RID stabilization

Question

I am having trouble in stabilizing my RID detector. Please provide me proper procedure for stabilization and getting good baseline in RID. Also when i am joining the column or removing the column there is no effect on the RID baseline.

rahusing · Accepted Answer

Please follow Below Procedure for RID Optimization. Follow these thirteen points to optimize the performance of your refractive index detector. 1 Position the solvent and waste reservoirs correctly Position the solvent and waste reservoirs above the level of the refractive index detector and solvent pump. This maintains a slight pressure in the sample cell and will improve the performance of the detector. 2 Do not over pressurize the flow cell Be aware to not exceed a 5 bar pressure drop after the flow cell when hooking up additional devices like other detectors or a fraction collector. If an additional detector is installed place upstream in the flow path it before the G1362A refractive index detector. 3 Use the correct solvents To minimize baseline noise and drift solvents must be LC grade and filtered prior to use. 4 Check for leaks Leaks within the LC instrument that the refractive index detector is connected to will cause problems with baseline long term noise or drift.Confirm that the instrument is free from leaks by performing the Agilent 1200 Series diagnostic pressure test (for the high pressure parts of the system between pump and column). Ensure that the connections from the on-line vacuum degasser to the pump and the detector inlet, waste and recycle connections are air tight. 5 Verify frit, filter and fitting quality Partially blocked frits, filters and fittings can cause baseline long term noise. Verify that the pressure drop across all such parts is within expected limits. 6 Control the optical unit temperature 1200 Series RID User Manual 69 Optimizing the Refractive Index Detector 5 Always control the optical unit temperature (heater = ON) for maximum detector sensitivity or with samples that could precipitate in the sample cell at room temperature and set an elevated optical unit temperature at least 5 °C above ambient conditions. 7 Use an appropriate response time For most applications a setting of 4 seconds is adequate. Only for high speed analyses (short columns at high flow rates) a lower setting is recommended. Bear in mind that even if the response time setting is too high fast peaks will appear a little smaller and broader but retention time and peak areas are still correct and reproducible. 8 Recycle mobile phase Use the recycle valve to allow automatic recycling of mobile phase delivered when no analysis is running. The pump flow can therefore continue uninterrupted until the next analysis without wasting mobile phase solvents. In addition the refractive index detector is always stabilized and ready for immediate use. 9 Consider using a degasser For many solvents you can achieve better baseline stability, when using a degasser. For some solvents a degasser might not lead to a better baseline quality. 10 Flush the degasser If flow is stopped and mobile phase remains inside the on-line vacuum degasser the solvent composition will change. When re-starting the flow or when using new mobile phase flush each degasser channel used for 10 minutes at the maximum flow rate of the pump (with the purge valve of the pump open to avoid a potential over-pressure in the RI detector’s flow cell). 11 Use pre-mixed solvents, only Don’t use a pump for mixing solvents. When operating the RI detector together with a quaternary pump, bypass the MCGV in the quaternary pump. You have to virtually convert the quaternary pump into an isocratic one, by directly connecting the solvent inlet tubing from degasser or solvent bottle to the active inlet valve of the pump (use adapter 0100-1847, which is delivered with the accessory kit of the detector). 12 Consider solvent changes with time 70 1200 Series RID User Manual 5 Optimizing the Refractive Index Detector Baseline drift can be caused by the tendency of certain solvents to change over time. For example the acetonitrile content of acetonitrile/water mixtures will decrease, tetrahydrofuran will form peroxides, the amount of water in hygroscopic organic solvents will increase and solvents such as tetrahydrofuran held in the reference cell may begin to regas. 13 Eliminate mobile phase/column combination problems Certain mobile phases in combination with specific columns can generate long term baseline noise. For example acetonitrile/water mobile phases with certain aminopropyl bonded phase columns. To eliminate the combination of mobile phase and column as a cause of long term noise replace the column with the restriction capillary (G1362-87301)

sschombu · Answer

And as a reminder:

- never ever operate an RID without a proper degasser. All Agilent degassers can be used with the exception of G1379A and G1379B.

- always have a TCC/MCT in your stack

- always have to heater in the optical unit turned on. We recommend to set a temperature of 10 degrees above ambient. The higher, the better, but check for the maximum temperature your column can stand

- Optical unit temperature and temperature set on the TCC/MCT should be identical

I'm not a big fan of building a hood over the detector. In some situations it might be of help, but often the problem lies with either the environmental conditions or an incorrect setup.

BTW: You can trust my answers, I'm the responsible Product Support Engineer for VWD, MWD, DAD, FLD and RID. What I tell here, is exactly what I teach in my trainings.

sschombu · Answer

Agreed.

I would never attempt an OQ unless the system was stabilizing overnight. The next morning you just press "Run" on the test and you don't touch or switch anything. This is how we do it in my trainings. However, fixing the environmental conditions (and, of course, have the correct setup) seems the better approach to me, although it's sometimes hard to achieve.

RID stabilization

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