Chromatography Forum

Hi,

I have am having a interesting issue with the D2887 method. I have installed a 2887 compatible column for use with the method, I would condition it per manufacture instructions (40C to 360C at 15C/min, hold for 1-3 hour until baseline is stable) and it would appear fine until I start running samples.

The first baseline would be perfect, and any baselines after that would be fine, I run the calibrant next and the peaks are nicely resolved and calibration takes, I would next run RGO 1 and the chromatography would appear okay, but everytime I run a baseline afterward the baseline would rise over 100pA when approaching the higher temp range of the method.

I have repeated this phenomenon with three different columns and at a loss as how to fix it.

I think I ruled out column damage because the baseline only rises at higher temperature (300C +) and the 40 to 200C baseline looks fine and 4 of us have swept through all the plumbing to rule out leaks.. Could be column contamination but then I am not sure how to fix it given the analytes. Could be incomplete conditioning but it looked complete when it was conditioned and this only occurs after a calibrant and rgo is analyzed.

Any ideas would be greatly appreciated

Thanks

Welcome to the forum.

Have mercy on those of us whose lives are not ruled by acronyms and official methods with serial numbers, but who nonetheless have some skills in troubleshooting, and tell us what you are actually doing instead of posting in official code.

You will get your answers quicker.

Peter

petrochem,

I assume you are using temp programmable inlet. Based on what you have described so far, troubleshooting wise, I would now focus on the inlet (suspected contamination.) You might run an RGO and then simply temperature program the inlet (raise it) with a cool oven. Then bring the inlet back down and simply hit the start button to do another run cycle without an injection. If you get a hairball it would suggest the inlet.

Divide and conquer. Seems to me like you have ruled out columns pretty well with three and all.

Best regards,

AICMM

Peter, 2887, SimDis of diesel range organics on a -1 type column with temperature programmed inlet and FID detector. Starts at ~C10 out to C44. The ones I am familiar with use on-column injection of the neat mixture and program the inlet and the oven to give boiling point distribution.

Hi AICMM,

I cleaned the injector and baked the column, this brought the baseline back down, i re cailbrated with the bp mix, the baseline was still good, inject the rgo and the baseline dies. I will post chromatographs later, but i am wondering how to combat this constant contamination issues, if that is what it is?

You mentioned that you have experience with this method doing neat injection using a on column set up,

1. Did you have to use a guard column or clean up runs after each sample?
2. How much sample did you inject per run? 1uL?
3. Did you use metal columns or normal packed?

Any info would be most appreciated.

Thanks

Perhaps you could give a bit more information on how you are running your system.

What GC are you using?

What inlet are you using?

I presume that you are using a capillary column.

Are you injecting the sample diluted in CS2 or are you injecting a neat sample. How much are you injecting.

Gasman

The RGO can leave the inlet pretty contaminated. A few solvent injections at high temp may help (unless the GC system has a backflush option - that would be preferable).

Hi,

I have am having a interesting issue with the D2887 method. I have installed a 2887 compatible column for use with the method, I would condition it per manufacture instructions (40C to 360C at 15C/min, hold for 1-3 hour until baseline is stable) and it would appear fine until I start running samples.

The first baseline would be perfect, and any baselines after that would be fine, I run the calibrant next and the peaks are nicely resolved and calibration takes, I would next run RGO 1 and the chromatography would appear okay, but everytime I run a baseline afterward the baseline would rise over 100pA when approaching the higher temp range of the method.

I have repeated this phenomenon with three different columns and at a loss as how to fix it.

I think I ruled out column damage because the baseline only rises at higher temperature (300C +) and the 40 to 200C baseline looks fine and 4 of us have swept through all the plumbing to rule out leaks.. Could be column contamination but then I am not sure how to fix it given the analytes. Could be incomplete conditioning but it looked complete when it was conditioned and this only occurs after a calibrant and rgo is analyzed.

Any ideas would be greatly appreciated

Thanks

Some usefull information about this method you may find here http://www.unichrom.com/simdis/simdise.shtml

Regards,
Siarhei

Petrochem, are you using Carbon Disulfide as your washing solvent and having an appropriate amount of syringe washes pre & post run?

One solution is to use a separate syringe for the RGO versus all other injections. The syringe needle can be as contaminated or more than the inlet.

Are you using a TPI/PTV or a COC? If TPI/PTV, what vendor?

Hi everyone,

Thank you all for your posts and tips.

The issue is partially resolved, here is the status so far

The system is a COC equipped with a 10m x .53 diameter x 2.65um. It runs Chemstation with AC SIMDIS software for analysis.

What we have been trying to do is neat injections of samples and get results consistent with our TPI driven systems that can inject neat and process samples in rapid succession.

I have determine that the primary problem is carryover, running blanks after samples show at the 200 C area peaks elut that are consistent with Middle distillates. I lowered the inject volume to .05ul, which helped lower the contamination level but did not suppress it. I turned off th the septum purge thinking that it was causing disturbances and kicking up sample underneath the septum, causing carryover but that did not help. It was recommended that I look at the inject itself that sample was getting blown back up to the septum as the needle was exiting. Adjusting the inject speed improved this but did not fully suppress the problem, instead of immediate baseline decay it is extended out 3-4 runs before back out is required.

Finally we tried dilution, which suppress the problem much better to the point the system could be used everyday with a quick bakeout conditioning run once a day

The thing is that if the system can not do neat injections, it is not really fit for service.

If anyone has any tips or tricks on using COC systems for this anaylsis with neat sampling, it would be greatly appreciated.

Again, I would like to thank everyone who has contributed to this post with ideas and suggestions, it has helped quite abit in terms of speeding up the troubleshooting and method development.

Cheers,

Petrochem

With any on-column injection you get liquid drawn back between the needle and the column by capillary attraction. When the needle withdraws some of this is carried back with it into the upper works of the inlet - and then you get carryover.

Try leaving the needle in the inlet until the inlet has heated up (I presume that it is temperature programmable ??). This will allow the bulk of the sample to evaporate / partition so that liquid can no longer be dragged upwards by the needle.

Reducing the needle diameter might help, paradoxically so might increasing it so that there is a faster flow of carrier gas between needle and column that will more effectively blow sample onto the column.

Peter

I think that you have the answer to your problem, use a Temperature Programmed Inlet. You do not mention which GC you are using, but HP/Agilent have always offered only a TPI for Simulated Distillation, even though they have a COC inlet.

Gasman

petrochem,

System I work on is a 0.53 X 10m (I think..) -1 column. Injections are into a temp programmable inlet starting cool and going to about 320 or so with the ramp running a bit steeper than the column oven. Injection is into a glass liner that is essentially press fit sealed into the column (or rather, the column is pushed into the liner to make a press fit seal) to make one contiguous injection path.

Samples are neats out to about c44. Injections are standard Agilent high speed autosampler injections.

If I were in your shoes, I would look at how the column and inlet marry to each other first. The other thing you might try, considering you have a 0.53, is inject your RGO directly onto the column, install the column, run the run then run a blank normally directly afterward. If blank is clean then you know inlet...

Best regards,

AICMM

Try using dedicated Tapered Syringes for each blank, RGO and Sample with slow speed injection (checked) in your method and see the difference !

FUR