Hi,
I have been having this baseline drift problem for a couple of days. I tried purging the reference cell overnight or shorter periods. It is not due to the pressure either. What could be the cause of it? How do i fix it? Any help would be really appreciated! 😊
Instrumentation, consumables, software, generalists etc.
What’s effective, what’s annoying, what’s your hot take? Any vendor specific insights?
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As title. I am in a situation where I have to choose one of these two for procurement without option of trail runs. Hence I need expert opinion.
What would be better got global untargeted metabolomics (Ultimate 3000 + Exploris 120 setup)?
I am a metabolomics noob. Please guide me. Both are 100 Angstrom.
I would be using it to do C13 tracer based work on mmmalian cells (after I gain expertise in basics, of course)
I also have option for ZIC-pHILIC (5 micron) 100mm x 4.6 mm
So my options are
ZIC-pHILIC (5 micron) 100mm x 4.6 mm
ZIC-pHILIC (5 micron) 50mm x 2.1 mm
ZIC-HILIC (3.5 micron) 100mm x 2.1 mm
Hello, we’re looking for a brand-new HPLC with a budget of around $25k, which mainly leaves us with Chinese or Korean manufacturers. The owner doesn't like my idea of a refurbished Agilient one :(
I’m hesitant about Chinese HPLCs after seeing a system develop serious issues after only 8 months in a lab.
We found a Korean manufacturer, YOUNG IN Chromass Co., Ltd. They seem to have been around since the early 1990s, but almost nobody I’ve spoken to has experience with them.
Has anyone here used their ChroZen HPLC? Are they reliable, and how are their service and spare parts?
Our use is simply routine QC: verifying raw-material and finished-product purity/assay and checking for impurities/contaminants.
Any firsthand experience would be appreciated or suggest any alternatives?
Hi so I deleted the CD channel in processing mode in chromeleon. Anyway how to get this back?
I went to get the column and when I twisted the head of the finger tight, the head broke.
EDIT: Wow, I love this community. I managed to remove it by heating a screwdriver and screwing it in the opposite direction.
Special thanks to sharing_violation.
Does anyone know why my baseline looks so bad? This is just a water sample that was run. I tried purging the RID and I don’t think it helped. What else can I try?
Hi there Reddit,
I feel like this might be a dumb question but since my Agilent 7890A only has 2 inlets if I were to convert one of them to take SPME arrows, could I still do ASD/manual injections into it as well? If it is what things do I have to consider when I do a normal injection?
The other inlet would be taken up by the transfer line of an Agilent 7697 headspace sampler so unless it's pretty easy and safe to remove that for an injection I assume I can only really treat the SPME inlet as my only functional port.
If it helps the conversion kit I plan to use is the Restek 27362 1.5mm inlet.
My collegue is currently analysing set of specific samples and made custom method for it. But he noticed that sometimes the signal goes numb and create "comb-like" signal. I've found, that this only happens in this specific set of samples and this method because the QC mixture (last pic) is fine.
Then we figured out that the method is not the problem and maybe the used solvent is at fault. In these samples he use isopropylalcohol. It's kinda weird since we didn't have any problems like this before. We use HP-5MS on Agilent 7890B GC + 5977B MSD.
Thanks everyone for help!
During an analysis, my equipment started exhibiting this problem. The needle goes up to the sample, goes down, but doesn't pierce the vial. Displays an error [9222]: "there is no sample vial set in autosampler rack."
We have a long backlog of samples and need to get the equipment up and running again. Support from Shimadzu will take a long time due to their schedule.
I welcome suggestions for tests to better evaluate the problem, and if you have experienced something similar, what was the solution?
UNICAMP - Campinas-SP, Brazil
It doesn't build pressure. Initially the pressure would go up to 150 bar in pressure test and do the jigsaw thing before quit, tried sonicating all the valves in water and IPA, intially it help a little, which means only less of jigsaw, but still never was able to build pressure above 150, after long time sonicate in 50C water and put back together it's even worse. How to tell what is the problem? Doesn't seem to be seal since it is not leaking, but which valve? Primary inlet, outlet or secondary outlet valve? Or more than one?
Do you really need a helium leak detector when changing a helium cylinder for GC-MS?
We normally check the regulator and fittings after a cylinder change, but I’m wondering if buying a dedicated helium leak detector is actually necessary for routine use.
Do most GC-MS labs use one?
Hello,
I am looking for recommendations for an analytical HPLC column to separate a mixture of four closely related diastereomers. All compounds contain the same disaccharide and differ only in the stereochemistry of the aglycone.
The best separation I have obtained so far is on a Luna Omega Polar C18, 5 µm, using an isocratic mobile phase of 12% ACN in water at 2.5 mL/min. The compounds elute at roughly 13–14 min. I can distinguish the individual components, but the peaks are broad and still overlap substantially.
The separation is very sensitive to the ACN content. At 15% ACN, I essentially lose the separation altogether, while at 10% ACN the retention becomes too long (no elution after 50 min) for a practical analytical method.
I also tested a Luna C18(2), 3 µm, which showed essentially the same behaviour with slightly worse separation.
I additionally varied the column temperature between 15 and 40 °C. Higher temperatures decreased the separation without noticeably improving the peak shape. Lower temperatures did not significantly improve the separation either and made the peak shape somewhat worse.
At this point I therefore suspect that I am mainly limited by stationary-phase selectivity rather than by further optimization of the current C18 conditions.
I have 800 Euros funding available to get a new column but without the option to test columns it is a bit of a coint toss. I was hoping to maybe get a recommendation here. I am currently considering trying a HILIC, C8, or a Macherey-Nagel NUCLEODUR ISIS column.
Has anyone dealt with a similar separation of highly polar/glycosylated diastereomers? Are there particular stationary phases or selectivities you would recommend trying?
Hi all!! I'm trying to run approximately 40 analyte SIM method at the moment but I keep encountering spectrums that look like this at around 500 ppb and below. They look fine at around 5 ppm and up. I've tried troubleshooting through all normal method avenues, though I haven't changed anything physically on the machine yet.
Before I do has anyone else encountered this before?
Hello everyone, for the last 2-3 weeks I’ve been battling this GC we inherited from another group that wasn’t very well taken care of. The initial issues were fairly simple fixes with replacing the FID jet, septa’s, split liner, needle, gas lines, etc. (really everything not electronic). It was working finally and I managed to get in a few runs that week before I left for the weekend, when I came back however, the GC refused to ignite in the first week of trying to fix it again. Myself and another colleague figured it was just a flow issue and swapped out gas lines again, that was only part of the problem though because since then every time I’ve run an Acetonitrile blank my baseline has been at ~32 pA where before it was solid at 4-5, you can also see in the chromatograms that after the ACN where there shouldn’t be anything my baseline continues to rise up to ~350 pA. I’ve confirmed by HPLC and another departments GC it’s just as pure as Fisher says. If anyone has encountered an issue like this or has any ideas I’m willing to try anything at this point. Please and thanks!
Hello!
We have a Dionex Easion CI, doing cations, chemical supression.
Thing is, base conductivity was ~1.8 uS before installing autosampler, and very steady.
Now we have three problems.
I'm suspecting of the autosampler, could that be the cause? Maybe problem is elsewhere, but it starded just as we installed autosampler.
Here's an example of a chromatogram of a pure water injection, it has a very random tendency. As you can see, it rises 0.2 uS (wich is a lot) and then drops 0.5 uS. And maybe the next injection does the same, or maybe it will only rise, who knows.
And here's a chromatogram of a Control Point.
Hey all, I’m doing work with alcohol and analyzing the methanol content of various types of distilled spirits. I’m about to start the analysis part using quantitative gas chromatography (and either FID or MS depending on which machine is working) but I’m a nice at it and running into some difficulty. Some of my samples may have levels around 1 to 10ppm while others might be above 1000, and im not sure how to effectively set up this calibration curve for such a wide range. Any advice would be greatly appreciated!
Hi everyone, I’m having an HPLC issue and could really use some help.
I’m analyzing PET degradation products (TPA, MHET, BHET) from enzymatic reactions (PETases).
I recently had to switch my sample preparation protocol because the products are precipitating in samples from high-yield reactions.
The new protocol is supposed to solve this, and it also works for my colleagues using the same system and method, but for me, all retention is completely gone. everything elutes in the void/injection peak.
Here are the method details:
System: Dionex Ultimate 3000
Column: YMC Triart C18 at 40 °C
Mobile Phase: Isocratic, 20% Acetonitrile / 80% Water (acidified with 0.05% TFA)
Flow Rate: 0.4 mL/min
Detection: UV (254 nm)
Injection Vol: 15 µL (I also tried 1 µL, didn't help)
Now for the Sample prep:
The "Old" Protocol (Works, but products precipitate in water at high conc.):
12.5 µL reaction supernatant added to 50 µL Acetonitrile (with 1% TFA). Let sit briefly at RT, then centrifuge to pellet proteins. Transfer supernatant into 150 µL MilliQ H2O.
Result: Good separation of TPA, MHET, and BHET.
The "New" Protocol:
Dilute the enzymatic reaction directly 1:10 in DMSO (10 µL sample into 90 µL DMSO) to keep products in solution.
I froze this DMSO stock until further preparation. (Note: We also freeze 1M TPA standards in 100% DMSO without issues).
Take 12.5 µL of the thawed DMSO-mix and add to 50 µL AcN (with 1% TFA). Centrifuge, take supernatant, add to 150 µL MilliQ H2O.
Result:
No separation. Everything co-elutes as one massive peak at the void volume. I suspected strong solvent effect, but the same method has worked before on the same HPLC system, same column, mobile phase and vials...
Following things I have already tried:
Diluting the final sample with 20% AcN and also injecting less volume (1 µL instead of 15 µL), but it didn't solve the issue.
I also tried making fresh preparations from the DMSO sample stocks, but still got the same result.
Do you have any suggestions what could be the issue here or what else to try?
I really hope to be able to somehow salvage my DMSO-diluted samples so i can avoid to repeat the whole experiment...
As title, not sure about the best way to get a clean cut.
