Chromatography Forum

Does anyone know how to keep the Shimadzu mobile phase degasser DGU-20A SR awake and operating on a LC-20A XR system after a run is complete?

We are using the standard Shimadzu software for UV/PDA analysis. The instrument goes into standby after the last sample, which puts the system to sleep, including the degasser.

We found settings to keep the column oven and cooled autosampler from sleeping, but there doesn't seem to be a control setting in the shutdown profile for the degasser.

(Ironically, the same degasser unit on our Sciex controlled system can never be turned off without powering it down.)

Two comments:
(1) The Shimadzu DGU0-20A-Series vacuum degasser modules DO NOT HAVE a power switch of any kind (By design, this is NORMAL). They are powered directly from an interconnecting cable to the PUMP modules (or optionally, via a separate standalone power supply if you are not using the degasser with a Shimadzu 20-series pump). When power is connected, they turn ON.
(2) Their is no sleep mode for the degasser, only 'ON' and 'OFF', but if connected via the optional remote cable to the HPLC, the HPLC pump can turn it off (removes power from it). This normally happens due to: (a) an error such as a leak etc; (b) a programmed step in your method which tells the HPLC system to go to standby mode (if the degasser is connected, which is optional, then it could turn off the degasser module). Just disconnect the remote cable to keep the degasser from being turned off (Never run the degasser if NO flow is running through it. You will decrease the lifetime of the degasser. Turn it OFF when not used).

Note: The Shimadzu DGU-20A# degassers have a lifetime of around 4-years. The DGU-20A#R degassers have a lifetime of around 3-4 years max before requiring replacement of professional service. If the degasser shows a flashing red error light (after the 8 minute warm up time), then it has already been broken for a ling time. The error lights only turn on long after the system is broken so they should always be professionally serviced BEFORE the red light appears. The best way to do this is to have them serviced on a regular schedule, every 3-years to prevent additional damage and flow path contamination of your entire HPLC system.

Ok, Thanks! That is great information.

We do get them professionally serviced.

I believe the degasser unit on our LC-MS/MS is constantly on, even without flow. I will have to find a manual way to power it off. There is no control from the Sciex software. The power wire and DGU pressure out wires go to our mobile phase 'A' pump.

The same degasser model on our UV/PDA instruments takes about 2 minutes for the red light to extinguish when we take it out of standby, but it takes nearly an hour of flowing for the baseline absorbance to settle completely and get maximum sensitivity, which I had attributed to poor degassing while idle. Maybe it isn't caused by the degassing.

You wrote: "but it takes nearly an hour of flowing for the baseline absorbance to settle completely and get maximum sensitivity, which I had attributed to poor degassing while idle. Maybe it isn't caused by the degassing." -

That may or may not mean you have a degasser issue. Poor degassing certainly can extend equilibration times, but so can many other things. As stated earlier, the "red" error light only turns ON AFTER the degasser has been broken for some time (even years). So it could already be broken right now and the light may take a year or more before it illuminates (the error light is nearly worthless). Instead, ask yourself, how old is the degasser OR when was it last professionally serviced? If the answer is more than three years ago, then it is due for service.

Long equilibration times (based on detector signal) are based on total column volume, mobile phase used and composition, flow rate, temperature stability etc. What is "normal" for each application will depend on all of these things.

If your software does not provide a degasser 'ON' or 'OFF' option, then disconnected the DC power cable going into the back of the degasser is the only way to shut it down.(this is specific to Shimadzu systems. A cost saving design (bad design).