Spike IS good, Blank IS low

[thanotosq]

Hello, I am new here and the reason that I even thought about posting was to ask about this:

I have a Tekmar Stratum purge trap concentrator with an Auquatek70 autosampler and an Agilent 6890/5973.

I have only had it in house for about 1-2 months and it has been a struggle to control, what I think, it water interfering with recoveries. Lately, it seems that the internal standard in spiked (8260 full list) samples and high client samples are fine; however, when method blanks or clean samples run they fail low!

I have tried everything that I know of and I have been going back and forth with Teladyne about this issue...

Any suggestions?
Thanks!!

[thanotosq]

No reply! Come on guys! I cant be the only person in the world that has seen this....

[JI2002]

This is likely a MS issue. Try second filament, if that doesn't work, try cleaning the ion source and replace the filaments if you haven't done so.

[thanotosq]

I thought the same thing at first, but i direct injected IS & Surrogate at 50ppb and it came out great. Furthermore, i did switch filaments and the chromatography actually got worse...the 2nd filament always seems to look worse than the 1st on that instrument...

However, it seems that as soon as i purge anything the IS & Surrogates drop off...

[AICMM]

Are you using needle sparging or frit sparging? If frit, I might buy your argument about water , except.... most of the water comes out early and should not really affect late IS's very much. Having said that, I have worked with a lab that has a devil of a time switching from 524 (frit 25mL) to 8260 (5 mL needle.) You might make the argument that blank has more water but the problem with that is the amount of analyte relative to the water is miniscule in either case, blank or standard.

What happens if you cut your sparge time in half? Probably can't for the real deal but could be diagnostic. If a water problem then less sparge means less water. Finally, do you have moisture control in play here?

Best regards.

[QPGirl]

What trap are you using? Full list 8260 may be too much for it. Something similiar happened to me.... but it was higher recovery in blanks and clean samples.....since there weren't any other compounds to compete with the IS/SURR. My trap was too saturated in calibration.... so, the IS/Surr was lower in calibration and high in blanks.

[danicrd]

Hello
have you resolved your problem? I have had same problem with my 5973 and I'd like to know what is your conclusion about this issue

thank you

[Ron]

I've heard about this problem from a variety of sources for at least 10 years. I don't think the problem is water, I suspect it may be methanol. I would try to reduce the amount of methanol introduced into the sample and see if that helps.

You version of the problem is a little than the most common version I have heard, in the more common problem the recoveries of the internals and surrogates goes down during a series of samples, then goes back up when a blank is run.

[thanotosq]

sorry for not responding sooner, but i have been a little busy...ok a lot busy....

Either way, we resolved the issue. We believe that it was the standards and/or the methanol (although neither companies will admit it).

I was not entirely sure that it was anything besides the methanol or the standards themselves, since the water was hplc grade and all the instruments are using standard traps and columns...

Thanks a lot for all the responses though... I'll just have to keep up with it more!