My Waters 717plus injector is horribly contaminated! Help!

[dkreller]

Hi,

In the last couple of months it has become apparent that a significant amount of contamination is originating in my autosampler/injection system. I have a Waters chromatograph system; this is a 717plus unit. On occasion I collect fractions to be sent out to external labs for other analyses, including detailed fluorescence characterization, UV/vis, and mass spectrometry. However, I have been getting some feedback that there is a problematic amount of contamination in my samples.

To give me some insight into the nature of the contamination, I did a little experiment in which I made 20 consecutive injections of HPLC grade water (nothing else in it). The mobile phase pumping through the system was straight up HPLC grade water. The results of the experiment can be seen here:

https://docs.google.com/present/view?id ... 90dxxps3f7

Anyone have suggestions for cleaning up autosampler/injection systems (717plus specifically, or similar)?

Thanks,

Dave

[tom jupille]

If this were my problem, I'd do one more check before concluding that the problem lies in the autosampler. Splice a manual injection valve into the line and do a couple of injections from that. The idea is to eliminate the possibility that the pressure shift when you inject is mobilizing garbage from somewhere else in the system (e.g., the stationary phase surface?).

If that looks OK, then you have to make a guess as to the possible nature of contamination. If it's non-polar, then organic solvent wash. If polar, perhaps a nitric acid passivation. If a thorough flush does't solve the problem, then the next step is to take everything apart, wash off-line, and carefully reassemble.

[HW Mueller]

could it be a tm system peak? What is the flow rate? I wonder what substance washed off with water + water mobile phase could fluoresce.

[dkreller]

The flow rate was 0.5 mL/min. I do a lot of experiments with dissolved humic substances, which have weak fluorescence. I am certainly suspicious that some humics could have built up in the injection system. However, there also is a strong possibility that the fluorescence is coming from an impurity in one or more of the buffers I use. I typically use either TEEN or DEPP, both of which I acquire from GFS Chemicals. The compounds are contaminated with colored compounds when I get them and I have to purify them (distillation). I am going to do fluorescence excitation -emission matrix analysis of some of my DEPP and TEEN containing mobile phases to see if I can get any useful evidence.

Thanks,

Dave

[Hollow]

what is your needle wash solvent?
try to thoroughly rinse the needle by manually turning the needle wash pump on (from the instruments menu), try different wash solvents, suitable for the supposed contaminants.

If it's not going to help, you maybe have to replace the whole seal pack (from the 717PM Kit). When was it replaced the last time?

Within the seal pack, there is the needle wash frit, where the wash solvents flows through and cleans the outer side of the needle... or contaminate the needle if the frit is too dirty

[dkreller]

Hi Hollow,

Thanks so much for your post. I have been doing more work to try to understand the contamination. It is definitely coming from the A/S. Even when I make injections of HPLC-grade water I see the contamination in the effluent. I don't see the stuff in the effluent when injections are not being made. Spectroscopic analysis on the contamination has shown me that the stuff looks somewhat like the samples that I typically work with. 90% of the samples I inject are dissolved humic substances.

This system is dedicated to aqueous mobile phases, which range in pH from 4.5-8.5 and in ionic strength. At this time the needle wash solvent is just HPLC-grade water, which is of course approx. neutral and has extremely low ionic strength. However, at about the exact time I saw your post I got to thinking about solubility issues. Dissolved humics tend to be less soluble when pH decreases. I could easily switch the needle wash solvent to a pH 8.5 buffered mobile phase, which I use from time to time. However, I am thinking that perhaps I should use something even more basic.

I will try switching the needle wash solvent to a more basic solution and I will make a bunch of injections of a NaOH solution (around 2M) and see if the situation is improved.

I am a bit embarassed to say that the seal pack has never been changed. Very good question BTW. The 717 is 4.5 years old and it has seen some heavy use. If switching the needle wash solution doesn't make a substantial improvement I'll order in a seal pack ASAP. That's probably at the heart of the matter.. I should have been quicker on the uptake but I had no real reason until now to think seriously about the insides of the A/S.

Thanks!

Dave

[Hollow]

Hi Dave

I've never tried but I wouldn't use a salty buffer for the needle wash. Maybe use just a plain solution of ammonia or similar?

After the basic rinse I suggest to have an additional rinse with strong organic solvent e.g. pure ACN or IPA or even a mixture of ACN/IPA/MeOH to get rid of as much as possible that has accumulated over these 4.5 years...

And of course, make sure that the neddle wash pump is working at all... (there should be drops mixed with a lot of air coming out from the yellow waste line).

If you're not going to change the seal pack, also have a look at the outer part of the pack in the sample tray compartment and do a "surface-cleaning" as well (when the needle is pulled up, the vial often is lifted and if you use only these plastic caps with no septum, it can spill some drops).

For the future work, if it's possible with your methods and samples, I would add some amount of organic to the wash solvent, e.g. MeOH 20% or IPA 10%.
Reduces microbio growth and improve the wash effect for organic compounds from your samples.

Sam