We are using DB-5 to analyze the samples. We once used this column in HP 5890 Series I, when the rate is high, like 15C/min, the baseline is drift, but is acceptable. Now we moved this column to HP 5890 Series II, keep the same method and analyze the same sample. The baseline drift a lot when the temperature beyond 160C. I tried decrease the rate to 2C/min. Still the baseline drift when the temperature beyond 160C. What's wrong? Any suggestion to solve this problem? Thank you very much.
By Les on Tuesday, January 13, 2004 - 03:55 pm:
Have you checked for leaks? Of course you did.
Have you looked at the injection port and septa? Are they clean and tight.
Assuming the column you're using is a previously used column and not a new column, has it been conditioned prior to use. Many questions. From my point of view, 5890I vs 5890II, not much of a difference. I use a 5890II, HP-1 5m x 0.53mm x 2.65u for D2887, oven ramp from 35C---15C/min--350C, baseline signal @45 ---> @140. Over 10 yrs I've had columns which performed well and a few that have been a bear to get going. The oven conditions are terrible on the columns, some last about 9 months while others last about 4 months. The samples don't change much. We run about 8 samples per day. Maybe you can add a little info on the sample types, the injection system...
By Anonymous on Tuesday, January 13, 2004 - 05:22 pm:
Thank you for your reply, Les.
I did check for leaks. Also the injection port and septa are clean and tight. I conditioned the column too.
Do you think sample type will change the baseline a lot?
I don't have problems from 30-150C even when I use high rate. I have problems beyond 150C even when I use low rate. My sample is perfume.
If your oven ramp from 35C---15C/min--350C, what temperature you use to condition your column and how long you kept at this temperature?
By Les on Thursday, January 15, 2004 - 03:10 pm:
Well, I'm at a loss. I use Thermo Green Septa, have you changed septa lately?
I've had some techs on occasion inject some really heavy material. I was searching around for a problem due to extreme baseline drift. Only after 2 hrs looking, someone fessed up to the heavy sample. I took PTV injection port out and had sample coating the glass liner...
I really don't condition the column. I allow the He to flow for about 15 to 20 minutes then attach to FID. I actually run a QC sample as many times as necessary to get the baseline under control. Then calibrate and run QC sample until satisfied. This is just for this particular GC. A few of the other systems get proper conditioning according to manufacturer.
I generally run to about 20C higher than the GC final temp if that doesn't exceed the column max temp.
You have check the FID, cleaned the collector. I'm baffled.....
By Bernd Mischke on Friday, January 16, 2004 - 05:18 am:
try to close Your FID in the oven and take out Your column first. See what drift You have ---> if no drift, bake out the column: 16 hours to 300°C is for DB5 ok. Check also the FID column connectors, sometimes enter compounds into the deadvolume (between column and tube wall).
If You need more input, email me.
regards - Bernd
By Anonymous on Friday, January 16, 2004 - 07:03 am:
How long has it been since the filters on the incoming carrier gas have been changed? If you have some contamination coming in with the carrier this kind of problem can occur, although generally this is seen at lower temperatures.