Loss of sensitivity (524.2)

[fishmon]

We are currently able to run two twelve hour batches of Drinking Water(524.2) before the RSD'S of the CCV EXCEED 20%. At this time we can analyze a batch of THM'S and pass all QC criteria.We have to clean the source after this to be able to analyze 524.2 Full List (approx. 70 compounds). If we try to run more Full List compounds and recalibrate, we can see the sensitivity drop with each level of calibration. Some would say the problem is the Pre Treatment of VOC's with Acsorbic Acid and HCl. I think the Tune and calibration curve RSD's should be more robust.System..... 5890 w/5973 MSD. Tekmar Purge and Trap w/ Archon autosampler..When cleaning the source after 24 hrs of VOC's it is suprising to see that much oxidation. Can any folks familiar w/ EPA 524.2 be of help? Ken

[tlahren]

After troubleshooting a similar problem for over two years on 8260 (VOCs in non-drinking water) we found that the problem was what all the service techs kept telling us: Water!!! Although we didn't have a very noticeable oxidation as you state, it turns out we were still getting too much water into the MS from the purge and trap. It sounds like you are getting a LOT of water in your MS or you have a good air leak in your system. Enough to oxidize the source in a couple runs. I don't recall all of the things we've tried (it's been over two years since I ran VOCs) but I know certain types of traps would "hang" on to water and MeOH a lot more than other traps. As a result we would have to change the bake out times resulting in longer analysis times. We were never able to fully resolve our issue as there was a fine balance of adjusting parameters that would sacrifice sensitivity for water. It was a trade off. I'm sure there are some other folks here that have had similar experiences and have more knowledge than myself on the topic.

Ty

[Bigbear]

There is quite a few posts on this site dealling with your problem. Check them out . Not to sound too grumpy, it's just I hate to type.
I bet you are putting too much water into your MS.

Post back if you don't get good results after checking out the history.

[LindseyPyron]

If you get frustrated, give our tech support team a call and they will help you out...no charge. 800-283-3510 . We also have a new source for the 73 and 75 which helps with stability issues!

Lindsey Pyron