Programming/pressure/temperature question

[chemwipe]

Hello all-

I'm running PCBs on a newly acquired (but not new!) instrument. I copied the temperature program from my other working GCs to run on this newly acquired one. I ran a 10 ppm Aroclor 1254 standard and it came out looking like this:



...but it should really look more like this:



Does this seem like something having to do with the pressure? Or maybe the split ratio?

I can post more info tomorrow if needed (yes, actually posting on here from home!).

Thanks!

John

[Don_Hilton]

Do you have the same type of column - phase and dimensions? do you have the same flow rate? Do you have the same type of inlet on new and old instruments inclulding manufacturer? And same types of liners?

It looks like everthing is coming out much faster on the new instrument and peaks tail badly.

[chemwipe]

Do you have the same type of column - phase and dimensions? do you have the same flow rate? Do you have the same type of inlet on new and old instruments inclulding manufacturer? And same types of liners?

It looks like everthing is coming out much faster on the new instrument and peaks tail badly.

Don-

The column on the newly acquired instrument (let's call it GC1) is an RTX-CLPesticides column; inlet is maybe as old as the GC itself, not sure. Using a gooseneck liner with glass wool, and GC1 has an EPC.

Here are my temperature and pressure programs:





Anything jump out as causing the tailing and generally terrrible chromatogram?

Thanks,
John

[chromatographer1]

Digital readings may not correspond to the actual condition of the GC, especially when it comes to flows.

Looks like you need to do a complete verification of the GC that all the components are working as intended.

Temperature is the easiest to check. Flows take more time. Of course, you might have a bad column.

Good luck,

Rodney George

[chemwipe]

Digital readings may not correspond to the actual condition of the GC, especially when it comes to flows.

Looks like you need to do a complete verification of the GC that all the components are working as intended.

Temperature is the easiest to check. Flows take more time. Of course, you might have a bad column.

Good luck,

Rodney George

Rodney-

So for the most part, the programming looks ok?

The column is new (installed it brand new fresh out of the last month), and has only been used for test runs of standards and solvent blanks for troubleshooting. I guess it wouldn't hurt to try out the column in another GC, though.

I'll also start checking flows and temperature as recommended.

Thanks!
John

[haiedc]

It's old chemstation (for 5890) and I remember that the pressures in the table are just apparent values. For setting the split ratio, you have to adjust the knob on the GC and measure the vent flow.

[chromatographer1]

The chromatogram is quite different.

The initial peak is much less (assuming temps are right, then flow is all wrong, assume the flow is right, then the temps are all wrong, assume both are right, then column is all wrong) and the resolution is poor and the peaks are tailing.

Troubleshoot until you find the problem.

best wishes,

Rodney George

[Rolandas Plausinaitis]

I did not use EPC on this type of HP instrument so not sure how You set up carrier gas flows in the software.

It struck me when looking at the chromatograms that compounds seem to elute much earlier. Then I looked at the parameters and there seems to be something wrong with the pressures. On the left you have "set pressure" 5 psi, on the right under column dimensions is 1.9 psi (calculated I presume). However both are somewhat away from what it is expected.

I have put your data in a calculator and column pressure should be 2.7-3.0 psi for flow 2.5 ml/min He using 30x0.53 column, (column temperatures 120-150 C).

[AICMM]

Chemwipe,

Swap the columns. Retention time for your blob is about the same (more or less....) but the separation is not very good. To me, a column problem as the starting point of all the subsequent troubleshooting.

Best regards.

[chemwipe]

Chemwipe,

Swap the columns.

I installed the column into a different GC and got a great looking chromatogram - so it's not the column (sorry I can't post a pic...networking issue).

Back to troubleshooting!

John

Note: I found some things that may be affecting everything, but I'll post them at a later time.

[chromatographer1]

I would guess it is the flow rate of the column then. A temperature issue would compress or broaden the peaks but the chromatogram would look similar to the model.

it is hard but not impossible to check the actual flow through the column directly.

You can inject methane isothermally and calculate the linear flow rate. This will give you an approximate volumetric flow rate. The linear flow rate is the better measurement as it adjusts for column size more easily.

Remember a poorly installed column in the injector can cause a multitude of problems.

Good luck,

Rodney George

[gcguy]

Looking at the peak heights....The bad chromatogram has larger peaks than the good chromatogram. Unless the 5890 has an epc unit controlling the split as well as the flow then you need to adjust the split flow manually. It looks like the split is not correct. I would also be tempted to check all the flows.
It could also be a problem with the nitrogen make up gas on the detector, I would look at the installation of coulmn as well, to me it looks likely to be a detector issue, I may of course be completely wrong!!
The retention times are comparable so it looks like the column flow rate is correct.

GCguy

[AICMM]

Chemwipe,

Gcguy makes a good point. Look at the column installation at the detector end and look at the make-up flow rate through the detector. The other thing, were you correct in saying 10 ppm? As in 10 ug/mL, 1 or 2 uL injection. Splitless or split? That should slam the ECD so you may simply be looking at a saturated signal.

Best regards.

[chemwipe]

Chemwipe,

Gcguy makes a good point. Look at the column installation at the detector end and look at the make-up flow rate through the detector. The other thing, were you correct in saying 10 ppm? As in 10 ug/mL, 1 or 2 uL injection. Splitless or split? That should slam the ECD so you may simply be looking at a saturated signal.

Best regards.

I should have been a little more clear from the start: The two chromatograms in the original post are from two different columns, two different instruments. I was just showing them for qualitative comparison.

AICMM:
Yes, it is a 10 ppm Aroclor 1254 solution.
1ul injection.
Splitless - according to the program, the split flow is 20ml/min (also from the split/splitless vent). They should be the same, right?
The split ratio in the program is listed as 3.99.

Thanks to everyone for their replies so far!

John

[AICMM]

Chemwipe,

Do me a favor, run a 100 ppb standard under the same conditions and post that for me.

Best regards.