professional training in how to use this complex HPLC detector (ELSD). Few have experience using them and you can not learn how to use one in a day. This detector is not a simple detector like an RID or UV/VIS is. An ELSD module is one of the more complex detectors you can use (similar to a MS or MS/MS system requiring many years of training).
We only recommend ELSD/CAD for advanced level users (> 10 years professional exp) as they are very difficult to use and obtain reliable data. *Be cautious of the sales people/vendors who provide misinformation about them to make a sale.
- IMHO: Due to the ELSD's (or CAD, same issues) complexity of operation, advanced level skill needed to use, lack of linearity and selectivity, high maintenance requirements and expense, they should also only be used when no other detector will work for the application.
Technical Report Evaporative Light-Scattering Detector (ELSD) Optimization Pr...
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