Internal standard ratios fluctuating - 8270, Agilent GC/MS

[warrender]

I use these six PAH internal standards as surrogate. I got six surrogates recovery increasingly high in some soil samples. For example, the recovery of the first three surrogate were around 80-90%, the forth one went up to 120%, the fifth one were 150%, and eventually, the sixth one went up to 200%, 300% sometimes. We don't do PAH soil and water sample cleanup. We use SIM mode. These surrogate peaks looks in good shape.
I suppose it's because of matrix interference, because most time these problem happened with dark sample(few times but still had sometimes happened with clear sample). But, how come interference could have the same RT and same ions with these deuterated compounds?
Can someone give some idea?

[625]

I use these six PAH internal standards as surrogate. I got six surrogates recovery increasingly high in some soil samples. For example, the recovery of the first three surrogate were around 80-90%, the forth one went up to 120%, the fifth one were 150%, and eventually, the sixth one went up to 200%, 300% sometimes. We don't do PAH soil and water sample cleanup. We use SIM mode. These surrogate peaks looks in good shape.
I suppose it's because of matrix interference, because most time these problem happened with dark sample(few times but still had sometimes happened with clear sample). But, how come interference could have the same RT and same ions with these deuterated compounds?
Can someone give some idea?

Are you using internal standards at all? That may make a big difference in your results. Internal standard techniques tend to compensate for changes in concentration due to evaporation, fluctuations in instrument sensitivity, etc. My problem is that my internal standard recoveries fluctuate independently of target compounds, which is not what you are looking for in an internal standard.

Your problem may be due to precipitation of the internal standards in your vial prior to cracking or to degradation of these compounds in your calibration standards. If you compare a calibration standard you injected yesterday to an injection of that same standard when it was first prepared, is there a large difference in abundance?

It may just be a matrix interference problem. Some of the heavier compounds may be more difficult to detect in a dirty matrix or may fluctuate in recovery as you are seeing.

I highly recomment you start using internal standard calibration techniques if you are not currently doing so. Use the standard 8270 base neutral and phenol surrogates (nitrobenzene-d5, 2-fluorobiphenyl, p-terphenyl-d-14, 2-fluorophenol, phenol-d6, 2,4,6-tribromophenol) and use these six compounds as internal standards.

[AICMM]

warrender,

The heavy PAH's should have quite a difference in mass between the deuterated and non-deuterated so that is a puzzle. On the other hand, from the sounds of things, there are a lot of heavy hydrocarbons in your sample. Three comments then. 1) Try a secondary ion for your internal standard (if there is one!) and 2) just for kicks run the sample with no IS to see how much of that ion shows up in the IS window or 3) try a chloro or fluoro PAH instead since it would give you a very different ion and probably have very low abundance in real world samples.

Best regards.

[GimmeYoLunchBox]

I use these six PAH internal standards as surrogate. I got six surrogates recovery increasingly high in some soil samples. For example, the recovery of the first three surrogate were around 80-90%, the forth one went up to 120%, the fifth one were 150%, and eventually, the sixth one went up to 200%, 300% sometimes. We don't do PAH soil and water sample cleanup. We use SIM mode. These surrogate peaks looks in good shape.
I suppose it's because of matrix interference, because most time these problem happened with dark sample(few times but still had sometimes happened with clear sample). But, how come interference could have the same RT and same ions with these deuterated compounds?
Can someone give some idea?

Sorry for rehashing an old thread.

Have you resolved your particular problem? I’m experiencing a similar issue, I’m running method TO-13A on an Agilent 7890B/5977A. We are analyzing for PAHs off of PUF plugs/XAD-2 Resin, of the 5 internal standards Chrysene-d12 and Perylene-d12 started to come out elevated, sometimes as high as 300%. It’s something that only appears in the samples, the calibration standards are fine and in range. This happened upon me changing the column, over a year or two I’ve noticed a slight variation of these 2 internal standards but they have always managed to stay within range (-50 % to 100%).

Since the column change the values are way out of range now. Taking old samples from previous batches that didn’t have this issue are now showing it, pointing back at the instrument. Over the last 1.5 years on an old Agilent 5890 I didn’t have any issue with the IS, on this new Agilent on its 2nd column change I’ve run upon this issue. I haven’t changed anything injection port wise, just the regular maintenance, It’s a rough one. Any suggestions? Thanks

Luke

[James_Ball]

I use these six PAH internal standards as surrogate. I got six surrogates recovery increasingly high in some soil samples. For example, the recovery of the first three surrogate were around 80-90%, the forth one went up to 120%, the fifth one were 150%, and eventually, the sixth one went up to 200%, 300% sometimes. We don't do PAH soil and water sample cleanup. We use SIM mode. These surrogate peaks looks in good shape.
I suppose it's because of matrix interference, because most time these problem happened with dark sample(few times but still had sometimes happened with clear sample). But, how come interference could have the same RT and same ions with these deuterated compounds?
Can someone give some idea?

Sorry for rehashing an old thread.

Have you resolved your particular problem? I’m experiencing a similar issue, I’m running method TO-13A on an Agilent 7890B/5977A. We are analyzing for PAHs off of PUF plugs/XAD-2 Resin, of the 5 internal standards Chrysene-d12 and Perylene-d12 started to come out elevated, sometimes as high as 300%. It’s something that only appears in the samples, the calibration standards are fine and in range. This happened upon me changing the column, over a year or two I’ve noticed a slight variation of these 2 internal standards but they have always managed to stay within range (-50 % to 100%).

Since the column change the values are way out of range now. Taking old samples from previous batches that didn’t have this issue are now showing it, pointing back at the instrument. Over the last 1.5 years on an old Agilent 5890 I didn’t have any issue with the IS, on this new Agilent on its 2nd column change I’ve run upon this issue. I haven’t changed anything injection port wise, just the regular maintenance, It’s a rough one. Any suggestions? Thanks

Luke

If I remember those samples are not extracted with Methylene Chloride directly, but you have a solvent exchange at some point. Could it be that the solvent exchange isn't complete and having a co-solvent in a sample at time of injection could cause increased vaporization of the heavier analytes?